Phase separation of a PKA type I regulatory subunit regulates β-cell function through cAMP compartmentalization

Area of Science:

• Cell Biology
• Biochemistry
• Endocrinology

Background:

• Cyclic adenosine monophosphate (cAMP) is a crucial second messenger regulating diverse cellular processes.
• The type I regulatory subunit of protein kinase A (PKA), RIα, undergoes liquid-liquid phase separation (LLPS) to compartmentalize cAMP.
• The precise cellular functions regulated by RIα LLPS remain largely uncharacterized.

Purpose of the Study:

• To investigate the role of RIα LLPS in pancreatic beta cell function.
• To identify the mechanisms by which RIα condensates influence cellular signaling and behavior.
• To establish a molecular tool for studying RIα LLPS.

Main Methods:

• CRISPR-based knockout of RIα in MIN6 beta cells.
• Utilized a Y122A RIα mutant with defective cAMP-induced LLPS.
• Assessed effects on calcium and cAMP oscillation frequency, insulin secretion, CREB-mediated gene expression, and cell proliferation.

Main Results:

• RIα condensates form in MIN6 beta cells, indicating functional LLPS.
• RIα LLPS is essential for regulating beta cell calcium and cAMP oscillation frequency.
• RIα LLPS controls insulin secretion, CREB-mediated gene expression, and prevents uncontrolled beta cell proliferation.

Conclusions:

• RIα LLPS plays a critical role in the spatial organization and function of pancreatic beta cells.
• The Y122A mutant serves as a valuable tool for dissecting the functional consequences of RIα LLPS.
• LLPS-driven protein assemblies significantly impact cellular signaling and physiological processes in beta cells.