RESTRICTED ENDOTHELIAL-CELL EXPRESSION OF GRAVIN IN-VIVO

Background: Gravin, a novel, high molecular weight, intracellular prot ein, is expressed in endothelial cells and several other adherent cell types in vitro. To gain insights into its function, we examined the d istribution of gravin in tissues. Methods: Affinity-purified polyclona l and monoclonal antibodies were raised against a bacterial fusion pro tein corresponding to the carboxyl terminus of gravin and against affi nity-isolated gravin. The specificity of the antibodies was characteri zed by immunoblotting bacterial, cell, and tissue extracts. The charac terized antibodies were used to localize gravin in baboon tissue secti ons by immunocytochemistry and immunofluorescence microscopy. Results: The antibodies specifically immunoblotted the fusion protein and reco gnized either a band at 250 kDa or a doublet at 300 kDa on immunoblots of MG63 cells, HEL cells stimulated with phorbol ester, and several b aboon tissues. In tissue sections, cell types that express gravin incl uded fibroblasts, components of the peripheral and central nervous sys tem, the adrenal medulla, the somatic layer of Bowman's capsule, cells associated with the glomerulus, and smooth muscle of certain organs. In contrast, most epithelia and all endothelia, with the exception of endothelia of the hepatic sinusoids and intestinal lacteals, lacked gr avin. Levels of gravin mRNA expression in stimulated HEL cells increas ed dramatically when cells were stimulated in the presence of cyclohex imide, suggesting that gravin expression may be partly regulated by pr otein-dependent mRNA catabolism. Conclusions: These data indicate that gravin expression is regulated in endothelial cells, possibly through protein-dependent mRNA catabolism, The strong expression of gravin in fibroblasts, neurons, and cells derived from neural crest in vivo and in adherent cells in vitro further suggests that this protein may pla y role in the modulation of cell motility and adhesion. (C) 1994 WiIey -Liss, Inc.