Chronic hypoxia induces LLC-PK1 cell proliferation and dedifferentiation by the activation of protein kinase C.

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Abstract
The effect of chronic hypoxia on the proliferation and dedifferentiation of LLC-PK1 cells was examined. Cultures were exposed either to hypoxia (3% O2) or normoxia (18% O2), and [3H]thymidine incorporation, cell number, and sodium-dependent glucose (Na/Glc) uptakes were assessed. Cultures exposed to hypoxia for 16 h significantly increased [3H]thymidine incorporation followed by a significant increase in cell number both at 24 and 48 h in comparison with respective normoxic controls. Cultures exposed to 24 and 72 h of hypoxia exhibited significant inhibition of Na/Glc uptake when compared with their respective normoxic counterparts. Significant inhibition of cell ATP levels were observed under hypoxic conditions. Acute reoxygenation of hypoxic cells normalized cell ATP levels without any effect on the Na/Glc uptake. Hypoxia also activated protein kinase C (PKC) at 1 and 4 h followed by a subsequent return to baseline with reactivation at 24 h, which remained sustained up to 72 h, suggesting both acute and sustained activation of PKC. Furthermore, the hypoxia-induced alterations in [3H]thymidine incorporation as well as Na/Glc uptake were mitigated by inhibitors of PKC. These results indicate that chronic hypoxia induces both proliferation and dedifferentiation of LLC-PK1 cells mediated, in part, by the activation of PKC.

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