Zinc blocks gene expression of mitochondrial aconitase in human prostatic carcinoma cells

Abstract

Mitochondrial aconitase (mACON) contains a [4Fe-4S] cluster as the key enzyme for citrate oxidation in the human prostatic epithelial cell. Although there is accumulating evidence indicating that accumulation of high levels of zinc in prostate epithelial cells causes reduced efficiency of citrate oxidation, zinc regulation on the mACON is still not well understood. From in vitro studies, zinc chloride treatment has been developed using humic acid as the carrier (Zn-HA) in human prostatic carcinoma cells, PC-3. Zn-HA treatment (0.1-10 lM) restricts mACON enzymatic activity, which attenuates citrate utility and decreases intracellular ATP levels in PC-3 cells, whereas the effect is blocked by adding the zinc chelator, diethylenetriaminepentaacetic acid (DTPA). Immunoblot, ribonuclease-protection and transient gene-expression assays indicate that Zn-HA treatments inhibit mACON gene expression. Mutation of the putative metal response element (MRE) from CTCGCCTTCA to TGATCC-TTCA abolishes Zn-HA inhibition of mACON promoter activity. Our results have demonstrated that zinc possesses a specific regulatory mechanism on the mACON gene, and a biologic function of the putative metal regulatory system in mACON gene transcription has been identified. ' 2005 Wiley-Liss, Inc.Key words: prostate; zinc; metal response element; humic acid; aconitase Zinc is a homeostatically regulated, essential mineral required for numerous metalloenzymes, which influence metabolic function for cell growth, replication, osteogenesis and immunity. 1Although studies of the relationship between zinc and prostate carcinogenesis remain controversial, the evidence suggests that zinc may play a significant role in the prostate.2-9 Total zinc levels in the prostate are 10 times higher than in other soft tissues, and this ability of zinc to accumulate in the prostate is lost during prostate carcinogenesis. 2,10 It has been demonstrated that zinc treatment restricts growth of prostate cancer cells via cell-cycle arrest, apoptosis and necrosis both in vitro and in vivo.3,6,11 Some studies have reported especially high levels of zinc in the mitochondria of prostate epithelial cells, where zinc inhibits mitochondrial aconitase (mACON), resulting in decreased citrate oxidation. 4,10,12,13 Aconitase (aconitase hydratase, EC4.2.1.3) is essential to carbohydrate and energy metabolism, and initiates the interconversion of citrate and isocitrate in the citric acid cycle.14 Our previous in vitro study using the stable transfected mACON antisense human prostate carcinoma cell, PC-3, has illustrated the key role of mACON in citrate utility, and regulation of intracellular ATP levels in the prostate.15 Zinc-based mACON regulation processes in the human prostate are still not fully understood. Previous study has determined conserved ironresponsive elements (IRE) in the 5 0 -untranslated region of the human mACON gene, showing that iron upregulates gene translation and transcription of mACON in human prostatic carcinoma cells. 16 The objective of our study was to deter...

Epigallocatechin-3-gallate affects the growth of LNCaP cells via membrane fluidity and distribution of cellular zinc

“…A growing body of evidence has suggested that the loss of this unique capacity to retain high levels of zinc is an important factor in the development and progression of malignant prostate cells (Tsui et al, 2006). EGCG entering into cells was able to affect the distribution of cellular zinc (Fig.6).…”

Zinc Supplementation and Prostate Cancer

“…It is reported in these studies that zinc inhibits in vitro cultured human prostate cell lines (LNCaP, PC3 and BPH-1) and rat ventral prostate epithelium cells proliferation by inducing mitochondrial apoptogenesis by releasing cytochrome c, which then activates subsequent caspase mediated-apoptotic cascading events leading to apoptosis. It is also shown that zinc inhibits the gene expression and activity of m-aconitase in prostate cells (Costello et al, 1997;Tsui et al, 2006). These findings led to the proposal that the presence of high zinc in normal prostate limits citrate oxidation via the Krebs cycle resulting in accumulation of high citrate levels for the secretion of prostatic fluids (Costello et al, 1997).…”

THE IMPORTANCE OF INHIBITORS FOR THE SIMULATION OF METABOLIC PROCESSES: IN SILICOZn2+ INHIBITION OF m-ACONITASE FROM ANALYSIS OF GLYCOLYSIS AND KREBS CYCLE KINETIC MODELS

“…It has been proposed that their ability to accumulate high cellular levels of zinc leads to inhibition of citrate oxidation, leading to the observed high levels of citrate. [4][5][6][7][8][9][10][11] In prostate cancer, the malignant cells undergo a metabolic transformation from zinc accumulating-citrate-producing to citrate-oxidizing cells metabolically more closely related to normal cells of other tissues. In fact, epidemiological studies have demonstrated an association between zinc (II) concentration and prostate cancer development.…”

“…The specific type of inhibition effect of zinc is still however not understood, with some published experimental work proposing a competitive inhibition route 11 and other published work indicating that zinc is affecting gene expression of m-aconitase and in this way regulating its function. 10 In addition, high levels of substrate present in the system make an uncompetitive inhibition a possible route as well.…”

“…First was the competitive inhibition suggested by the experimental work of Costello et al 11 ; second was the model of inhibition through the effect on m-aconitase expression suggested by Tsui et al 10 Finally, we have tried uncompetitive inhibition model which is a form of enzyme inhibition where the inhibitor binds to an already established enzyme and substrate complex. Ordinary differential equation (ODE) models of glycolysis and the Krebs cycle including molecular shuttling across the mitochondrial membrane were developed.…”