Cell cycle arrest, apoptosis and p53 expression in nickel(II) acetate- treated Chinese hamster ovary cells

Nickel(II) compounds are known human and animal carcinogens. In this study,the effects of nickel(II) acetate on cell cycle, apoptosis and p53expression were investigated in order to unveil the elements of earlycellular responses to the metal. Chinese hamster ovary (CHO) cells weregrown for 72 h in Ham's F-12 medium containing 0, 40, 80, 160, 240, 320,480 or 640 microM nickel(II) acetate. DNA fragmentation, representative ofapoptosis, was examined by agarose gel electrophoresis. The distribution ofcells among various phases of cell cycle was determined by DNA flowcytometry. Expression of p53 protein was measured by the Western blottingtechnique. DNA fragmentation was detectable in cells treated with > or =160 microM nickel(II) and its intensity increased with increasingnickel(II) concentration. The proportion of cells at S phase declined in anickel(II) concentration- dependent manner. The decline was accompanied byan increase of cell proportion in G2/M phase and the increase becamestatistically significant in cells exposed to at least 480 microMnickel(II). Expression of p53 protein was not different from that in thecontrol among samples treated with < or = 480 microM nickel(II).However, an extra fraction that migrated close to the p53 protein fractionwas detected in cells treated with 640 microM nickel(II). Our findingssuggest that nickel(II) modulates cellular response through effectorsinvolved in both G2/M arrest and apoptosis regulatory pathways. Theproportion of cells arrested at G2/M phase or undergoing apoptosis dependsdirectly on nickel(II) concentration. High concentration of nickel(II)appears to up-regulate protein(s) other than the common form of p53protein.