Green tea (-)-epigallocatechin gallate inhibits insulin stimulation of 3T3-L1 preadipocyte mitogenesis via the 67-kDa laminin receptor pathway.
Insulin and (-)-epigallocatechin gallate (EGCG) have been reported to regulate fat cell mitogenesis and adipogenesis, respectively. This study investigated the pathways involved in EGCG modulation of insulin-stimulated mitogenesis in 3T3-L1 preadipocytes. EGCG inhibited insulin stimulation of preadipocyte proliferation in a dose- and time-dependent manner. EGCG also suppressed insulin-stimulated phosphorylation of the insulin receptor-beta, insulin receptor (IR) substrates 1 and 2 (IRS1 and IRS2), and mitogen-activated protein kinase pathway proteins, RAF1, MEK1/2, and ERK1/2, but not JNK. Furthermore, EGCG inhibited the association of IR with the IRS1 and IRS2 proteins, but not with the IRS4 protein. These data suggest that EGCG selectively affects particular types of IRS and MAPK family members. Generally, EGCG was more effective than epicatechin, epicatechin gallate, and epigallocatechin in modulating insulin-stimulated mitogenic signaling. We identified the EGCG receptor [also known as the 67-kDa laminin receptor (67LR)] in fat cells and found that its expression was sensitive to growth phase, tissue type, and differentiation state. Pretreatment of preadipocytes with 67LR antiserum prevented the effects of EGCG on insulin-stimulated phosphorylation of IRS2, RAF1, and ERK1/2 and insulin-stimulated preadipocyte proliferation (cell number and bromodeoxyuridine incorporation). Moreover, EGCG tended to increase insulin-stimulated associations between the 67LR and IR, IRS1, IRS2, and IRS4 proteins. These data suggest that EGCG mediates anti-insulin signaling in preadipocyte mitogenesis via the 67LR pathway.
Ku
Hui-Chen
HC
Dept. of Life Science, College of Science, National Central Univ., Jhong-li, Taiwan 32054.
Chang
Hsin-Huei
HH
Liu
Hsien-Chun
HC
Hsiao
Chiao-Hsin
CH
Lee
Meng-Jung
MJ
Hu
Yu-Jung
YJ
Hung
Pei-Fang
PF
Liu
Chi-Wei
CW
Kao
Yung-Hsi
YH
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D019440:Anti-Obesity Agents / Q000302:isolation & purification / Q000494:pharmacology*; D028241:Camellia sinensis / Q000737:chemistry; D002392:Catechin / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D007106:Immune Sera; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D017474:Receptors, Laminin / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors
D019440:Anti-Obesity Agents; D007106:Immune Sera; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D017474:Receptors, Laminin; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482127:Map2k1 protein, mouse; C482129:Map2k2 protein, mouse; C057580:gallocatechol