Modulation of opioid signal transduction in SH-SY5Y neural cells by differentiating agents: Concurrent mu receptor upregulation and effector desensitization by phorbol ester

Abstract

Long-term exposure of SH-SY5Y human neural cells to retinoic acid (RA) increased the binding of [3H]DAMGO and [3H]DPDPE by up to 3-fold compared to membranes of untreated cells. In contrast, incubation of the cells with phorbol ester (TPA) selectively up-regulated the binding of [3H]DAMGO. RA enhanced the maximal inhibition of cAMP formation in SH-SY5Y cells by both DAMGO and DPDPE from 20% for both opioids in control cells to 75% and 50%, respectively. On the other hand, the effect of TPA was limited to a marginal increase in the inhibition of cAMP formation by DAMGO. Parameters of GTP[gamma]35S binding as well as low-Km GTPase activity revealed no deterioration in the structure or function of total G protein in the TPA-treated cells, and initial Western blots showed no difference in the cell content of Go. Ongoing experiments are focusing on the covalent modification of specific G protein subtypes involved in [mu] and [delta] opioid signal transduction in SH-SY5Y cells differentiated by TPA.