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Zinc at concentrations of 150, microM or higher induced necrosis as well as apoptosis in thyroid cancer cell lines. Necrosis was induced by zinc in a dose-dependent manner, whereas apoptosis did not increase at higher concentrations of zinc. The expression of the antiapoptotic protein phosphorylated Bad was markedly increased, whereas the expression of the proapoptotic proteins Bax and Bad decreased following Zn(2+) exposure. Zn(2+) induced rapid degradation of IkappaB, and an increase in the binding of nuclear transcription factor-kappaB (NF-kappaB). These observations indicate that antiapoptotic pathways were activated in thyroid cancer cells following exposure to Zn(2+). This may be a self-defence mechanism against apoptosis and may underlie the general resistance of thyroid cancer cells to apoptotic stimuli. Zinc may be a potential cytotoxic agent for the treatment of thyroid cancer.
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This study examined whether type 1 angiotensin II receptor (AT1) and angiotensin-converting enzyme (ACE) mRNAs are regulated during dietary salt loading in angiotensinogen gene-knockout (Atg-/-) mice which are genetically deficient in endogenous production of angiotensin II. Wild-type (Atg+/+) and Atg-/- mice were fed a normal-salt (0.3% NaCl) or a high-salt (4% NaCl) diet for 2 weeks. The mRNA levels were measured by Northern blot analysis. In Atg+/+ mice, concentrations of plasma angiotensin peptides were decreased by salt loading, whereas the treatment increased the brainstem, cardiac, pulmonary, renal cortex, gastric and intestinal AT1 mRNA levels. Salt loading also enhanced renal cortex ACE mRNA levels in Atg+/+ mice. Although plasma angiotensin peptides and urinary aldosterone excretion were not detected in Atg-/- mice, salt loading increased blood pressure in Atg-/- mice. In Atg-/- mice, pulmonary, renal cortex, gastric and intestinal AT1, and renal cortex and intestinal ACE mRNA levels were higher than those in Atg+/+ mice. However, salt loading upregulated AT1 mRNA expression only in the liver of Atg-/- mice, and the treatment did not affect ACE mRNA levels in Atg-/- mice. Furthermore, although the levels of ACE enzymatic activity showed the same trend with the ACE mRNA levels in the lung, renal cortex and intestine of both Atg-/- and Atg+/+ mice, the results of radioligand binding assay showed that cardiac expression of AT1 protein was regulated differently from AT1 mRNA expression both in Atg-/- and Atg+/+ mice. Thus, expression of AT1 and ACE is regulated by salt loading in a tissue-specific manner that appears to be mediated, at least partly, by a mechanism other than changes in the circulating or tissue levels of angiotensin peptides.