Epidermal growth factor induces the accumulation of calpactin II on the cell surface during membrane ruffling

Abstract

Confluent and proliferatively quiescent T51B rat liver epithelial cells provide a cellular model for the study of epidermal growth factor (EGF) effects in non‐neoplastic cells. Immunoreactive calpactin II, a well‐known substrate for EGF‐receptor kinase, was found predominantly in the cytosol, although a second im‐munoreactive pool was found in a Triton X‐100‐extractable membrane fraction. Stimulation with EGF resulted in a rapid and transient (2–;5 min) formation of ruffles at the cell surface and at the cell‐cell contacts. Both calpactin II and filamentous actin were found co‐localized at the membrane ruffles. Immunopre‐cipitations of membrane‐bound calpactin II from ³²P‐labeled cells indicate a transient EGF‐dependent phosphorylation of calpactin II correlating with membrane ruffling. These results suggest a temporal (2–5 min) function for calpactin II at the plasma membrane during the EGF‐induced mitogenesis of T51B cells.