Nuclear expression of the p16CDKN2 gene product during senescence of human pharyngeal epithelial cells

Abstract Objective: It has been proposed that a gene mapping to human chromosome 9p21 plays a critical role in cellular senescence. CDKN2 is a tumor suppressor gene on chromosome 9p21. It encodes a nuclear protein, p16, which inhibits the D-type cyclin/cyclin-dependent kinase complexes that phosphorylate the retinoblastoma protein, thus blocking cell cycle progression through G1. The purpose of this study was to determine whether nuclear p16 expression is altered during the senescence of human pharyngeal epithelial cells (HPECs) m vitro. Methods: An immunocytochemical study was performed to examine a panel of cultured HPECs with a finite lifespan for the nuclear p16 expression. All HPEC cultures were also subjected to a histochemical assay that identifies senescent cells by their positive β-galactosidase activity. Results: Nuclear p16 was undetectable when HPECs were initially cultured in serum-free low-calcium medium. However, nuclear p16 was clearly detected when the cultured HPECs exhibited β-galactosidase activity in the same medium. Conclusion: These results suggest that immunocytochemically detectable amounts of nuclear p16 are associated with senescence of HPECs in vitro.