Diacylglycerols and the protein kinase inhibitor H‐7 suppress cell polarity and locomotion of walker 256 carcinosarcoma cells

Abstract

We show that diacylglycerols, like phorbol myristate acetate (PMA), suppress cell polarity and locomotor activity of Walker carcinosarcoma cells in a dose-dependent fashion in vitro. OAG and diC8 show significant activity at concentrations above 3 x 10(-5) M. The inhibitory effect on locomotion is due to a reduction in the proportion of locomoting cells rather than gradual lowering of the speed of individual cells. Measurement of protein kinase C (PKC) activity in isolated fractions showed a substantial reduction of the total cellular PKC activity and of the activity in the cytosolic fraction following incubation of cells with 10(-8) M PMA for 30 min. In contrast, the total and relative PKC activity associated with the membrane fraction was increased by PMA. The effect of H-7, an inhibitor of PKC as well as of cAMP-dependent kinase, has been tested. H-7 suppressed cell polarity of "unstimulated" control cells (ID50 = 6.5 microM H-7), colchicine-stimulated cells (ID50 = 92 microM H-7) or cells treated with both PMA and colchicine (ID50 = 15 microM H-7), in a dose-dependent fashion. The locomotor activity of the cells was also suppressed. LTB4 had no clearcut activity in this system. Our findings suggest that diacylglycerols and H-7 are of interest as physiological or pharmacological stop signals for tumor-cell locomotion. Contrary to our expectations, PMA and diacylglycerols vs. H-7 did not produce opposing or antagonistic effects on cell polarity and locomotion. This similarity may be due to down-regulation of PKC by PMA and inhibition of PKC by H-7. However, the mechanisms underlying these novel effects of diacylglycerols and of H-7 on cell polarity and locomotion may be even more complex; they require further studies.