Shikonin stimulates glucose uptake in 3T3-L1 adipocytes via an insulin-independent tyrosine kinase pathway.
Type 2 diabetes is due to defects in both insulin action and secretion. In an attempt to discover small molecules that stimulate glucose uptake, similar to insulin, a cell-based glucose uptake screening assay was performed using 3T3-L1 adipocytes. Shikonin, a substance originally isolated from the root of the Chinese plant that has been used as an ointment for wound healing, was thus identified. Shikonin stimulated glucose uptake and potentiated insulin-stimulated glucose uptake in a concentration-dependent manner in 3T3-L1 adipocytes. Stimulation of glucose uptake was also observed in rat primary adipocytes and cardiomyocytes. Like insulin, shikonin-stimulated glucose uptake was inhibited by genistein, a tyrosine kinase inhibitor, and enhanced by vanadate, a tyrosine phosphatase inhibitor. However, in contrast to insulin, shikonin-stimulated glucose uptake was not strongly inhibited by wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K). In vitro phosphorylation analyses revealed that shikonin did not induce tyrosine phosphorylation of the insulin receptor, but significantly induced both Thr-308 and Ser-473 phosphorylation of Akt. Our results suggest that in 3T3-L1 adipocytes, shikonin action is not mediated primarily via the insulin receptor/PI3K pathway, but rather via another distinct tyrosine kinase-dependent pathway leading to glucose uptake involving Akt phosphorylation.
Kamei
Reiko
R
Suntory Biomedical Research Limited, 1-1-1 Wakayamadai, Shimamoto-cho, Mishima-gun, Osaka 618-8503, Japan.
Kitagawa
Yoshinori
Y
Kadokura
Michinori
M
Hattori
Fumiyuki
F
Hazeki
Osamu
O
Ebina
Yousuke
Y
Nishihara
Tatsuro
T
Oikawa
Shinzo
S
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology*; D004365:Drugs, Chinese Herbal / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008297:Male; D008516:Medicine, Chinese Traditional; D051379:Mice; D015394:Molecular Structure; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D009285:Naphthoquinones / Q000494:pharmacology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014638:Vanadates / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D000894:Anti-Inflammatory Agents, Non-Steroidal; D004365:Drugs, Chinese Herbal; D004791:Enzyme Inhibitors; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D009285:Naphthoquinones; D011518:Proto-Oncogene Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; C016101:shikonin; D014638:Vanadates; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose; D000077191:Wortmannin