GHRH proliferative action on somatotrophs is cell-type specific and dependent on Pit-1/GHF-1 expression.
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 p27(Kip1). 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.
Solloso
A
A
Department of Physiology, School of Medicine, University of Santiago de Compostela, Santiago de Compostela, Spain.
Barreiro
L
L
Seoane
R
R
Nogueira
E
E
Cañibano
C
C
Alvarez
C V
CV
Zalvide
J
J
Diéguez
C
C
Pombo
C M
CM
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000096:biosynthesis; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006801:Humans; D009928:Organ Specificity / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D051381:Rats; D018013:Receptors, Neuropeptide / Q000378:metabolism; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000378:metabolism; D016196:S Phase / Q000187:drug effects; D044967:Serum; D052683:Somatotrophs / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology; D050817:Transcription Factor Pit-1 / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
D050759:Cyclin-Dependent Kinase Inhibitor p21; D016271:Proto-Oncogene Proteins c-myc; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D050817:Transcription Factor Pit-1; D019938:Cyclin D1; D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; D048049:Extracellular Signal-Regulated MAP Kinases; C048250:somatotropin releasing hormone receptor