Tions in diseases such as cancer in which there is an

Tions in diseases such as cancer in which there is an imbalance in cellular proliferation, differentiation and apoptosis. Our results indicate that GSTA1 expression influences the proliferative status of Caco-2 cells, such that low GSTA1 expression provides cellular conditions that are conducive to enhanced proliferation. The evidence is as follows: i) GSTA1 expression in preconfluent cells is low compared to the higher levels observed in differentiated postconfluent cells, ii) NaB at a concentration of 1 mM increases GSTA1 activity, suppresses Caco-2 cell proliferation in MTS assays and induces a differentiated phenotype, iii) overexpression of GSTA1 suppresses proliferation in Caco-2 cells transfected with a GSTA1 pcDNAGSTA1 and Caco-2 Cell ProliferationFigure 5. Distinct doses of NaB differently affect cell proliferation and AlkP and GSTA1 enzyme activities. Preconfluent Caco-2 cells were treated with NaB (1 mM and 10 mM) in serum-free media. (A) Cellular proliferation was assessed from 24?6 h. Asterisks depict significant differences between control and NaB treatments (*, p#0.05; **, p#0.01 and ***, p#0.001). (B) Cytotoxicity was determined in preconfluent and postconfluent Caco-2 cells treated with 1 mM and 10 mM NaB at 48 h. Cytotoxicity measured LDH release and presented as cytotoxicity. (C) AlkP activity (mmol/mg/min) and (D) GSTA1 activity (nmol/mg/min) was determined. Values represent the 23408432 mean 6 S.E. of three independent experiments with six replicates each. Bars indicated by 520-26-3 site different letters differ significantly from one another (p#0.001). doi:10.1371/journal.pone.0051739.g3.1/V5-His TOPO vector, iv) suppression of GSTA1 expression in Caco-2 cells transfected with GSTA1 siRNA increases the percentage of cells in S phase as determined by flow cytometry as well as the overall proliferative rate in MTS assays. Previous studies have shown that GSTA1 over-expression in cell lines with no detectable GSTA1 levels such as the human retinal 94361-06-5 site pigment epithelial (RPE) cells and human lung cancer (H69) cells does not affect growth rate [24,25]. However, in both studies data was not presented to support the claim that overexpression of hGSTA1-1 did not alter growth kinetics and details regarding the timeframe over which cell growth was assessed was not clearly indicated. In the current study, the most profound reduction in cell growth due to GSTA1 overexpression was observed at 72 h suggesting that the assessment of GSTA1-1 effects on the proliferation of RPE andH69 cells may have occurred too early. Other studies have shown both in vivo and in vitro that GST Pi influences cellular proliferation [8,26,27]. Ruscoe et al., (2001) demonstrated that mouse embryo fibroblasts, isolated from GSTP1-1 knock-down mice (GSTPi 2/ 2 ), doubled at a faster rate compared to the cells from GSTPi +/+ wild-type mice [26]. Their results indicated a mechanism involving GSTP1-1-mediated control of cellular mitogenic pathways including signalling kinases JNK1 and ERK1/ERK2 that influence proliferation. Another study demonstrated differential effects of GSTP1 on cell proliferation dependent on haplotype with GSTP1*A reducing cellular proliferation and GSTP1* C allele having no effect in NIH3T3 fibroblasts [8]. In contrast, Hokaiwado (2008) demonstrated that GSTPi knock down using siRNA resulted in significant decrease in proliferation rate ofGSTA1 and Caco-2 Cell ProliferationFigure 7. GSTA1 down-regulation does not affect the sensitivity of Caco-2 cells to N.Tions in diseases such as cancer in which there is an imbalance in cellular proliferation, differentiation and apoptosis. Our results indicate that GSTA1 expression influences the proliferative status of Caco-2 cells, such that low GSTA1 expression provides cellular conditions that are conducive to enhanced proliferation. The evidence is as follows: i) GSTA1 expression in preconfluent cells is low compared to the higher levels observed in differentiated postconfluent cells, ii) NaB at a concentration of 1 mM increases GSTA1 activity, suppresses Caco-2 cell proliferation in MTS assays and induces a differentiated phenotype, iii) overexpression of GSTA1 suppresses proliferation in Caco-2 cells transfected with a GSTA1 pcDNAGSTA1 and Caco-2 Cell ProliferationFigure 5. Distinct doses of NaB differently affect cell proliferation and AlkP and GSTA1 enzyme activities. Preconfluent Caco-2 cells were treated with NaB (1 mM and 10 mM) in serum-free media. (A) Cellular proliferation was assessed from 24?6 h. Asterisks depict significant differences between control and NaB treatments (*, p#0.05; **, p#0.01 and ***, p#0.001). (B) Cytotoxicity was determined in preconfluent and postconfluent Caco-2 cells treated with 1 mM and 10 mM NaB at 48 h. Cytotoxicity measured LDH release and presented as cytotoxicity. (C) AlkP activity (mmol/mg/min) and (D) GSTA1 activity (nmol/mg/min) was determined. Values represent the 23408432 mean 6 S.E. of three independent experiments with six replicates each. Bars indicated by different letters differ significantly from one another (p#0.001). doi:10.1371/journal.pone.0051739.g3.1/V5-His TOPO vector, iv) suppression of GSTA1 expression in Caco-2 cells transfected with GSTA1 siRNA increases the percentage of cells in S phase as determined by flow cytometry as well as the overall proliferative rate in MTS assays. Previous studies have shown that GSTA1 over-expression in cell lines with no detectable GSTA1 levels such as the human retinal pigment epithelial (RPE) cells and human lung cancer (H69) cells does not affect growth rate [24,25]. However, in both studies data was not presented to support the claim that overexpression of hGSTA1-1 did not alter growth kinetics and details regarding the timeframe over which cell growth was assessed was not clearly indicated. In the current study, the most profound reduction in cell growth due to GSTA1 overexpression was observed at 72 h suggesting that the assessment of GSTA1-1 effects on the proliferation of RPE andH69 cells may have occurred too early. Other studies have shown both in vivo and in vitro that GST Pi influences cellular proliferation [8,26,27]. Ruscoe et al., (2001) demonstrated that mouse embryo fibroblasts, isolated from GSTP1-1 knock-down mice (GSTPi 2/ 2 ), doubled at a faster rate compared to the cells from GSTPi +/+ wild-type mice [26]. Their results indicated a mechanism involving GSTP1-1-mediated control of cellular mitogenic pathways including signalling kinases JNK1 and ERK1/ERK2 that influence proliferation. Another study demonstrated differential effects of GSTP1 on cell proliferation dependent on haplotype with GSTP1*A reducing cellular proliferation and GSTP1* C allele having no effect in NIH3T3 fibroblasts [8]. In contrast, Hokaiwado (2008) demonstrated that GSTPi knock down using siRNA resulted in significant decrease in proliferation rate ofGSTA1 and Caco-2 Cell ProliferationFigure 7. GSTA1 down-regulation does not affect the sensitivity of Caco-2 cells to N.