Involvement of p73-dependent apoptosis pathway in the process of acquisition of drug-resistance in human lung cancer cell lines

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p73 is a candidate tumor suppressor gene with substantial DNA and protein homology to the p53 tumor suppressor gene. In the first part of this study, we have investigated two hypotheses: (a) p73 is mutated in diverse types of human cancer, and (b) p73 is functionally redundant with p53 in carcinogenesis so that mutations would be exclusive in these two genes. The entire coding region and intronic splice junctions of p73 were examined in 54 cancer cell lines. Three lung cancer cell lines contained mutations that affected the amino acid sequence. One amino acid substitution was in a region with homology to the specific DNA binding region of p53 and two microdeletions were outside the region of homology. Two of the cell lines with p73 mutations also carried p53 mutations. Our results are inconsistent with the two hypotheses tested. Next we checked hypotheses for p63 that (a) p63 is mutated in diverse types of human cancers and (b)p63 functions in the same pathway as p53 and p73 in the pro … More cess of carcinogenesis, so that mutations in these three genes would be mutually exclusive. We analyzed the genomic structure of the p63 gene and have performed mutational analyses using the same set of cell lines as for p73. We have shown that DLD1 and SKOV3 cells have either heterozygous mutations or polymorphisms in the putative DNA binding domain of p63. In these cell lines, p63 is biallelically expressed. In the last part of the study, we analyzed three naturally occurring p73 mutants found in lung cancer cell lines. NCI-H1155 has a p73 mutation, p73(G264W), in the DNA binding domain, as well as a "gain-of-function" p53 mutation, p53(R273H). p73α(G264W) lacks the transactivation activity itself, and suppressed the transactivation activity of wild-type p73α, indicating that p73α(G264W) is a dominant negative mutant. Consistently, p73α(G264W) failed to suppress colony formation. p73 mutants found in DMS 92 or in A427 showed no functional abnormalities. In NCI-H1155 cells the coexistence of mutations that abrogate the normal function of p73 and p53 may indicate that each mutation confers an additive growth advantage on the cells. Less