Proteome of H-411E (liver) cells exposed to insulin and tumor necrosis factor-α: Analysis of proteins involved in insulin resistance

Insulin resistance may be modeled in H-411E liver cells in tissue culture with the use of the cytokine tumor necrosis factor-α (TNF-α) and insulin. This tissue-culture model nicely mimics IR in human type 2 diabetes mellitus. After incubation of liver cells in tissue culture with INS alone, TNF-α alone, and TNF-α plus insulin, as well as a control sample, liver-cell extracts were separated on 2D polyacrylamide-gel electrophoresis on the basis of isoelectric point and molecular weight. We analyzed the gel images with the use of PD Quest software (Bio-Rad Laboratories, Hercules, Calif) to identify differentially expressed protein spots (ie, up or down with insulin vs down or up with TNF-α plus insulin). In separate experiments, phosphorus-32 incorporation/autoradiography and phosphoprotein staining were used to characterize treatment-induced phosphorylations. Affected protein spots were identified with the use of peptide fingerprinting and matrix-assisted laser desorption ionization time of flight mass spectrometry. The first series of experiments identified 6 differentially expressed proteins: eukaryotic translation initiation factor-3, subunit 2, regulator of G-protein signaling-5, superoxide dismutase, protein disulfide isomerase A6, proteasome subunit-α type 3, and regucalcin. In addition, we observed changes in the phosphorylation of protein disulfide isomerase A6. A second series of experiments identified 7 additional proteins with significantly altered differential expression: cell-division protein kinase-4, kinogen heavy chain, carbonic anhydrase-7, E 3 ubiquitin protein ligase, URE-B1; Rab GDP dissociation inhibitor-β, Rab GDP dissociation inhibitor-β2, and MAWDBP. It can be seen that differentially expressed proteins, affected by treatment with insulin or with TNF-α plus insulin, include regulators of translation, protein degradation, cellular Ca++, G-proteins, and free-radical production. Although one cannot detail the mechanism or mechanisms of TNF-α induced IR from this data alone, it is easy to relate all of these proteins to a role in insulin signal transduction and, hence, insulin resistance.