Journal: International journal of molecular sciences

Article Title: Regulation of Mertk Surface Expression via ADAM17 and γ-Secretase Proteolytic Processing.

doi: 10.3390/ijms25084404

Figure Lengend Snippet: Figure 1. Differentiation of THP-1 cells induced by PMA. (A) THP-1 monocytes are differentiated to macrophages and induced to express Mertk by the addition of 100 ng/mL of PMA for at least 24 h, while Axl expression is not induced. Likewise, Tyro3 expression remains stable and is unaffected by treatment. H1299 and Beas2B cells are used as positive controls for Mertk/Axl and Tyro3, respec- tively. The observed doublet for Mertk corresponds to fully glycosylated and partially glycosylated glycoforms. (B) THP-1 cells treated with 100 ng/mL of PMA over 48 h exhibit a decreased expression of Gas6 but an increased expression of Protein S. (C) MertK and Gas6 expression patterns over a time of 48 h after 100 ng/mL of PMA treatment as quantified from Western blots. (D) Bar plots showing MerTK and Gas6 expression quantified from Western blots at 0 h and post 72 h of 100 ng/mL of PMA treatment (significant differences were observed between the 0 h and 72 h time points for Gas6 (* p = 0.029) and MerTK (** p = 0.003), as determined by independent t-tests). (E) THP-1 cells were treated with 100 ng/mL of PMA over 72 h. mRNA was analyzed via qRT-PCR for Mertk, Axl, Protein S (ProS), Tyro3, and Gas6. Mertk transcription was highly elevated, more than 10-fold, due to PMA treatment, while Gas6 transcription was repressed more than 10-fold. (F) PMA treatment of THP-1s illustrates a complimentary phenomenon. As a monocyte, Gas6 is expressed with little Mertk expression; however, when differentiated, Mertk is highly expressed in favor of Gas6.

Article Snippet: Concentrated Gas6 reagents were analyzed for concentration via Western blotting using a Gas6 standard (R&D Systems, 885-GSB-050).

Techniques: Expressing, Western Blot, Quantitative RT-PCR

Journal: International journal of molecular sciences

Article Title: Regulation of Mertk Surface Expression via ADAM17 and γ-Secretase Proteolytic Processing.

doi: 10.3390/ijms25084404

Figure Lengend Snippet: Figure 3. γ-carboxylated Gas6 Reduces Full-length Mertk Expression and Decreases sMertk. (A) γ- carboxylation status (Gla) of Gas6 is regulated with the addition of Vitamin K or warfarin, producing either a γ-carboxylated, active ligand or a non-γ-carboxylated, inactive ligand, respectively. The carboxylation status (Gla) domain of Gas6 can bind with externalized PS. (B) Recombinant inactive (Gas6-W) and active (Gas6-VK) were produced via HEK293 transfection, with a mock transfection control (Mock). The amount of Gas6 was observed (bottom), while the carboxylation status that is responsible for ligand activity was determined for each (left, top). (C) PMA-differentiated THP-1s were treated for 4 h with either serum-free RPMI only (-), a mock transfection control, 10 nM of active Gas6 (Gas6-VK), or 10 nM of inactive Gas6 (Gas6-W). Treatments were alone or combined with inhibitors of 3 µM of GW280264X (an ADAM17 inhibitor), 5 µM of DAPT (a γ-secretase inhibitor), or 10 µM of MG132 (a proteasomal inhibitor). (D) Quantitative results indicate that Gas6, either active or inactive, does not stabilize the C-terminal fragments as shown in the DAPT and MG132 treatments (bands at 75 kDa). As denoted by sMertk (top), the cleavage is decreased with GW280264X treatment compared to the untreated control.

Article Snippet: Concentrated Gas6 reagents were analyzed for concentration via Western blotting using a Gas6 standard (R&D Systems, 885-GSB-050).

Techniques: Expressing, Recombinant, Produced, Transfection, Control, Activity Assay

Journal: International journal of molecular sciences

Article Title: Regulation of Mertk Surface Expression via ADAM17 and γ-Secretase Proteolytic Processing.

doi: 10.3390/ijms25084404

Figure Lengend Snippet: Figure 5. γ-carboxylated Gas6 reduces the tagged Mertk construct on cell membranes of THP-1 cells. (A) THP-1s expressing the tagged construct were starved for 18 h in serum-free RPMI and treated for 3 h. Flow cytometry data shows positive GFPs without staining. As expected, CHX treatment after 3 h reduces the expression of the construct. Gas6-VK, used at a concentration > 10 nM, decreases the FLAG-PE signal more when compared to other treatments known to induce cleavage (PMA, LPS). GW280264X is used as a control for Mertk cleavage. (B) Histogram analysis of “A.” Gas6-VK induces a shift in the FLAG-PE signal, showing that less surface Mertk is present. γ-Carboxylated Gas6 induced the degradation of Mertk on the cell membrane. (C) THP-1s treated with γ-Carboxylated Gas6 at a 10 nM concentration show increased MerTK phosphorylation, detected by immunoblotting against pMerTK. (D) THP-1s expressing the tagged construct, treated with >10 nM of Gas6-VK + 1 µM of PS, show a reduced level of both domains of the tagged construct, suggesting that the Gas6-VK + PS treatment is leading to a degradation of the full-length receptor.

Article Snippet: Concentrated Gas6 reagents were analyzed for concentration via Western blotting using a Gas6 standard (R&D Systems, 885-GSB-050).

Techniques: Construct, Expressing, Flow Cytometry, Staining, Concentration Assay, Control, Membrane, Phospho-proteomics, Western Blot

Journal: International journal of molecular sciences

Article Title: Regulation of Mertk Surface Expression via ADAM17 and γ-Secretase Proteolytic Processing.

doi: 10.3390/ijms25084404

Figure Lengend Snippet: Figure 6. Confocal imaging of the GFP-tagged MerTK construct displayed the differential localization of MerTK upon ligand stimulation and the inhibition of proteases. (A) DAPT and MG132 treatments induce increased cytoplasmic GFP signals compared to untreated cells. (B) Confocal imaging shows GFP localized on the cell membrane, indicating the presence of tagged Mertk constructs on the cell surface. γ-Carboxylated Gas6-treated tagged THP-1 cells showed a reduction in the MerTK construct from the membrane and the localization in lysosomes. (C) Quantification of the GFP fluorescence intensity per cell, calculated from confocal images in mock, γ-carboxylated Gas6, and non-γ-carboxylated Gas6, with the bar plots showing the mean and standard error of each treatment. ns; non-significant; *** p < 0.001; **** p < 0.0001.

Article Snippet: Concentrated Gas6 reagents were analyzed for concentration via Western blotting using a Gas6 standard (R&D Systems, 885-GSB-050).

Techniques: Imaging, Construct, Inhibition, Membrane, Fluorescence

Journal: International journal of molecular sciences

Article Title: Regulation of Mertk Surface Expression via ADAM17 and γ-Secretase Proteolytic Processing.

doi: 10.3390/ijms25084404

Figure Lengend Snippet: Figure 7. γ-carboxylation of Gas6 induces Mertk degradation independent of phosphorylation. (A) Mutants of the tagged construct were created. K619M, a substitution in the ATP-binding site (underlined) of the Mertk kinase domain, inhibits autophosphorylation by preventing ATP binding and the exchange of phosphate molecules. * Amino acid position for ADAM17 cleavage. (B) Constructs are treated with 10 nM ofGas6-VK for 30 min after a 6 h serum starvation. With the ability to bind ATP and phosphorylate, the WT construct becomes phosphorylated while the kinase dead K619M mutant does not. (C) Mutant constructs were treated with 3 µM of GW280264X (an ADAM17 inhibitor; GW), 5 µM of DAPT (a γ-secretase inhibitor), or 10 µM of MG132 (a protea- somal inhibitor) for 4 h. Results show that the absence of the K619M C-terminal fragment from the MG132 treatment with the addition of GW indicates the fragment is a product of cleavage. (D) Confocal images indicated that the K619M mutants have more cytoplasmatic c-Mertk than WT Mertk with MG132 treatment. (E) Comparison of the contrasting pathways between Notch Recep- tor and MerTK Signaling Models. In the absence of a ligand, Notch is not cleaved, while MerTK undergoes homeostatic cleavage, leading to proteasomal degradation. Upon ligand binding, Notch is cleaved at the ADAM 17 site, revealing the gamma-secretase site. Subsequent gamma-secretase cleavage releases the Notch intracellular domain, translocating it to the nucleus for transcriptional activation. Conversely, MerTK, upon ligand (Gas6) interaction, is internalized into endosomal compartments and localizes within lysosomes.

Article Snippet: Concentrated Gas6 reagents were analyzed for concentration via Western blotting using a Gas6 standard (R&D Systems, 885-GSB-050).

Techniques: Phospho-proteomics, Construct, Binding Assay, Mutagenesis, Comparison, Ligand Binding Assay, Activation Assay

Journal: Molecular Cancer Therapeutics

Article Title: Evaluation of the Role of AXL in Fusion-positive Pediatric Rhabdomyosarcoma Identifies the Small-molecule Inhibitor Bemcentinib (BGB324) as Potent Chemosensitizer

doi: 10.1158/1535-7163.mct-23-0285

Figure Lengend Snippet: Figure 2. Gas6 stimulates Axl signaling in FP-RMS cells. A, Representative Western blot images showing AXL expression in IC-pPDX-104 and Rh41 WT, KO (sgAXL-1) and OE lines. GAPDH was used as loading control. B, Morphologic appearance of IC-pPDX-104 and Rh41 cells with AXL WT, KO and OE. Scale bar, 70 mm. C, Schematic representation of the AXL signaling pathway. D, Representative Western blot images of AXL WT, KO (sgAXL-1) and OE cells stimulated with 400 ng/mL GAS6 for 10 minutes. E, Quantification of Western blots measuring the phosphorylation of downstream targets of AXL in AXL WT, KO (sgAXL-1) and OE cells stimulated with 400 ng/mL GAS6 for 10 minutes. Data are represented as mean SEM of the indicated number of independent biological replicates; ordinary two-way ANOVA with Sidak multiple comparisons test. ns, nonsignificant.

Article Snippet: The next day, we stimulated cells with the indicated concentration of GAS6 (R&D Systems, 885-GSB-050) for 10 minutes at 37 C, and processed them for Western blot analysis.

Techniques: Western Blot, Expressing, Control, Phospho-proteomics

Journal: Molecular Cancer Therapeutics

Article Title: Evaluation of the Role of AXL in Fusion-positive Pediatric Rhabdomyosarcoma Identifies the Small-molecule Inhibitor Bemcentinib (BGB324) as Potent Chemosensitizer

doi: 10.1158/1535-7163.mct-23-0285

Figure Lengend Snippet: Figure 5. Axl contributes to the migratory phenotype of Rh41 cells. A–C, Effect of AXL expression levels on the migratory phenotype of Rh41 cells. Representative images of Rh41 AXL WT (sgAAVS1), KO (sgAXL-1, sgAXL-2) and OE cells (A) and quantification (B) of wound-healing assay. Scale bar, 100 mm. C, Wound area remaining after 20 hours. D–F, Effect of bemcentinib on the migratory phenotype of Rh41 cells. Representative images (D) and quantification (E) of wound-healing assay performed on Rh41 WT cells treated with the indicated concentrations of bemcentinib. Scale bar, 100 mm. F, Wound area remaining after 12 hours in Rh41 cells. G and H, Effect of bemcentinib and AXL stimulation with GAS6 on the migratory phenotype of AXL KO cells. G, Quantification of wound-healing assay performed on Rh41 AXL WT (sgAAVS1) and KO (sgAXL-1, sgAXL-2) cells treated with the indicated concentrations of bemcentinib or with 400 ng/mL GAS6. H, Wound area remaining after 15 hours in Rh41 cells. Data are represented as mean þ SEM of n ¼ 3 biological replicates. Ordinary one-wayANOVA with Dunnett multiple comparison test againstthe control group (WT or 0 mmol/L bemcentinib).

Article Snippet: The next day, we stimulated cells with the indicated concentration of GAS6 (R&D Systems, 885-GSB-050) for 10 minutes at 37 C, and processed them for Western blot analysis.

Techniques: Expressing, Wound Healing Assay, Comparison, Control