INTRACELLULAR RESPONSES TO GONADOTROPIN-RELEASING-HORMONE IN A CLONAL CELL-LINE OF THE GONADOTROPE LINEAGE

We recently derived a GnRH-responsive pituitary cell line of the gonadotrope lineage (alpha-T3-1) by targeted oncogenesis in transgenic mice. Here, we report studies characterizing the GnRH receptors present in these cells and the intracellular responses to GnRH treatment. The receptors in alpha-T3-1 cells show specificity for different GnRH analogs, with dissociation constants very similar to those found in normal rat and mouse pituitary. The concentration of receptors is within the range found in normal pituitary. The addition of GnRH or GnRH agonists increases phosphoinositide turnover and protein kinase-C translocation to membranes, and enhances activation of voltage-sensitive calcium channels. However, GnRH does not affect cAMP levels. Analysis of alpha-subunit mRNA levels demonstrated induction by GnRH and phorbol esters. Our results indicate that GnRH initiates a cascade of intracellular events that generate a set of second messengers, one or more of which is involved in the regulation of gene expression. The responses of alpha-T3-1 cells to GnRH appear to have characteristics equivalent to those of primary pituitary gonadotropes, indicating the utility of this cell line as a model system for the study of GnRH responses.