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Biochem Biophys Res Commun. 1997 May 19;234(2):386-92.

Effects of exogenous p16INK4a on growth of cells with various status of cell-cycle regulators.

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Banyu Tsukuba Research Institute, Merck Research Laboratories, Japan.


p16INK4a, a protein that inhibits cyclin-dependent kinase 4 (Cdk4) and Cdk6, is deficient in many human cancers and in established lines of tumor cells. It has been reported that transfection with cDNA for p16INK4a inhibits the growth of cell lines that express retinoblastoma protein (pRB). However, it is unclear whether the introduction of cDNA for p16INK4a affects the growth of cells that express p16INK4a protein. Moreover, the effects of other cell-cycle regulators on the inhibition of cell growth by p16INK4a remain unknown. In this study, cDNA for p16INK4a was used to transfect human cell lines that had various status of expression of RB pathway-related proteins, such as members of the RB family proteins and Cdk-inhibitory proteins. We found that status of p107, p130, p15INK4b, p18INK4c, p21Cip1, p27Kip1, cyclin D1, and Cdk4 were not correlated with the growth-inhibitory activity of exogenous p16INK4a. By contrast, transfection with cDNA for p16INK4a had a significant effect on the growth of cells depended on the status not only of pRB but also of p16INK4a. Although exogenous p16INK4a inhibited the growth of cells that expressed pRB but did not express p16INK4a (pRB+/p16- cells), it had little affect on either pRB+/p16+ cells or pRB-/p16+ cells. Moreover, transfection with cDNA for p16INK4a also inhibited the activity of the E2 promoter of the dehydrofolate reductase gene in the same manner that depended on the absence of p16INK4a, as well as on the presence of pRB. These results suggest that deregulation of the RB pathway by p16INK4a deficiency plays a very important role in the proliferation of cells that lack p16INK4a protein.

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