Stabilization of tumor necrosis factor α mRNA by chronic ethanol -: Role of A + U-rich elements and p38 mitogen-activated protein kinase signaling pathway

Increased expression of tumor necrosis factor a (TNF alpha) in response to chronic ethanol has been implicated in the pathogenesis of alcoholic liver disease. However, the molecular mechanisms by which ethanol increases the levels of TNF alpha are not well characterized. Utilizing Kupffer cells isolated from rats fed an ethanol containing diet and a murine macrophage cell line, RAW264.7, exposed to ethanol in culture, we have demonstrated that exposure to chronic ethanol results in an enhanced expression of lipopolysaccharide (LPS)-induced TNFa. While chronic ethanol had no effect on the rate of LPS-induced TNF alpha transcription as measured by nuclear run-on experiments, TNF alpha mRNA half-life was increased by chronic ethanol. Chronic ethanol also potentiated the activation of LPS-induced p38 mitogen-activated protein (MAP) kinase in Kupffer cells, as well as in RAW264.7 cells. Specific inhibition of p38 MAP kinase activation by SB203580 in Kupffer cells or by overexpression of dominant negative p38 MAP kinase in RAW264.7 cells blocked ethanol-mediated TNF alpha mRNA stabilization. Furthermore, using chimeric reporter constructs, we have shown that A + U-rich elements in the W-untranslated region of TNFa mRNA are not sufficient to impart ethanol-mediated stabilization on TNF alpha mRNA.