VEGF/neuropilin-2 regulation of Bmi-1 and consequent repression of IGF-IR define a novel mechanism of aggressive prostate cancer

Abstract

We show that the VEGF receptor neuropilin-2 (NRP2) is associated with high-grade, PTEN-null prostate cancer and that its expression in tumor cells is induced by PTEN loss as a consequence of c-Jun activation. VEGF/NRP2 signaling represses insulin-like growth factor-1 receptor (IGF-IR) expression and signaling, and the mechanism involves Bmi-1-mediated transcriptional repression of the IGF-IR. This mechanism has signifi cant functional and therapeutic implications that were evaluated. IGF-IR expression positively correlates with PTEN and inversely correlates with NRP2 in prostate tumors. NRP2 is a robust biomarker for predicting response to IGF-IR therapy because prostate carcinomas that express NRP2 exhibit low levels of IGF-IR. Conversely, targeting NRP2 is only modestly effective because NRP2 inhibition induces compensatory IGF-IR signaling. Inhibition of both NRP2 and IGF-IR, however, completely blocks tumor growth in vivo. SIGNIFICANCE: These results identify a causal role for NRP2 and VEGF/NRP2 signaling in the behavior of aggressive prostate cancers by a mechanism that involves regulation of Bmi-1, a transcriptional repressor implicated in the etiology of prostate cancer induced by loss of PTEN function, and the repression of the IGF-IR. The therapeutic implications are signifi cant because combined inhibition of NRP2 and IGF-IR overcomes the resistance induced by targeting each receptor individually. © 2012 American Association for Cancer Research.