We have also used these adipocytes to see if IRS 1 and IRS 2 are required for activation of Cbl , which is required for insulin stimulated glucose transport and has been found to function upstream of both PI3K / aPKC and Crk during thiazolidinedione action in 3T3 / L1 adipocytes [ Miura et al . ( 2003 ) Biochemistry 42 , 14335 ] . ^^^