mef cells  (ATCC)

Journal: iScience

Article Title: Localized phosphoinositide metabolism regulates STIM1/ORAI1 fast inactivation

doi: 10.1016/j.isci.2026.115543

Figure Lengend Snippet: Catalytically active MTMR7 is essential for STIM1/ORAI1 activity (A) Schematic representation of the MTMR7 protein domains. The PH-GRAM domain is shown in yellow, the catalytic protein tyrosine phosphatase (PTP) domain in green, and the coiled-coil (CC) domain in pink. The location of the STIM1 binding region at the C-terminus of MTMR7 is indicated in the figure. The location of the stop codon introduced at the N-terminal amino acid residues of the STIM1 interaction site (S569∗) is indicated by a red X, the location of C338S and D343A mutations in the catalytic PTP domain is indicated by blue arrows. (B) Immunoblot analysis of wild-type and MTMR7 mutants expressed in HEK293T cells. Anti-GAPDH was used as a loading control. (C and D) Co-immunoprecipitation of MTMR7 and STIM1 in HEK293T cells co-transfected with STIM1-YFP and either MTMR7, MTMR-C338S, or MTMR-D343A mutants. Immunoprecipitation was performed using GFP-Trap agarose beads, followed by immunoblotting with anti MTMR7 ( C ) and anti STIM1 ( D ) antibodies. (E) Representative whole-cell current traces of heterologously expressed ORAI1 and STIM1, along with MTRM7 or MTMR7 mutants MTMR7-C338S, MTMR7-D343A, and MTMR7-S569∗ in MTMR7 −/− cells. Cells were transfected in a 1:2:1 (ORAI1:STIM1:MTMR7 or MTMR7 mutants) ratio. Currents were recorded in 20 mM Ca 2+ during 200 ms hyperpolarizing test voltages (−60, −80, −100, and −120 mV) from a 30-mV holding potential. (F) Current density (pA/pF) analysis of current from a −100-mV hyperpolarizing pulse at 3 min following whole-cell break-in (white bars; n = 6–13 for each group). Green bar denotes the current density measured from a −100-mV pulse at 15 min following whole-cell break-in ( n = 3). A nonparametric Kruskal-Wallis ANOVA on ranks test, followed by a multiple comparison (Dunn’s) post hoc test, was used to compare each group against either the control ( Ctrl ) condition in wild-type or MTMR7 −/− MEF cells (∗ p < 0.001 vs. wild-type, # p < 0.01 vs. MTMR7 −/− ). (G) Extent of STIM1/ORAI1 CDI from recordings of each group shown in F. Line and scatterplot summarizing the fraction of current remaining for each group, measured as the percent of peak current from the beginning and the end of the 200 ms hyperpolarizing steps. Each data point represents the mean ± SEM ( n = 6–15 cells for each group). For comparison, the data from wild-type or MTMR7 −/− cells were superimposed from D in gray and black dashed lines, respectively. A one-way ANOVA followed by a Dunnett’s post hoc test was used to compare the residual current of all groups against the control (WT) (∗ p < 0.05 at all test potentials). Data are represented as mean ± SEM.

Article Snippet: Both MEF cells and human embryonic kidney cells (HEK293T; female, ATCC Cat# MSPP-CRL3216) were cultured in accordance with established protocols using DMEM-10 (Dulbecco’s Modified Eagle’s Medium supplemented with 10% Fetal Bovine Serum, Gibco) under standard cell culture conditions of 37°C and 5% CO 2 .

Techniques: Activity Assay, Binding Assay, Western Blot, Control, Immunoprecipitation, Transfection, Comparison

Journal: iScience

Article Title: Localized phosphoinositide metabolism regulates STIM1/ORAI1 fast inactivation

doi: 10.1016/j.isci.2026.115543

Figure Lengend Snippet: MTMR7 double mutants and ORAI1 inactivation (A) Immunoblot analysis of HEK293T cells expressing MTMR7 and MTMR7 mutants (MTMR7-C338S, MTMR7-D343A, MTMR7-C338S + S569∗, and MTMR7-D343A + S569∗). (B) Representative whole-cell current traces of heterologously expressed ORAI1 and STIM1, along with MTMR7 double mutants; MTMR7-C338S + S569∗ or MTMR7-D343A + S569∗ in MTMR7 −/− cells. Cells were transfected in a 1:2:1 (ORAI1:STIM1:MTMR7 double mutants) ratio. Currents were recorded in 20 mM Ca 2+ during 200 ms hyperpolarizing test voltages (−60, −80, −100, −120 mV) from a 30-mV holding potential. (C) Current density (pA/pF) analysis of current from a −100-mV hyperpolarizing pulse at 3 min following whole-cell break-in (white bars; n = 7 for each group). (D) Extent of STIM1/ORAI1 CDI from recordings of each group shown in F. Line and scatterplot summarizing the fraction of current remaining for each group, measured as the percent of peak current from the beginning and the end of the 200 ms hyperpolarizing steps. Each data point represents the mean ± SEM (n = 8–9 cells for each group). For comparison, the data from wild-type MEF or MTMR7 −/− cells were superimposed from D in gray and black dashed lines, respectively. A one-way ANOVA followed by a Dunnett’s post hoc test was used to compare the residual current of all groups against the control (WT) (∗ p < 0.05 at all test potentials). Data are represented as mean ± SEM.

Article Snippet: Both MEF cells and human embryonic kidney cells (HEK293T; female, ATCC Cat# MSPP-CRL3216) were cultured in accordance with established protocols using DMEM-10 (Dulbecco’s Modified Eagle’s Medium supplemented with 10% Fetal Bovine Serum, Gibco) under standard cell culture conditions of 37°C and 5% CO 2 .

Techniques: Western Blot, Expressing, Transfection, Comparison, Control

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Multidirectional fatty acid (FA) trafficking pathways between lipid droplets (LDs) and mitochondria. Terms: FAO, fatty acid oxidation; NG497, an ATGL inhibitor; Triacsin C, an inhibitor of long FA acyl-CoA synthetase. (B) BODIPY 493/503-labeled LDs detected via confocal microscopy before and after 6-h incubation with 10 µM Triacsin C in wildtype (WT) and OPA1 knockout (KO) U2OS cells treated with 100 µM oleic acid (OA) overnight. Maximal intensity projected (MIP) confocal images from whole cells are shown. Dashed lines mark cell boundary. (C) Quantification of BODIPY 493/503-positive LD content as described in (B). Mean ± standard deviation from three independent experiments are shown (total of 99–161 cells). n.s., no significance, **P ≤ 0.001, as assessed by one-way ANOVA. (D) Quantification of monodansylpentane (MDH)-positive LD content in WT, OPA1 KO, and OPA1-expressing OPA1 KO U2OS cells treated with 100 µM OA overnight followed by 10 µM Triacsin C incubation for 6 h. Mean ± standard deviation from three independent experiments are shown (total of 81–115 cells). n.s., no significance, **P ≤ 0.01, *P ≤ 0.05, as assessed by one-way ANOVA. (E) Subcellular localization of TopFluor (TF)-OA and TOM20-Halo (JF646) detected via confocal microscopy in WT and OPA1 KO U2OS cells treated with 20 µM DGAT1 and DGAT2 inhibitors. MIP confocal images from three axial slices (∼0.6 µm total thickness) are shown. (F) Quantification of the intensity of peripheral mitochondria (mito) of TF-OA as described in (E) and in cells pretreated with 10 µM Triacsin C, 1 µM BODIPY-linoleic acid (LA), or 1 µM NBD-arachidonic acid (AA). Mean ± standard deviation from three independent experiments are shown (total of 38–50 cells). n.s., no significance, ****P ≤ 0.0001, *P ≤ 0.05, as assessed by one-way ANOVA. (G) Scintillation counts per minute (CPM) for complete 14 C-OA oxidation in WT and OPA1 KO U2OS cells under control and Triacsin C-treated conditions. Mean ± standard deviation from three independent experiments are shown. n.s., no significance, ***P ≤ 0.001, *P ≤ 0.05, as assessed by one-way ANOVA. (H) Concentration of cholesterol-ester (CE), diacylglycerol (DAG), triglyceride (TAG), and monoacylglycerol (MAG) in steady-state WT and OPA1 KO U2OS cells determined via liquid chromatography–mass spectrometry. Mean ± standard deviation from four replicates are shown. n.s., no significance, ****P ≤ 0.0001, as assessed by unpaired t -test. (I) Variance in acyl-carnitine levels across acyl-chain length in steady-state WT and OPA1 KO U2OS cells determined using liquid chromatography–mass spectrometry. Mean ± standard deviation from four replicates are shown. n.s., no significance, ****P ≤ 0.0001, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05, as assessed by unpaired t -test.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Labeling, Confocal Microscopy, Incubation, Knock-Out, Standard Deviation, Expressing, Control, Concentration Assay, Liquid Chromatography, Mass Spectrometry

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Diagram illustrating the generation of OPA1 knockout (KO) U2OS cells via CRISPR-genome editing. Sequencing data validating OPA1 KO is shown in the top right, and deleted OPA1 genome sequences are represented as dashed lines highlighted in red. (B) Western blot analysis of OPA1, ATGL, DGAT1, and GAPDH in wildtype (WT) and OPA1 KO U2OS cells -/+ overnight 100 µM oleic acid (OA) treatment. (C) Immunostaining of endogenous OPA1 and TOM20 in WT and OPA1 KO U2OS cells detected by confocal microscopy. Maximal intensity projected confocal images from whole cells with min-max intensity range (gray boxes) are shown. (D) Western blot analysis of OPA1 and GAPDH in HeLa cells transfected with scramble siRNA (siCtrl) or OPA1 siRNA. (E) Western blot analysis of OPA1 and GAPDH in WT and OPA1 KO mouse embryonic fibroblasts (MEFs) -/+ overnight 100 µM OA treatment. (F) Western blot analysis of HSL, CGI-58, and GAPDH in WT and OPA1 KO U2OS cells -/+ overnight 100 µM OA treatment.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Knock-Out, CRISPR, Sequencing, Western Blot, Immunostaining, Confocal Microscopy, Transfection

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) BODIPY 493/503-positive area in U2OS cells treated with 100 µM oleic acid (OA) overnight followed by 10 µM Triacsin C incubation in the presence of 10 µM NG497 (NG) or 5 µM Lalistat 2 (LALi) for 6 h. Mean ± standard deviation from three independent experiments are shown (total of 129–148 cells). For statistics in panels A–E, n.s., no significance, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05, as assessed by one-way ANOVA. (B) BODIPY 493/503-positive area in U2OS cells treated with 100 µM OA overnight followed by 6-h co-incubation of 10 µM Triacsin C and 10 µM H89. (C) BODIPY 493/503-positive area in HeLa cells transfected with scramble siRNA (siCtrl) or OPA1 siRNA (siOPA1) treated with 100 µM OA overnight before 6-h incubation with 10 µM Triacsin C. Mean ± standard deviation from three independent experiments are shown (total of 107–122 cells). (D) BODIPY 493/503-positive area in WT and OPA1 knockout (KO) mouse embryonic fibroblasts (MEFs) treated with 100 µM OA overnight before 6-h incubation with 10 µM Triacsin C. Mean ± standard deviation from three independent experiments are shown (total of 83–105 cells). (E) BODIPY 493/503-positive area in WT and OPA1 KO U2OS cells treated with 100 µM OA overnight followed by 20-h incubation in glucose-free Dulbecco’s Modified Eagle Medium. Mean ± standard deviation from three independent experiments are shown (total of 79–87 cells). (F and G) Levels of (F) glycerophospholipids and (G) sphingolipids in steady-state WT and OPA1 KO U2OS cells determined using liquid chromatography–mass spectrometry. Mean ± standard deviation from four replicates are shown. For statistics in panels F and G, n.s., no significance, ***P ≤ 0.001, **P ≤ 0.01, as assessed by unpaired t -test. Abbreviations: PC, phosphatidylcholine; PE, phosphatidylethanolamine; LPC, lysophosphatidylcholine; LPE, lysophosphatidylethanolamine; PI, phosphatidylinositol; CER, ceramide; DCER, dihydroceramide; HCER, hexosylceramide; LCER, lactosylceramide; SM, sphingomyelin.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Incubation, Standard Deviation, Transfection, Knock-Out, Modification, Liquid Chromatography, Mass Spectrometry

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Localization of OPA1-YFP (lentiviral), mitochondria (labeled with MitoTracker Deep Red), and lipid droplets (LDs; labeled with MDH) in U2OS cells -/+ overnight 100 µM oleic acid (OA) treatment. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. Cyan arrowheads indicate area with LDs. (B) Relative enrichment of MitoTracker and OPA1 on LDs from (A) and in cells treated with 100 µM linoleic acid (LA) or arachidonic acid (AA) overnight. Mean ± standard deviation from 3–5 independent experiments are shown (total of 43–74 cells). n.s., no significance, ****P ≤ 0.0001, assessed by one-way ANOVA. (C) Subcellular localization of endogenous OPA1 on mitochondria (anti-TOM20) and LDs labeled by BODIPY 493/503 in an OA-treated U2OS cell monitored with confocal microscopy. Sum of confocal images from five axial slices (∼1.2 µm in total thickness) are shown. (D) Relative intensity profiles of OPA1, TOM20, and BODIPY measured along the white-dashed arrow from lower left panel in (C). (E) Western blot analysis of endogenous OPA1, PLIN 2 (an LD protein), and PHB 2 (a mitochondrial inner membrane protein) in sucrose-gradient cellular fractionations from U2OS cells treated with 500 μM OA. (F) Correlative confocal-scanning electron microscopy (SEM) images of OPA1 on LDs and in mitochondria in OPA1-mhYFP–expressing U2OS cells treated with 100 µM OA overnight. Confocal and SEM images from a single axial slice are shown. EM, electron microscopy. Inset outlined in blue is shown in . (G) Subcellular distribution of inducible OPA1 (iOPA1)-YFP on LDs (BODIPY 665/676) and in mitochondria (MitoTracker Red) in OPA1 KO U2OS cells following treatment with 4 µg/mL doxycycline for 4 h. Confocal images from a single axial slice are shown. Cyan arrowheads indicate regions containing LDs. (H) Fraction of cells with iOPA1 localized to indicated organelle as described in (G). Mean ± standard deviation from three independent experiments are shown. (I) Localization of OPA1-YFP, mitochondria (MitoTracker Deep Red), LDs (MDH) in U2OS cells treated with 100 µM OA and 20 µM FCCP (an uncoupler of mitochondria oxidative phosphorylation) overnight detected by confocal microscopy. MIP confocal images from four axial slices (∼1 µm total thickness) are shown. (J) Relative enrichment of OPA1 on LDs in U2OS cells treated with 100 µM OA -/+ 20 µM FCCP for overnight in (I). Mean ± standard deviation from four independent experiments are shown (total of 57–73 cells). **P ≤ 0.01, as assessed by unpaired t -test.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Labeling, Standard Deviation, Confocal Microscopy, Western Blot, Membrane, Electron Microscopy, Expressing, Phospho-proteomics

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Localization of OPA1-YFP (lentiviral), mitochondria (labeled with MitoTracker Deep Red), and lipid droplets (LDs, labeled with MDH) in U2OS cells treated with 100 µM linoleic acid (LA) or 100 µM arachidonic acid (AA) overnight. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. (B) Localization of OPA1-YFP, mitochondria (MitoTracker Deep Red), and LD (MDH) in HeLa and Huh7 cells treated with 100 µM oleic acid (OA) overnight, detected with confocal microscopy. MIP confocal images from four axial slices (∼1 µm total thickness) are shown. Cyan arrowheads indicate area with LDs. ( C ) Inset from the correlative confocal-scanning electron microscopy (SEM) image in , outlined in blue, showing OPA1-mhYFP localization in mitochondria in a U2OS cell treated with 100 µM OA overnight. (D) Subcellular localization of endogenous OPA1 (anti-Opa1) on mitochondria (anti-TOM20) and LDs (BODIPY 493/503) in a U2OS cell treated with 100 µM OA and 20 µM FCCP (an uncoupler of mitochondria oxidative phosphorylation) overnight and monitored via confocal microscopy. Sum of confocal images from five axial slices (∼1.2 µm total thickness) are shown. (E) Relative intensity profiles of OPA1, TOM20, and BODIPY measured from lower right panel in (D), indicated by white-dashed arrows. (F) Properties of representative mitochondrial targeting sequences (MTSs) for mitochondrial protein import. Asterisk indicates the predicted import velocity of the OPA1 MTS. Max μH, maximal helical hydrophobic moment. (G) Correlation between the amphiphilicity of MTS and the protein import velocity from (F). (H) Localization of truncated YFP-tagged OPA1 fragments (frag.), mitochondria (labeled with TOM20-Halo; JF646), and LDs (MDH) in U2OS cells treated with 100 µM OA overnight and detected by confocal microscopy. MIP confocal images from four axial slices (∼1 µm total thickness) are shown.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Labeling, Confocal Microscopy, Electron Microscopy, Phospho-proteomics

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Constructs expressing full-length and truncated OPA1, as well as summary of their primary subcellular localizations. Amino acid number and protein domains are indicated. MTS, mitochondria targeting sequence; GED, GTPase effector domain; LD, lipid droplet; mito, mitochondria. (B) Localization of OPA1 ΔMTS -YFP, mitochondria (labeled with MitoTracker Deep Red), and lipid droplets (LDs; labeled with MDH) in U2OS cells treated with 100 µM oleic acid (OA) overnight and detected by confocal microscopy. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. (C) Relative enrichment of OPA1 ΔMTS from (B) and OPA1 on LDs in U2OS cells treated with 100 µM OA overnight. Mean ± standard deviation from three independent experiments are shown (total of 48–55 cells). ****P ≤ 0.0001, as assessed by unpaired t -test. (D) Amphipathic helix structure of exon 4 as predicted by AlphaFold. Cyan and yellow indicate polar and non-polar amino acids, respectively, and black arrows indicate location of residues for mutagenesis. (E) Localization of YFP-tagged exon 4 in MDH-stained U2OS cells treated with 100 µM OA overnight and detected by confocal microscopy. MIP confocal images from four axial slices (∼1 µm total thickness) are shown. (F) Correlative confocal-scanning electron microscopy (SEM) images of exon 4 on LDs in exon 4-mhYFP expressing U2OS cells treated with 100 µM OA overnight. Confocal and SEM images from a single axial slice are shown. (G) Localization of exon 4 mutants relative to LDs (MDH) in U2OS cells treated with 100 µM OA overnight and detected by confocal microscopy. MIP confocal images from four axial slices (∼1 µm total thickness) are shown. LFAA, a double mutation of L156 and F169 to alanines. (H) Relative enrichment of exon 4 and mutants (described in E and G), as well as PLIN 2-GFP on LDs in U2OS cells treated with 100 µM OA overnight. Mean ± standard deviation from two or three independent experiments are shown (total of 30–52 cells). ****P ≤ 0.0001, ***P ≤ 0.001, as assessed by one-way ANOVA. (I) Localization of OPA1 and OPA1 LFAA , mitochondria (MitoTracker Deep Red), and LD (MDH) in U2OS cells treated with 100 µM OA overnight and detected by confocal microscopy. MIP confocal images from four axial slices (∼1 µm total thickness) are shown. (J) Relative enrichment of OPA1 and OPA1 LFAA from (I) on LDs in cells treated with 100 µM OA overnight. Mean ± standard deviation from three independent experiments are shown (total of 63–65 cells). ****P ≤ 0.0001, as assessed by one-way ANOVA.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Construct, Expressing, Sequencing, Labeling, Confocal Microscopy, Standard Deviation, Mutagenesis, Staining, Electron Microscopy

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Percentage of OPA1 exon 4 inclusion and exclusion, representing OPA1 isoform 1 and isoform 2, respectively, across various human tissues analyzed from the Genotype-Tissue Expression (GTEx) database. Raw data and median values with quartile ranges are shown. (B) Profiling of OPA1 exon 4 inclusion (incl.) and exclusion (excl.) from cDNA of HeLa and U2OS cells. (C) Localization of OPA1-YFP or OPA1 iso2 -YFP, mitochondria (labeled with MitoTracker Deep Red), and lipid droplets (LDs; labeled with MDH) in HeLa cells treated with 100 µM oleic acid (OA) -/+ 20 µM FCCP (an uncoupler of mitochondria oxidative phosphorylation) overnight and detected by confocal microscopy. Maximal intensity projected confocal images from four axial slices (∼1 µm in total thickness) are shown. (D) Relative enrichment of OPA1 and OPA1 iso2 on LDs as described in (C). Mean ± standard deviation from three-four independent experiments are shown (total of 31–42 cells). Yellow dashed line indicates the relative enrichment of OPA1 on LDs in U2OS cells as described in . n.s., no significance, ***P ≤ 0.001, *P ≤ 0.05, as assessed by one-way ANOVA. (E) BODIPY-positive LD content in siCtrl and siOPA1 4-5 junc transfected HeLa cells treated with 100 µM OA overnight followed by incubation with 10 µM Triacsin C for 6 h. Mean ± standard deviation from four independent experiments are shown (total of 107–122 cells). n.s., no significance, **P ≤ 0.01, as assessed by one-way ANOVA.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Expressing, Labeling, Phospho-proteomics, Confocal Microscopy, Standard Deviation, Transfection, Incubation

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Localization of OPA1 iso2 -YFP, mitochondria (labeled with MitoTracker Deep Red), lipid droplets (LDs; labeled with MDH) in U2OS cells treated with 100 µM oleic acid (OA) -/+ 20 µM FCCP (an uncoupler of mitochondria oxidative phosphorylation) overnight detected by confocal microscopy. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. (B) Relative enrichment of OPA1 iso2 as described in (A) and OPA1 on LDs in U2OS cells treated with 100 µM OA overnight. Mean ± standard deviation from three independent experiments are shown (total of 43–51 cells). n.s., no significance, ****P ≤ 0.0001, as assessed by one-way ANOVA. (C) Subcellular distribution of inducible OPA1 iso2 (iOPA1 iso2 )-YFP on LDs (BODIPY 665/676) and mitochondria (MitoTracker Red) in OPA1 knockout (KO) U2OS cells following 4 µg/mL doxycycline treatment for 4 h. Confocal images from a single axial slice are shown. (D) Fraction of cells with iOPA1 iso2 localized to indicated organelle as described in (C). Mean ± standard deviation from three independent experiments are shown. (E) Design of an siRNA targeting the OPA1 exon 4–exon 5 junction for selective depletion of isoform 1. (F and G) Levels of (F) OPA1 isoform-specific mRNA or (G) protein in U2OS cells transfected with the indicated siRNAs. Mean ± standard deviation from two or three independent experiments are shown in (F). (H) Relative BODIPY-positive area indicating LD content in siCtrl and siOPA1 4-5 junc transfected U2OS cells treated with 100 µM OA overnight followed by 10 µM Triacsin C incubation for 6 h. Mean ± standard deviation from three independent experiments are shown (total of 90–101 cells). n.s., no significance, ***P ≤ 0.001, as assessed by one-way ANOVA.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Labeling, Phospho-proteomics, Confocal Microscopy, Standard Deviation, Knock-Out, Transfection, Incubation

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Western blot analysis of endogenous ATGL, HSL, and PLIN 2 in sucrose-gradient cellular fractionations from wildtype (WT) and OPA1 knockout (KO) U2OS cells treated with 500 μM oleic acid (OA). (B) ATGL and HSL abundance in lipid droplet (LD) fractions normalized to PLIN2 as described in (A). Mean ± standard deviation from three independent experiments are shown. **P ≤ 0.01, *P ≤ 0.05, as assessed by unpaired t -test. (C) Localization of ATGL S47A-Halo and LDs (labeled with BODIPY-493/503) in WT and OPA1 KO U2OS cells treated with 100 µM OA overnight. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. (D) Relative enrichment of endogenous PLIN 2 (detected by immunostaining), ATGL S47A -Halo, and mApple-CGI-58 on LDs from , and , respectively. Mean ± standard deviation from three independent experiments are shown (total of 72–74 cells for ATGL S47A -Halo; total of 50-52 cells for PLIN 2, and total of 34–46 cells for mApple-CGI-58). n.s., no significance, **P ≤ 0.01, as assessed by unpaired t -test. (E) Relative enrichment of ATGL S47A -Halo on LDs in OPA1 KO U2OS cells and OPA1 KO cells reconstituted with lenti-OPA1-YFP or lenti-OPA1 LFAA -YFP. Mean ± standard deviation from three independent experiments are shown (total of 56–60 cells). For statistics in panels E and F, n.s., no significance, **P ≤ 0.01, *P ≤ 0.05, as assessed by one-way ANOVA. (F) MDH-positive LD content in WT and OPA1 KO U2OS cells, as well as OPA1 KO cells reconstituted with lenti-OPA1-YFP or lenti-OPA1 LFAA -YFP. Cells were treated with 100 µM OA overnight followed by 6-h incubation with 10 µM Triacsin C. Mean ± standard deviation from three independent experiments are shown (total of 71–97 cells).

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Western Blot, Knock-Out, Standard Deviation, Labeling, Immunostaining, Incubation

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Localization of endogenous PLIN 2 on lipid droplets (LDs) labeled with BODIPY-493/503 in wildtype (WT) and OPA1 knockout (KO) U2OS cells treated with 100 µM oleic acid (OA) overnight. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. (B) Localization of mApple-CGI-58 and LDs labeled with BODIPY-493/503 in WT and OPA1 KO U2OS cells treated with 100 µM OA overnight. MIP confocal images from four axial slices (∼1 µm total thickness) are shown. (C–E) Two-dimensional ‘mitochondria analyzer’ analysis of mitochondrial morphology and connectivity measuring (C) form factor, (D) total branch length, and (E) branch junction in MitoTracker DeepRed–stained WT and OPA1 KO U2OS cells -/+ overnight 100 µM OA treatment. Mean ± standard deviation from three independent experiments are shown (total of 74–100 cells). For panels C–E, n.s., no significance, ****P ≤ 0.0001, ***P ≤ 0.001, *P ≤ 0.05, as assessed by one-way ANOVA.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Labeling, Knock-Out, Staining, Standard Deviation

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) A schematic illustrating two-dimensional (2D) analysis of mitochondrial morphology and connectivity using the Fiji plugin, ‘Mitochondria-Analyzer’. Representative MitoTracker DeepRed images (maximal intensity projected confocal images from three axial slices; 0.6 µm in thickness) from OPA1 knockout (KO) U2OS cells and the corresponding analyses are shown. (B–D) Two-dimensional analysis of mitochondrial morphology and connectivity measuring (B) form factor, (C) total branch length, and (D) branch junction in MitoTracker DeepRed-stained OPA1 KO U2OS cells and OPA1 KO U2OS cells reconstituted with lenti-OPA1-YFP or lenti-OPA1 LFAA -YFP. Mean ± standard deviation from three or four independent experiments are shown (total of 80–133 cells). n.s., no significance, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05, as assessed by one-way ANOVA. Black asterisks represent comparisons with OPA1 KO, and purple asterisks represent the indicated comparison.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Knock-Out, Staining, Standard Deviation, Comparison

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet:

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques:

Journal: bioRxiv

Article Title: Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

doi: 10.64898/2026.05.07.723579

Figure Lengend Snippet: (A) Amphipathic helix structures and hydrophobicity distributions of exon 4 and exon 4 S158N, predicted by AlphaFold and illustrated in ChimeraX. Cyan and yellow indicate polar and non-polar amino acids, respectively, and arrows denote locations of indicated residues. (B) Localization of YFP tagged OPA1 or OPA1 S158N (lentiviral), mitochondria (labeled with MitoTracker Deep Red), and lipid droplets (LDs; labeled with MDH) in U2OS cells treat with 100 µM oleic acid (OA) overnight. Maximal intensity projected (MIP) confocal images from four axial slices (∼1 µm total thickness) are shown. (C) Relative enrichment of OPA1 on LDs in U2OS cells as described in (B). Mean ± standard deviation from three independent experiments are shown (total of 50-60 cells). **P ≤ 0.01, assessed by unpaired t -test. (D) MDH-positive LD content in wildtype (WT) and OPA1 KO U2OS cells, and in OPA1 KO cells reconstituted with lenti-OPA1-YFP or lenti-OPA1 S158N -YFP. Cells were treated with 100 µM OA overnight followed by incubation with 10 µM Triacsin C 6 h. Mean ± standard deviation from three independent experiments are shown (total of 63-83 cells). (E–G) Two-dimensional analysis of mitochondrial morphology and connectivity via measuring (E) form factor, (F) total branch length, and (G) branch junction in MitoTracker DeepRed-stained OPA1 KO U2OS cells and OPA1 KO cells reconstituted with lenti-OPA1-YFP or lenti-OPA1 S158N -YFP. Mean ± standard deviation from 3-4 independent experiments are shown (total of 55-83 cells). For panels D-G, n.s., no significance, ***P ≤ 0.001, **P ≤ 0.01, *P ≤ 0.05, assessed by one-way ANOVA. (H–J) Clinical data was mined from the St. Jude LIFE database to assess (H) body fat percentage, (I) blood triacylglycerol levels, and (J) blood cholesterol levels in patients with different S158N genotypes. (K) Proposed model of OPA1’s functions and impacts on LDs and mitochondria depending on its alternative targeting and its implication in human metabolic outcomes. OPA1-mediated lipase recruitment to LDs is indicated with a dashed arrow. Abbreviations: FAO, fatty acid oxidation; MTS, mitochondria targeting sequence.

Article Snippet: U2OS cells (HTB-96), HeLa (CCL-2) cells, and OPA1 KO MEFs (CRL-2995) were purchased from American Type Culture Collection (ATCC); Huh7 (JCRB0403) cells were purchased from the Japanese Cancer Research Bank.

Techniques: Labeling, Standard Deviation, Incubation, Staining, Sequencing

Journal: Frontiers in Immunology

Article Title: Mouse TAPBPR shows functional similarity to human TAPBPR in shaping the MHC-I immunopeptidome

doi: 10.3389/fimmu.2026.1756668

Figure Lengend Snippet: Feature of mouse TAPBPR protein. (A) ClustalWS alignment comparison between mouse TAPBPR (mouse TAPBPR, UniProt Q8VD31 ) and human TAPBPR (UniProt Q9BX59 ) proteins. Blosum62 scoring system was generated by Jalview 2.11.4.0 software. Boxes highlight the peptide editing loop (blue), MHC-I binding sites characterized as TN5, TN6, TC2 and TC3 (red), the free cysteine residue (black), two predicted N-linked glycosylation sites in mouse TAPBPR (purple, with the asparagine indicated by an asterisk) and the cytoplasmic tail regions (yellow). The endogenous mouse TAPBPR sequence in MC-38, B16-F10, and MEF-BL/6–1 cells was confirmed as equivalent to the UniProt reference. (B) Predicted AlphaFold2 structure of mouse TAPBPR (green) bound to H2-D b (blue) with N-linked glycosylations (pink) modelled using GLYCAM ( https://glycam.org ). For H2-D b , only two of the three glycans are visible in the image, with N86 obscured by the orientation depicted. (C) Representative histograms and bar graphs showing mean fluorescence intensity (MFI) of intracellular TAPBPR expression, detected using AnDi3 antibody, on IFNγ-treated wildtype (WT) MC-38, B16-F10, and MEF-BL/6–1 cells compared to TAPBPR knockout (KO) and mouse TAPBPR overexpressed (OE) equivalents, which serve as negative and positive controls, respectively. Error bars show MFI -/+ standard error of mean (SEM) from three independent experiments. *p ≤ 0.05, **p ≤ 0.01 using unpaired t-test. (D) Histograms showing IFNγ inducibility of intracellular TAPBPR expression in WT MC-38 and B16-F10 cells and in cells transduced to overexpress (OE) mouse TAPBPR.

Article Snippet: Murine colon adenocarcinoma MC-38 (Kerfast, Newark, CA 94560, USA), mouse melanoma B16-F10, Lewis lung carcinoma LL/2 and mouse stromal fibroblast MEF-BL/6-1 (ATCC SCRC-1008) cells were maintained in Dulbecco’s Modified Eagle’s medium (DMEM)(CAT: 41966052, GibcoTM, Thermo Fisher Scientific, Paisley, Renfrewshire, UK), supplemented with 10% fetal bovine serum (FBS)(CAT: 10500064, GibcoTM) and 100 units/mL penicillin-streptomycin (CAT: 15140122, GibcoTM) at 37 °C, 5% CO 2 , and humid atmosphere.

Techniques: Comparison, Generated, Software, Binding Assay, Residue, Glycoproteomics, Sequencing, Fluorescence, Expressing, Knock-Out

Journal: Frontiers in Immunology

Article Title: Mouse TAPBPR shows functional similarity to human TAPBPR in shaping the MHC-I immunopeptidome

doi: 10.3389/fimmu.2026.1756668

Figure Lengend Snippet: Mouse TAPBPR interaction partners identified in B16-F10, MC-38 and MEF-BL/6–1 cell lines. Mouse TAPBPR was isolated by immunoprecipitation, using Andi38 antibody, from TAPBPR knockout (KO) or mouse TAPBPR overexpressing (OE) from (A) B16-F10 cells, (B) MC-38 cells, (C) MEF-BL/6–1 cells or (D) MC-38 cells with β2m knocked out. Scatterplots show all proteins identified via mass spectrometry in the mouse TAPBPR pull-downs in cells overexpressing mouse TAPBPR compared to the equivalent TAPBPR KO cell line. Selected significant interaction partners highlighted are TAPBPR (pink), H2-D b (red), H2-K b (yellow), MHC-I (orange), which covers peptides common to H2 molecules and therefore cannot be assigned to a specific MHC-I molecule, β2m (navy) and known components of the MHC-I antigen presentation pathway (purple). (E) Confirmation of mouse TAPBPR binding partners at endogenous TAPBPR levels in MC-38 cells. Immunoblots indicating abundance of mouse TAPBPR (mTAPBPR), MHC-I, β2m, calnexin, tapasin, TAP2, and GAPDH (loading control) in the whole cell lysates and mouse TAPBPR immunoprecipitates (IP: mTAPBPR) from WT MC-38 cells. MC-38 with TAPBPR knocked out (KO) or overexpressing mouse TAPBPR (OE) are included as controls. Cells competent for β2m expression or with β2m knocked down (β2m KD) were compared to assess the importance of the TAPBPR/MHC-I interaction in the observed associations. An antibody-only lane is included to highlight the antibody’s heavy chain used in the immunoprecipitation. N = 1, for tapasin and TAP2 blot. (F) Endogenously expressed mouse TAPBPR exhibits a prolonged association with H2-D b compared to H2-K b in both MC-38 and B16 cells. Immunoblots indicating abundance of mTAPBPR, MHC-I, β2m, calnexin, and GAPDH (loading control) in the whole cell lysate and mTAPBPR immunoprecipitated fraction (IP: mTAPBPR) with Andi 38 from MC-38 or B16-F10 WT cells, and variant cell lines expressing H2-D b only (H2-K b knockout), H-2K b only (H2-D b knockout) or lacking efficient expression of both H2-D d and -K b following β2m knock down (KD). Representative of three independent experiments. Note: Arrowheads indicate the positioning of the major TAPBPR and MHC-I bands in the gels, where background bands were present in the immunoprecipitations. The position of TAPBPR relative to the antibody control also varies due to minor changes in running conditions between experiments. Note: WT cells in F were treated with a non-targeting RNA guide in the RNP.

Article Snippet: Murine colon adenocarcinoma MC-38 (Kerfast, Newark, CA 94560, USA), mouse melanoma B16-F10, Lewis lung carcinoma LL/2 and mouse stromal fibroblast MEF-BL/6-1 (ATCC SCRC-1008) cells were maintained in Dulbecco’s Modified Eagle’s medium (DMEM)(CAT: 41966052, GibcoTM, Thermo Fisher Scientific, Paisley, Renfrewshire, UK), supplemented with 10% fetal bovine serum (FBS)(CAT: 10500064, GibcoTM) and 100 units/mL penicillin-streptomycin (CAT: 15140122, GibcoTM) at 37 °C, 5% CO 2 , and humid atmosphere.

Techniques: Isolation, Immunoprecipitation, Knock-Out, Mass Spectrometry, Immunopeptidomics, Binding Assay, Western Blot, Control, Expressing, Variant Assay, Knockdown