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T. Li, L. Lu; Corneal Epithelial Cell Fate Determined by CCCTC Binding Factor (CTCF) in Response to UV Irradiation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4912.
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The purpose of the present study is to investigate the role of CTCF in UV–induced and stress–related responses in corneal epithelial cells based on our previous evidence that CTCF regulates growth factor–stimulated corneal epithelia cell proliferation.
Human corneal epithelial (HCE) cells were cultured in DMEM/F12 medium with 10% FBS and 5 µg/ml insulin. Northern and Western analysis were employed to detect CTCF expression and MAP kinase activities. NF–ΚB activity was determined by electrophoresis mobility shift assay (EMSA). UV–induced cell death was evaluated by MTT assay and by measurement of caspase–3 activation.
We found that exposure of HCE cells to UV–C (42 µJ/cm2) light induced significant decreases in CTCF mRNA and protein levels. UV–induced changes in CTCF expression were intensified following incubating time after UV induction. UV irradiation in HCE cells also activated MAPK cascades including JNK, ERK and P38 pathways and NF–ΚB. Inhibitors specific to JNK, Erk, p38 and NF–ΚB were applied to HCE cells before UV irradiation. Interestingly, we observed that only PDTC (a NF–ΚB inhibitor) demonstrated the inhibitory effect on UV–induced decreases in CTCF expression, suggesting that NF–ΚB may play a role in mediating the effect of UV irradiation on CTCF expression. Over–expression of full length cDNA encoding human CTCF in HCE cells significantly prevented UV–induced caspase–3 activation and cell death. In addition, UV–sensitive pro–apoptotic gene (c–Jun and c–Myc) expressions were also inhibited by overexpression of CTCF. Moreover, inhibition of NF–ΚB by PDTC significantly protected HCE cells from UV–induced apoptosis.
Our results for the first time demonstrate that UV irradiation down–regulates CTCF expression downstream from NF–ΚB. Our results further indicate that UV–induced suppression of CTCF plays an important role in cell apoptosis.
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