Different effect of cadmium and copper on H+-ATPase activity in plasma membrane vesicles from Cucumis sativus roots.

The effect of heavy metals on plasma membrane (PM) H(+)-ATPase (EC 3.6.3.14) activity in cucumber (Cucumis sativus) roots was studied. The aim of this work was to explain the mechanism of modification of the PM H(+)-ATPase activity in plants subjected to heavy metals. Plants were treated with 10 µM Cd or Cu for 6 d. After 3 d exposure to the heavy metals, some of the plants were transferred to control conditions for a further 3 d (3/3 plants). The activity of PM H(+)-ATPase was found to be increased in plants treated with heavy metals. The highest activity measured as proton transport was observed in 3/3 plants. Estimation of transcript levels of C. sativus PM H(+)-ATPase in roots indicated that the action of Cd, but not Cu, affected the gene expression level. Transcript levels of C. sativus PM H(+)-ATPase (CsHA2, CsHA3, CsHA4, CsHA8, and CsHA9) genes increased in roots treated with Cd. Moreover, Western blot analysis with antibody against phosphothreonine and 14-3-3 protein indicated that increased activity of PM H(+)-ATPase under heavy-metal stress resulted from phosphorylation of the enzyme. It was found that Cu markedly increased the activity of catalase and ascorbate peroxidase and reduced the level of H(2)O(2) in cucumber roots. In contrast, Cd did not affect these parameters. These results indicate that Cd and Cu can, in different ways, lead to modification of PM H(+)-ATPase activity. Additionally, it was observed that treatment of plants with heavy metals led to an increased level of heat-shock proteins in the tissues. This suggests that the plants had started adaptive processes to survive adverse conditions, and increased PM H(+)-ATPase activity could further enhance the repair processes in heavy-metal-stressed plants.

135G>C and 172G>T polymorphism in the 5' untranslated region of RAD51 and sporadic endometrial cancer risk in Polish women.

BACKGROUND: Despite advanced diagnostic and therapeutic procedures, endometrial cancer (EC) is still responsible for high morbidity and mortality of women. The genetic variability in RAD51 may contribute to the appearance and progression of various cancers including EC. AIM: We investigated the association of polymorphisms in the DNA repair genes RAD51 135G>C and 172G>T with endometrial cancer risk. MATERIAL AND METHODS: The genotypes of RAD51 135G>C and 172G>T polymorphism were determined by PCR-RFLP methods in endometrial tissue of 240 cancer subjects and 240 healthy subjects who served as controls. RESULTS: In the present work we demonstrated a significant positive association between the RAD51 C/C genotype and endometrial carcinoma, with an adjusted odds ratio (OR) of 13.0 (p < 0.0001). The distribution of genotypes for 135G>C SNP in endometrial cancer patients vs. controls was: 10% vs. 27% for GG, 13% vs. 58% for GC and 77% vs. 15% for CC genotype, respectively. Variant 135C allele of RAD51 increased the cancer risk (OR = 1.81; 95% CI 0.11-2.93, p = 0.022). The higher risk of EC occurrence was associated with the combined C135C-G172T genotype (OR = 7.69; 95% CI 3.45-17.12). CONCLUSION: The results indicated that the polymorphism 135G>C of the RAD51 gene may be positively associated with endometrial carcinoma in the Polish population. Further studies, conducted on a larger group, are required to clarify this point.

Response of plasma membrane H+-ATPase to heavy metal stress in Cucumis sativus roots.

The effect of heavy metals on the modification of plasma membrane H(+)-ATPase (EC 3.6.3.14) activity in cucumber roots was studied. In plants stressed for 2 h with 10 microM or 100 microM Cd, Cu or Ni the hydrolytic as well as the transporting activity of H(+)-ATPase in the plasma membranes of root cells was decreased. Transcript levels of Cucumis sativus plasma membrane H(+)-ATPase in roots treated with 10 microM Cd, Cu, or Ni as well as with 100 microM Cu or Ni were similar to the control, indicating that the action of metals did not involve the gene expression level. Only in roots exposed to 100 microM Cd was the level of plasma membrane H(+)-ATPase mRNA markedly decreased. The inhibition of the plasma membrane proton pump caused by 100 microM Cd, Cu and Ni was partially diminished in the presence of cantharidin, a specific inhibitor of protein phosphatases. Western blot analysis with the antibody against phosphothreonine confirmed that decreased activity of plasma membrane H(+)-ATPase under heavy metals resulted from dephosphorylation of the enzyme protein. Taken together, these data strongly indicated that alteration of the enzyme under heavy metal stresses was mainly due to the post-translational modification of its proteins in short-term experiments.

Comparison of heavy metal effect on the proton pumps of plasma membrane and tonoplast in cucumber root cells.

The effects of 10 microM cadmium, copper and nickel on the activities of vacuolar membrane and plasma membrane (PM) ATP-dependent proton pumps was investigated in Cucumis sativus L. root cells. It was demonstrated that vacuolar H+-ATPase (EC 3.6.3.14) and PM H+-ATPase (EC 3.6.3.6) differed in sensitivity to heavy metals. Exposure of cucumber seedlings to Cd, Cu and Ni had no significant effect on the activity of the vacuolar proton pump and, in the case of Ni, also on the activity of the PM proton pump. In contrast, Cd and Cu ions diminished both ATP hydrolysis and proton transport in plasma membranes. Transcript levels of genes encoding PM enzyme as well as the subunit A of tonoplast enzyme in roots stressed with heavy metals were similar to the control. Cd, Cu and Ni were accumulated in cucumber roots with similar efficiency, but their relative distribution between the symplast and apoplast differed. To explain the mechanism of heavy metal action on the plasma membranes of cucumber roots, the MDA content, as a lipid peroxidation product, and fatty acid composition were analyzed. It was shown that exposure of plants to Cd, Cu and Ni did not enhance the lipid peroxidation in the PM fraction. However, all metals caused an increase in the saturation of PM fatty acids and a decrease in the length of the fatty acid chain.