Transgenic mice overexpressing GH exhibit hepatic upregulation of GH-signaling mediators involved in cell proliferation

Chronically elevated levels of GH in GH-transgenic mice result in accelerated growth and increased adult body weight. We have previously described that the GH-induced JAK2/STAT5-signaling pathway is desensitized in the liver of transgenic mice overexpressing GH. However, these annuals present increased circulating IGF-I levels, increased hepatic GHR expression, and liver organomegaly due to hypertrophy and hyperplasia, which frequently progress to hepatomas as the animals age, indicating that action of GH oil the fiver is not prevented. In the present study, we have evaluated other GH-signaling pathways that could be activated in the liver of GH-transgenic mice. Upon GH administration, normal mice showed all important increment ill STAT3 phosphorylation level, but transgenic mice did not respond to acute GH stimulation. However, STAT3 was constitutively phosphorylated in transgenic mice, whereas its protein content was not increased. GH-transgenic mice showed overexpression of c-Src, accompanied by an elevation of its activity Other signaling mediators including focal adhesion kinase, epidermal growth factor receptor, Erk, Akt, and mammalian targer of rapamycin displayed elevated protein and basal phosphorylation levels in these annuals. Thus, GH-overexpressing transgenic mice exhibit hepatic upregulation of signaling mediators related to cell proliferation, Survival, and migration. The upregulation of these proteins may represent GH-signaling pathways that are constitutively activated in the presence of dramatically elevated GH levels throughout life. These molecular alterations could be implicated in the pathological alterations observed in the liver of GH-transgenic mice.