Post-transcriptional regulation of insulin mRNA storage by G3BP1/2+ condensates in beta cells

Quezada, E.; Vasiljevic, J.; Pal, A.; Münster, C.; Friedland, D.; Schöniger, E.; Sönmez, A.; Seiler, A.; Roch, P.; Wegbrod, C.; Ganss, K.; Knoch, K.-P.; Kipke, N.; Alberti, S.; Nano, R.; Piemonti, L.; Aust, D.; Weitz, J.; Distler, M.; Solimena, M.

doi:10.1101/2024.05.25.595863

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bioRxiv · 10.1101/2024.05.25.595863

Post-transcriptional regulation of insulin mRNA storage by G3BP1/2+ condensates in beta cells

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Abstract

Hyperglycemia upregulates insulin translation in pancreatic beta cells. Several RNA- binding proteins involved in this process have been identified, including G3BP1, a stress granule marker downregulated in islets of subjects with type 2 diabetes. We show that in mouse insulinoma MIN6-K8 cells exposed to fasting glucose levels G3BP1 and its paralog G3BP2 colocalize to cytosolic condensates with eIF3b and Ins1/2 mRNA. Upon glucose stimulation, the condensates dissolve and G3BP1/2, eIF3b, and insulin mRNAs redistribute throughout the cytosol. Intriguingly, G3BP1+ condensates in MIN6-K8 cells differ from sodium arsenate-induced stress granules in regards to eIF2 and AMPK phosphorylation. Knockout of G3BP1 or G3BP2 prevented condensate assembly, but only G3BP1 deletion decreased the levels of Ins1/2 mRNA and proinsulin and impaired polysome formation. Like glucose, other insulin secretagogues such as Exendin-4 and palmitate, but not high KCl, prompted the dissolution of G3BP1+ condensates. G3BP1+/Ins mRNA+ condensates were also present in mouse and human beta cells from normoglycemic donors. Hence, G3BP1+ condensates represent a glucose-regulated compartment for the physiological storage and protection of insulin mRNA in resting beta cells.

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Quezada, E., Vasiljevic, J., Pal, A., Münster, C., Friedland, D., Schöniger, E., Sönmez, A., Seiler, A., Roch, P., Wegbrod, C., Ganss, K., Knoch, K.-P., Kipke, N., Alberti, S., Nano, R., Piemonti, L., Aust, D., Weitz, J., Distler, M., Solimena, M.. 2024-05-25. Post-transcriptional regulation of insulin mRNA storage by G3BP1/2+ condensates in beta cells. https://doi.org/10.1101/2024.05.25.595863

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