No abstract

Met-overaccumulating mutants provide a powerful genetic tool for examining both the regulation of the Met biosynthetic pathway and in vivo developmental responses of gene expression to altered Met levels. We have previously reported the identification of two Arabidopsis thaliana Met over-accumulation ( mto ) mutants, mto1-1 and mto2-1 , that carry mutations in the genes encoding cystathionine γ -synthase (CGS) and threonine synthase (TS), respectively. A third mutant, mto3-1 , has recently been reported to carry a mutation in the gene encoding S -adenosylmethionine synthetase 3 (SAMS3). Here, we report the isolation of a new ethionine-resistant A. thaliana mutant that over-accumulates soluble Met approximately 20-fold in young rosettes. The causal mutation was determined to be a single, recessive mutation that was mapped to chromosome 3. Sequence analysis identified a single nucleotide change in the gene encoding SAMS3 that was distinct from the mto3-1 mutation and altered the amino acid sequence of the enzyme active site. This mutation was therefore referred to as mto3-2 . Although Met over-accumulation in the mto3-2 mutant was similar to that in the mto2-1 mutant, CGS mRNA levels did not respond to the mto3-2 mutation and were similar to that in equivalent wild-type plants.

In order to clarify intraglomerular cellular activation and cytokine involvement in IgA nephropathy, the glomerular expression of MHC class II antigens (HLA-DR and DQ) and cellular proliferative nuclear antigen (Ki-67), and serum γ-interferon (γ-IFN) levels were evaluated in 49 patients with IgA nepropathy. HLA-DR was detected in all but 4 patients in whom glomerular sclerosis was present. HLA-DQ and Ki-67 were observed in 51 and 38% of the patients, respectively. Proteinuria, recent macroscopic hematuria, mesangial proliferation, and extracapillary and endocapillary lesions were more frequent and more severe in HLA-DQ-positive than in HLA-DQ-negative patients. In 10 patients with acute exacerbation, endocapillary lesions and HLA-DQ and Ki-67 expression were present in 70,80 and 88%, respectively. Serum γ-IFN levels were high in the patients (2.0 ± 0.3 U/ml, n = 40), especially during acute exacerbation (3.4 ± 1.1 U/ml, n = 9). Glomerular HLA-DQ and Ki-67 expression correlated with serum γ-IFN levels (r = 0.73, p < 0.01 for HLA-DQ; r = 0.75, p < 0.01 for Ki-67). Renal biopsy specimens taken before and after prednisolone and/or urokinase therapy were available from 4 patients. There was strong reactivity to HLA-DQ in the glomerular tufts of all 4 pretreatment samples. However, HLA-DQ reactivity disappeared after treatment in 3 samples, concomitant with normalization of serum γ-IFN levels. We conclude that serum γ-IFN levels are related to glomerualr HLA-DQ and Ki-67 expression and acute exacerbation in patients with IgA nephropathy. These data suggest that γ-IFN and MHC class II antigens play an important role in the immune-mediated glomerular injury of IgA nephropathy.

The negative charges of dextran-sulfate (DS) used for low-density lipoprotein (LDL) apheresis activates the intrinsic coagulation pathway, in which plasma kallikrein acts on high-molecular-weight kininogen (HMWK) to produce large amounts of bradykinin. This study was undertaken to see whether bradykinin generated during DS LDL apheresis has some physiologic effects in vivo. The plasma levels of bradykinin and nitric oxide derivatives (NOx) were examined when either of 2 anticoagulants, heparin or nafamostat mesilate (NM), was used during DS LDL apheresis. Although anticoagulative action by NM depends on the inhibition of thrombin activity, this substance also inhibits the activity of plasma kallikrein. During apheresis using heparin, the marked increase in bradykinin levels (before apheresis, 18 +/- 3 (mean +/- SE, n = 5) pg/ml; after apheresis 470 +/- 140, p < 0.01) was associated with the increase in NOx (before apheresis 50 +/- 11 pg/ml; after apheresis 66 +/- 15). Interestingly, these changes in bradykinin and NOx levels were suppressed during apheresis using NM. The changes in plasma NOx levels were negatively correlated with those in blood pressures. These findings suggest that bradykinin generated during apheresis exerts some physiologic effects by means of activation of endothelium-derived relaxant factor (EDRF). Our results support the view that bradykinin produced during DS LDL apheresis has physiologic significance.