METASTASIS-ASSOCIATED MTS1 (S100A4) PROTEIN MODULATES PROTEIN-KINASE-C PHOSPHORYLATION OF THE HEAVY-CHAIN OF NONMUSCLE MYOSIN

Mts1 protein (S100A4 according to a new classification) has been impli cated in the formation of the metastatic phenotype via regulation of c ell motility and invasiveness, Previously we have demonstrated that Mt s1 protein interacted with the heavy chain of nonmuscle myosin in a ca lcium-dependent manner. To elucidate the role of the Mts1-myosin inter action, we mapped the Mts1-binding region on the myosin heavy chain mo lecule. We prepared proteolytically digested platelet myosin and a ser ies of overlapped myosin heavy chain protein fragments and used them i n a blot overlay with Mts1 protein. Here we report that the Mts1-bindi ng site is located within a 29-amino acid region, at the C-terminal en d of the myosin heavy chain (between 1909-1937 amino acids). Two-dimen sional phosphopeptide analysis showed that Mts1 protein inhibits prote in kinase C phosphorylation of the platelet myosin heavy chain at Ser- 1917. We hypothesize that Mts1 protein regulates cytoskeletal dynamics of the metastatic cells through modulation of the myosin phosphorylat ion by protein kinase C in calcium-dependent fashion.