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G. Chandrasekher, G. Maharaj, S. Pothula, H. Bazan; Differential Effects of Keratinocyte Growth Factor (KGF) and Hepatocyte Growth Factor (HGF) on the Regulation of Cell Cycle Protein Expression in Corneal Epithelium and Its Relevance in Cell Survival. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1964.
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© ARVO (1962-2015); The Authors (2016-present)
Rapid regeneration of cells and their survival is critical for proper healing of corneal epithelial injuries. Our previous studies showed that HGF and KGF play a key role in corneal epithelial wound repair and cell survival. Since cell cycle progression is vital for tissue growth, we have investigated the influence of these growth factors on the expression of corneal epithelial cell cycle progression machinery during normal growth and apoptosis.
Epithelial cells derived from rabbit cornea primary cultures grown in DMEM/F12 were employed in various experiments. Cells were treated with or without HGF and KGF (20 ng/ml) and sataurosporine (10 ng/ml). Expression of cell cycle proteins was analyzed by westernblotting using specific antibodies. Staurosporine-induced apoptosis of corneal epithelial cells was characterized by DNA ladder and Hoehst staining assays.
In growth cultures HGF and KGF up-regulated the expression of cell cycle proteins cyclins (A, D and E) and cyclin-dependent kinases (Cdk2 and Cdk4) and down regulated the cell cycle arresting CDK inhibitor protein p27kip but not p21cip. While the HGF-mediated regulation was effective for shorter duration (about 8-10 hrs), KGF effect was sustained for longer periods (24 hrs or more). In apoptotic conditions p27kip expression increased several folds, but p21cip levels decreased considerably. While the presence of KGF and HGF suppressed the up-regulation of p27kip in apoptosis induced cells for 8-10 hrs, KGF but not HGF was able to sustain such effect for 24 hrs. Similarly, while HGF was efficient in protecting cells from apoptosis for only 8-10 hrs after staurosporine treatment, KGF maintained its anti-apoptosis capability beyond 24 hrs. Both HGF and KGF showed no influence on the regulation of p21cip expression in apoptotic conditions.
Our studies suggest that activation of intracellular apoptotic pathways leads to the up-regulation of p27kip expression which promotes cell cycle arrest and renders cell susceptible to death. KGF but not HGF protects cells from apoptotic death for prolonged periods due to its ability to diminish the expression of p27kip and increase the levels of cell cycle progression cyclins and CDKs for timely promotion of cell propagation.
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