Characterization of insulin-like growth factor-binding protein-related proteins (IGFBP-rPs) 1, 2, and 3 in human prostate epithelial cells: Potentialroles for IGFBP-rP1 and 2 in senescence of the prostatic epithelium

Insulin-like growth factor (IGF)-binding protein (IGFBP)-related proteins ( IGFBP-rPs) are newly described cysteine-rich proteins that share significan t aminoterminal structural similarity with the conventional IGFBPs and are involved in a diversity of biological functions, including growth regulatio n. IGFBP-rP1 ((MAC25/Angiomodulin/prostacyclin-stimulating factor) is a pot ential tumor-suppressor gene that is differentially expressed in meningioma s, mammary and prostatic cancers, compared with their malignant counterpart s. We have previously shown that IGFBP-rP1 is preferentially produced by pr imary cultures of human prostate epithelial cells (HPECs) and by poorly tum origenic P69SV40T cells, compared with the cancerous prostatic LNCaP, DU145 , PC-3, and M12 cells. We now show that IGFBP-rP1 increases during senescen ce of HPEC. IGFBP-rP2 (also known as connective tissue growth factor), a downstream eff ector of transforming growth factor (TGF)-beta and modulator of growth for both fibroblasts and endothelial cells, was detected in most of the normal and malignant prostatic epithelial cells tested, with a marked up-regulatio n of IGFBP-rP2 during senescence of HPEC. Moreover, IGFBP-rP2 noticeably in creased in response to TGF-beta1 and all-trans retinoic acid (atRA) in HPEC and PC-3 cells, and it decreased in response to IGF-I in HPEC. IGFBP-rP3 [nephroblastoma overexpressed (NOV)], the protein product of the NOV protooncogene, was not detected in HPEC but was expressed in the tumori genic DU145 and PC-3 cells. It was also synthesized by the SV40-T antigen-t ransformed Peg and malignant M12 cells, where it was down-regulated by atRA . These observations suggest biological roles of IGFBP-rPs in the human prost ate. IGFBP-rP1 and IGFBP-rP2 are likely to negatively regulate growth, beca use they seem to increase during senescence of the prostate epithelium and in response to growth inhibitors (TGF-beta1 and atRA). Although the data co llected on IGFBP-rP3 in prostate are modest, its role as a growth stimulato r and/or protooncogene is supported by its preferential expression in cance rous cells and its downregulation by atRA.