Upregulation of the cochaperone Mdg1 in endothelial cells is induced by stress and during in vitro angiogenesis

Angiogenesis research has focused on receptors and ligands mediating endoth elial cell proliferation and migration. Little is known about the molecular mechanisms that are involved in converting endothelial cells from a prolif erative to a differentiated state. Microvascular differentiation gene 1 (Md g1) has been isolated from differentiating microvascular endothelial cells that had been cultured in collagen type I gels (3D culture). In adult human tissue Mdg1 is expressed in endothelial and epithelial cells. Sequence ana lysis of the full-length cDNA revealed that the N-terminal region of the pu tative Mdg1-protein exhibits a high sequence similarity to the J-domain of Hsp40 chaperones. We show that this region functions as a bona fide J-domai n as it can replace the J-domain of Escherichia coli DnaJ-protein. Mdg1 is also upregulated in primary endothelial and mesangial cells when subjected to various stress stimuli. GFP-Mdg1 fusion constructs showed the Mdg1-prote in to be localized within the cytoplasm under control conditions. Stress in duces the translocation of Mdg1 into the nucleus, where it accumulates in n ucleoli. Costaining with Hdj1, Hdj2, Hsp70, and Hsc70 revealed that Mdg1 co localizes with Hsp70 and Hdj1 in control and stressed HeLa cells. These dat a suggest that Mdg1 is involved in the control of cell cycle arrest taking place during terminal cell differentiation and under stress conditions. (C) 2001 Academic Press.