Altered expression and activity of G1/S cyclins and cyclin-dependent kinases characterize squamous cell carcinomas of the head and neck.
Progressive deregulation of the cell-division cycle is thought to contribute to the establishment and progression of neoplasia. Previously, we have documented the in vivo inactivation of p16INK4A, an inhibitor of G1 cyclin-dependent kinases, in squamous cell carcinomas of the head and neck region. In the present study, we extend these findings by examining the expression and functional activity of cyclin-dependent kinases (CDKs) and their regulatory subunits using a model system of cell lines derived from squamous cell carcinomas. Increased activity of CDK4 and 6 was universal in tumor cells compared with normal keratinocytes, reflecting over-expression of either or both kinases. In contrast to other studies, over-expression of cyclin D1, a regulatory subunit of CDK4 and 6, was not observed. Increased activity of CDK2 was less frequent and was related to over-expression of cyclin A and/or E. All tumor cell lines showed increased expression of proliferating cell nuclear antigen compared to normal keratinocytes. Four SCC cell lines, including one tumor-metastasis pair derived from a single patient, failed to express the p15INK4B transcript. Western blot analysis of cell lysates revealed normal or reduced levels of p27KIP1 in tumor cells compared to normal keratinocytes. However, failure to express wild-type p53 was not reflected by lower levels of p21WAF1. Our data suggest that cell-cycle deregulation is likely to occur by multiple mechanisms during the genesis of head and neck squamous cell carcinomas. Furthermore, p16INK4A is likely to be the primary target for inactivation on chromosome 9p21 in these tumors as p15INK4B loss occurs less frequently.
Patel
V
V
Oral and Pharyngeal Cancer Branch, National Institute of Dental Research, Bethesda, MD, USA. vpatel@yoda.nidr.nih.gov
Jakus
J
J
Harris
C M
CM
Ensley
J F
JF
Robbins
K C
KC
Yeudall
W A
WA
D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D056746:Cyclin G; D056766:Cyclin G1; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D006258:Head and Neck Neoplasms / Q000378:metabolism*; D006801:Humans; D009363:Neoplasm Proteins / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D014407:Tumor Cells, Cultured
C534702:CCNG1 protein, human; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D009363:Neoplasm Proteins; D018809:Proliferating Cell Nuclear Antigen; D018844:Cyclin-Dependent Kinases