Role of extracellular signal-regulated kinase pathway in diepoxybutane-induced apoptosis of human lymphoblasts.

3384 Diepoxybutane (DEB) is the most potent metabolite of the environmental chemical 1, 3-butadiene (BD), which is prevalent in petrochemical industrial areas. BD is a known mutagen and human carcinogen, and possesses multi-organ systems toxicity that includes bone marrow depletion, spleen and thymus atrophy. Although the toxic effects of BD are known to be mediated through its epoxy metabolites, the cellular and molecular mechanisms of BD toxicity are not well understood. In working towards the elucidation of the cellular and molecular mechanisms of BD toxicity, our laboratory has recently reported the occurrence of apoptosis, but not necrosis, in human lymphoblasts exposed to low micromolar concentrations of DEB. The objective of this study was to identify apoptotic signaling pathways responsible for mediating DEB-induced apoptosis in human lymphoblasts. The mitogen-activated protein kinase (MAPK) pathways provide a mechanism by which signals are transduced from the cell surface to the nucleus, leading to activation of genes involved in a wide variety of cellular processes, including cell survival. We thus investigated the role of MAPKs in mediating DEB-induced apoptosis in human lymphoblasts. We found that the extracellular signal regulated kinase (ERK) was activated (as deduced by western blot analysis utilizing activation-specific antibodies) in response to DEB in an exposure time and DEB-concentration dependent manner; under these conditions levels of total ERK protein remained unchanged. A specific pharmacological inhibitor (PD98059) of MAPK kinase inhibited 60% of the DEB-induced apoptosis in human lymphoblasts at 24h post-exposure; under these experimental conditions the activation of the extracellular-signal regulated kinase (ERK) was inhibited. This is the first report to implicate the ERK MAPK pathway in mediating DEB-induced apoptosis. Since this pathway is known to control cell growth in most cell types, its involvement in mediating apoptosis may select for mutations which enable cells to escape apoptosis, leading to butadiene-induced carcinogenesis.
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