PKCα Phosphorylates FACI to Switch Its Function in Clathrin-mediated Endocytosis to a Presumed Role in Macropinocytosis in Intestinal and Hepatic Cells.

BACKGROUND & AIMS: We previously identified a fasting- and CREB-H-induced (FACI) protein and defined its adaptor function in clathrin-mediated endocytosis. Both CREB-H and FACI are specifically expressed in the liver and intestine. Here, we investigated the role of FACI in macropinocytosis and its activation by protein kinase Cα.

METHODS

We employed a combination of biochemical, proteomic, cell biological, and microbiological assays to investigate the function of FACI in cultured cells and FACI mice.

RESULTS

Phosphorylation of FACI at S9 and S37 by protein kinase Cα induces its detachment from clathrin-coated pits and relocation to the plasma membrane. FACI promotes phorbol ester-induced macropinocytosis in intestinal and hepatic cells. Interactome analysis reveals that FACI interacts with several actin remodeling proteins. FACI interacts with 14-3-3ζ to release SSH1 phosphatase from sequestration. Free SSH1 activates cofilin-1, which in turn enhances actin remodeling and macropinocytosis. Intestinal pathogens such as Salmonella typhimurium exploit FACI to facilitate their entry into host cells through macropinocytosis.

CONCLUSION

FACI modulates clathrin-mediated endocytosis and macropinocytosis in intestinal and hepatic cells. Protein kinase Cα phosphorylates FACI to switch its function in endocytosis to a presumed role in macropinocytosis in these cells. FACI facilitates enteric pathogen invasion by enhancing macropinocytosis in the intestine.