Manganese antagonizes iron blocking mitochondrial aconitase expression in human prostate carcinoma cells

p53 downregulates the gene expression of mitochondrial aconitase in human prostate carcinoma cells

BACKGROUND

Mitochondrial aconitase (mACON) is regarded as the key enzyme in citrate oxidation in human prostate epithelial cells, and its abnormal expression has been implicated in tumorigenesis of the prostate. Evidence also supports a broad role for the p53 gene in suppressing prostatic tumorigenesis. We investigated whether p53 regulates mACON expression and explore the potential mechanisms responsible for its effect on prostate cancer cells.

METHODS

Camptothecin (CPT) treatments and transient overexpression of p53 were used to investigate p53 regulation of mACON and may effects were assessed using immunoblotting and transient gene expression assays.

RESULTS

In vitro enzymatic activity assays and immunoblot assays showed that CPT treatment induced p53 expression while reducing mACON protein biosynthesis in wild-type p53 expressing LNCaP cells. Immunoblot assays and reporter assays revealed that transient transfection of a p53 expression vector into p53-null PC-3 cells decreased mACON expression. Cyclic pifithrin-α, an inhibitor of p53 transcriptional activity, blocked the decrease in mACON gene expression resulting from CPT treatment in LNCaP cells. Two putative p53 response elements were identified within the mACON promoter; however, mutation of these putative p53 response elements did not abolish the effect of CPT whereby it decreased mACON expression. A similar result was obtained for the effect of these mutants on the promoter activity of the mACON gene after transient overexpression of p53.

CONCLUSIONS

Together these results suggest that p53 downregulation of mACON gene expression in human prostate carcinoma cells may not occur through the putative consensus p53 response elements found within the mACON promoter.

The mutagenicity and carcinogenicity of inorganic manganese compounds: a synthesis of the evidence

Manganese (Mn), a naturally occurring element present in many foodstuffs, is an essential trace element with many biological functions. In industry, inorganic Mn compounds have a range of different applications, although the majority of Mn is used to make alloys and steel. For the general population, the major source of exposure to Mn is dietary, although drinking water may constitute an additional source in some regions. However, in occupationally exposed humans, inhalation of Mn is likely to be an important additional route. In general, Mn and its inorganic compounds are considered to possess low mutagenic or carcinogenic potential compared with some heavy metals. In this review, an up-to-date analysis of the available published studies on the carcinogenic and genotoxic potential of inorganic Mn is provided (organic Mn compounds are not considered). The current literature indicates that Mn may be weakly mutagenic in vitro and possibly clastogenic in vivo, with unknown genotoxic effects in humans; the possible mechanisms underlying these effects are discussed. The experimental evidence on carcinogenicity (quantitative increase in incidence of thyroid tumors in mice but not rats) does not provide any clear evidence, while the available occupational and environmental epidemiological evidence is equivocal as to whether exposure to inorganic Mn is associated with a significant cancer risk. Hence, it is concluded that there is insufficient evidence to indicate that inorganic Mn exposure produces cancer in animals or humans.

Expression of interleukin-6 is downregulated by 17-(allylamino)-17-demethoxygeldanamycin in human prostatic carcinoma cells

AIM

Interleukin-6 (IL-6) is a pleiotropic cytokine that is associated with tumor metastasis and prostate cancer. We evaluated the mechanism and effect of 17-(allylamino)-17-demethoxygeldanamycin (17AAG), a novel inhibitor of heat shock protein 90 (Hsp90), on the IL-6 gene expression in human prostatic carcinoma (PC-3) cells.

METHODS

Quantitative IL-6 and IL-6 receptor (IL-6R) expressions were assessed using RT-PCR. The deregulation of 17AAG and phorbol 12-myristate 13-acetate (PMA) on the IL-6 gene was determined by ELISA and transient gene expression assays using an IL-6 reporter vector.

RESULTS

Although the IL-6R is ubiquitously expressed by prostatic epithelium cells, the IL-6 expression is only found in advanced prostatic carcinoma cells, such as PC-3 and DU145. Further studies using RT-PCR indicated that 17AAG downregulated the gene expression of IL-6. ELISA and the transient gene expression assay revealed that 17AAG blocked the stimulation of PMA of IL-6 gene expression in PC-3 cells. The PMA-induced IL-6 gene expression is dependent on the NF-kappaB response element. However, the effect of 17AAG appears to be mediated via a region located at -149 to +8 bp upstream of the transcriptional starting site of the IL-6 gene, and might not be through the NF-kappaB signaling pathway.

CONCLUSION

The present study reveals that IL-6 is transcriptionally downregulated in human prostatic carcinoma cells in response to 17AAG. This result suggests the presence of a novel Hsp90 mediation pathway that is involved in the deregulation on the transcription of the human IL-6 gene in human prostate cancer.

Aconitate hydratase of mammals under oxidative stress

Data on the structure, functions, regulation of activity, and expression of cytosolic and mitochondrial aconitate hydratase isoenzymes of mammals are reviewed. The role of aconitate hydratase and structurally similar iron-regulatory protein in maintenance of homeostasis of cell iron is described. Information on modifications of the aconitate hydratase molecule and changes in expression under oxidative stress is generalized. The role of aconitate hydratase in the pathogenesis of some diseases is considered.