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Shlomo Melmed
Published in Volume 119, Issue 11
J Clin Invest. 2009; 119(11):3189–3202 doi:10.1172/JCI39375
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Figure 4
Depiction of intracellular pathways associated with somatotroph transformation and proliferation.

GH transcription and somatotroph proliferation are induced by cAMP acting through CREB (26). SRIF inhibits cAMP and CREB activity (S43) to suppress GH secretion. Pituitary CDKs likely exhibit overlapping functions in G1 cell-cycle progression. Somatotroph mitogenic factors include POU1F1, GHRH, and GNAS as well as endocrine hormones. Mitogenic constraints include SRIF and tumor suppressor genes, including MEN1. Cell-cycle progression through G/S is mediated by CDKs that phosphorylate Rb to release E2F proteins that drive DNA synthesis. In somatotroph tumors, the cAMP pathway may be constitutively activated. Furthermore, HMGA2 and PTTG, overexpression, and CDK inhibitor loss have been shown to result in experimental pituitary tumorigenesis. Chromosomal instability, DNA damage, and senescence, hallmarks of GH-secreting adenomas, may act to constrain malignant transformation of somatotroph tumors. Modified with permission from the Journal of molecular endocrinology (ref. S44, S45; copyrighted by the Society for Endocrinology).