CHRONIC HYPOXIA INDUCES LLC-PK1 CELL-PROLIFERATION AND DEDIFFERENTIATION BY THE ACTIVATION OF PROTEIN-KINASE-C

The effect of chronic hypoxia on the proliferation and dedifferentiati on of LLC-PK1 cells was examined. Cultures were exposed either to hypo xia (3% O-2) or normoxia (18% Ga), and [3H]thymidine incorporation, ce ll number, and sodium-dependent glucose (Na/Glc) uptakes were assessed . Cultures exposed to hypoxia for 16 h significantly increased [H-3]th ymidine incorporation followed by a significant increase in cell numbe r both at 24 and 48 h in comparison with respective normoxic controls. Cultures exposed to 24 and 72 h of hypoxia exhibited significant inhi bition of Na/Glc uptake when compared with their respective normoxic c ounterparts. Significant inhibition of cell ATP levels were observed u nder hypoxic conditions. Acute reoxygenation of hypoxic cells normaliz ed cell ATP levels without any effect on the Na/Glc uptake. Hypoxia al so activated protein kinase C (PKC) at 1 and 4 h followed by a subsequ ent return to baseline with reactivation at 24 h, which remained susta ined up to 72 h, suggesting both acute and sustained activation of PKC . Furthermore, the hypoxia-induced alterations in [3H]thymidine incorp oration 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 acti vation of PKC.