Retinol-binding protein 4 (RBP-4)
This protein belongs to the lipocalin family and is the specific carrier for retinol (vitamin A), delivering retinol from the liver stores to the peripheral tissues. The RBP4-retinol complex interacts with transthyretin and prealbumin, which increases the serum half-life of RBP4. RBP4 promotes hyperglycemia through downregulation of the glucose transporter GLUT4 in adipocytes, upregulation of PEPCK, and attenuation of insulin receptor signaling in skeletal muscle. Serum RBP4 levels are elevated in type 2 diabetes and obesity, due primarily to increased production by visceral and liver adipocytes. Elevated levels have also been associated with pancreatic cancer.
Swiss-Prot Accession Number: P02753