Biology subjects

Quezada, E.

Publications and source records attributed to Quezada, E..

2 recordsLinked to original sources

bioRxiv2024

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

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.

molecular biology↗

bioRxiv2021

Insulin mRNA is stored in RNA granules in resting beta cells

The glucose-stimulated biosynthesis of insulin in pancreatic islet beta cells is post-transcriptionally regulated. Several RNA-binding proteins (RBPs) that regulate Insulin mRNA stability and translation also bind mRNAs coding for other insulin secretory granule (ISG) proteins. However, an overview of these interactions and their glucose-induced remodelling is still missing. Here we identify two distinct sets of RBPs that were preferentially pulled down with the 5-UTRs of mouse Ins1, Ins2, spliced Ins2, Ica512/Ptprn and Pc2/Pcsk2 mRNAs from extracts of either resting or stimulated mouse insulinoma MIN6 cells. Among RBPs binding to all tested transcripts in resting conditions was hnRNP A2/B1. Hnrnpa2b1 KO MIN6 cells contained lower levels of Ins1 mRNA, proinsulin and insulin, and had reduced insulin secretion. In resting cells, both hnRNP A2/B1 and Insulin mRNAs localized to stress granules, which dissolved upon glucose stimulation. Insulin mRNA-positive RNA granules were also found in human pancreatic beta cells in situ. Our results suggest that resting beta cells store mRNAs for insulin secretory granule proteins in stress granules through specific RNA protein interactions. Glucose stimulation remodels these interactions, releasing the transcripts, and another set of RBPs coordinates their translation.

cell biology↗