Interleukin-6 stimulation of growth of prostate cancer in vitro and in vivo through activation of the androgen receptor Kamilla Malinowska 1 , Hannes Neuwirt 1 , Ilaria T Cavarretta 1 , Jasmin Bektic 1 , Hannes Steiner 1 , Hermann Dietrich 3 , Patrizia L Moser 2 , Dietmar Fuchs 4 , Alfred Hobisch 5 and Zoran Culig 1 1 Department of Urology 2 Department of Pathology 3 Laboratory Animal Facilities and 4 Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria 5 Department of Urology, General Hospital Feldkirch, Feldkirch, Austria (Correspondence should be addressed to Z Culig; Email: zoran.culig@i-med.ac.at) Abstract It is hypothesized that ligand-independent activation of the androgen receptor is one of the mechanisms implicated in tumour progression. However, supportive evidence is limited to the effect of HER-2/neu that stimulates prostate cancer progression through activation of the androgen receptor. In the present study, we have asked whether the proinflammatory cytokine interleukin-6 (IL-6), which is known to stimulate androgen receptor activity and expression of its downstream target genes, may also induce growth of androgen-sensitive cells. We have found that IL-6 differentially regulates proliferation of LAPC-4 and MDA PCa 2b cells. In MDA PCa 2b cells, growth stimulation by IL-6 was reversed by administration of either the non-steroidal anti-androgen bicalutamide or the inhibitor of the mitogen-activated protein kinase pathway PD98059. Neither cell line was found to express endogenous IL-6. Interestingly, the treatment of those prostate cancer cells did not increase phosphorylation of STAT3. The effect of IL-6 on stimulation of androgen receptor activity in MDA PCa 2b cells was lower than that of androgen, comparable with findings reported by other researchers. However, growth of MDA PCa 2b xenografts in castrated animals treated with IL-6 was similar to that in non-castrated animals. In addition, bicalutamide showed an inhibitory effect on IL-6-regulated growth in vivo. Taken together, data in the present study demonstrate that IL-6 may cause growth of androgen receptor- positive tumours in vitro and in vivo through activation of the androgen receptor. Endocrine-Related Cancer (2009) 16 155–169 Introduction Prostate cancer whose growth is regulated largely through activation of the androgen receptor (AR) is the most common malignancy in the western world in men. Most small tumours detected by prostate-specific antigen (PSA) screening are nowadays cured by radical prostatectomy and radiation therapy. By contrast, patients with non-organ-confined tumours receive palliative treatment with androgen ablation or block- ade of the AR (Huggins et al. 1941). This therapy is effective for an average of 3–5 years before tumours regrow and metastasize to bone and visceral organs. The AR is a ligand-mediated transcription factor that belongs to the superfamily of steroid receptors. They have similar structures containing the N-terminal domain (NTD) that harbours activation function-1 (AF-1), the DNA-binding domain, hinge region and the ligand-binding domain (LBD) in which AF-2 is located. After ligand binding, the complex between a ligand and receptor is formed. Following translocation to the nucleus, the ligand-AR complex binds to specific androgen response elements, interacts with coactiva- tors and modulates the expression of androgen- regulated genes. Several mechanisms implicated in prostate cancer progression are AR-related. They involve AR gene amplification and overexpression, mutations or ligand- independent activation. A number of mutations in AR Endocrine-Related Cancer (2009) 16 155–169 1351–0088/09/016–155 q 2009 Society for Endocrinology Printed in Great Britain DOI: 10.1677/ERC-08-0174 Online version via http://www.endocrinology-journals.org Endocrine-Related Cancer (2009) 16 155–169