Differential induction of premature chromosome condensation by calyculin Ain human fibroblast and tumor cell lines

The feasibility of chemically-induced premature chromosome condensation (PC C) was tested in two human fibroblast and two human malignant melanoma cell lines. To induce PCCs, calyculin A, a potent protein phosphatase inhibitor was used at a final concentration of 80 nM. Attached cells and cells put i nto suspension by trypsinization were incubated with calyculin A at 37 degr ees C for 1 hour Calyculin A was able to induce PCCs in all the phases of t he cell cycle with the tumour cell lines giving the highest PCC frequency. No systematic differences were observed between attached cells and cells pu t into suspension by trypsinization. However, a cytotoxic effect that led t o the loss' of 50% to 80% of the treated cells was observed The cytotoxic e ffect was more severe in the fibroblast than in the tumour cell lines. The appearance of deformed, fragile and fragmented nuclei with no particular ch romatin condensation would explain to some extent this cytotoxic effect. A better understanding of the mechanism of action of calyculin A would help g eneralising its use to study interphase chromosome aberrations.