Oxidative stress plays an important role in various types of cell injury and tumor promotion. Cells respond to oxidative stress in many ways including changes in membrane organization, ion movements, and altered gene expression, all of which contribute to the subsequent fate of affected cells. In this study, we investigated the expression of the proto-oncogenes c-fos, c-myc, and c-jun, which play a key role in proliferation and differentiation, using primary cultures of rat proximal tubular epithelium exposed to oxidative stress generated by the xanthine/xanthine oxidase system. This system generates superoxide and H2O2 in the extracellular space stimulating the release of active oxygen species from inflammatory cells. c-fos mRNA was expressed within 15 min, peaked at 30 min, and returned to constitutive levels by 3 h. c-jun mRNA began to rise after 30 min, peaked at 120 min, and remained above the constitutive levels up to 180 min. c-myc mRNA expression was less affected by the treatment, with levels increasing gradually over the 180 min period. The expression of c-fos was inhibited by superoxide dismutase but not by catalase and was super-induced by cycloheximide. H2O2 alone did not induce any c-fos mRNA in this system. Chelation of extracellular ionized calcium by EGTA or of intracellular ionized calcium by Quin 2/AM resulted in a marked decrease of c-fos expression. Two protein kinase C inhibitors, H-7 and staurosporine, partly diminished the expression of c-fos, whereas a third, 2-aminopurine, which has a broader spectrum of inhibiting protein kinases, almost completely abolished it. A poly ADP-ribosylation inhibitor, 3-aminobenzamide, had no effect on c-fos expression in this system. Our results show that oxidative stress provokes sequential expression of c-fos, c-jun, and c-myc, mRNA in this order. This c-fos expression appears to be largely controlled by calcium ion movement, which could include protein kinase C activation. Another protein kinase or kinases also appear to play an important role.
The role of cytosolic Ca2+ ([Ca2+]i) and protein kinases in the hsp70 induction following heat shock was investigated in cultured rat proximal tubular epithelial (PTE) cells. Changes in [Ca2+]i were measured by digital imaging fluorescence microscopy using fura 2. Steady state levels of hsp70 mRNA were examined by either Northern or dot blot analyses. [Ca2+]i increased within 10 minutes and continued to increase following heat shock. The increases in [Ca2+]i were reduced in nominally Ca(2+)-free media with or without EGTA. [Ca2+]i also increased within 0.5 minutes following ionomycin, but then declined to normal levels by 1.0 to 1.5 minutes. Heat shock induced hsp70 mRNA within 15 minutes, which continued to increase up to three hours. Ionomycin also induced hsp70 mRNA, which peaked at 30 minutes, and gradually decreased thereafter. The hsp70 induction following heat shock was attenuated when extracellular Ca2+ was reduced. Chelation of [Ca2+]i by quin-2 also reduced the hsp70 induction. Inhibitors of protein kinases, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), calphostin C, genistein, and 2-aminopurine, also had inhibitory effects on the hsp70 induction. In contrast, a calmodulin inhibitor, chlorpromazine, had little effect. These results suggest that heat shock increases [Ca2+]i in rat PTE cells and that [Ca2+]i and protein kinases are involved in the hsp70 induction following heat shock.
The redox tolerance test introduced in this article attempts to quantify the deterioration of hepatic mitochondrial energy metabolism by measuring the changes in arterial ketone body ratio in response to 75-g oral glucose loading, and is discussed in relation to its predictive value for assessing surgical risk in hepatectomy. The indicator, called redox tolerance index (RTI), represents a 100-fold cumulative enhancement of ketone body ratio relative to glucose level (100 x delta KBR/delta glucose). The redox tolerance index was significantly different between 31 liver cirrhotics and 10 normal volunteers (p less than 0.001). Subjects were divided into three classes (I: RTI greater than or equal to 1.0, II: 0.5 less than or equal to RTI less than 1.0, III: RTI less than 0.5). Postoperative mortality was significantly different among the three classes in 127 hepatic resections (chi 2 = 9.843, p less than 0.01). Of 97 hepatocellular carcinoma cases, major hepatic resections in class III showed significantly higher postoperative morbidity and mortality rates (p less than 0.05 and p less than 0.05, respectively). The present findings indicate that RTI based on redox theory is of potential value in predicting posthepatectomy outcome.
This study was designed to investigate the influence of intracellular ionized calcium ([Ca2+]i) on the induction of c-fos, c-jun, c-myc, and hsp70 genes after oxidant stress induced by xanthine/xanthine oxidase (X/XOD) treatment or after heat shock using primary cultures of rat proximal tubule epithelium (PTE). X/XOD (500 microM/25 mU/mL) induced all of these genes; ionomycin also resulted in similar kinetics of induction of all genes. The expression of both c-fos following X/XOD treatment and hsp70 following heat shock was markedly decreased through chelation of [Ca2+]i by Quin 2/AM. The c-fos expression following X/XOD treatment was partly reduced by a protein kinase C inhibitor, staurosporine (ST), and markedly inhibited by another protein kinase inhibitor, 2-aminopurine (2AP), while both ST and 2AP markedly reduced hsp70 expression. The ADP-ribosylation transferase inhibitor 3-aminobenzamide had no effect on either c-fos or hsp70 expression. These results suggest that cell injuries leading to increased [Ca2+]i in PTE result in induction of c-fos, c-jun, c-myc, and hsp70; and that the activation of c-fos and hsp70 genes may be regulated by [Ca2+]i and [Ca2+]i-dependent protein kinases.
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