Deletion of the INK4a/ARF locus in hamster oral and pancreatic carcinoma cell lines

Abstract

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The INK4a-ARF (CDKN2A) locus, located on chromosome 9p21, encodes two functionally distinct tumor suppressor genes, p14ARF and p16INK4a, which play active roles in the p53 and Rb tumor suppressive pathways. Previous studies have shown that the p16INK4a gene is inactivated in up to 98% of human pancreatic tumor specimens and 83% of oral squamous cell carcinoma samples. Similarly, p14ARF has been shown to be inactivated in up to 85% of HNSCC and 57% of pancreatic tumors, respectively. Chemically-induced tumors in the Syrian Golden hamster (Mesocricetus auratus) have been shown to be excellent animal models for the comparative development and progression of pancreatic and oral carcinomas. The purpose of this study was to determine the importance of the INK4a/ARF locus using these two experimental hamster models of carcinogenesis. First, hamster p16INK4a (GenBank Accession AF292567) and p13ARF (GenBank Accession AF443796) cDNAs were cloned and sequenced. The hamster p16INK4a cDNA coding region (CDS) shares 78%, 80%, and 81% identity with the human, mouse, and rat p16INK4a nucleotide sequences, respectively. Similarly, the hamster p13ARF cDNA CDS shares 79%, 76% and 80% sequence identity with human p14ARF, mouse p19ARF and rat p19ARF nucleotide sequences, respectively. Interestingly, the predicted size of the hamster p13ARF protein is closer in size to the human ortholog (13.1 kDa versus 13.9 kDa, respectively) than that of other rodents (mouse, rat)(13.1 kDa versus 19.2 kDa and 17.3 kDa, respectively). Second, genomic deletion analysis for hamster p16INK4a and p13ARF genes was performed using tumorigenic and non-tumorigenic hamster cell lines. Both p16INK4a (Exon 2) and p13ARF (Exon 1β) were homozygously deleted in a cheek pouch carcinoma cell line (HCPC) and two pancreatic adenocarcinoma cell lines (KL5B, H2T), but not in tissue-matched, non-tumorigenic cheek pouch epithelial (POT2) or pancreatic ductal (KL5N) cell lines. These data strongly suggest that inactivation of the p16INK4a and p13ARF genes by homozygous deletion plays a prominent role in hamster pancreatic and oral tumorigenesis, as has been well established in correlative studies in comparable human tumors. Furthermore, this study reinforces the importance of the hamster models as appropriate surrogates for examining pancreatic and cheek pouch carcinogenesis in subsequent mechanistic-, therapeutic-, and preventive-based studies to providing translational data for pancreatic adenocarcinoma and oral squamous cell carcinoma in humans.