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Updated: Aug 7, 2026
Analysis of Cell Cycle Position in Mammalian Cells
Published on: January 21, 2012
Effects of exogenous p16INK4a on growth of cells with various status of cell-cycle regulators
I Suzuki-Takahashi1, H Higashi, E Yoshida
1Banyu Tsukuba Research Institute, Merck Research Laboratories, Japan.
Abstract:
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.
Insights
The cell cycle regulator p16INK4a inhibits tumor cell growth, but only in cells lacking this protein and expressing retinoblastoma protein (pRB). Its deficiency is key in cancer cell proliferation.
Area of Science:
- Molecular Biology
- Cancer Biology
- Cell Cycle Regulation
Background:
- p16INK4a inhibits cyclin-dependent kinases 4 and 6 (Cdk4/6), crucial for cell cycle progression.
- p16INK4a deficiency is common in human cancers.
- The impact of p16INK4a on cells already expressing it, and its interaction with other cell cycle regulators, remains unclear.
Purpose of the Study:
- To investigate the effect of introducing p16INK4a on cell growth in human cell lines with varying retinoblastoma (RB) pathway protein expression.
- To determine if other cell cycle regulators influence p16INK4a's growth-inhibitory activity.
Main Methods:
- Transfection of human cell lines with p16INK4a cDNA.
- Analysis of RB pathway-related proteins, including RB family proteins and Cdk-inhibitory proteins.
- Assessment of cell growth inhibition and E2 promoter activity of the dehydrofolate reductase gene.
Main Results:
- Exogenous p16INK4a inhibited cell growth only in cells expressing retinoblastoma protein (pRB) but lacking endogenous p16INK4a (pRB+/p16- cells).
- Cells expressing both pRB and p16INK4a (pRB+/p16+), or lacking pRB but expressing p16INK4a (pRB-/p16+), showed little growth inhibition.
- Expression status of p107, p130, p15INK4b, p18INK4c, p21Cip1, p27Kip1, cyclin D1, and Cdk4 did not correlate with p16INK4a's growth-inhibitory activity.
- p16INK4a transfection inhibited dehydrofolate reductase E2 promoter activity in a manner dependent on pRB presence and p16INK4a absence.
Conclusions:
- Cell growth inhibition by exogenous p16INK4a is dependent on the absence of endogenous p16INK4a and the presence of pRB.
- Deregulation of the RB pathway due to p16INK4a deficiency is critical for cancer cell proliferation.
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