Pituitary Adenylate Cyclase Activating Polypeptide and Neuropeptide Y Regulation of Gonadotropin Subunit Gene Expression in Tilapia: Role of PKC, PKA and ERK

Abstract

There is ample information on the hypophysiotropic function of pituitary adenylate cyclase-activating polypeptide (PACAP) and neuropeptide Y (NPY) in fish as in mammals, although evidence as to their direct effects on gonadotropic cells is scarce. We have previously reported that NPY and PACAP38 augment gonadotropin-releasing hormone (GnRH)-induced expression of glycoprotein α (α) subunit gene in the teleost fish, tilapia. The aim of the present study was to elucidate possible direct effects of these peptides on gonadotropin subunit gene expression in culture of tilapia pituitary cells, as well as the transduction pathways involved. Both NPY and PACAP38 (0.001–10 nM) increased the level of phosphorylated extracellular signal-regulated kinase (pERK) dose-dependently, reaching a peak at 0.1 and 0.01 nM, respectively. Inhibition of protein kinase C (PKC) by GF109203X (GF; 0.01–10 nM) suppressed NPY-stimulated pERK levels and its effect on α and luteinizing hormone (LH) β subunit mRNA levels. However, NPY had no effect on follicle stimulating hormone (FSH) β mRNA levels. NPY-elevated α, LHβ mRNA and pERK levels were also attenuated by inhibition of protein kinase A (PKA) with H89 (0.01–10 nM). Exposure of the cells to the MAPK kinase (MEK) inhibitor (PD98059; PD 10, 25 and 50 µM) completely blocked NPY-induced ERK activity. In addition, this inhibitor abated the α and LHβ mRNA responses to NPY. Similar experiments conducted to elucidate PACAP38 signaling revealed that PACAP38 (0.01 nM) elevated all three-gonadotropin subunit gene expression via both PKC-ERK and PKA-ERK cascades. It is suggested that both NPY and PACAP38 act directly on gonadotropes to elevate gonadotropin subunit gene expression. Whereas the expression of α and LHβ subunit genes is regulated by both NPY and PACAP, the effect on the FSHβ transcript is elicited only by PACAP38. NPY and PACAP38 stimulatory actions are mediated via protein kinase C (PKC) and protein kinase A (PKA), converging at the MEK-ERK cascade. These findings represent one of the fine tuning levels that differentially regulates gonadotropin subunit gene expression.

5-hydroxy-L-tryptophan Suppressed Food Intake in Rats Despite an Increase in the Arcuate NPY Expression

“…NPY dose-dependently increased cellular level of phosphorylated extracellular signal-regulated protein kinase (pERK1/2) in cultured cells (Gur et al, 2002). It has been shown that food deprivation increases neuronal level of pERK1/2 in the hypothalamic paraventricular nucleus (PVN) of mice (Ponsalle et al, 1992) and rat (Ueyama et al, 2004; Lee et al, 2010).…”

Nerve Growth Factor Regulates Adrenergic Expression

“…The present study now provides evidence that these changes in NGF-regulated adrenergic expression in PC-12 cells are at least in part mediated through an increase in PNMT promoter-driven gene transcription. Furthermore, although NGF activates a number of intracellular signaling pathways, including those of PKA (Schubert et al, 1977;Gur et al, 2002;Vaudry et al, 2002), PKC (Hama et al, 1986;Gur et al, 2002;Sakai et al, 2004), p38 MAPK (Xing et al, 1996;Dohi et al, 2002;Gur et al, 2002;Vaudry et al, 2002;Sakai et al, 2004), and ERK1/2 MAPK (Xing et al, 1996;Dohi et al, 2002;Gur et al, 2002;Vaudry et al, 2002;Sakai et al, 2004), only the ERK1/2 MAPK pathway seems involved in PNMT promoter activation by NGF. In the case of PKA and PKC signaling, we provide direct evidence that activation of these pathways produces an incremental rise in NGF-mediated PNMT promoter-driven luciferase expression (Figs.…”

Neuropeptide Y in the forebrain of the adult male cichlid fish Oreochromis mossambicus: Distribution, effects of castration and testosterone replacement

“…In spite of this, the response of NPY-containing nuclei in the forebrain of teleost following gonadectomy and gonadal steroid replacement remained unexplored. Among teleosts, tilapia may be considered as a suitable model with which to address this issue, because background information on 1) its GnRH system (Parhar et al, 1996a;Parhar, 1997), 2) the response of the system to castration and testosterone replacement , 3) the absence of ER␣ in the GnRH neurons , and 4) the role of NPY in GnRH induced up-regulation of the GtH mRNA subunits (Yaron et al, 2001(Yaron et al, , 2003Gur et al, 2002) is already available. Because information about the organization of the NPY neuronal system in this fish is not available, we first describe the distribution of the NPY-immunoreactive (-ir) system in the forebrain of sexually mature male tilapia (Oreochromis mossambicus).…”