Table 1. Some Substances With Possible Roles in Insulin Signaling ^a (11, 12, 16, 21).

Substance Name	Role in Insulin Signaling
GLUT	Translocated to plasma membrane for glucose influx
IL-6	Impairs/inhibits insulin signaling; suppresses adipogenesis and secretion of adiponectin
NF-κB	Influences gene transcription; inhibited by adiponectin
PPAR-γ	Stimulates free fatty acid (FFA) catabolism; thiazolidinediones (TZDs) are PPAR-γ agonists
TNFα	Main factor for stimulating the secretion of FFAs from adipose tissue into circulation; impairs insulin signaling
MCP-1	Impairs insulin-stimulated glucose uptake; promotes atherosclerosis
FFAs	Adipocytes decrease glucose uptake in peripheral tissues by releasing free fatty acids
Akt	A key regulator of insulin action and glucose uptake in mammals
IRS-1	Plays a key role in transmitting signals from insulin receptor to intracellular PI3K/Akt pathways and Ras/mitogen activated protein kinase, which eventually mediate various actions of insulin
PTP1B	A negative regulator of insulin signaling which targets tyrosine-phosphorylated insulin receptor β and IRS-1
mTOR	Inhibits IRS-1 tyrosine phosphorylation

^aGLUT, Glucose transporter; IL-6, Interleukin-6; NF-κB, Nuclear transcription factor κB; PPAR-γ, Peroxisome proliferator-activated receptor-gamma; TNFα, Tumor necrosis factor alpha; MCP-1,Monocyte chemoattractant protein-1; FFAs, free fatty acids; Akt, protein kinase B; IRS-1, insulin receptor substrate-1; PTP1B, protein–tyrosine phosphatase 1B; mTOR, mammalian target of rapamycin.