1. ¹Department of Medicine, National University of Singapore, 30 Medical Dr., Singapore 117609, Republic of Singapore
2. ²Institute of Molecular and Cell Biology, National University of Singapore, 30 Medical Dr., Singapore 117609, Republic of Singapore
3. ³The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, USA
4. ⁴CNRS UMR 5578, Physiologies Energetiques Cellulaires et Moléculaires, Université Claude Bernard, Lyon-1, France
5. ⁵Liggins Institute and National Research Centre for Growth and Development, University of Auckland, 2-6 Park Avenue, Private Bag 92019, Auckland, New Zealand

Correspondence: PE Lobie, E-mail: [email protected]

Received 06 December 2004; Revised 05 January 2005; Accepted 05 January 2005; Published online 14 March 2005.

Abstract

Previous microarray expression analyses have indicated autocrine human growth hormone (hGH) regulation of genes involved in the oxidative stress response. Expression analysis of antioxidant enzymes revealed that autocrine hGH increased both the mRNA and protein levels of catalase, superoxide dismutase 1 (SOD1), glutathione peroxidase and glutamylcysteine synthetase but not that of SOD2. As a consequence, autocrine hGH increased the antioxidant capacity of mammary carcinoma cells and protected against oxidative stress-induced apoptosis. Catalase activity was increased by autocrine production of hGH in mammary carcinoma cells and a catalase inhibitor abrogated protection from oxidative stress afforded by autocrine hGH. Autocrine hGH transcriptionally regulated catalase gene expression in a p44/42 MAP kinase-dependent manner and inhibition of MEK concordantly abrogated the protective effect of autocrine hGH against oxidative stress-induced apoptosis. Given that increased cellular oxidative stress is a key effector mechanism of specific chemotherapeutic agents, we propose that antagonism of autocrine hGH will improve the efficacy of chemotherapeutic regimes utilized for human mammary carcinoma.