The main focus of this project is to investigate the complex cytokine regulatory network involved in arsenic-induced dermatotoxicity. Pathway mapping studies using normal human epidermal keratinocytes (NHEK) indicated that short-term, non-toxic arsenic-exposure results in the modulation of multiple genes from several classes (e.g., oxidative stress, glutathione metabolism, heat shock/stress response, cell proliferation and DNA damage). Array studies further revealed that the expression of cyclooxygenase-2 (COX-2), a gene that plays a prominent role in skin cancer, is highly induced in a dose-dependent manner following arsenic exposure. Subsequent studies indicate that arsenic also elevates the level of COX-2 protein in NHEK. These events appear to be dependent on signaling via mitogen- and stress-related kinases; the activities of which are modulated by arsenic. The induction of COX-2 by arsenic also correlated with increased prostaglandin levels, an end product of COX-2 activty, in culture media and increased DNA synthesis. We have determined that the induction of COX-2 following arsenic exposure is, in part, dependent on activation of specific MAP kinase (MAPK) signaling pathways, in particular the ERK or p42/44 MAPK. Our studies indicate that the induction of COX-2 is independent of p38 MAPK phosphorylation. This pattern is similar to that observed with growth factors specific for keratinocytes, such as Fibroblast Growth Factor-7, but contrasts with that of Epidermal Growth Factor, which activates both p38 and p42/44. Interestingly, compounds that inhibit either the p38 and p42/44 pathway can attenuate elevation of COX-2. COX-2 inhibitors suppress biological processes in keratinocytes that we associate with the neoplastic process, including cell proliferation and TGF alpha secretion. We are currently examining the role of several antioxidants in modulating arsenic-induced alterations in signal transduction and cytokine production. We have continued an on-going collaboration with Drs. Miroslav Styblo and Luz Maria Del Razo to evaluate the utility of Transforming Growth Factor alpha as a biomarker for arsenic exposure in individuals consuming arsenic contaminated drinking water in Mexico. In collaboration with Dr. Michael Waalkes laboratory, we have conducted and published microarray studies in the liver from in vivo studies conducted using the Tg.AC mouse to evaluate alterations in genes associated with oxidative stress, metabolism, heat shock/stress response, cell proliferation and DNA damage. Tissues from these studies have also been provided to a number of collaborators and are being used to develop models of tissue distribution of arsenic, effects on signaling pathways in the brain and the effects on enzymes associated with oxidative stress. Additional in vivo studies examined the efficacy of Celecoxib, a COX-2 inhibitor, in modulating papillomagenesis in Tg.AC mice following arsenic exposure. Studies evaluating gene expression in the skin from these Tg.Ac studies are ongoing. As an outgrowth of this project collaborative studies were begun with Dr. Brion McCutcheon of the University of NC at Wilmington, to investigate cytokine gene expression in dermal cancers prior to and following treatment of specific therapeutics. Tumor biopsies from 13 patients were evaluated by PCR (polymerase chain reaction) for inflammatory and growth promoting cytokine gene expression. Eight out of these 13 individuals with basal cell carcinoma (one with micronodular BCC) were re-biopsied after therapy. The remaining 5 patients received no follow-up biopsy. Expression of IL-8, IL-6, IL-1b, TNF-a, IL-12p40, GM-CSF and TGF-b was seen tumor tissue from most patients. Tumor tissue from four out of 8 patients (50%), who were biopsied before and after drug treatment, displayed a general reduction in IL-8, IL-6, IL-1b expression following treatment. Our data indicate that in aa subset of patients BCC cytokine expression is dramatically reduced following therapy.
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