Cooperation between p53 and hMLH1 in a human colocarcinoma cell line in response to DNA damage

We have studied the possible interactions between the mismatch repair syste m and p53 in a human colon cancer cell line, HCT-116 (known to have a homoz ygous mutation in mismatch repair gene hMLH1 on chromosome 3) and in a clon e obtained after insertion of a single copy of chromosome 3 (HCT-116+ ch3). Loss of DNA mismatch repair activity resulted in resistance to cisplatin (D DP), p53 accumulated differently in these cell lines after treatment with D DP, Initially at similar high levels after DDP treatment, p53 maintained th e increase in HCT-116 cells, even 72-96 h after drug exposure, whereas HCT- 116+ch3 mismatch-proficient cell line p53 declined to basal levels after 48 h, The higher levels of p53 in mismatch-deficient HCT-116 cells were accom panied by increased transcriptional activity as assessed by the gel-retarda tion assay and by activation of a promoter containing a p53 DNA binding sit e. To better understand the role of p53, if any, in cell sensitivity to DDP, w e disrupted p53 in both cell lines by stable transfection with the human pa pillomavirus type 16 Ed gene. HCT-116/E6 cells were more sensitive to DDP t han the parental cell line, whereas HCT-116+ch3/E6 were fairly similar to H CT-116+ch3 with normal p53 function. Although in our system the transfer of the entire chromosome 3 was used (th us not excluding a possible role of other genes localized on this chromosom e), our data indicate that p53 can cooperate with the mismatch repair syste m. In role of p53 in protecting the cells from DDP-induced DNA damage.