title: Impaired dephosphorylation renders G6PD-knockdown HepG2 cells more susceptible to H(2)O(2)-induced apoptosis.
abstract: Glucose-6-phosphate dehydrogenase (G6PD) plays a key role in the regeneration of NADPH and maintenance of cellular redox balance. In the present study, we investigate the effect of G6PD deficiency on H(2)O(2)-elicited signaling in HepG2 cells. H(2)O(2) was found to inhibit cellular protein tyrosine phosphatase (PTP) activity, resulting in activation of MAPKs. MKP-1 expression increased in the late phase of H(2)O(2) signaling. Using RNAi technology, we found that G6PD knockdown enhanced the inhibitory effect of H(2)O(2) on PTPs and led to sustained MAPK activation. This was accompanied by delayed expression and inhibition of MKP-1. Using a pharmacological inhibitor and siRNA, we demonstrate that MKP-1 acts as a regulator of MAPK activation in H(2)O(2) signaling. The prolonged MAPK activation in G6PD-knockdown cells was associated with an increased susceptibility to H(2)O(2)-induced apoptosis and growth retardation. Treatment with p38 and JNK inhibitors or N-acetylcysteine ameliorated such cellular effect, while triptolide and MKP-1-siRNA did the opposite. Glucose oxidase treatment had similar effects as addition of H(2)O(2). Taken together, these findings suggest that G6PD knockdown enhances the magnitude and duration of H(2)O(2)-induced MAPK signaling through inhibition of cellular PTPs, and the resultant anomalous signaling may lead to cell demise.
authors.affiliation: Graduate Institute of Medical Biotechnology, Chang Gung University, Tao-Yuan, Taiwan.
authors.forename: Chang-Jun
authors.initials: CJ
authors.lastname: Lin
authors.forename: Hung-Yao
authors.initials: HY
authors.lastname: Ho
authors.forename: Mei-Ling
authors.initials: ML
authors.lastname: Cheng
authors.forename: Tsai-Hong
authors.initials: TH
authors.lastname: You
authors.forename: Tsai-Hong
authors.initials: TH
authors.lastname: Cheng
authors.forename: Jau-Song
authors.initials: JS
authors.lastname: Yu
authors.forename: Daniel Tsun-Yee
authors.initials: DT
authors.lastname: Chiu
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000873:Anthracenes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D054638:Dual Specificity Phosphatase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics*; D056945:Hep G2 Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors; D011725:Pyridines / Q000494:pharmacology
chemical_list: D000873:Anthracenes; D005419:Flavonoids; D007093:Imidazoles; D011725:Pyridines; C432165:pyrazolanthrone; D006861:Hydrogen Peroxide; D005954:Glucosephosphate Dehydrogenase; D020928:Mitogen-Activated Protein Kinases; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1; D017027:Protein Tyrosine Phosphatases; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000111:Acetylcysteine