44 We further demonstrated that hCRP may impair insulin signaling through activation of the MAPK signaling pathway. Activation of MAPKs has been linked to the development of insulin resistance.2, 45, 46 p38 MAPK plays a key role in hepatic glucose metabolism,13 and ERK1/2 see more activation stimulates IRS-1 Ser612 phosphorylation
and thereby inhibits insulin signaling.47 Consistent with reported hCRP activation of p38 MAPK and ERK1/2 in endothelial cells and macrophages,10, 48 we found that hCRP increased phosphorylated p38 MAPK and ERK1/2 ex vivo in liver tissues and in vitro in hepatocytes. No activation of JNK by hCRP was observed in rat liver or hepatocytes in our study, which was contrary to the reports that CRP activates
the JNK pathway in endothelial cells.9, 10 The discrepancy could be attributed to tissue differences (liver versus extrahepatic), the different time course or source of CRP as recombinant hCRP used in previous studies may have affected the JNK pathway, the latter due to contamination. It has been suggested that ERK1/2 inhibits insulin signaling at the level of IRS proteins in adipocytes to a greater extent than JNK and p38 MAPK.44 Our in vitro study suggests that ERK1/2 plays a more important role than the other MAPKs in hCRP-mediated hepatic insulin resistance. In summary, we have find more provided the first in vivo evidence that hCRP induces hepatic insulin resistance accompanied by a defect in the IRS/PI3K/Akt pathway, suggesting a causative link between hCRP
and insulin resistance. Furthermore, in vitro evidence has implicated ERK1/2 as the primary MAPK that plays a role in hCRP-impaired insulin signaling, providing a molecular mechanism for such effect of hCRP. The current study suggests that hCRP, in addition to being a biomarker for inflammation, may be a potential target for treatment and prevention of hepatic insulin resistance. CRP gain and loss of function studies in humans are required to determine its relevance to the development of insulin resistance in humans. We thank Mark Dekker for comments on the article and for Methisazone technical assistance. Additional Supporting Information may be found in the online version of this article. “
“In hepatocellular carcinoma (HCC), intrahepatic metastasis frequently correlates with epithelial to mesenchymal transition (EMT) of malignant hepatocytes. Several mechanisms have been identified to be essentially involved in hepatocellular EMT, among them transforming growth factor (TGF)-β signaling. Here we show the upregulation and activation of the receptor tyrosine kinase Axl in EMT-transformed hepatoma cells.