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Contributed by Michael Karin, August 27, 2014 (sent for review June 30, 2014)
Significance
Prostate cancer often responds to hormone ablation therapy or chemotherapy by becoming more aggressive and metastatic. B cells recruited into hormone-deprived tumors by C-X-C motif chemokine 13 (CXCL13) play an important role in this process. We investigated how androgen ablation induces CXCL13 expression and found that CXCL13 is expressed by myofibroblasts within the tumor microenvironment that become activated as a result of low oxygen tension and hypoxia in androgen-deprived tumors. Hypoxia activates hypoxia-inducible factor 1 (HIF-1) and induces TGF-β expression, which converts fibroblasts to myofibroblasts and stimulates CXCL13 production. We show that several treatments that block CXCL13 expression, including immunodepletion of myofibroblasts, blockade of TGF-β signaling, and phosphodiesterase-5 (PDE5) inhibitors, inhibit B-cell recruitment into androgen-deprived prostate tumors and prevent the emergence of a more aggressive type of cancer.
Abstract
Prostate cancer (PC) is a slowly progressing malignancy that often responds to androgen ablation or chemotherapy by becoming more aggressive, acquiring a neuroendocrine phenotype, and undergoing metastatic spread. We found that B lymphocytes recruited into regressing androgen-deprived tumors by C-X-C motif chemokine 13 (CXCL13), a chemokine whose expression correlates with clinical severity, play an important role in malignant progression and metastatic dissemination of PC. We now describe how androgen ablation induces CXCL13 expression. In both allografted and spontaneous mouse PC, CXCL13 is expressed by tumor-associated myofibroblasts that are activated on androgen ablation through a hypoxia-dependent mechanism. The same cells produce CXCL13 after chemotherapy. Myofibroblast activation and CXCL13 expression also occur in the normal prostate after androgen deprivation, and CXCL13 is expressed by myofibroblasts in human PC. Hypoxia activates hypoxia-inducible factor 1 (HIF-1) and induces autocrine TGF-β signaling that promotes myofibroblast activation and CXCL13 induction. In addition to TGF-β receptor kinase inhibitors, myofibroblast activation and CXCL13 induction are blocked by phosphodiesterase 5 (PDE5) inhibitors. Both inhibitor types and myofibroblast immunodepletion block the emergence of castration-resistant PC in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model of spontaneous metastatic PC with neuroendocrine differentiation.
Footnotes
- ↵1To whom correspondence should be addressed. Email: karinoffice{at}ucsd.edu.
Author contributions: M.A. and M.K. designed research; M.A., S.S., and Y.K. performed research; C.A.M.J. contributed new reagents/analytic tools; M.A. and S.S. analyzed data; and M.A. and M.K. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1416498111/-/DCSupplemental.
Myofibroblasts promote prostate cancer progression
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