Involvement of protein kinase C in taxol-induced polyploidization in a cultured sarcoma cell line

Taxol was found to inhibit the proliferation and to induce the polyploidiza tion of cultured methylcholanthrene-induced sarcoma cells (Meth-A cells). T o investigate whether protein kinase C is involved in taxol-induced polyplo idization. phorbol 12-myristate 13-acetate (PMA), which regulates the activ ity of protein kinase C, was used along with taxol to treat the cells. We f ound that PMA did not interfere with the proliferation and did not induce p olyploidization by itself. However, at low concentration, taxol, which by i tself did not induce polyploidization, clearly induced polyploidization in the presence of PMA. To explore the mechanism by which PMA potentiates poly ploidization, the levels of the G1 checkpoint-related proteins cyclin E and cdk2, and those of the G2 checkpoint-related proteins cyclin B and cdc2 we re determined by flow cytometry. We found that both G1 and G2 checkpoint-re lated proteins increased during the induction of polyploidization. To verif y the relationship between protein kinase C and tubulin polymerization, flo w cytometry was used to determine the total content of tubulin protein, and morphological observation was used to examine spindle organization. PMA di d not affect the taxol-induced increase in tubulin protein, but markedly po tentiated taxol-induced spindle disorganization. These findings suggest tha t protein kinase C plays an important role in regulating the induction of p olyploidization in Meth-A cells. (C) 2000 Elsevier Science B.V. All rights reserved.