Oncotarget

Research Papers:

Vitamin D receptor activation reduces VCaP xenograft tumor growth and counteracts ERG activity despite induction of TMPRSS2:ERG

Justin M. Roberts, Rebeca San Martin, D. Badrajee Piyarathna, James G. MacKrell, Guilherme V. Rocha, Jeffery A. Dodge, Cristian Coarfa, Venkatesh Krishnan, David R. Rowley and Nancy L. Weigel _

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Oncotarget. 2017; 8:44447-44464. https://doi.org/10.18632/oncotarget.17968

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Abstract

Justin M. Roberts1, Rebeca San Martin1, D. Badrajee Piyarathna1,2, James G. MacKrell3, Guilherme V. Rocha3, Jeffery A. Dodge3, Cristian Coarfa1,2, Venkatesh Krishnan3, David R. Rowley1 and Nancy L. Weigel1,4

1Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA

2Alkek Center for Molecular Discovery, Baylor College of Medicine, Houston, TX, USA

3Lilly Research Labs, Eli Lilly and Company, Indianapolis, IN, USA

4Scott Department of Urology, Baylor College of Medicine, Houston, TX, USA

Correspondence to:

Nancy L. Weigel, email: [email protected]

Keywords: vitamin D, prostate cancer, CYP24A1, TMPRSS2:ERG, VCaP

Received: November 30, 2016     Accepted: May 04, 2017     Published: May 18, 2017

ABSTRACT

Whether vitamin D is chemopreventive and/or has potential therapeutically in prostate cancer is unresolved. One confounding factor is that many prostate cancers express a TMPRSS2:ERG fusion gene whose expression is increased both by androgens and by vitamin D receptor (VDR) activation. Two challenges that limit VDR agonist use clinically are hypercalcemia and the cooperation of VDR with ERG to hyper-induce the 1α,25-dihydroxyvitamin D3 metabolizing enzyme, CYP24A1, thus reducing VDR activity. Using the VCaP TMPRSS2:ERG positive cell line as a model, we found that a nonsecosteroidal CYP24A1 resistant VDR agonist, VDRM2, substantially reduces growth of xenograft tumors without inducing hypercalcemia. Utilizing next generation RNA sequencing, we found a very high overlap of 1,25D(OH)2D3 and VDRM2 regulated genes and by drawing upon previously published datasets to create an ERG signature, we found activation of VDR does not induce ERG activity above the already high basal levels present in VCaP cells. Moreover, we found VDR activation opposes 8 of the 10 most significant ERG regulated Hallmark gene set collection pathways from Gene Set Enrichment Analysis (GSEA). Thus, a CYP24A1 resistant VDR agonist may be beneficial for treatment of TMPRSS2:ERG positive prostate cancer; one negative consequence of TMPRSS2:ERG expression is inactivation of VDR signaling.


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