Growth Hormone Induces Colon DNA Damage Independent of IGF-1.

DNA damage occurs as a result of environmental insults and aging and, if unrepaired, may lead to chromosomal instability and tumorigenesis. Because GH suppresses ataxia-telangiectasia mutated kinase phosphorylation, decreases DNA repair, and increases DNA damage accumulation, we elucidated whether GH effects on DNA damage are mediated through induced IGF-1. In nontumorous human colon cells, GH, but not IGF-1, increased DNA damage. Stably disrupted IGF-1 receptor (IGF-1R) by lentivirus-expressing short hairpin RNA in vitro or treatment with the IGF-1R phosphorylation inhibitor picropodophyllotoxin (PPP) in vitro and in vivo led to markedly induced GH receptor (GHR) abundance, rendering cells more responsive to GH actions. Suppressing IGF-1R triggered DNA damage in both normal human colon cells and three-dimensional human intestinal organoids. DNA damage was further increased when cells with disrupted IGF-1R were treated with GH. Because GH induction of DNA damage accumulation appeared to be mediated not by IGF-1R but probably by more abundant GH receptor expression, we injected athymic mice with GH-secreting xenografts and then treated them with PPP. In these mice, high circulating GH levels were associated with increased colon DNA damage despite disrupted IGF-1R activity (P < 0.01), whereas GHR levels were also induced. Further confirming that GH effects on DNA damage are directly mediated by GHR signaling, GHR-/- mice injected with PPP did not show increased DNA damage, whereas wild-type mice with intact GHR exhibited increased colon DNA damage in the face of IGF-1 signaling suppression. The results indicate that GH directly induces DNA damage independent of IGF-1.

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