Cyclin D-1 amplification is independent of p16 inactivation in head and neck squamous cell carcinoma

Progression through the G(1) phase of the cell cycle is mediated by phospho rylation of the retinoblastoma protein (pRb) resulting in the release of es sential transcription factors such as E2F-1. The phosphorylation of pRb is regulated positively by cyclin D-1/CDK4 and negatively by CDK inhibitors, s uch as p16 (CDKN2/MTS-1/INK4A), The p16/cyclin D-1/Rb pathway plays a criti cal role in tumorigenesis and many tumor types display a high frequency of inactivation of at least one component of this pathway. In order to determi ne the overall contribution of these three components to progression of hea d and neck squamous cell carcinoma (HNSCC), we examined p16 inactivation, c yclin D-1 amplification, and pRb expression in 23 primary HNSCC tumors and five cell lines, p16 inactivation was detected in 19/23 (83%) primary tumor s by detailed genetic analysis and was confirmed by immunohistochemistry (M C), Absence of Ph protein expression indicative of pRb inactivation was ide ntified in 2/23 (9%) tumors, In this set of tumors, there was a perfect inv erse correlation between p16 and pRb inactivation, Using fluorescence in si tu hybridization (FISH) cyclin D-1 amplification was identified in 4/5 (80% ) cell lines and 4/11 (36%) primary tumors. However, 2/4 cell lines and all four primary tumors with cyclin D-1 amplification contained a concomitant alteration of p16, Therefore 21/23 (91%) of primary HNSCC contained at leas t one alteration in the p16/cyclin D-1/Rb pathway. Although p16 and Rb alte ration are apparently exclusive, cyclin D-1 amplification occurs concomitan tly with the loss of p16 suggesting an additional role for this amplificati on in HNSCC.