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Transforming growth factor-beta1 up-regulates p15, p21 and p27 and blocks cell cycling in G1 in human prostate
C N Robson1, V Gnanapragasam, R L Byrne
1School of Surgical Sciences, Medical School, Framlington Place, University of Newcastle upon Tyne NE2 4HH, UK.
Abstract:
Transforming growth factor-beta1 (TGFbeta1) is inhibitory to most epithelia, but its role in the control of proliferation of prostatic epithelium is unclear. In some cells, TGFbeta1 inhibition is achieved by up-regulation of cyclin-dependent kinase (cdk) inhibitors including p15, p21 and p27. Our aims were to determine whether the effects of TGFbeta1 on human prostatic epithelial cell cycle kinetics were mediated by alterations in the levels of the cdk inhibitors p15, p16, p21 and p27 and hypo-phosphorylated retinoblastoma protein (Rb). Human prostatic epithelial cells in primary culture were grown in the presence of TGFbeta1 (0-10 ng/ml) for up to 4 days and proliferation assessed using a [3H]thymidine uptake assay. Levels of p15, p16, p21 and p27 were measured at both mRNA and protein level by means of a reverse transcriptase PCR-based assay and Western analysis. Rb and cdk2 levels were measured. Exogenous TGFbeta1 (0-5 ng/ml) inhibited proliferation. This was associated with blocking of the cell cycle at G1, and up to 4-fold increases in p15, p21 and p27 mRNA levels, but no change was observed in p16 mRNA levels; these changes were not blocked by cycloheximide. Increased levels of p15, p21 and p27 protein were also accompanied by increased levels of hypo-phosphorylated Rb and decreased cdk2 kinase activity. TGFbeta1 has mainly inhibitory effects on benign human prostatic epithelium, which are caused by up-regulation of cdk inhibitors, hypo-phosphorylation of Rb and delaying of the cell cycle in G1.
Insights
Transforming growth factor-beta1 (TGFbeta1) inhibits human prostatic epithelial cell proliferation by increasing cyclin-dependent kinase inhibitors and delaying the cell cycle. This study clarifies TGFbeta1
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- Transforming growth factor-beta1 (TGFbeta1) typically inhibits epithelial cell growth, but its effect on prostate epithelium proliferation is not well understood.
- TGFbeta1 can impede cell cycle progression by increasing cyclin-dependent kinase (cdk) inhibitors like p15, p21, and p27 in some cell types.
Purpose of the Study:
- To investigate if TGFbeta1's impact on human prostatic epithelial cell cycle kinetics is mediated by changes in cdk inhibitors (p15, p16, p21, p27) and retinoblastoma protein (Rb) phosphorylation.
- To elucidate the molecular mechanisms underlying TGFbeta1's role in regulating prostate epithelial cell proliferation.
Main Methods:
- Human prostatic epithelial cells were cultured with varying concentrations of TGFbeta1.
- Proliferation was assessed using a [3H]thymidine uptake assay.
- mRNA and protein levels of cdk inhibitors (p15, p16, p21, p27), Rb, and cdk2 were measured using RT-PCR and Western analysis.
Main Results:
- Exogenous TGFbeta1 significantly inhibited prostate cell proliferation, causing a G1 cell cycle block.
- TGFbeta1 treatment led to a 4-fold increase in p15, p21, and p27 mRNA levels, but not p16 mRNA.
- Increased p15, p21, and p27 protein levels correlated with elevated hypo-phosphorylated Rb and reduced cdk2 kinase activity.
Conclusions:
- TGFbeta1 primarily exerts inhibitory effects on benign human prostatic epithelium.
- These inhibitory effects are mediated by the upregulation of specific cdk inhibitors (p15, p21, p27).
- TGFbeta1 induces hypo-phosphorylation of Rb, leading to G1 cell cycle arrest in prostate epithelial cells.