Genetic alterations of the p14(ARF)-hdm2-p53 regulatory pathway in breast carcinoma

TP53 is the most commonly mutated tumor suppressor gene in human cancers. T he amplification and overexpression of HDM2 plays a role in tumorigenesis v ia inactivation of p53-dependent cell cycle arrest. p14(ARF), an alternate transcript of the INK4A tumor suppressor locus, prevents hdm2-induced trans criptional silencing of p53 by binding hdm2. The role of this p14(ARF)-hdm2 -p53 regulatory pathway in breast carcinoma is unknown. We hypothesized tha t p14(ARF) mutations and HDM2 gene amplification may be alternative mechani sms of p53 inactivation in breast cancer. Mutational analysis of TP53 (exon s 5-9) and exon 1 beta of p14(ARF) was performed by PCR-SSCP and putative m utations were confirmed by sequencing. p14(ARF) mRNA expression was evaluat ed by RT-PCR and the presence of HDM2 gene amplification by differential PC R. Among the cell lines, 7/14 (50%) harbored TP53 mutations and 2/14 (14%) had a deletion of p14(ARF) exon 1 beta with no detectable p14(ARF) mRNA. No ne demonstrated HDM2 gene amplification. TP53 mutations were identified in 7/36 (19%) breast tumors and HDM2 amplification in 2/30 (7%) tumors. All th e tumors contained an intact p14(ARF) exon 1 beta with corresponding expres sion of the mRNA. Alterations in the various components of this regulatory pathway were identified in nine (64%) cell lines and 25% of the 36 breast c ancers with TP53 mutation being the predominant aberration. Although p14(AR F) mutations and HDM2 gene amplification appear to be uncommon events in br east carcinoma, deregulation of this pathway may occur via alternative mech anisms in breast carcinogenesis.