TRANSFORMING GROWTH-FACTOR-BETA RECEPTOR EXPRESSION ON ENDOTHELIAL-CELLS - HETEROGENEITY OF TYPE-III RECEPTOR EXPRESSION

Recent studies of whole animal responses have defined a role for circu lating TGF-beta in the preservation and stabilization of microvascular endothelial function (Lefer et al. [1993] Proc. Natl. Acad. Sci. U.S. A., 90:1018-1022; Pfister et al. [1992] J. Exp. Med., 176:265-269). In order to determine which TGF-beta receptor types are responsible for this endothelial cell responsiveness, we used an affinity-labeling tec hnique with I-125-TGF-beta 1 and -beta 2 to characterize TGF-beta rece ptors on five different endothelial cell cultures: early passage bovin e lung and rat epididymal fat pad microvascular endothelial cells (BLM EC and REEC), established endothelial cell lines from bovine adrenal m edulla capillaries (EJG), fetal bovine heart (FBHE), and bovine pulmon ary artery (CPAE). Since it is known that endothelial cells from diffe rent parts of the vasculature vary with respect to cell surface antige n expression (McCarthy et al. [1991] Trends Pharmacol. Sci., 12:462-46 7; Augustin et al. [1994] Bioessays, 16:901-906), it is important to c ompare TGF-beta receptor expression on microvascular and macrovascular endothelial cells. We observed 85 kDa and 200-400 kDa labeled recepto r bands and analyzed their relationship to the cloned Type II and III receptors using peptide antibodies. We used dithiothreitol and phospho inositol-phospholipase C pretreatments to establish whether the 65 kDa labeled band which we observed corresponded to the Type I receptor or a glycophosphotidylinositol-linked binding protein. The results demon strated that microvascular but not macrovascular endothelial cells exp ress high levels of the Type III receptor. This differential expressio n of the Type III receptor indicates that distinct anatomical segments of the vasculature have distinct TGF-beta receptor profiles. The pres ence of the Type III receptor on micro- but not macrovascular endothel ial cells may account for the reportedly different potency of TGF-beta 1 and TGF-beta 2 on these two endothelial cell types. Analysis of the 85 kDa and 65 kDa affinity-labeled bands revealed that all the endoth elial cells express the Type II receptor and a band consistent with th e presence of a dithiothreitol-sensitive Type I receptor. Two isoform- specific phosphoinositol-phospholipase C releasable TGF-beta binding p roteins were also detected: a 60 kDa protein on one micro- (EJG) and o ne macro- (FBHE) vascular endothelial cell line and a 150/180 kDa prot ein on the macrovascular cell lines (FBHE and CPAE). These studies emp hasize the heterogeneous nature of endothelial cells and underline the importance of using microvascular endothelial cells when examining TG F-beta responses related to microvascular function. (C) 1995 Wiley-Lis s, Inc.