p12(DOC-1) is a growth suppressor identified using an animal oral cancer model. 63.8% of human oral cancer expressed reduced levels of p12(DOC-1) (Clin Cancer Res 7: 2776-2782, 2001). We have recently shown that p12(DOC-1) specifically associates with CDK2 (Mol Cell Biol 20:6300-6307, 2000). Recent data further ties p12(DOC-1) to the TGF-b anti-proliferative pathway as a potential negative regulator of CDK2 in the TGF-b-mediated hypophosphorylation of pRB. Objectives: The aim of this study is to examine if p12(DOC-1) can regulate CDK2 activities in vivo, under physiological conditions. Methods: The hypothesis was tested by generating inducible p12(DOC-1) antisense and sense human keratinocytes cell lines (HaCaT). The HaCaT cells express p12(DOC-1) and are TGF-b responsive. Results: Induction of the p12(DOC-1) antisense and sense transgene caused the expected reduction and increase of endogenous p12(DOC-1) mRNA and protein levels. Immunoprecipitation of CDK2 revealed that the inducible transgene altered the CDK2-kinase activities (pRBc and H1). Phosphorylation of endogenous pRB was dramatically affected by the inducible transgene. Most interesting is that concurrent treatment of these cells with TGF-b and induction of the antisense and sense transgene led to the modulation of endogenous CDK2 activities and pRB phosphorylation that supports p12(DOC-1) as a negative regulator of CDK2 in the TGF-b antiproliferation pathway. Cellular proliferation was significantly altered with ± p12(DOC-1) transgene induction as shown by tritiated thymidine incorporation (p<0.05 at 48hr). Conclusions: These data collectively support that p12(DOC-1) is a negative regulator of CDK2 kinase activities in vivo. In addition, p12(DOC-1) mediated the antiproliferative signaling of TGF-b by suppressing CDK2 mediated phosphorylation of pRB.

Back to the Oral Medicine & Pathology Program
Back to the IADR/AADR/CADR 80th General Session (March 6-9, 2002)

Top Level Search