Characterization of p53 in Chinese hamster cell lines CHO-K1, CHO-WBL, andCHL: implications for genotoxicity testing

Since the p53 gene function is critical to how a cell responds to DNA damag e, We investigated the p53 status in Chinese hamster cell lines commonly us ed in genotoxicity tests for cytogenetic damage around the world. These inc luded: Chinese hamster ovary K1 (CHO-K1), Chinese hamster ovary WBL (CHO-WB L), and Chinese hamster lung (CHL) cells. The results of DNA sequencing, pr otein analysis, and cell cycle analysis demonstrate that the CHO-K1 and CHO -WBL cell lines have mutant p.53 sequence [a mutation in codon 211 in exon 6 resulting in a change from Thr (ACA) to Lys (AAA)], mutant protein (high spontaneous levels that are non-inducible after X-irradiation), and mutant function (lack of G1 checkpoint). Interestingly, the CHL cell line has a co mpletely wild-type p53 DNA sequence. However, the CHL cells have an abnorma lly high spontaneous level of wild-type p53 protein expression that is not inducible after X-irradiation, yet there is some evidence of G1 delay after irradiation. The protein data suggests that p53 in CHL cells is not being regulated normally, and thus is probably not functioning normally. The mech anism leading to this abnormal regulation of p53 in CHL cells clearly does not involve mutation in the p53 gene. Overall, the CHL cell line may be sim ilar to the CHO cell lines, in that they all appear to have abnormal p53 fu nction. Further work is needed to determine whether the presence of spontan eously high levels of wild-type p53 in CHL cells results in a difference in response to DNA damage (quantitatively or qualitatively) compared to the p 53 mutant CHO cell lines. (C) 1999 Elsevier Science B.V. All rights reserve d.