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Hypoxia stimulates p16 expression and association with cdk4
Adam Zygmunt1, Vivienne C Tedesco, Eshwar Udho
1Department of Biological Sciences, Pace University, Pleasntville, New York 10570, USA.
Experimental Cell Research
|July 20, 2002
Summary
Hypoxia inhibits cell proliferation by inactivating cyclin-dependent kinase 4 (cdk4). This inactivation is mediated by increased levels of p16, a cyclin-dependent kinase inhibitor, which binds to cdk4 under hypoxic conditions.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Hypoxic conditions trigger cell proliferation inhibition.
- Hypoxia leads to the accumulation of hypophosphorylated retinoblastoma protein (pRb), a growth-suppressive form.
- This inhibition is partly due to reduced activity of pRb-directed cyclin-dependent kinases (cdk4 and cdk2).
Purpose of the Study:
- To elucidate the mechanism of cdk4 inactivation under hypoxic conditions.
- To investigate the role of cyclin-dependent kinase inhibitors (cdkis) in hypoxia-induced cell cycle arrest.
Main Methods:
- Cell cycle analysis of CV-1P cells under hypoxic and aerobic conditions.
- Analysis of cdk4, cdk6, D-type cyclins, and various cdkis (p16, p18, p19, p57) levels.
- Immunoprecipitation assays to detect p16-cdk4 binding.
Main Results:
- Hypoxia inhibited CV-1P cell progression from G1 to S phase after 18 hours.
- Dephosphorylation of serine-795, a putative cdk4 substrate, occurred under hypoxia.
- While cdk4, cdk6, and D-type cyclin levels remained unchanged, p16 levels significantly increased under hypoxia.
- Immunoprecipitation confirmed p16 binding to cdk4 specifically under hypoxic conditions.
Conclusions:
- Hypoxia-induced cell proliferation inhibition in CV-1P cells is associated with cdk4 inactivation.
- Increased p16 levels and its subsequent binding to cdk4 appear to mediate cdk4 inhibition under hypoxia.
- p16 may play a crucial role in the growth inhibitory effects of hypoxia.