The cAMP-Dependent induction of LH receptors in primary cultures of porcine granulosa cells is not due to the expression of an intracellular pool of LH receptors.

Abstract

The present studies examined whether the increase in cell surface LH receptors in primary cultures of porcine granulosa cells after exposure to FSH or cholera toxin, agents that increase intracellular cAMP, is due to de novo synthesis of the receptor or to a cAMP-dependent translocation of an intracellular pool of LH receptors to the cell surface. LH receptor induction by FSH was fully inhibited by the addition of cycloheximide to the incubation media, but resumed after cycloheximide was removed. These data suggest that FSH-induced LH receptor appearance requires protein synthesis. However, to be confident that the inhibition of LH receptor appearance did not result from lack of transit of preformed receptors requiring a rapidly turning over pool of proteins, we assayed for possible latent receptors in the cell interior by extracting granulosa cells with Triton X-100. Under conditions which detected about 74% of LH receptors in cells exposed to cholera toxin, little [125]iodo-hCG-binding activity was detected in cells not exposed to a cAMP-promoting stimulus. These findings suggest that a preformed pool of LH receptors does not exist in untreated cells, and that the cAMP-mediated induction of LH receptors requires de novo synthesis of the receptor.