Growth Hormone Induces Cellular Insulin Resistance by Uncoupling Phosphatidylinositol 3-Kinase and Its Downstream Signals in 3T3-L1 Adipocytes
- Atsuko Takano,
- Tetsuro Haruta,
- Minoru Iwata,
- Isao Usui,
- Tatsuhito Uno,
- Junko Kawahara,
- Eiichi Ueno,
- Toshiyasu Sasaoka and
- Masashi Kobayashi
Growth hormone (GH) is well known to induce in vivo insulin resistance. However, the molecular mechanism of GH-induced cellular insulin resistance is largely unknown. In this study, we demonstrated that chronic GH treatment of differentiated 3T3-L1 adipocytes reduces insulin-stimulated 2-deoxyglucose (DOG) uptake and activation of Akt (also known as protein kinase B), both of which are downstream effects of phosphatidylinositol (PI) 3-kinase, despite enhanced tyrosine phosphorylation of insulin receptor substrate (IRS)-1, association of IRS-1 with the p85 subunit of PI 3-kinase, and IRS-1–associated PI 3-kinase activity. In contrast, chronic GH treatment did not affect 2-DOG uptake and Akt activation induced by overexpression of a membrane-targeted form of the p110 subunit of PI 3-kinase (p110CAAX) or Akt activation stimulated by platelet-derived growth factor. Fractionation studies indicated that chronic GH treatment reduces insulin-stimulated translocation of Akt from the cytosol to the plasma membrane. Interestingly, chronic GH treatment increased insulin-stimulated association of IRS-1 with p85 and IRS-1–associated PI 3-kinase activity preferentially in the cytosol. These results indicate that cellular insulin resistance induced by chronic GH treatment in 3T3-L1 adipocytes is caused by uncoupling between activation of PI 3-kinase and its downstream signals, which is specific to the insulin-stimulated PI 3-kinase pathway. This effect of GH might result from the altered subcellular distribution of IRS-1–associated PI 3-kinase.
Address correspondence and reprint requests to Tetsuro Haruta, MD, PhD, First Dept. of Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan. E-mail:.
Received for publication 19 September 2000 and accepted in revised form 8 May 2001.
BSA, bovine serum albumin; DMEM, Dulbecco’s modified Eagle’s medium; DOG, deoxyglucose; FBS, fetal bovine serum; GH, growth hormone; HDM, high-density microsome; IR, insulin receptor; IRS, IR substrate; JAK2, Janus kinase 2; KRP, Krebs-Ringer phosphate; LDM, low-density microsome; MOI, multiplicity of infection; PDGF, platelet-derived growth factor; PDK-1; phosphoinositide-dependent protein kinase 1; PH, pleckstrin homology; PI, phosphatidylinositol; PM, plasma membrane; PMSF, phenylmethylsulfonyl fluoride; SH2, Src homology 2; STAT, signal transducers and activators of transcription.