Inhibition of Gap Junctional Intercellular Communication and Activation of Mitogen-Activated Protein Kinase by Tumor-Promoting Organic Peroxides and Protection by Resveratrol

Abstract

Dicumyl peroxide (di-CuOOH) and benzoyl peroxide (BzOOH) act as tumor promoters in SENCAR mice, whereas di-tert-butylhydroperoxide does not. Tumor promotion requires the removal of growth suppression by inhibition of gap junctional intercellular communication (GJIC) and the induction of mitogenic intracellular pathways. We showed that di-CuOOH and BzOOH both reversibly inhibited GJIC and transiently activated mitogen-activated protein kinase, specifically, the extracellular receptor kinase at noncytotoxic conditions in WB-F344 rat liver epithelial cells, whereas the non-tumor-promoting di-tert-butylhydroperoxide did not inhibit GJIC or activate extracellular receptor kinase. di-CuOOH but not BzOOH inhibited GJIC through a phosphatidylcholine-specific phospholipase C-dependent mechanism. N-acetylcysteine (NAC) was needed to prevent a cytotoxic, glutathione-depleting effect of BzOOH, whereas di-CuOOH was noncytotoxic and did not alter glutathione levels at all doses and times tested. Pretreatment of WB-F344 cells with resveratrol, a polyphenolic antioxidant present in red wine, prevented at physiological doses the inhibition of GJIC by di-CuOOH but not from BzOOH and was effective in significantly preventing extracellular receptor kinase activation by both peroxides. NAC did not prevent any of the peroxide effects on either GJIC or extracellular receptor kinase, suggesting a specific antioxidant effect of resveratrol.

Methoxychlor and Vinclozolin Induce Rapid Changes in Intercellular and Intracellular Signaling in Liver Progenitor Cells

“…GJIC dysregulation by VIN has not been previously reported. Effective concentrations of VIN for inhibition of GJIC (30-min EC 50 ¼ 126 mM) are comparable with the chemicals like alachlor, perfluoroheptanoic acid, benzoylperoxide, or lipidic compounds, which required higher concentrations (>100 mM) to rapidly induce >50% inhibitory effect (Sovadinova et al, 2015;Upham et al, 1998Upham et al, , 2007. Also, endogenous or synthetic estrogens and androgens were found to affect GJIC and connexins not only via classical genomic mechanism (Ren et al, 2013), but also via rapid actions of non-genomic signaling (Iwase et al, 2006;Lyng et al, 2000;Pluciennik et al, 1996).…”

“…These effects, which are relevant for transcriptional and epigenetic control of gene expression and normal cell behavior (Trosko, 2011), were studied in a rat liver epithelial cell line WB-F344. This cell line is a well-established in vitro model for assessment of GJIC and mechanistic studies in responses to environmental contaminants (Sovadinova et al, 2015;Upham et al, 2007Upham et al, , 2008, which has been validated by in vivo studies (Sai et al, 2000;Upham et al, 2009) and matches the most extensively used rodent model system, F344 rats, in the National Toxicology Program. Both of these EDCs exhibited dose, time and mechanistic differences on GJIC, MAPKs, and phospholipase C, which were elicited by the parental compounds and occurred independently of ER-or AR-mediated genomic mechanisms.…”

Oxidative-Dependent Integration of Signal Transduction with Intercellular Gap Junctional Communication in the Control of Gene Expression

“…Considerable progress has been achieved in defining specific redox-dependent targets of intracellular oxidants (26) and the role of antioxidants similarly play specific roles, both redox sensitive and redox insensitive, in cell signaling and consequent gene expression profiles (4). Thus, understanding the mechanisms by which oxidative compounds promote and antioxidants prevent the development of tumors must begin integrating the different forms of cell signaling (102). To continue using the simple assumption that ROS are always detrimental to the organism and that high levels of antioxidants must be beneficial due to their scavenging properties of ROS is no longer acceptable.…”

“…Homeostatic regulation of cell proliferation, differentiation, and apoptosis of these three cell types was facilitated via extra-(hormones, cytokines, growth factors), intra-(different intracellular signaling mechanisms, such as MAPK; NF-B), and gap-junctional intercellular communication mechanisms needed to be delicately integrated, with the demonstration that stem cells seem to lack GJIC to restrict differentiation but still maintain growth control via negative secreted growth factors (96,102). In addition, with experimental evidence linking gap junctions to growth control in progenitor cells (92,94,102), and apoptosis in solid tissues (112), the demonstration that cancer cells, characterized by being a disease of homeostasis, lacks growth control, can not terminally differentiate or apoptose properly, seems to support the role of gap junction genes as the "biological Rosetta Stone" that allows one to view them as allowing a systems mechanism to create higher order structures and functions. Without gap junctions, the higher order phenotypes and functions existing during different stages of embryonic/fetal/neonatal, adolescent, adult, and geriatric development could not exist.…”

Indole-3-Carbinol Prevents H2O2-Induced Inhibition of Gap Junctional Intercellular Communication by Inactivation of PKB/Akt

“…In addition, it has been proposed that prevention of the inhibition of GJIC by various tumor promoters or restoration of GJIC in cancer cells can be a strategy for cancer chemoprevention and chemotherapy [41]. Since Indole-3-carbinol (I3C), a presumptive cancer chemopreventive phytochemical found in cruciferous vegetables, such as cabbage, broccoli, cauliflower and brussel sprouts, possesses a variety of biological and biochemical effects, it has been hypothesized that it might work by preventing inhibition of GJIC [38], such as through consumption of green tea [33], resveratrol [30,42], caffeic acid ethyl ester [28] and β-sitosterol [29]. It has also been reported that I3C might play an important role in prevention of human prostate [3], colon [8] and breast cancers [26].…”