Phosphorylation of 558T of moesin detected by site-specific antibodies in RAW264.7 macrophages.

To determine, whether 558Thr in the carboxyl-terminal domain of moesin is phosphorylated in cells other than platelets, rabbit phosphorylation state-specific antibodies were made to the chemically phosphorylated synthetic hexapeptide KYKpTLR of the moesin sequence, as well as to the unphosphorylated form. The affinity-purified antibody populations were specific for either the phosphorylated or the unmodified peptide conjugated to BSA. Site-specific phosphorylation of moesin is detected in RAW macrophages by Western blot analysis, and immunofluorescence studies demonstrate that phosphorylated moesin is localized in filopodial protrusions. After pretreatment with the phosphatase inhibitor calyculin A, a similar effect to that seen in platelets in found, namely a substantial increase in moesin phosphorylation at 558Thr and redistribution of phospho-moesin together with F-actin into one or more ring-like structures in the cytoplasm, presumably due to binding of phosphorylated moesin to F-actin.