Previous work has shown that PMA and
diacylglycerols, activators of
protein kinase C (PKC) can suppress cell polarity and locomotor activity of Walker
carcinosarcoma cells in vitro, suggesting that PKC activation may result in a stop signal for
tumor cell locomotion. This hypothesis was further analysed. The present results show that the
DAG kinase inhibitor,
R 59022, suppressed
tumor cell polarity and strongly inhibited cell locomotion at a concentration of 10(-4), thus supporting the earlier finding that an increased availability of DAGs can suppress the locomotor activity of Walker
carcinosarcoma cells. The results support the stop-signal hypothesis of PKC activation insofar as
DAG kinase inhibition mimics the effects of DAGs and PMA. In order to clarify further the effects of
protein kinase modulation on locomotion, we now extended our studies on structurally different inhibitors of
protein kinases. In contrast to
H-7,
HA-1004 had no effect on cell polarity and did not reduce cell locomotion in the presence of
colchicine, but reduced the proportion of spontaneously locomoting cells by 70% at 3 x 10(-4) M.
Polymyxin B suppressed cell polarity and locomotion only at concentrations that proved to be toxic.
Tamoxifen had no significant effect on cell polarity and locomotor activity.
Sangivamycin did not suppress cell polarity and spontaneous locomotion at a concentration range of 10(-9) M to 10(-4) M. However,
at 10(-4) M it decreased the proportion of migrating,
colchicine-stimulated cells by 50%. The diverse responses to structurally different PKC inhibitors may be explained by their limited and variable specificity for PKC and different mechanisms of action on PKC.