Circulating anti-actin and anti-ATP synthase antibodies identify a sub-set of patients with idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome (iNS) with resistance or dependence to steroids is a common disease in children but in spite of an increasing clinical impact its pathogenesis is unknown. We screened for the presence of circulating antibodies against glomerular (podocytes, mesangium) and tubular cells (tubular epithelia) a cohort of 60 children with iNS including 8 patients with a familial trait of iNS or with proven mutation of NPHS1-NPHS2 and 12 with good sensitivity to steroids. Positive sera were found in 8 cases, all belonging to the category without familial trait/molecular defects. The targets of antibodies were characterized with Western blot and MALDI-Mass utilizing beta-hexyl cell extracts separated with two-dimensional electrophoresis. In all cases antibodies of the IgM class were directed against ATP synthase beta chain alone (4 cases) or in combination with actin (3 cases); one child presented IgG against aldose reductase. The clinical picture was nephrotic syndrome with steroid resistance or dependence and variable cyclosporin sensitivity; 3 patients developed end stage renal failure. The basic pathology picture was focal segmental glomerulosclerosis (FSGS) in 4 cases and mesangial proliferative glomerulonephrites with deposition of IgM in 2. Overall, patients with circulating auto-antibodies could not be readely differentiated on clinical grounds with the exception of 3 children who developed positivity for antinuclear antibodies during the follow-up. Affinity-purified IgM from one patient who underwent plasmapheresis for therapeutical pourposes (but not from a normal pool) induced proteinuria in Sprague-Dawley rats and concomitant human IgM deposition within glomeruli. This is the first report of circulating anti-actin/ATP synthase beta chain antibodies in a subset of patients with iNS. Both pathological significance and clinical impact given by the presence of these antibodies and the relationship with other conditions such as lupus-erythematosus, characterized by their presence, must be defined.

Down-regulation of lysyl oxidase-induced tumorigenic transformation in NRK-49F cells characterized by constitutive activation of ras proto-oncogene

Several investigations have suggested a putative tumor suppressor role for lysyl oxidase because it is down-regulated in many human and oncogene-induced tumors. To address this issue we down-regulated the enzyme in normal rat kidney fibroblasts by stable transfection of its cDNA in an antisense orientation. The selected clones revealed an absence of lysyl oxidase and dramatic phenotypic changes, interpretable as signs of transformation. The antisense lysyl oxidase clones showed, indeed, loose attachment to the plate and anchorage-independent growth and were highly tumorigenic in nude mice. Moreover, we found an impaired response of the PDGF and IGF-1 receptors to their ligands. In particular, the transformed cells showed a down-regulation of both PDGF receptors and expressed the 105-kDa isoform of the IGF-1 beta receptor, which was not present in the normal control cells. The lack of response to PDGF-BB has been described as a feature of many ras-transformed phenotypes. Therefore, we looked at the status of the p21(ras). Indeed, we found a significantly higher level of active p21(ras) both during steady-state growth and prolonged starvation. Our data reveal new evidence for a tumor suppressor activity of lysyl oxidase, highlighting its particular role in controlling Ras activation and growth factor dependence.

Lysyl oxidase activates the transcription activity of human collagene III promoter. Possible involvement of Ku antigen

Lysyl oxidase is an extracellular enzyme that controls the maturation of collagen and elastin. Lysyl oxidase and collagen III often show similar expression patterns in fibrotic tissues. Therefore, we investigated the influence of lysyl oxidase overexpression on the promoter activity of human COL3A1 gene. Our results showed that when COS-7 cells overexpressed the mature form of lysyl oxidase, the activity of the human COL3A1 promoter was increased up to an average of 12 times when tested by luciferase reporter assay. The effect was specific, because other promoters were not affected. Moreover, lysyl oxidase effect was abolished by beta-aminopropionitrile, a specific inhibitor of its catalytic activity. Electrophoretic mobility shift assay showed a binding activity in the region from -101 to -77 that was significantly increased by lysyl oxidase overexpression. The binding was specifically competed by the cold probe, and the mutagenesis of this region abolished both the binding activity in gel retardation and lysyl oxidase stimulation of COL3A1 promoter in transfection experiments. We identified the binding activity as Ku antigen in its two components: Ku80 and Ku70. This study suggests a new coordinated mechanism by which lysyl oxidase might control the development of fibrosis.

Micro-injection of recombinant lysyl oxidase blocks oncogenic p21-Ha-Ras and progesterone effects on Xenopus laevis oocyte maturation

Previous evidence suggested an anti-oncogenic role for lysyl oxidase, mainly in ras-transformed cells. Here we prove that recombinant lysyl oxidase is actually able to antagonize p21-Ha-Ras-induced Xenopus laevis oocyte maturation. Lysyl oxidase was also effective on progesterone-dependent maturation, indicating a block lying downstream of Ras. Maturation induced by activated 'maturation promoting factor', normally triggered by progesterone, was also inhibited by lysyl oxidase. Finally, lysyl oxidase did not abolish p42Erk2 phosphorylation upon maturation triggering, suggesting a block downstream of Erk2. Further investigation showed that lysyl oxidase action depends on protein synthesis and is therefore probably mediated by a newly synthesized protein.