INSULIN-LIKE GROWTH FACTOR-BINDING PROTEINS (IGFBP)-4, (IGFBP)-5, AND(IGFBP)-6 IN THE BENIGN AND MALIGNANT HUMAN PROSTATE - IGFBP-5 MESSENGER-RIBONUCLEIC-ACID LOCALIZATION DIFFERS FROM IGFBP-5 PROTEIN LOCALIZATION

Insulin-like growth factor (IGF)-binding proteins (IGFBPs) modulate th e actions of IGF. We have previously reported that IGFBP-2 messenger r ibonucleic acid (mRNA) and protein are increased, and IGFBP-3 protein decreased in malignant prostate epithelium compared to benign epitheli um. In this study, we examined the other IGFBPs secreted by prostate c ells in vitro, namely IGFBP-4, -5, and 6. Immunoreactivity and mRNA si gnals for IGFBP-4 and -6 were localized to epithelial cells, with less signal in stroma. IGFBP-4 immunostaining and hybridization signal wer e significantly increased in prostate adenocarcinoma compared to those in benign epithelium. Immunostaining for IGFBP-5 was localized to the epithelium and stroma. IGFBP-5 immunoreactivity was significantly inc reased in malignant compared to benign epithelium. IGFBP-5 mRNA signal was not localized to epithelial cells; rather, the signal was over st romal cells surrounding the acinar structures. These cells are thought to be fibroblasts. We show that IGFBP-4 mRNA and protein and IGFBP-5 protein are increased in malignant epithelium compared to benign epith elium, that IGFBP-6 is present in benign and malignant epithelium, and that there is differential localization of IGFBP-5 mRNA and protein i n prostate tissue. IGFBP-5 that is made by fibroblasts appears to be s equestered by epithelial cells. IGFBP-5 may, therefore, be a factor in cellular interactions between stromal and epithelial cells that are o f fundamental importance for normal prostatic development and function .