Interaction of metastasis associated Mts1 protein with nonmuscle myosin.

The mts1 gene codes for a 101 amino acid protein which belongs to the subfamily of S100 Ca(2+)-binding proteins and is overexpressed in metastatic cancers as compared to their nonmetastatic counterparts. While the Mts1 protein is putatively involved in cytoskeletal-membrane interactions, its exact physiological role is not known. In order to gain insight into the biological function of Mts1, its expression was monitored throughout mouse embryogenesis as well as in normal adult mouse tissues. In situ hybridizations of mouse embryos showed expression of mts1 mRNA to be highest in trophoblast cells of a day 8 old embryo. In normal adult mouse tissues, immunocytochemistry revealed Mts1 expression in a T-cell specific pattern in both the thymus and spleen. These results indicate that the expression of mts1 is prevalent in motile cell types, and to further elucidate the role of Mts1, gel overlay and GST-fusion protein experiments were performed to identify proteins that interact with the Mts1 protein. Nonmuscle myosin II was found to interact with Mts1, suggesting a role for Mts1 in the process of motility and lending credence to the hypothesis that Mts1 may enhance metastatic potential by increasing the motility of cancerous cells.