Chemokine Stromal Cell-Derived Factor 1α Induces Proliferation and Growth Hormone Release in GH4C1 Rat Pituitary Adenoma Cell Line through Multiple Intracellular Signals

Abstract

We used GH4C1 cells as a model to study the effects of the chemokine stromal cell-derived factor 1 (SDF1) in pituitary functions. In these cells, SDF1␣ induced proliferation and growth hormone secretion, suggesting a possible regulatory role for this chemokine at pituitary level. We evaluated the intracellular signaling involved in these effects: SDF1␣ increased cytosolic [Ca 2ϩ ] and activated Pyk2, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and large-conductance Ca 2ϩ -activated K ϩ channels (BK Ca ) channels. To correlate these intracellular effectors with the proliferative and secretory effects, we inhibited their activity using BAPTA-AM (Ca 2ϩ chelator), 2Ј-amino-3Ј-methoxyflavone (PD98059; a mitogen-activated protein kinase kinase inhibitor), salicylate (Pyk2 inhibitor), and tetraethyl ammonium (K ϩ channel blocker). All of these compounds reverted SDF1␣-induced proliferation, suggesting the involvement of multiple intracellular pathways. Conversely, only BAPTA-AM reverted growth hormone secretion. To identify a possible cross-talk and a molecular ordering among these pathways, we tested these antagonists on SDF1␣-dependent activation of ERK1/2, Pyk2, and BK Ca channels. From these experiments, we observed that the inhibition of [Ca 2ϩ ] i increase or BK Ca channel activity did not affect ERK1/2 activation by SDF1␣; Pyk2 activation was purely Ca 2ϩ -dependent, not involving ERK1/2 or BK Ca channels; and BK Ca channel activity was antagonized by Pyk2 but not by ERK1/2 inhibitors. These data suggest that an SDF1␣-dependent increase of [Ca 2ϩ ] i activates Pyk2, which in turn regulates BK Ca channel activity. Conversely, ERK1/2 activation is an independent phenomenon.In conclusion, we demonstrate that SDF1␣ causes both proliferation and growth hormone release from pituitary adenoma cells, suggesting that the activation of CXCR4 may represent a novel regulatory mechanism for growth hormone secretion and pituitary cell proliferation, which may contribute to pituitary adenoma development.

Role of stromal cell-derived factor 1 (SDF1/CXCL12) in regulating anterior pituitary function

“…These data indicate that SDF1 activity requires the activation of a G-protein of the Gi/Go subfamily, and that its effects are responsive to inhibitory stimuli as observed in both normal pituitary and secreting adenomas. Interestingly, pertussis toxin was able to abolish both the stimulatory effects of SDF1 (Florio et al 2006) and the inhibitory effects of somatostatin (Florio & Schettini 1996). SDF1 was also a powerful mitogen for GH4C1 cells, with a statistically significant effect already evident at a concentration of 6 .…”

“…We used GH4C1 cells to evaluate the intracellular mechanisms activated by SDF1 to induce hormone release and cell proliferation (Florio et al 2006). We analyzed a set of intracellular mediators that were previously involved in CXCR4 effects, namely the regulation of the intracellular Ca CC concentration, the activation of ERK1/2 and of the cytosolic Ca CC -dependent tyrosine kinase, Pyk2, and the stimulation of the large conductance, Ca CC -activated K C channels BK Ca .…”

“…We used the rat pituitary adenoma cell line GH4C1 to analyze the potential role of the SDF1/CXCR4 network in the regulation of pituitary function and, possibly, pituitary tumorigenensis (Florio et al 2006). These cells represent one of the most studied model to evaluate pituitary regulation in vitro (Westendorf & Schonbrunn 1982).…”

Chemokines and chemokine receptors in the brain: implication in neuroendocrine regulation

“…In the same study, it was also observed that CINC stimulates adrenocorticotrophin but not thyrotrophin secretion and that CINC suppresses the basal luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretions from normal anterior pituitary cells in a dose-dependent manner (Sawada et al 1994). Moreover, a recent study shows that CXCR4 mRNA is expressed in the rat pituitary adenoma cell line GH4C1 (a cell line that releases growth hormone) and that SDF-1a/CXCL12 causes both proliferation and growth hormone release, suggesting that the activation of CXCR4 may represent a novel regulatory mechanism for growth hormone secretion and pituitary cell proliferation, which may contribute to pituitary adenoma development (Florio et al 2006). .…”

Multiple roles of chemokine CXCL12 in the central nervous system: A migration from immunology to neurobiology

“…Transient Ca 2+ elevation is an important consequence of ligand-induced chemokine receptor activation (Boutet A et al, 2001;Gillard SE et al, 2002). Binding of CXCL12 to CXCR4 also induces the activation of phosphoinositide-3 kinase (PI3K) that activates downstream AKT, PyK2 and nuclear transcriptional factor NF κ B signaling pathways (Bajetto A et al, 2001;Han Y et al, 2001a;Fernandis AZ et al, 2004;Lee BC et al, 2004;Alvarez S et al, 2005;Kukreja P et al, 2005;Florio T et al, 2006). G-protein dependent activation of CXCR4 also induces several MAPKs signaling pathways such as ERK, JNK and P38 (Bajetto A et al, 2001;Han Y et al, 2001a;Han Y et al, 2001b;Fernandis AZ et al, 2004;Alvarez S et al, 2005).…”