Excess growth hormone suppresses DNA damage repair in epithelial cells
Vera Chesnokova, Svetlana Zonis, Robert Barrett, Hiraku Kameda, Kolja Wawrowsky, Anat Ben-Shlomo, Masaaki Yamamoto, John Gleeson, Catherine Bresee, Vera Gorbunova, Shlomo Melmed
Vera Chesnokova, Svetlana Zonis, Robert Barrett, Hiraku Kameda, Kolja Wawrowsky, Anat Ben-Shlomo, Masaaki Yamamoto, John Gleeson, Catherine Bresee, Vera Gorbunova, Shlomo Melmed
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Research Article Endocrinology

Excess growth hormone suppresses DNA damage repair in epithelial cells

Abstract

Growth hormone (GH) decreases with age, and GH therapy has been advocated by some to sustain lean muscle mass and vigor in aging patients and advocated by athletes to enhance performance. Environmental insults and aging lead to DNA damage, which — if unrepaired — results in chromosomal instability and tumorigenesis. We show that GH suppresses epithelial DNA damage repair and blocks ataxia telangiectasia mutated (ATM) kinase autophosphorylation with decreased activity. Decreased phosphorylation of ATM target proteins p53, checkpoint kinase 2 (Chk2), and histone 2A variant led to decreased DNA repair by nonhomologous end-joining. In vivo, prolonged high GH levels resulted in a 60% increase in unrepaired colon epithelial DNA damage. GH suppression of ATM was mediated by induced tripartite motif containing protein 29 (TRIM29) and attenuated tat interacting protein 60 kDa (Tip60). By contrast, DNA repair was increased in human nontumorous colon cells (hNCC) where GH receptor (GHR) was stably suppressed and in colon tissue derived from GHR–/– mice. hNCC treated with etoposide and GH showed enhanced transformation, as evidenced by increased growth in soft agar. In mice bearing human colon GH-secreting xenografts, metastatic lesions were increased. The results elucidate a mechanism underlying GH-activated epithelial cell transformation and highlight an adverse risk for inappropriate adult GH treatment.

Authors

Vera Chesnokova, Svetlana Zonis, Robert Barrett, Hiraku Kameda, Kolja Wawrowsky, Anat Ben-Shlomo, Masaaki Yamamoto, John Gleeson, Catherine Bresee, Vera Gorbunova, Shlomo Melmed

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Figure 2

GH suppresses ATM kinase activity.

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GH suppresses ATM kinase activity. (A) ATM kinase assay. hNCC were pretr...
(A) ATM kinase assay. hNCC were pretreated with GH and treated with etoposide for 3 hours. Cell extracts were immunoprecipitated with total ATM antibody. (B) Controls using IgG or in which the peptide was omitted were included. Assays were conducted in triplicate. Results shown are mean ± SEM of 3 independent experiments. Each dot represents 1 independent experiment. Data are graphed as fold-change, but statistical testing was performed on raw numbers. Differences were assessed with Tukey-adjusted mixed model regression. *P < 0.0 5 vs. IgG + Etop. (B) For ATM kinase assay, Western blotting was used to detect total ATM or autophosphorylated ATM (phospho-Ser 1981) and to verify equal protein amount in the immunoprecipitated samples for each experiment. Representative blots are shown. Quantification of protein expression is depicted in Supplemental Figure 1C. (C) Comet assay of hNCC harvested 24 hours after etoposide treatment. Single-cell gel electrophoresis was conducted and Olive Tail Moments assessed on at least 200 cells/per slide for each experiment. Results shown are mean ± SEM. Control, untreated cells. **P < 0.01 vs. control. Differences were assessed with Tukey-adjusted mixed model regression.