ER-tethered RNA-binding protein controls NADPH oxidase translation for hydrogen peroxide homeostasis.

Hydrogen peroxide (H2O2) functions as a signaling molecule in diverse cellular processes. While cells have evolved the capability to detect and manage changes in H2O2 levels, the mechanisms regulating key H2O2-producing enzymes to maintain optimal levels, especially in pancreatic beta cells with notably weak antioxidative defense, remain unclear. We found that the protein EI24 responds to changes in H2O2 concentration and regulates the production of H2O2 by controlling the translation of NOX4, an enzyme that is constitutively active, achieved by recruiting an RNA-binding protein, RTRAF, to the 3'-UTR of Nox4. Depleting EI24 results in RTRAF relocating into the nucleus, releasing the brake on NOX4 translation. The excessive production of H2O2 by liberated NOX4 further suppresses the translation of the key transcription factor MafA, ultimately preventing its binding to the Ins2 gene promoter and subsequent transcription of insulin. Treatment with a specific NOX4 inhibitor or the antioxidant NAC reversed these effects and alleviated the diabetic symptoms in beta-cell specific Ei24-KO mice. This study revealed a new mechanism through which cells regulate oxidative stress at the translational level, involving an ER-tethered RNA-binding protein that controls the expression of the key H2O2-producing enzyme NOX4.

The core autophagy protein ATG5 controls the polarity of the Golgi apparatus and insulin secretion of pancreatic beta cells.

Pancreatic beta cells are insulin-producing cells that are structurally and functionally polarized in the islets of Langerhans. The organization and position of the Golgi complex play a key role in maintaining a polarized cell state, but the factors and molecular mechanisms determining the Golgi polarization of pancreatic beta cells are still unknown. In the current study, using pancreatic beta cell-specific Atg5 knockout mice, we found that Atg5, an essential gene for autophagy, plays a pivotal role in regulating Golgi integrity and polarization by affecting the expression of genes involved in vesicle transport. Deletion of Atg5 led to endoplasmic reticulum (ER) stress and impaired the distribution of proinsulin and insulin secretion of pancreatic beta cells, which further exacerbates diabetes. These results contribute to a comprehensive understanding of autophagy-mediated Golgi polarization and its regulation of the function of pancreatic beta cells.