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The Mitogen-Activated Protein Kinase Phosphatase Vaccinia H1–Related Protein Inhibits Apoptosis in Prostate Cancer Cells and Is Overexpressed in Prostate Cancer

¹ Department of Molecular Biosciences and ² Center for Cancer Biomedicine, University of Oslo; ³ Institute for Medical Informatics, Divisions of ⁴ Pathology and ⁵ Surgery, and ⁶ Department of Tumor Biology, Rikshospitalet University Hospital, Oslo, Norway

Requests for reprints: Fahri Saatcioglu, University of Oslo, P.O. Box 1041, Blindern, Oslo, 0316, Norway. Phone: 47-22854569; Fax: 47-22857207; E-mail: fahris{at}imbv.uio.no.

Key Words: prostate cancer • apoptosis • MKPs • VHR • androgens

Androgen ablation during the initial stages of prostate cancer causes regression of the tumor due to an increase in apoptosis and reduced cellular proliferation. However, prostate cancer invariably progresses to an androgen-independent state for poorly understood reasons. Previous studies showed that c-Jun NH₂ terminal kinase (JNK) is required for 12-O-tetradecanoylphorbol-13-acetate (TPA)– and thapsigargin (TG)–induced apoptosis in the androgen-responsive prostate cancer cell line LNCaP. Androgens protect LNCaP cells from TPA-induced or TG-induced apoptosis via down-regulation of JNK activation. However, the molecular mechanisms of this inhibition are not clear. Here, we systematically investigated the possible regulation of mitogen-activated protein kinase phosphatases/dual-specificity phosphatases during apoptosis of LNCaP cells and found that Vaccinia H1–related protein (VHR/DUSP3) is up-regulated by androgens during inhibition of apoptosis in LNCaP cells, but not in androgen-independent DU145 cells. Ectopic expression of wild-type VHR, but not a catalytically inactive mutant, interfered with TPA- and TG-induced apoptosis. Consistently, small interfering RNA–mediated knockdown of endogenous VHR increased apoptosis in response to TPA or TG in the presence of androgens. Furthermore, COS7 cells stably expressing wild-type VHR, but not a mutant, had a decrease in JNK phosphorylation. In vivo, VHR expression decreased in the androgen-dependent human prostate cancer xenograft CWR22 upon androgen withdrawal and was inversely correlated to JNK phosphorylation. Expression analysis in human prostate cancer specimens showed that VHR is increased in prostate cancer compared with normal prostate. These data show that VHR has a direct role in the inhibition of JNK-dependent apoptosis in LNCaP cells and may therefore have a role in prostate cancer progression. [Cancer Res 2008;68(22):9255–64]