Publications

Mesangial cell (MC) activation plays a pivotal role in the development of the end stage sclerotic lesion characteristic of most forms of chronic glomerular disease. We have previously demonstrated that MC activation is directly linked to high level expression of the matrix metalloproteinase-2 (MMP-2) enzyme (Turck, J., Pollock, A. S., Lee, L., Marti, H.-P., and Lovett, D. H. (1996) J. Biol. Chem. 25, 15074-15083), the transcription of which is regulated in a tissue-specific fashion. Recent studies (Harendza, S., Pollock, A., Mertens, P. R., and Lovett, D. H. (1995) J. Biol. Chem. 270, 18786-18796) delineated a strong cis-acting enhancer element, designated MMP-2 RE1, within the 5'-flanking region of the rat MMP-2 gene. Gel shift, DNA footprint, and transcriptional analyses mapped the enhancer element to a unique 40-base pair (bp) sequence located at -1322 to -1282 bp relative to the translational start site. Bromodeoxyuridine-substituted UV cross-linking of the 40-bp enhancer element with MC nuclear extracts yielded a single protein of 52 kDa, while Southwestern blot analysis with MMP-2 RE1 demonstrated three hybridizing nuclear proteins of 52, 62, and 86 kDa size. Screening of a human MC cDNA expression library with MMP-2 RE1 exclusively yielded clones with the identical sequence of the transcription factor YB-1. Western blot and supershift gel analysis of MC nuclear extracts with an anti-YB-1 antibody confirmed the presence of YB-1 within the shifted complex. Examination of the MMP-2 RE1 sequence revealed an incomplete Y-box sequence (CTGCTGGGCAAG), which specifically interacted with recombinant YB-1 on DMS protection footprinting analysis. YB-1 protein preferentially bound the single-stranded components of the 40-bp MMP-2 RE1 and, with increasing concentrations, formed multimeric complexes. Co-transfection of YB-1 in MC increased the enhancer activity within the context of the native MMP-2 promoter, while transfection of non-MMP-2-synthesizing glomerular epithelial cells with YB-1 led to transcriptional suppression. This study indicates that YB-1 is a major, cell type-specific transactivator of MMP-2 transcription by glomerular mesangial cells.

The activation of naive CD4+ T cells requires two discrete signals: a signal delivered by the T cell receptor following recognition of antigen and an accessory signal transduced when costimulatory receptors interact with their ligands. Particularly important in the development of an immune response to foreign antigens is the T cell molecule CD28, which delivers a potent costimulus when engaged by ligands, B7-1 and B7-2, on antigen-presenting cells. It is interesting that blockade of B7 molecules, which disrupts interactions with CD28 and prevents delivery of the CD28 costimulus, also alters the immune responses to self antigens and prevents the development of clinical disease in murine models of systemic and organ-specific autoimmunity. Herein we review the roles of CD28 and its B7 ligands in the pathogenesis of autoimmunity, discuss efforts to treat animal models of autoimmunity by modifying the CD28 signal, and consider the mechanisms by which manipulation of the CD28 signal alters the course of experimental autoimmune disease.