Low metastatic parent B16 melanoma and isolated B16-F1 cell lines have a third actin designated as βm(Ax:previously). ßm actin is scantily or not at all detected in highly metastatic cell lines, such as B16-F10 and BL6. To directly assess the physiological role of ßm in phenotypic changes of B16 melanoma, we transfected expression plasmids of βm into B16-F10 cells. The actin expressed in the transfectants is located largely in cytoskeletal fractios. The transfectants exhibited a larger number of stress fibers and a lower invasiveness than did the recipient cells. Thus, βm actin plays an important role in the organization of actin stress fibers, the result being a decrease in invasiveness of B16 melanoma.
