[The effects of exogenous p16 expression on CDK4, Cyclin D1 and pRb in nasopharyngeal carcinoma cell lines].
OBJECTIVE
To investigate the effect of exogenous p16 on Cyclin D1, CDK4 and pRb, and to explore the mechanism of the growth suppression of p16 in nasopharyngeal carcinoma cell lines.


METHODS
The curve of cell growth rate in three kinds of HNE1, # 3-2 and # 4-2 cell lines was analyzed and their double time was compared. Then the distribution of the cell cycle was detected by flow cytometry. The expression of p16 and the effect of exogenous p16 expression on CDK4, Cyclin D1 and pRb are studied by means of Western Blot.


RESULTS
As compared with HNE1, # 3-2 and # 4-2 showed a longer double time(23.4 h vs 28.8 h, 31.2 h). # 4-2 showed a significant accumulation of cells in G0/G1 phase(P < 0.01) and decreasing in S phase(P < 0.05) while HNE1 and # 3-2 had no obvious difference(P > 0.05). Cyclin D1 expression was upregulated in # 4-2 but downregulated in # 3-2 by exogenous expressed p16. No obvious difference on CDK4 expression was found. Hypophosphorylated pRb was detected in three cell lines. The expression was stronger in # 4-2, and # 3-2 than that in HNE1 and Hela. Hyperphosphorylated pRb was also detected in HNE1.


CONCLUSIONS
Exogenous p16 expression may arrest cell cycle in G0/G1 phase and suppress cell growth. The major mechanism is not to regulate the level of the expression of CDK4. There might be a threshold in p16 regulating Cyclin D1 expression. However, the final result contributes to the inhibition of pRb phosphorylation.
Zhao
X R
XR
Cancer Research Institute, Hunan Medical University, Changsha 410078.
Deng
L
L
Weng
X X
XX
D002453:Cell Cycle; D002455:Cell Division; D019938:Cyclin D1 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis* / Q000235:genetics; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D014407:Tumor Cells, Cultured
D019941:Cyclin-Dependent Kinase Inhibitor p16; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D019938:Cyclin D1; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases