Numerous studies have previously revealed the various mechanisms of insulin resistance in vivo and in vitro, in which insulin receptor functions and receptor substrates played important roles. For example, inflammatory mediators induce serine/threonine phosphorylation and subsequent degradation of insulin receptor substrate-1 (IRS-1), which causes interference of insulin receptor signaling and insulin resistance. Here, we show the additional findings of insulin receptor function, suggesting the novel mechanism of insulin resistance in adipose tissues and stem cells.