Saul J. Karpen

TNF-α downregulates murine hepatic growth hormone receptor expression by inhibiting Sp1 and Sp3 binding

Children with chronic inflammatory diseases experience growth failure and wasting. This may be due to growth hormone resistance caused by cytokine-induced suppression of growth hormone receptor (GHR) gene expression. However, the factors governing inflammatory regulation of GHR are not known. We have reported that Sp1 and Sp3 regulate hepatic GHR expression. We hypothesized that TNF-alpha suppresses GHR expression by inhibiting Sp1/Sp3 transactivators. LPS administration significantly reduced murine hepatic GHR expression, as well as Sp1 and Sp3 binding to GHR promoter cis elements. TNF-alpha was integral to this response, as LPS did not affect hepatic Sp1/Sp3 binding or GHR expression in TNF receptor 1-deficient mice. TNF-alpha treatment of BNL CL.2 mouse liver cells reduced Sp1 and Sp3 binding to a GHR promoter cis element and downregulated activity of a GHR promoter-driven luciferase reporter. Combined mutations within adjacent Sp elements eliminated GHR promoter suppression by TNF-alpha without affecting overall nuclear levels of Sp1 or Sp3 proteins. These studies demonstrate that murine GHR transcription is downregulated by LPS, primarily via TNF-alpha-dependent signaling. Evidence suggests that inhibition of Sp transactivator binding is involved. Further investigation of these mechanisms may identify novel strategies for preventing inflammatory suppression of growth.

HNF3β and GATA-4 transactivate the liver-enriched homeobox gene, Hex

The orphan homeobox gene, Hex, has a limited domain of expression which includes the developing and adult mouse liver. Hex is expressed in the developing liver coincident with the forkhead/winged helix transcription factor, Hepatocyte Nuclear Factor 3beta (HNF3beta). Although preliminary characterization of the mouse Hex promoter has recently been reported, the identity of the molecular regulators that drive liver expression is not known. We hypothesized that putative HNF3beta and GATA-4 elements within the Hex promoter would confer liver-enriched expression. A series of Hex promoter-driven luciferase reporter constructs were transfected in liver-derived HepG2 and fibroblast-like Cos cells+/-HNF3beta or GATA expression plasmids. The Hex promoter region from nt -235/+22 conferred basal activity in both HepG2 and Cos cells, with the region from -103/+22 conferring liver-enriched activity. HNF3beta and GATA-4 transactivated the promoter via response elements located within nt -103/+22, whereas Sp1 activated the -235/+22 construct. Mutation of the HNF3 element significantly reduced promoter activity in HepG2 cells, whereas this element in isolation conferred HNF3beta responsiveness to a heterologous promoter. Electrophoretic mobility shift assays were performed to confirm transcription factor:DNA binding. We conclude that HNF3beta and GATA-4 contribute to liver-enriched expression of Hex.

Assignment of a rat liver Na+/bile acid cotransporter gene to Chromosome 6q24

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