Specific deletion of p16(INK4a) with retention of p19(ARF) enhances the development of invasive oral squamous cell carcinoma.

The cyclin dependent kinase inhibitor 2A (CDKN2A)/alternate reading frame (ARF) locus consists of two overlapping tumor suppressor genes, p16INK4a and p14ARF (p19Arf in mice), encoding two unrelated proteins in alternative reading frames. Previous reports suggest that p16INK4a and p14ARF alterations independently exhibit differential roles, and p16INK4a is more closely associated with a poor prognosis in oral cancer. However, the role of p16INK4a -specific loss in oral squamous cell carcinogenesis remains unclear. We assessed chemical carcinogen 4-nitroquinoline 1-oxide (4NQO)-induced multistep oral squamous cell carcinogenesis in mice carrying p16INK4a -specific loss with retention of the p19ARF gene (p16 INK4a -/-). 4NQO-treated p16-/- mice exhibited a higher incidence and multiplicity of oral squamous cell carcinoma (OSCC) development relative to 4NQO-treated wild-type mice. 4NQO-treated p16 INK4a -/- OSCC cells exhibited higher proliferation and upregulation of Arf, transcription factor E2f1, tumor protein p63 (tp63), and oncogenic DeltaNp63, an isoform p63, compared with observations in 4NQO-treated wild-type OSCC cells. Furthermore, the overexpression of oncogenic DeltaNp63 was associated with human OSCC. In conclusion, these results in mice indicate the biological significance of p16INK4a-specific loss with retention of p19Arf in oral squamous cell carcinogenesis, and DeltaNp63 may be a potential target for OSCC.