Phosphorylation of moesin by Rho-associated kinase (Rho-kinase) plays a crucial role in the formation of microvilli-like structures

Rho-associated kinase (Rho-kinase), which is activated by the small GTPase Rho, phosphorylates moesin at Thr(558) in vitro. Here, using a site- and ph osphorylation state-specific antibody, we found that the expression of domi nant active RhoA in COS7 cells induced moesin phosphorylation and the forma tion of microvilli-like structures at apical membranes where the Thr(558)-p hosphorylated moesin accumulated, whereas the expression of dominant negati ve Rho-kinase inhibited both of these processes. The expression of dominant active Rho-kinase also induced moesin phosphorylation. When COS7 cells exp ressing moesin or moesin(T558A) (substitution of Thr by Ala) were cultured under serum-depleted conditions, there were few microvilli-like structures, whereas microvilli-like structures remained in the cells expressing moesin (T558D) (substitution of Thr by Asp). The expression of moesinT558A inhibit ed the dominant active RhoA-induced formation of microvilli-like structures . These results indicate that Rho-kinase regulates moesin phosphorylation d ownstream of Rho in vivo and that the phosphorylation of moesin by Rho-kina se plays a crucial role in the formation of microvilli-like structures.