In order to elucidate the function of the nifU gene product in nitrogenase maturation in Azotobacter vinelandii. the gene product has been hyperexpressed in Escherichia coli and characterized by various biophysical techniques. Following the initial characterization, site-directed mutagenesis of conserved cysteinyl residues was performed in order to gain further insight into the structure/function relationship of NifU. Both the Fe protein and the MoFe protein of nitrogenase require processing by additional nif genes including nifM (Fe protein), and nifE, N, B, H, V, and Q (MoFe protein). Two additional genes, nifU and nifS, are required for the maturation of both nitrogenase component proteins. It has been proposed that they may somehow be involved in metallocluster biosynthesis (Jacobson et al., 1989b). Our laboratory has determined that the nifS gene product (Nifs) is a pyridoxal-phosphate containing enzyme capable of catalyzing the desulfurization of L-cysteine and can provide the inorganic sulfide necessary for in vitro metallocluster biosynthesis of the Fe protein (Zheng, et al., 1993: Zheng, et al., 1994). / Ph. D.

Rapidly progressive glomerulonephritis (RPGN) is a clinical syndrome characterized by loss of renal function within days to weeks and by glomerular crescents on biopsy. The pathogenesis of this disease is unclear, but circulating factors such as antineutrophil cytoplasmic antibodies (ANCA) are believed to play a major role. In this thesis, we show that deletion of the Von Hippel-Lindau gene (Vhlh) from intrinsic glomerular cells of mice is sufficient to initiate a necrotizing crescentic glomerulonephritis and the clinical features that accompany RPGN. Loss of Vhlh leads to stabilization of hypoxia-inducible factor alpha subunits (HIFαs). Using gene expression profiling, we identified de novo expression of the HIFα target gene Cxcr4. In glomeruli from mice with RPGN, the course of RPGN is markedly improved in mice treated with a blocking antibody to Cxcr4, whereas overexpression of Cxcr4 alone in podocytes of transgenic mice is sufficient to cause glomerular disease. Despite the development of glomerular disease in mice that overexpress Cxcr4, their disease was milder and lacked features of full-blown RPGN. The Vhlh gene encodes VHL protein (pVHL, product of the Von Hippel-Lindau gene) that functions as the substrate recognition component of an E3 ubiquitin ligase. Although HIFα subunits are the best characterized substrates for pVHL, additional non-HIF mediated targets have been identified. To determine the role of HIF stabilization in this RPGN model, we generated double mutants that lack aryl hydrocarbon receptor nuclear translocator gene (Arnt, also called HIF1beta), an obligate dimerization partner for HIFα subunit function. Podocyte-selective deletion of Arnt in Vhlh mutant mice completely rescued the RPGN phenotype and mice survived longer than 8 months of age. Furthermore, stabilization of HIF2α alone led to glomerular disease characterized by crescentic transformation. Collectively, these results indicate an alternative mechanism for the pathogenesis of RPGN and glomerular disease in an animal model and suggest novel molecular pathways for intervention in this disease. In addition, we demonstrate a key role for VHL-HIF-Cxcr4 molecular pathway for the integrity of the glomerular barrier.

Rapidly progressive glomerulonephritis (RPGN) is a clinical syndrome characterized by loss of renal function within days to weeks and by glomerular crescents on biopsy. The pathogenesis of this disease is unclear, but circulating factors such as antineutrophil cytoplasmic antibodies (ANCA) are believed to play a major role. In this thesis, we show that deletion of the Von Hippel-Lindau gene (Vhlh) from intrinsic glomerular cells of mice is sufficient to initiate a necrotizing crescentic glomerulonephritis and the clinical features that accompany RPGN. Loss of Vhlh leads to stabilization of hypoxia-inducible factor alpha subunits (HIFαs). Using gene expression profiling, we identified de novo expression of the HIFα target gene Cxcr4. In glomeruli from mice with RPGN, the course of RPGN is markedly improved in mice treated with a blocking antibody to Cxcr4, whereas overexpression of Cxcr4 alone in podocytes of transgenic mice is sufficient to cause glomerular disease. Despite the development of glomerular disease in mice that overexpress Cxcr4, their disease was milder and lacked features of full-blown RPGN. The Vhlh gene encodes VHL protein (pVHL, product of the Von Hippel-Lindau gene) that functions as the substrate recognition component of an E3 ubiquitin ligase. Although HIFα subunits are the best characterized substrates for pVHL, additional non-HIF mediated targets have been identified. To determine the role of HIF stabilization in this RPGN model, we generated double mutants that lack aryl hydrocarbon receptor nuclear translocator gene (Arnt, also called HIF1beta), an obligate dimerization partner for HIFα subunit function. Podocyte-selective deletion of Arnt in Vhlh mutant mice completely rescued the RPGN phenotype and mice survived longer than 8 months of age. Furthermore, stabilization of HIF2α alone led to glomerular disease characterized by crescentic transformation. Collectively, these results indicate an alternative mechanism for the pathogenesis of RPGN and glomerular disease in an animal model and suggest novel molecular pathways for intervention in this disease. In addition, we demonstrate a key role for VHL-HIF-Cxcr4 molecular pathway for the integrity of the glomerular barrier.