p53 apoptotic pathway molecules are frequently and simultaneously altered in nonsmall cell lung carcinoma.

Background: Lung carcinomas show frequent inactivation of the p53 tumor suppressor, which regulates an apoptotic pathway. The objective of the current study was to assess how the p53 apoptotic pathway is altered in nonsmall cell lung carcinoma (NSCLC), especially in tumors without p53 alterations.

Methods: p53, its upstream regulators (p14(ARF) and HDM2), and downstream effectors of the apoptotic pathway (BAX and BCL2) were studied in 118 NSCLC specimens. p53 was analyzed by single-stranded conformation polymorphism analysis covering exons 2-11 and by immunohistochemistry (IHC). p14(ARF) was analyzed by methylation-specific polymerase chain reaction and IHC. HDM2 was analyzed using Southern blot analysis and IHC. BAX and BCL2 were analyzed by IHC. Two other upstream regulators that regulate the stability of HDM2, PTEN and HAUSP, also were studied.

Results: Of 118 NSCLC specimens that were analyzed, p53 alterations were detected in 74 tumors (63%), p14(ARF) inactivation was detected in 53 tumors (45%), and overexpression of HDM2 was found in 31 tumors (26%), including 6 tumors with gene amplification. Although p53 inactivation and HDM2 overexpression were detected simultaneously, HDM2 gene amplification was observed only in tumor specimens without p53 mutations. IHC revealed PTEN down-regulation in 22 of 88 tumors (25%). HAUSP Northern blot analysis demonstrated several-fold differences in gene expression that did not correlate with p53 alterations. Of 118 NSCLC specimens, expression of BAX and BCL2 expression were detected in 46 tumors (39%) and 17 tumors (14%), respectively. Finally, ASPP1 and ASPP2, molecules involved in mediating the transcription function of p53, were not found to be aberrantly expressed when tested by Northern blot analysis.

Conclusions: Overall, two or more p53 pathway components were found to be frequently altered in patients with NSCLC. Greater than 90% of the alterations were due to abnormalities of p53, p14(ARF), or HDM2. Therefore, the inactivation of one or more components of the p53 pathway appears to be a prerequisite for the development of most NSCLCs.