Decrease in gamma-actin expression, disruption of actin microfilaments and alterations in cell adhesion systems associated with acquisition of metastatic capacity in human salivary gland adenocarcinoma cell clones.

In order to clarify how cytoskeletons and adhesion systems change through acquisition of metastatic capacity in a cancer cell, we examined the expressions of beta- and gamma-actin, the morphology of actin microfilaments and focal contacts, and also the expression of vinculin in a salivary gland adenocarcinoma cell clone cl-1, which acquired metastatic capacity, in comparison with its original clone HSGc lacking metastatic ability. Two-dimensional gel electrophoresis of Triton-insoluble fractions and combined Western blot analysis by immunostaining with anti actin-isoform antibodies showed that the expression of gamma-actin was somewhat lower than that of beta-actin in HSGc, and cl-1 expressed a comparable amount of beta-actin to HSGc, whereas gamma-actin expression by cl-1 was far less than that by HSGc. Northern blot analysis demonstrated that there was little difference in the level of beta-actin mRNA between HSGc and cl-1, while the level of gamma-actin was markedly decreased in cl-1 as compared with HSGc. In terms of morphology, cl-1 cells showed disruption of actin microfilaments and a decrease in the size and number of focal contacts on the cell surface. Furthermore, cl-1 showed decreased expression of vinculin, which became obscured even at the end of actin microfilaments. These results demonstrated that a decrease in gamma-actin, disruption of actin microfilaments, and suppression of focal contacts as well as vinculin take place in the transformation from a non-metastatic condition to a metastatic one in the human salivary gland adenocarcinoma cell clones. Thus, it was strongly suggested that these changes contribute to a decrease in cell adhesiveness and an increase in cell motility, which is probably a major cause for acquisition of metastatic potential.