G protein-coupled receptors as targets for prolactin actions

Prolactin (PRL) is known to be involved in a wide range of biological funct ions including osmoregulation, lactation, reproduction, and immunomodulatio n. The first step in PRL action involves its interaction with a specific me mbrane receptor that belongs to the cytokine receptor superfamily, In spite of the lack of a kinase domain, receptors of the cytokine superfamily indu ce tyrosine phosphorylation of cellular substrates including the receptors. The role of PRL in female reproductive functions is well known and a direc t effect on ovarian and testicular steroidogenesis has been established, In the ovary, PRL binds to a specific membrane receptor and exerts an inhibit ory effect on follicular steroidogenesis. This effect is the result of an i mpairment involving FSH stimulation of G protein-coupled receptors (GPCR) a nd cyclic AMP-mediated activation of aromatase cytochrome P450 gene express ion. This observation may indicate a direct connection between tyrosine pho sphorylation and follicle stimulating hormone (FSH)receptor (FSHR) transduc tion pathways, as is the case for growth factor receptors with intrinsic ty rosine kinase activity, which share several downstream signaling elements w ith GPCRs. Some studies leading to bur understanding of these pathways are reviewed, (C) 2000 IMSS. Published by Elsevier Science Inc.