INCREASED EXPRESSION OF OPIOID-DELTA RECEPTORS BY DEOXY CONFORMATION HEME-PROTEINS IN NG108-15 CELLS

Adaptations to prolonged hypoxia include an increase in the expression of proteins that may facilitate survival. One mechanism by which hypo xia increases protein expression involves a change of heme proteins fr om oxygenated to deoxygenated conformations. In the present study, we tested the hypothesis that treatment of NG108-15 cells with metallic c ations, which are known to induce a deoxygenated conformation of heme proteins, would increase delta opioid receptor (DOR) expression. Cells were treated with cobalt and nickel, which induce deoxygenated heme p rotein conformation, or zinc as a control for 48 h prior to quantifyin g DOR expression. Cobalt and nickel, but not zinc, significantly incre ased DOR expression. Heme synthesis inhibitors would block the synthes is of cobalt-substituted heme proteins which are locked in a deoxygena ted conformation. The cobalt-induced increase in DOR expression was bl ocked by the heme synthesis inhibitor, 4,6-dioxoheptanoic acid. These experiments indicate that deoxygenated conformation heme proteins, whi ch are thought to partially mimic hypoxia, increase DOR expression. Th e increase in DOR expression suggests that the DOR gene may be hypoxia -sensitive. Further, the increase in DOR expression suggests a potenti al adaptation strategy to hypoxia and may represent one of the first f indings of physiological regulation of DOR expression.