GHRH proliferative action on somatotrophs is cell-type specific and dependent on Pit-1/GHF-1 expression

• Published in: Journal of cellular physiology 2008-04, Vol.215 (1), p.140-150
• Main Authors: Solloso, A, Barreiro, L, Seoane, R, Nogueira, E, Cañibano, C, Alvarez, C.V., Zalvide, J, Diéguez, C, Pombo, C.M.
• Format: Article
• Language: English
• Subjects: Animals; Cell Line; Cell Proliferation - drug effects; CHO Cells; Cricetinae; Cricetulus; Cyclic AMP - biosynthesis; Cyclin D1 - genetics; Cyclin D1 - metabolism; Cyclin-Dependent Kinase Inhibitor p21 - genetics; Cyclin-Dependent Kinase Inhibitor p21 - metabolism; Down-Regulation - drug effects; Extracellular Signal-Regulated MAP Kinases - metabolism; Growth Hormone-Releasing Hormone - pharmacology; Humans; Organ Specificity - drug effects; Phosphorylation - drug effects; Proto-Oncogene Proteins c-myc - genetics; Rats; Receptors, Neuropeptide - metabolism; Receptors, Pituitary Hormone-Regulating Hormone - metabolism; S Phase - drug effects; Serum; Somatotrophs - cytology; Somatotrophs - drug effects; Somatotrophs - enzymology; Transcription Factor Pit-1 - metabolism; Transcription, Genetic - drug effects
• ISSN: 0021-9541; 1097-4652
• DOI: 10.1002/jcp.21295

To investigate the mechanisms by which the hypothalamic peptide GHRH influences cell division, we analyzed its effects on the proliferation of two different cell lines: CHO‐4, an ovary‐derived cell line, and GH3, a pituitary‐derived cell line. We found that GHRH induces the proliferation of pituitary‐derived cells but inhibits the proliferation of ovary‐derived cells. We further characterized this dual effect of GHRH to find that the cytoplasmic signals induced by this hormone are similar in both cell lines. Moreover, in CHO‐4 cells GHRH stimulates two well‐known positive cell cycle regulators, c‐myc and cyclin D1, but is unable to induce the degradation of the negative cell cycle regulator p27Kip1. Significantly, when the Pit‐1/GHF‐1 gene is exogenously expressed in CHO‐4 cells, the negative effect of GHRH on the proliferation of these cells is attenuated. Furthermore, when the levels of Pit‐1 are downregulated by siRNA in GH3‐GHRHR cells, the positive effects of GHRH on the proliferation of these cells are diminished. These findings add to our understanding of the molecules involved in the regulation of cell proliferation by GHRH, as we demonstrate for the first time that Pit‐1 is not only required to drive the expression of the GHRH receptor, as previously described, but is also needed for the downstream effects that occur after its activation to modulate cell proliferation. These data suggest that the regulation of cell proliferation in response to a specific growth factor depends in certain cell populations on the presence of a tissue‐specific transcription factor. J. Cell. Physiol. 215: 140–150, 2008. © 2007 Wiley‐Liss, Inc.