Stromal–epithelial interactions are important in both development and prostate cancer. Stromal changes have been shown to be powerful prognostic indicators of prostate cancer progression and of patient death helping to define lethal versus indolent phenotypes. The specific molecular underpinnings of these interactions are incompletely understood. We investigated whether stromal cathepsin D (CathD) overexpression affects prostate tumorigenesis through a paracrine mechanism.
Normal prostate fibroblasts (NPF) were retrovirally transduced to overexpress cyclin D1 (CD1) and were designated NPFCD1. Cathepsin D expression was knocked down using shRNA in cancer associated fibroblasts (CAF) and NPFCD1. We analyzed these stromal cell lines using immunohistochemistry, Western blot, and tissue recombination.
An examination of human prostate tissue revealed significantly increased stromal staining of CathD in malignant prostate tissue. Overexpression of CD1 in normal prostate fibroblasts (NPFCD1) produced a phenotype similar to, but more moderate than, CAF in a tissue recombination model. Knockdown studies revealed that CathD is required for NPFCD1 motility and invasive growth in vitro. BPH-1 cell proliferation was found to be induced when cultured with NPFCD1 conditioned medium, this effect was inhibited when CathD was knocked down in NPFCD1 cells. Overexpression of CathD in prostate stromal cells induced malignancy in adjacent epithelium, and this transformation was inhibited when stromal CathD expression was knocked down in CAF.
The study presented here demonstrates increased CathD expression is seen in human CAF. The upregulation of CD1 results in concomitant increases in CathD expression. Elevated CathD expression in the stroma contributes to tumor promotion. Prostate 73: 476–488, 2013. © 2012 Wiley Periodicals, Inc.