INHIBITION BY KINASE INHIBITORS OF THE DEVELOPMENT AND THE DISAPPEARANCE OF THE PREPROPHASE BAND OF MICROTUBULES IN TOBACCO BY-2 CELLS

The effects of two kinase inhibitors, staurosporine and K-252a, on the development and the disappearance of the preprophase band of microtubules (PPB) were studied in tobacco BY-2 cells, the cell cycle of which had been synchronized. Treatment of cells at late G2 phase or at prophase with 20 muM staurosporine or 2 muM K-252a for 2 or 3 h caused a decrease in the rate of development of PPBs and inhibited the disappearance of PPBs once they had developed, with the resultant accumulation of cells with a PPB. Cortical microtubules (MTs) or PPBs on protoplast ghosts, which were prepared from BY-2 cells in late G2 phase or at prophase, disappeared on treatment of the ghosts with ATP or ATPgammaS but not on treatment with AMP-PNP. The effect of ATP on the disappearance of MTs on the ghosts was suppressed by 20 pM staurosporine. Although 2 muM K-252a applied to the culture medium suppressed the anticipated disappearance of PPBs, it did not suppress the disappearance of MTs on the ghosts that was caused by ATP. We propose tentatively that a kinase sensitive to staurosporine but not to K-252a is directly involved in the disappearance of MTs and that a kinase that is sensitive to K-252a is indirectly involved in this process. The disappearance of MTs on protoplast ghost that was induced by ATP did not occur in the presence of 20 muM taxol.