Journal: bioRxiv
Article Title: The proteasome maturation factor POMP moonlights as a stress-induced transcriptional regulator
doi: 10.1101/2025.04.25.650603
Figure Lengend Snippet: (A) Representative immunofluorescence images of HEK293 cells expressing either an empty vector control or a POMP plasmid for 72h treated with either DMSO or MG132 for 5h. The formation of POMP nuclear puncta is observed only in response to proteasome inhibition and is independent of POMP overexpression. Scale bars = 5 µm. (B) Analysis of the POMP expression levels in the HEK293 cells of the experiment shown in A. While proteasome inhibition leads to a modest but significant increase in POMP levels, POMP overexpression in combination with proteasome inhibition leads to significant and progressively large increase in cellular POMP levels. *p≤0.05, ****p≤0.0001, Welch’s ANOVA test and post-hoc Dunnett’s T3 multiple comparisons test, n=15 (Cntrl DMSO), 14 (Cntrl MG132), 30 (POMP DMSO) and 18 (POMP MG132), mean±SD, FC=fold change. (C) Analysis of the number of nuclear POMP puncta in the HEK293 cells of the experiment shown in A. The formation of POMP nuclear puncta is independent of POMP expression levels in cells and only proteasome inhibition leads to a significant increase in their number. ns=p>0.05, ****p≤0.0001, Welch’s ANOVA test and post-hoc Dunnett’s T3 multiple comparisons test, n=17 (Cntrl DMSO), 16 (Cntrl MG132), 30 (POMP DMSO) and 18 (POMP MG132), mean±SD. (D) Representative immunofluorescence images of HEK293 cells expressing either POMP-Scarlet or NLS-POMP-Scarlet (nuclear localised) overexpression plasmids for 72h treated with either DMSO or MG132 for 5h. Enforcing nuclear localisation of POMP was not sufficient to drive puncta formation, which requires proteasome inhibition.Scale bars = 5 µm. (E) Analysis of the nuclear POMP expression levels in the HEK293 cells of the experiment shown in D. Overexpression of POMP-Scarlet +/- MG132 and NLS-POMP-Scarlet +/- MG132 led to a significant and progressive rise in nuclear POMP levels. ns=p>0.05, *p≤0.05, ***p≤0.001, one-way ANOVA and post-hoc Tukey’s multiple comparisons test, n= 76 (POMP-Scarlet DMSO), 70 (POMP-Scarlet MG132), 56 (NLS-POMP-Scarlet DMSO), 76 (NLS-POMP-Scarlet MG132), mean±SD, FC=fold change. (F) Analysis of the number of nuclear POMP puncta in the HEK293 cells of the experiment shown in D. The formation of POMP nuclear puncta was independent of nuclear POMP levels in cells and only proteasome inhibition led to a significant increase in their number. ns=p>0.05, ****p≤0.0001, one-way ANOVA and post-hoc Tukey’s multiple comparisons test, n=50 (POMP-Scarlet DMSO), 55 (POMP-Scarlet MG132), 54 (NLS-POMP-Scarlet DMSO), 54 (NLS-POMP-Scarlet MG132), mean±SD. (G) Representative immunofluorescence images of hippocampal neurons treated with either DMSO, the proteasome inhibitors MG132, Carfilzomib or the ROS precursor H₂O₂, and stained for MAP2, the nucleolar marker Fibrillarin and the oxidative stress probe CellROX Green. Treatment with H₂O₂ and proteasome inhibition lead to an increase in cellular ROS levels, measured by the increase in CellROX Green fluorescence. Scale bars = 5 µm. (H) Analysis of the CellROX Green fluorescence intensity in the hippocampal neurons of panel G. Treatment with H₂O₂ and proteasome inhibitors led to a significant increase in CellROX Green fluorescence. *p≤0.05, ****p≤0.0001, one-way ANOVA and post-hoc Dunnett’s multiple comparisons test, n=24 (DMSO), 21 (MG132), 27 (Carfilzomib) and 18 (H₂O₂), Boxplots show the median (line), interquartile range (box), and Min-Max whiskers. FC=fold change. (I) Representative immunofluorescence images of hippocampal neurons treated with either DMSO, MG132 alone or MG132 in combination with the reducing agent DTT (1 mM), and immunostained for POMP, MAP2 and the nucleolar marker Fibrillarin. Preventing ROS production with DTT blocked POMP relocalisation to the nucleolus. Scale bar in the low and high-magnification images 10 and 5 µm, respectively. (J) Analysis of neuronal nucleolar POMP levels in the the experiment in I. While proteasome inhibition led to a significant increase in nucleolar POMP levels, blocking ROS production by DTT treatment prevented the nucleolar relocalisation of POMP. ns=p>0.05, ****p≤0.0001, one-way ANOVA and post-hoc Dunnett’s multiple comparisons test, n=54, Boxplots show the median (line), interquartile range (box), and Min-Max whiskers, FC=fold change. (K) Representative non-reducing SDS-PAGE Western blot analysis of cortical neurons treated with either DMSO, MG132 or MG132+1 mM DTT for 5h. Treatment with MG132 led to elevated POMP levels and the appearance of higher molecular species that were redox sensitive and reduced by co-incubation of MG132 with 1 mM DTT on cells. LaminB1 was used as loading control. (L) Analysis of the Western blot shown in K. DTT blocked the relocalization of POMP. The discrepancy in the size of the effects seen for POMP relocalisation I,J and POMP higher molecular weight species levels in K and L can be explained by the re-oxidation POMP during non-reducing SDS-PAGE in atmospheric oxygen. ns=p>0.05, *p≤0.05, RM one-way ANOVA and post-hoc Dunnett’s multiple comparison test, n=4, mean±SD. (M) Analysis of the Western blots shown in of HEK293 treated with pro-inflammatory cytokines (TNFα, INFα, IL1β, GM-CSF) or water control for four days. Treatment with all four cytokines leads to a significant upregulation in P-HSF1 and its downstream targets Hsp70 and POMP. *p≤0.05, **p<0.01, ****p≤0.0001, RM one-way ANOVA and post-hoc Dunnett’s multiple comparison test, n=4, mean±SD. FC=fold change. (N) Analysis of the CellROX Green fluorescence intensity in HEK293 treated with pro-inflammatory cytokines for four days. In all cases treatment leads to a significant increase in CellROX Green fluorescence. ****p≤0.0001, one-way ANOVA and post-hoc Kruskal-Wallis multiple comparisons test, n=57 (Cntrl), 60 (TNFα, IL1β, GM-CSF), 120 (INFα), Boxplots show the median (line), interquartile range (box), and Min-Max whiskers. FC=fold change. (O) Analysis of the nucleolar POMP levels in HEK293 treated with pro-inflammatory cytokines for four days. Treatment with all four cytokines leads to a significant increase in nucleolar POMP levels. *p≤0.05, ****p≤0.0001, one-way ANOVA and post-hoc Dunnett’s multiple comparison test, n=712 (Cntrl), 795 (TNFα), 472 (IFNα), 291 (IL1β), 272 (GM-CSF), mean±SD. FC=fold change.
Article Snippet: The compounds and cytokines used for cell treatment along with vendor and catalog number, the solvent used for reconstitution, the concentration used and treatment duration (in those cases where only one was used) are hereby listed: Carfilzomib (Abcam, ab216469, DMSO, 2 µM), Epoxomicin (Millipore, 324800, DMSO, 2 µM), MG132 (Invitrogen, J63250.MCR, DMSO, 10 µM), Bortezomib (Invitrogen, J60378, DMSO, 1 µM), HSF1B (Axon Medchem, 2101, DMSO, 70 µM, 7 hr), KNK-437 (Sigma-Aldrich, SML0964, DMSO, 100 µM, 5hr in combination with proteasome inhibition), DTT (Millipore, 111474, 1 mM, H2O, 5hr in combination with proteasome inhibition), H2O2 (AlfaAesar, L13235, H2O, 1 mM, 1hr) TNFα (Peprotech, 300-01A-50UG, PBS+0.1%BSA, 0.2 µg/ml, 4 days), IFNα (Abcam, ab48750, PBS+0.1%BSA, 0.2 µg/ml, 4 days), IL1β (CST, 54059, PBS+0.1%BSA, 0.2 µg/ml, 4 days), GM-CSF (CST, 87015, PBS+0.1%BSA, 0.2 µg/ml, 4 days), chloroquine (Fisher Scientific, C230125G, H2O, 100 µM), (Tocris, 0130, DMSO, 10 µM), CNQX (Tocris, 1045, H2O, 20 µM), APV (Tocris, 0106, H2O, 50 µM).
Techniques: Immunofluorescence, Expressing, Plasmid Preparation, Control, Inhibition, Over Expression, Staining, Marker, Fluorescence, Blocking Assay, SDS Page, Western Blot, Incubation, Molecular Weight, Comparison