The Islet-1 Interaction Partner Rnf20 Regulates Glucose Homeostasis and Pancreatic β-Cell Identity.

Diabetes is characterized by a loss of functional β-cell mass; therefore, identifying factors involved in establishing and preserving β-cells is critical to combat rising diabetes incidence. While transcription factors are crucial β-cell regulators, knowledge of coregulators facilitating gene expression is limited. Previously, we demonstrated that the islet-1 (Isl1) transcription factor forms complexes with ubiquitin ligases ring finger 20 (Rnf20) and Rnf40 to regulate β-cells in vitro. Here, we investigated whether Rnf20-mediated complexes are required for β-cell function in adult islets by characterizing a novel β-cell-enriched Rnf20 knockout mouse model. Tamoxifen induction of Rnf20 recombination prompted a robust loss of histone 2B monoubiquitination, imparted severe hyperglycemia and glucose intolerance, and elicited an overall reduction in insulin content. Expression of mRNAs and proteins involved in glucose-stimulated insulin secretion and β-cell identity were also dysregulated in Rnf20Δβ-cell mice. Comparative analyses of the loss of either Rnf20 or Isl1 yielded similar changes in the β-cell regulome, supporting that Isl1::Rnf20 complexes are critical regulators of β-cell identity and function. Isl1::Rnf20 complexes are maintained in human tissues wherein they regulate insulin expression, secretion, and content. These findings increase our understanding of key players in β-cell maintenance, which is crucial for the advancement of β-cell derivation diabetes therapeutics. ARTICLE HIGHLIGHTS: Transcription factor Islet-1 (Isl1) and ubiquitin ligase Ring Finger 20 (Rnf20) complexes regulate insulin secretion and β-cell gene expression in vitro. Loss of Rnf20 in adult β-cells disrupts β-cell identity and insulin processing, production, and secretion. In complex with Isl1, Rnf20 influences the β-cell regulome and supports proper glucose homeostasis.