ROLE OF INSULIN-RECEPTOR SUBSTRATE-1 AND PP60 IN THE REGULATION OF INSULIN-INDUCED GLUCOSE-TRANSPORT AND GLUT4 TRANSLOCATION IN PRIMARY ADIPOCYTES

In muscle and fat, glucose transport occurs through the translocation of GLUT4 from an intracellular pool to the cell surface. Phosphatidyli nositol (PI) 3-kinase has been shown to be required in this process. I nsulin is thought to activate this enzyme by stimulating its associati on with tyrosine-phosphorylated proteins such as insulin receptor subs trate (IRS)-1, IRS-2, Grb2-associated binder-1, and pp60. To study the role of these endogenous substrates in glucose transport, we analyzed adipocytes from IRS-1 null mice that we previously generated (Tamemot o, H., Kadowaki, T., Tobe, K., Yagi, T., Sakura, H., Hayakawa, T., Ter auchi, Y., Ueki, K., Kaburagi, Y., Satoh, S., Sekihara, H., Yoshioka, S., Horikoshi, H., Furuta, Y., Ikawa, Y., Kasuga, M., Yazaki Y., and A izawa S. (1994) Nature 372, 182-186). In adipocytes from these mice, w e showed that: 1) insulin-induced PI 3-kinase activity in the antiphos photyrosine immunoprecipitates was 54% of wild-type; 2) pp60 was the m ajor tyrosine-phosphorylated protein that associated with PI 3-kinase, whereas tyrosine phosphorylaion of IRS-2 as well as its association w ith this enzyme was almost undetectable; and 3) glucose transport and GLUT4 translocation at maximal insulin stimulation were decreased to 5 2 and 68% of those from wild-type. These data suggest that both IRS-1 and pp60 play a major role in insulin-induced glucose transport in adi pocytes, and that pp60 is predominantly involved in regulating this pr ocess in the absence of IRS-1.