The IGF-independent role of IRS-2 in the secretion of MMP-9 enhances the growth of prostate carcinoma cell line PC3

Abstract

Insulin receptor substrate-2 (IRS-2), a substrate of the insulin-like growth factor (IGF)-I receptor, is highly expressed in the prostate cancer cell line, PC3s. We recently demonstrated that extracellular signal-regulated kinase (Erk1/2), a kinase downstream of IGF signaling, is activated in PC3 cells under serum starvation, and this activation can be inhibited by IRS-2 knockdown. Here, we found that the addition of an IGF-I neutralizing antibody to the culture medium inhibited the activation of Erk1/2. Further, suppression of Erk1/2 in IRS-2 knockdown cells was restored by the addition of PC3 serum-free conditioned medium. In contrast, IRS-2-silenced PC3 conditioned medium could not restore Erk1/2 activation, suggesting that IRS-2 promotes the secretion of proteins, yet to be identified that activate the IGF signaling pathway. Gelatin zymography analysis of conditioned medium showed that matrix metalloproteinase-9 (MMP-9) was secreted extracellularly in IRS-2 dependent manner when PC3s were cultured under serum starvation conditions. Finally, MMP-9 knockdown suppressed Erk1/2 activation, DNA synthesis, and migratory activity. Taken together with the positive correlation of IRS-2 levels with Gleason Grade in human prostate cancer tissues, this suggests that highly expressed IRS-2 activates IGF signaling by enabling the secretion of MMP-9, which is associated with hyperproliferation and malignancy of prostate cancer.