EFFECT OF IONIZING-RADIATION ON CELL-CYCLE PROGRESSION AND CYCLIN BETA-1 EXPRESSION IN HUMAN-MELANOMA CELLS

In the present study we investigated the effect of gamma-irradiation ( 2.5 and 10 Gy) on cell-cycle progression of a human melanoma cell line , M14, characterized by a moderate radiosensitivity (SF2 = 0.5). Flow cytometric analysis showed a dose-dependent S-phase accumulation, whic h was detectable 8 hr after treatment with 2 and 5 Gy and was still pe rsistent at 12 hr after 10 Gy exposure. Such a delay in S-phase was pa ralleled or followed by an accumulation of cells in G(2)M, which was t ransient at the lowest radiation doses and still persistent at 72 hr a fter 10 Gy, Such an accumulation was, at least in part, due to a block in G(2)-M transition, as demonstrated by mitotic index analysis. Biva riate flow cytometric analysis of DNA content and cyclin B-1 expressio n showed that, following 2 and 5 Gy, the fraction of cyclin B-1-expres sing cells was superimposable upon that of G(2)M cells. Conversely, in cells treated with 10 Gy, the fraction of cyclin B-1-expressing cells was half the G(2)M cell fraction, Northern-blot analysis indicated th at the radiation-induced decrease in cyclin B-1 protein expression was accompanied by a reduced cyclin B mRNA level. On the whole, our resul ts indicate a direct inhibitory effect of 10 Gy irradiation on cyclin B-1 expression as a possible cause for the persistent G(2) block in ir radiated M14 cells. (C) 1996 Wiley-Liss, Inc.