In situ detection of unexpected patterns of mutant p53 gene expression in non-small cell lung cancers

Many solid tumors, including non-small cell lung cancers (NSCLCs), are char acterized by heterogenous expression of p53 protein in the neoplastic cells . To analyse the molecular implications of this finding, we examined topogr aphic distribution of p53 mutations using in situ polymerase chain reaction (PCR) in primary NSCLCs, showing distinct patterns of variable p53 overexp ression by immunohistochemistry, Unique sets of primers for each mutation w ere designed, and optimal PCR conditions were determined by standard PCR us ing DNA from cloned mutants or cell lines established from these tumors. Ai l tumor cell nuclei, regardless of the status of p53 overexpression, demons trated homogeneous distribution of mutant p53 with specific primers, indica ting that only subgroups of the mutated cells overexpressed p53 protein. In situ reverse transcription (RT)-PCR was applied to detect mutant mRNA in t he individual tumor cells using specific primers. We found that in each cas e the distribution of mutant p53 mRNA coincided with that of immunohistoche mical overexpression of p53 protein. Our results suggest that the regulatio n of mutant p53 expression, but not the genotype, is heterogeneous in the n eoplastic cells, The topographic genomapping of p53 in NSCLC using in situ PCR provides a novel approach to view molecular mechanisms of lung carcinog enesis.