title: Overexpression of Bcl-2 induces STAT-3 activation via an increase in mitochondrial superoxide.
abstract: We recently reported a novel interaction between Bcl-2 and Rac1 and linked that to the ability of Bcl-2 to induce a pro-oxidant state in cancer cells. To gain further insight into the functional relevance of this interaction, we utilized computer simulation based on the protein pathway dynamic network created by Cellworks Group Inc. STAT3 was identified among targets that positively correlated with Rac1 and/or Bcl-2 expression levels. Validating this, the activation level of STAT3, as marked by p-Tyr705, particularly in the mitochondria, was significantly higher in Bcl-2-overexpressing cancer cells. Bcl-2-induced STAT3 activation was a function of GTP-loaded Rac1 and NADPH oxidase (Nox)-dependent increase in intracellular superoxide (O2•-). Furthermore, ABT199, a BH-3 specific inhibitor of Bcl-2, as well as silencing of Bcl-2 blocked STAT3 phosphorylation. Interestingly, while inhibiting intracellular O2•- blocked STAT3 phosphorylation, transient overexpression of wild type STAT3 resulted in a significant increase in mitochondrial O2•- production, which was rescued by the functional mutants of STAT3 (Y705F). Notably, a strong correlation between the expression and/or phosphorylation of STAT3 and Bcl-2 was observed in primary tissues derived from patients with different sub-sets of B cell lymphoma. These data demonstrate the presence of a functional crosstalk between Bcl-2, Rac1 and activated STAT3 in promoting a permissive redox milieu for cell survival. Results also highlight the potential utility of a signature involving Bcl-2 overexpression, Rac1 activation and STAT3 phosphorylation for stratifying clinical lymphomas based on disease severity and chemoresistance.
authors.affiliation: Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Jia
authors.initials: J
authors.lastname: Kang
authors.affiliation: Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Stephen Jun Fei
authors.initials: SJ
authors.lastname: Chong
authors.affiliation: Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
authors.forename: Vignette Zi Qi
authors.initials: VZ
authors.lastname: Ooi
authors.affiliation: Cellworks Group Inc., San Jose, CA, USA.
authors.forename: Shireen
authors.initials: S
authors.lastname: Vali
authors.affiliation: Cellworks Research India Private Limited, Bangalore, India.
authors.forename: Ansu
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Cellworks Research India Private Limited, Bangalore, India.
authors.forename: Shweta
authors.initials: S
authors.lastname: Kapoor
authors.affiliation: Cellworks Group Inc., San Jose, CA, USA.
authors.forename: Taher
authors.initials: T
authors.lastname: Abbasi
authors.affiliation: Experimental Therapeutics Program, Cancer Science Institute, Singapore, Singapore.
authors.forename: Jayshree L
authors.initials: JL
authors.lastname: Hirpara
authors.affiliation: Department of Otolaryngology, National University Healthcare System, Singapore, Singapore.
authors.forename: Thomas
authors.initials: T
authors.lastname: Loh
authors.affiliation: Experimental Therapeutics Program, Cancer Science Institute, Singapore, Singapore.
authors.forename: Boon Cher
authors.initials: BC
authors.lastname: Goh
authors.affiliation: Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.|NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore.|National University Cancer Institute, NUHS, Singapore, Singapore.|School of Biomedical Sciences, Curtin University, Perth, Australia.
authors.forename: Shazib
authors.initials: S
authors.lastname: Pervaiz
mesh_terms: D015153:Blotting, Western; D003198:Computer Simulation; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D006801:Humans; D016393:Lymphoma, B-Cell / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D013481:Superoxides; D020830:rac1 GTP-Binding Protein
keywords: Bcl-2; Rac1; STAT3; mitochondria; superoxide