Publications

The nuclear factor (NF)-kappa B transcription factor system is composed of at least four inducible nucleoprotein adducts termed p50, p55 (NF-kappa B p50), p75 (NF-kappa B p65), and p85 (c-Rel). These proteins are expressed in the nuclei of activated T cells in a distinctly biphasic fashion, with p55 and p75 induction occurring within minutes whereas the induction of p50 and p85 occurs after several hours. In contrast, p50 and p55 are constitutively expressed in the nuclei of U937 and THP-1 monocytic cells. However, cellular activation is required for the nuclear expression of p75 in these cells. Additionally, activation of monocytic cells does not result in a significant induction of p85. Tumor necrosis factor alpha induces the nuclear expression of p55 and p75 in these monocytic cells within 20 min, presumably reflecting the liberation of these proteins from I kappa B. In contrast, phorbol myristate acetate (PMA) induces the expression of these proteins with delayed kinetics, raising the possibility that PMA is incapable of mediating the efficient release of p55 and p75 from I kappa B in these cells. These findings highlight important differences in the regulation of these proteins in monocytic cells versus T cells and suggest that the induced expression of NF-kappa B p65 in monocytes may play a central role in the activation of HIV-1 gene expression.

Using electrophoretic mobility shift assays and DNA-protein cross-linking techniques, we demonstrate that IL-2 binding to functional forms of the human IL-2R activates nuclear expression of the eukaryotic transcription factor NF-kappa B. These inductive effects of IL-2 were observed in three different cellular systems including human Jurkat T cells stably transfected with IL-2R beta cDNA, mouse pro-B BA/F3 cells stably expressing human IL-2R beta chains either alone or in combination with human or murine IL-2R alpha chains, and purified primary resting human T cells constitutively displaying small numbers of IL-2R beta molecules. IL-2 activation of nuclear NF-kappa B expression is regulated in part at a post-translational level, involving the rapid translocation of both the 50- and 65-kDa subunits of NF-kappa B from the cytoplasm to the nucleus. However, IL-2 induction also produced an increase in mRNA for NF-kappa B p105, indicating an additional pretranslational component of regulation. In contrast, IL-2 exerts only minor effects on NF-kappa B p65 mRNA expression. IL-2 induction of NF-kappa B through the IL-2R beta subunit was both correlated with activation of the endogenous IL-2R alpha gene and critically dependent upon the presence of a serine-rich cytoplasmic domain within IL-2R beta (amino acid residues 267-312). This domain has previously been shown to be essential for IL-2-induced cell growth and may correspond to a binding site for an IL-2R beta-associated tyrosine kinase. Together, these findings suggest that NF-kappa B may play an important role as one intracellular second messenger relaying signals from the plasma membrane to cell nucleus that leads to IL-2-induced activation and growth.

The 27-kDa Rex trans-acting protein appears to be essential for replication of human T-cell leukemia virus type I. Mutations introduced outside of the Rex RNA-binding domain-nucleolar localization signal display either wild-type activity or, conversely, yield dominant-negative proteins. We generated missense mutations in a particular domain of the Rex protein (amino acid residues 54 to 69) which is characterized by a cluster of dominant-negative mutants. Our results indicate that amino acids 57 to 67 are critically important for Rex function mediated through the RxRE cis-acting RNA sequence. Within this domain, only amino acids 61 to 63 could be mutated without loss of function. All other missense and deletion mutants yielded dominant-negative proteins. In vitro RNA-binding studies performed with glutathione S-transferase-Rex fusion proteins demonstrated that all of the mutant Rex proteins interacted specifically with RxRE RNA. Analysis of chimeric Rex-Rev proteins suggests that this Rex domain is important for oligomerization.

Secretion of glomerular cell-derived matrix metalloproteinases (MMPs) and their specific inhibitors, TIMP-1,2, may play an important role in the turnover of the glomerular extracellular matrix under basal and pathologic conditions. A 66-68 kd MMP secreted by cultured mesangial cells (MC) with activity against Type IV collagen and gelatin was purified and shown by amino-acid sequence analysis to be identical with a Type IV collagenase/gelatinase secreted by certain transformed tumor cell lines. The expression of the mesangial MMP in vivo was limited within the kidney to a small subset of the intrinsic glomerular mesangial cell population. After induction of acute anti-Thy 1.1 glomerulonephritis, there was a large increment in the number of Type IV collagenase-secreting MC, temporally coincident with the development of mesangial hypercellularity. The expression of the MMP inhibitor protein, TIMP-1, was not changed over this period. Ultrastructural studies localized the mesangial MMP to areas of evolving mesangiolysis and at sites of glomerular basement membrane disruption. Enhanced expression of the mesangial cell-derived Type IV collagenase may contribute to the evolution of glomerular injury in this model of immune complex-mediated glomerulonephritis or may be involved in the extensive matrix remodeling process that accompanies this form of glomerular injury.