MODULATION OF OPIOID BINDING ASSOCIATED WITH NUCLEAR MATRIX AND NUCLEAR-MEMBRANES OF NG108-15 CELLS

Opioid binding sites were found in nuclear matrix preparations from NG 108-15 neurohybrid cells. Binding parameters of delta-specific radioli gands indicated that high-affinity binding sites discovered in purifie d nuclei were present in nuclear membranes and nuclear matrix fraction s. Agonists bind with low affinity, if at all, to nuclear matrix prepa rations. Neither sensitivity of agonist binding to the GTP analog 5-gu anylylimido-diphosphate nor adenylyl cyclase activity were detected in this fraction, suggesting the presence of guanine nucleotide binding regulatory protein/effector uncoupled sites. Opioid inhibition of basa l and forskolin-stimulated adenylyl cyclase activity was found in nucl ear membrane preparations. Cycloheximide treatment of cells inhibited opioid binding to nuclear membrane fractions to a greater extent than that associated with membranes sedimenting at 20,000 x g (P-20) or nuc lear matrix. Colchicine, a microtubule disrupter and inhibitor of rece ptor internalization, caused up-regulation of nuclear membrane and P-2 0 opioid receptors and a loss in nuclear matrix associated sites. Taxo l, a microtubule stabilizing agent, prevented the effect of colchicine . Etorphine-elicited down-regulation increased nuclear matrix associat ed binding while diminishing that in nuclear membranes and P-20 fracti ons. Agonist-induced desensitization completely abolished nuclear matr ix binding. In vitro preincubation of nuclear matrix preparations with protein kinase A catalytic subunit mimicked the desensitization effec t. Forskolin treatment of cells potentiated nuclear matrix and P-20 bi nding. These data suggest that nuclear membrane opioid receptors repre sent newly synthesized molecules en route to the cell surface, whereas nuclear matrix contains internalized delta sites.