title: Cellular steatosis in ethanol oxidizing-HepG2 cells is partially controlled by the transcription factor, early growth response-1.
abstract: Recent studies have shown that the transcription factor early growth response-1 (Egr-1) regulates ethanol-induced fatty liver. However, the mechanism(s) through which ethanol oxidation controls Egr-1 is unknown. Here, using recombinant hepatoma (HepG2; VL-17A) cells that metabolize ethanol, we show that alcohol dehydrogenase catalysis of ethanol oxidation and subsequent acetaldehyde production controls Egr-1 expression. Further, the induction of Egr-1 enhances expression of other steatosis-related genes, resulting in triglyceride accumulation. Ethanol exposure increased Egr-1 promoter activity, messenger RNA and Egr-1 protein levels in VL-17A cells. Elevated Egr-1 protein was sustained by an ethanol-induced decrease in proteasome activity, thereby stabilizing the Egr-1 protein. Egr-1 induction depended on ethanol oxidation, as it was prevented when ethanol oxidation was blocked. Ethanol exposure induced Egr-1 and triglyceride accumulation only in alcohol dehydrogenase-expressing cells that produced acetaldehyde. Such induction did not occur in parental, non-metabolizing HepG2 cells or in cells that express only cytochrome P450 2E1. However, direct exposure of HepG2 cells to acetaldehyde induced both Egr-1 protein and triglycerides. Egr-1 over-expression elevated triglyceride levels, which were augmented by ethanol exposure. However, these triglyceride levels did not exceed those in ethanol-exposed cells that had normal Egr-1 expression. Conversely, Egr-1 knockdown by siRNA only partially blocked ethanol-induced triglyceride accumulation and was associated not only with lower Egr-1 expression but also attenuation of SREBP1c and TNF-α mRNAs. Double knockdown of both Egr-1 and SREBP-1c abolished ethanol-elicited steatosis. Collectively, our findings provide important new insights into the temporal regulation by ethanol oxidation of Egr-1 and cellular steatosis.
authors.affiliation: VA-Nebraska-Western Iowa Health Care System, Omaha, NE 68105, USA. pthomes@unmc.edu
authors.forename: Paul G
authors.initials: PG
authors.lastname: Thomes
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Osna
authors.forename: John S
authors.initials: JS
authors.lastname: Davis
authors.forename: Terrence M
authors.initials: TM
authors.lastname: Donohue
mesh_terms: D000079:Acetaldehyde / Q000378:metabolism; D000426:Alcohol Dehydrogenase / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D000431:Ethanol; D005234:Fatty Liver / Q000139:chemically induced* / Q000473:pathology; D015870:Gene Expression; D056945:Hep G2 Cells; D006801:Humans; D050356:Lipid Metabolism; D010084:Oxidation-Reduction; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014280:Triglycerides / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D051780:Sterol Regulatory Element Binding Protein 1; D014280:Triglycerides; D014409:Tumor Necrosis Factor-alpha; D000431:Ethanol; D000426:Alcohol Dehydrogenase; D019392:Cytochrome P-450 CYP2E1; D046988:Proteasome Endopeptidase Complex; D000079:Acetaldehyde