Ras Oncogene-Mediated Progressive Silencing of Extracellular Superoxide Dismutase in Tumorigenesis

Figure 5

Self-regulation of SOD3 expression is mediated by GEF small GTPase regulatory proteins. (a-b) The analysis of the effects of low and high SOD3 transgene transfection on endogenous sod3 mRNA synthesis in rat PC E1A cells. Transfection of low amounts of human SOD3 into PC E1A cells significantly increased the endogenous rat sod3 expression, whereas high amounts of human SOD3 levels in PC E1A cells significantly reduced the endogenous rat sod3 mRNA synthesis. (c-d) Western blot analysis of ERK1/2 phosphorylation in PC E1A cells suggested greater MAPK ERK1/2 activation at low SOD3 transgene expression levels compared to high transgene levels. (e) Comparison of rabbit transgene sod3 expression to human endogenous SOD3 mRNA synthesis in HEK 293T cells. The expression analysis performed on five consecutive days demonstrated a gradual decrease in the transgene expression that correlated with a gradual increase in the endogenous SOD3 mRNA synthesis. (f) The effect of the H₂O₂ concentration on SOD3 mRNA expression. HEK 293T cells were treated with different concentrations of H₂O₂. Low H₂O₂ concentrations caused increased SOD3 mRNA synthesis, and high H₂O₂ levels caused decreased SOD3 expression. (g) The effects of low and high SOD3 transgene expression on SOS1 and SOS2 GEF mRNA expression in 8505c cells. A low level of transgene expression caused an increase in SOS1 and SOS2 mRNA production, whereas high transgene SOD3 levels decreased the expression of both GEFs. The data are expressed as the mean ± SD. The values are represented (, , and ).

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