GDP-bound Rab27a regulates clathrin disassembly through HSPA8 after insulin secretion.

Area of Science:

• Cell Biology
• Molecular Biology
• Endocrinology

Background:

• Clathrin-dependent endocytosis is crucial for secretory cells, regulating plasma membrane molecule turnover.
• Disruptions in endocytosis are linked to diseases, including impaired insulin secretion in pancreatic beta cells, potentially contributing to diabetes mellitus.
• The molecular mechanisms of endocytosis in pancreatic beta cells are less understood compared to exocytosis.

Purpose of the Study:

• To identify novel proteins interacting with GDP-bound Rab27a in pancreatic beta cells.
• To elucidate the role of GDP-bound Rab27a and its effectors in regulating glucose-induced endocytosis.
• To investigate the specific contribution of HSPA8 to endocytic processes in pancreatic beta cells.

Main Methods:

• Protein-protein interaction studies to identify novel interactors of GDP-bound Rab27a.
• Biochemical assays using purified clathrin-coated vesicles (CCVs) to assess the effect of protein fragments on clathrin dynamics.
• Functional assays in pancreatic beta cells to evaluate the impact on glucose-induced endocytosis.

Main Results:

• Heat shock protein family A member 8 (HSPA8) was identified as a novel interacting protein for GDP-bound Rab27a.
• HSPA8 directly binds GDP-bound Rab27a via the β2 region of its substrate binding domain.
• The HSPA8 β2 fragment inhibited the interaction with GDP-bound Rab27a and suppressed glucose-induced clathrin-dependent endocytosis in pancreatic beta cells, also affecting clathrin dynamics on CCVs.

Conclusions:

• The interaction between GDP-bound Rab27a and HSPA8 plays a significant role in regulating clathrin disassembly from CCVs and subsequent vesicle transport.
• HSPA8 acts as a specific effector of GDP-bound Rab27a, regulating distinct stages of endocytosis in pancreatic beta cells.
• GDP-bound Rab27a differentially regulates stages of glucose-induced endocytosis through specific effectors in pancreatic beta cells, providing mechanistic insights into insulin secretion regulation.