REGULATION OF THE HEPATIC NEGATIVE ACUTE PHASE RESPONSE

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DESCRIPTION (adapted from the application) Dr. Denson will devote the majority of his time to clinically-oriented basic research. This award will provide for protected time for research, additional didactic training, and the purchase of reagents. It will support pursuit of the immediate research aims, as well as the establishment of an independent laboratory. The Department of Pediatrics has assured that 80% of Dr. Denson's time over the next five years will be dedicated to research activities. The hepatocyte's response to cytokines includes a reduction in the synthesis of key metabolic proteins; this constitutes the negative acute phase response (APR). Adverse clinical consequences include impairments of linear growth, hepatocyte transport, and glucose and drug metabolism, due to down-regulation of regulatory genes. The primary objective of this proposal will be to determine the cytoplasmic signaling mechanisms by which cytokines suppress expression of clinically important hepatic genes, including the growth hormone receptor and albumin. Our prior studies have demonstrated suppression of hepatocyte transporter and albumin promoter-driven luciferase activity by tumor necrosis factor alpha (TNF-a) or interleukin-1 Beta (IL-1B). Retinoid response elements have been shown to mediate coordinate reduction of hepatocyte transporter expression by IL-1B and ceramide. The goal of AIM I will be to identify cytokine response elements and associated transcription factors which regulate growth hormone receptor and albumin expression in HepG2 cells and primary rat hepatocytes. The goal of AIM 2 will be to characterize the cytoplasmic signal transduction mechanisms mediating cytokine suppression of these transactivators and associated target genes. Initial studies will define the role of ceramide signaling in acute phase down-regulation of these genes. The goal of AIM 3 will be to confirm the significance of cytokine signaling pathways identified in Aims I and 2 to in vivo acute phase gene regulation. Wild type and IL-1B and TNF-a receptor deficient mice will be treated with endotoxin and effects upon cytoplasmic signaling proteins and target regulatory transactivators and genes will be determined. Clarification of these molecular mechanisms will contribute to a broader understanding, of the regulatory links between several important hepatic metabolic pathways in both health and disease, and may ultimately lead to more specific treatments for cytokine-induced complications of inflammatory diseases such as linear growth failure.