Hideharu Odai

Dietary isohumulones, the bitter components of beer, raise plasma HDL-cholesterol levels and reduce liver cholesterol and triacylglycerol contents similar to PPARα activations in C57BL/6 mice

The effects of dietary isohumulones, the main components accounting for the bitter taste of beer, on lipid metabolism were examined. Young female C57BL/6N mice were fed diets containing isomerized hop extract (IHE), which consists mainly of isohumulones. Administration of IHE with an atherogenic (high-fat and high-cholesterol) diet for 2 weeks resulted in a significant increase in plasma HDL-cholesterol (P<0.01), along with a concomitant reduction in the atherosclerosis index, an increase in liver weight and a decrease in body weight gain in a dose-dependent manner. When animals received IHE with either a cholesterol or a basal diet for 1 week, significant decreases in the liver content of cholesterol (P<0.01) and triacylglycerol (cholesterol diet, P<0.01) were observed. Quantitative analyses of hepatic mRNA levels revealed that IHE administration resulted in up-regulation of mRNA for acyl-CoA oxidase, acyl-CoA synthetase, hydroxymethylglutaryl-CoA synthetase, lipoprotein lipase and fatty acid transport protein, and down-regulation of mRNA for Apo CIII and Apo AI. Administration of purified isohumulones effectively resulted in the same changes as IHE. Administration of fenofibrate, an agonist for PPARalpha, with a cholesterol diet caused marked hepatomegaly, an increase in plasma HDL-cholesterol, a decrease in hepatic cholesterol content, and alterations in hepatic mRNA levels similar to those observed in mice given IHE. Taken together, these results suggest that the modulation of lipid metabolism observed in mice fed diets containing isohumulones is, at least in part, mediated by activation of PPARalpha.

c-Cbl is inducibly tyrosine-phosphorylated by epidermal growth factor stimulation in fibroblasts, and constitutively tyrosine-phosphorylated and associated with v-Src in v-src-transformed fibroblasts.

The c‐cbl gene was cloned as the cellular homolog of the v‐cbl oncogene that is the transforming component of a marine tumorigenic retrovirus, CAS NS‐1, though the biological roles of c‐Cbl remain to be elucidated. We have previously reported that c‐Cbl is implicated in the signal transduction triggered by granulocyte‐macrophage colony‐stimulating factor or erythropoietin in hematopoietic cells. Here, we observed tyrosine phosphorylation of c‐Cbl in cells expressing epidermal growth factor receptor depending on EGF stimulation and in v‐src transformed cells. Furthermore, c‐Cbl was revealed to associate with v‐Src in vivo. By means of binding experiments using glutathione S‐transferase fusion proteins, we have found that the SH2 and SH3 domains of many proteins bind to c‐Cbl. These findings strongly suggest that c‐Cbl is implicated in a wide variety of signal transduction pathways, including those of EGF receptor and Src protein, as well as in the signaling pathways of hematopoietic cells.

Proto-oncogene products Vav and c-Cbl are involved in the signal transduction through Grb2/Ash in hematopoietic cells

Grb2/Ash is composed of one SH2 and two SH3 domains and functions as an adapter linking tyrosine kinase receptors and Ras in fibroblasts. We have investigated the nature of proteins interacting with Grb2/Ash in hematopoietic cells. The product of the vav proto-oncogene (Vav) is expressed exclusively in hematopoietic cells and has guanine nucleotide exchange activity. Here we report that granulocyte/macrophage-colony- stimulating factor (GM-CSF), interleukin-3, and erythropoietin (Epo) induce rapid and transient tyrosine phosphorylation of Vav and that Vav is constitutively associated with the SH3 domain of Grb2/Ash in a human leukemia cell line UT-7. These data implicate Vav in a signaling pathway leading to activation of Ras or Ras-related proteins in hematopoietic cells. Furthermore, we have shown that the proto-oncogene c-cbl product (c-Cbl) is also tyrosine-phosphorylated by stimulation with GM-CSF or Epo and is constitutively associated with the SH3 domain of Grb2/Ash in UT-7. However, we could not find the homologous regions with guanine nucleotide exchange factors or GTPase-activating proteins in the c-cbl gene. Therefore, Grb2/Ash might also transduce a signal that is different from the signal leading to the small-G protein regulation.