Correlation of beta-actin messenger RNA localization with metastatic potential in rat adenocarcinoma cell lines.

The actin cytoskeleton is involved in the motility of tumor cells. It has been shown in several cell types that beta-actin mRNA is localized in the protrusions of cells in which actin is actively polymerized, and the ability to localize mRNA is correlated with the efficiency of motility. In this context, we studied the distribution of beta-actin mRNA in two different tumor cell lines and correlated it with their metastatic potential. The two cell lines used were the highly metastatic MTLn3 cells and nonmetastatic MTC cells. Nonmetastatic MTC cells have two different pools of beta-actin mRNA (perinuclear and at the leading edge), whereas highly metastatic MTLn3 cells have only a perinuclear distribution of beta-actin mRNA. These differences in mRNA localization are correlated with profound differences in the polarity and plasticity of cell motility of these cells in culture and the histopathology of primary breast tumors derived from these cells. In particular, MTLn3 cells are unpolarized by all cell shape and motility criteria in culture and in their histopathological organization in primary tumors. By comparison, MTC cells are polarized in all identical measurements. These results suggest that the increased plasticity of cell locomotion and the invasiveness of MTLn3 cells result from the failure of metastatic cells to localize beta-actin mRNA properly, causing them to be less polarized and therefore more flexible in their direction of motility. Thus, differences in the polarized organization of cells in the primary tumor that are correlated with beta-actin mRNA localization may have prognostic value in predicting metastatic potential.