Signalling Pathways Mediating Secretory and Mitogenic Responses to Galanin and Pituitary Adenylate Cyclase‐Activating Polypeptide in the 235‐1 Clonal Rat Lactotroph Cell Line

Abstract

The neuropeptides galanin and pituitary adenylate cyclase-activating peptide (PACAP) have been implicated in the physiological regulation of lactotroph function. Using the 235-1 clonal lactotroph rat cell line we have studied the signalling pathways mediating the secretory and mitogenic responses to galanin and PACAP. Both peptides stimulated prolactin release to a similar maximal extent. PACAP (100 nM) stimulated an increase in the proliferation rate of 235-1 cells, but was significantly less effective than 100 nM galanin (161.8 +/- 2.3% vs 296.1 +/- 9.1% of control). PACAP stimulated cAMP accumulation with an ED50 of 3.2 nM, and a maximal effect of almost two-fold at a concentration of 100 nM. Galanin depleted cAMP, by 30% at a concentration of 100 nM. The aminosteroid phospholipase C (PLC) inhibitor U-73122 virtually abolished maximal peptide stimulated prolactin release. Depletion of inositol phosphates or downregulation of protein kinase C reduced maximal peptide stimulated prolactin release from about 260% to about 160% of unstimulated release. Both peptides at a concentration of 100 nM caused a sustained increase in intracellular calcium when incubated with cells for 30 min. These results demonstrate that both peptides stimulate prolactin release and the proliferation rate of 235-1 cells. The most important signalling pathway for prolactin release activated by both peptides is via PLC, although they also regulate cAMP levels, which are increased by PACAP and decreased by galanin. Despite maximal peptide stimulated prolactin release being equal, galanin has a greater mitogenic effect on 235-1 cells than PACAP, raising the possibility that it activates an additional mitogenic signalling pathway.

Galanin Is Up-Regulated in Colon Adenocarcinoma

“…Interestingly, cytolytic effects in tissues were occasionally correlated with the presence of galanin in the study. By contrast, mitogenic effects of galanin have been previously described on 235-1 clonal rat lactotroph cell (15)(16)(17). Thus, it is indeed plausible that galanin could contribute to cancer cell selection by promoting proliferation of a subset of malignant cells.…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…For instance, PACAP stimulates the catalytic and regulatory subunits of PKA in the mouse gonadotrope ␣T3-1 cell line (Garrel et al, 1997) and inhibits TGF-␤-induced apoptosis in the human pituitary adenoma cell line HP75 (Oka et al, 1999). In the lactotrope 235-1 cell line, PACAP stimulates prolactin release through activation of the PLC pathway and exerts mitogenic effects (Hammond et al, 1996). In the lactotrope/somatotrope GH3 cell lines, nanomolar concentrations of PACAP stimulate GH and PRL release through activation of type II receptors and recruitment of voltage-gated sodium channels (Propato-Mussafiri et al, 1992;Murakami et al, 1995).…”

Roles and Mechanisms of Action of Pituitary Adenylate Cyclase-Activating Polypeptide(PACAP) in Growth Hormone and Prolactin Secretion.

“…It was also reported that PACAP at a concentration of a picomolar range increased PRL mRNA level independently of the cAMP/PKA pathway [33]. In the lactotroph 235-1 cell line, PACAP stimulates PRL release through activation of the PLC pathway and exerts mitogenic effects [34]. in rat somatotrophs [35].…”