EFFECT OF STAUROSPORINE ON MOLT-4 CELL PROGRESSION THROUGH G(2) AND ON CYTOKINESIS

Staurosporine (SSP) is an inhibitor of a variety of protein kinases wi th an especially high affinity towards protein kinase C. Whereas SSP h as been shown to halt the cell cycle progression of various normal, no ntransformed cell types in G(1), most virus transformed or tumor cells are unaffected in G(1) but arrest in G(2) phase. SSP has also been ob served to increase the appearance or cells with higher DNA content, su ggestive of endoreduplication, in cultures of tumor cells. Using multi variate flow cytometry (DNA content vs. expression of cyclin B, nucleo lar p120 protein, or protein reactive with Ki-67 antibody) which makes it possible to discriminate cells with identical DNA content but at d ifferent phases of the cycle, we have studied the cell cycle progressi on of human lymphocytic leukemic MOLT-4 cells in the presence of 0.1 m u M SSP.MOLT-4 cells did not arrest in G(1) or G(2) phase in the prese nce of the inhibitor. Rather, they failed to undergo cytokinesis, ente ring G(1) phase at higher DNA ploidy (tetraploidy; G(1T)), and then pr ogressed through S-T (rereplication) into G(2T) and M(T). The rates of entrance to G(2) and G(2T) were essentially identical, indicating tha t the rates of cell progression through S and S-T as well as through G (2) and G(2T), respectively, were similar. Cells entrance to mitosis a nd mitotic chromatin condensation were also similar at the diploid and tetraploid DNA content level and were unaffected by 0.1 mu M SSP. No evidence of growth imbalance (altered protein or RNA to DNA ratio) was observed in the case of tetraploid cells. The data show that, in the case of MOLT-4 cells, all events associated with the chromosome or DNA cycle were unaffected by SSP; the only target of the inhibitor appear s to be kinase(s) controlling cytokinesis. (C) 1994 Wiley-Liss, Inc.