Regulation of glucose-transporter gene expression in vitro and in vivo

Understanding of the fundamental mechanisms underlying the complex regulation of glucose homeostasis has been dramatically transformed recently by the realization that glucose transport in mammalian tissues is mediated by a family of structurally related but genetically distinct glucose-transporter proteins. The regulatory factors and intracellular signaling pathways that influence expression of the genes encoding these proteins are just being identified. Factors that regulate glucose-transporter gene expression in vitro include oncogenes, growth factors, insulin, oral hypoglycemic agents, vanadate, glucocorticoids, ambient glucose levels, and the state of cellular differentiation. In vivo, glucose-transporter gene expression in adipose cells, skeletal muscle, and liver is markedly affected by various altered nutritional and metabolic states. Recent studies have demonstrated that two glucose transporters expressed in the same tissue may be regulated differently in response to the same metabolic perturbation. Furthermore, transporter regulation appears to be tissue specific. These observations lay the groundwork for future studies aimed at unraveling the functional roles of the individual transporter species in different tissues, the molecular processes involved in regulating the expression of these genes, and the impact of dysregulated glucose-transporter gene expression in the pathogenesis of insulin-resistant states such as diabetes.