MOLECULAR-CLONING AND MESSENGER-RNA EXPRESSION OF THE BOVINE INSULIN-RESPONSIVE GLUCOSE-TRANSPORTER (GLUT4)

Insulin-responsive glucose transporter GLUT4, is a member of the gluco se transporter family (GLUT) and is present exclusively in muscle and adipose tissue. It is a target of insulin action in humans and rodents . To clarify the molecular structure of bovine GLUT4, its GLUT4 cDNA w as cloned by the RT-PCR method. Several cDNA clones corresponding to t he different regions of GLUT4 were obtained by amplifying reverse-tran scriptase products of RNA extracted from Holstein cattle skeletal musc le. Nucleotide sequence analysis of the cDNA clones revealed that bovi ne GLUT4 cDNA was composed of 2,656 base pairs with a coding region fo r a 509 amino acid protein. The deduced amino acid sequence was 64% an d 92% identical with bovine GLUT1 (GLUT ubiquitously expressed in all tissues) and rat GLUT4, respectively. Although the amino acid sequence of the GLUT4 COOH-terminal region is highly conserved among the speci es so far reported, one amino acid (Asp) of this region was replaced b y His in bovine GLUT4. The tissue distribution of GLUT4, was also exam ined by Northern blot analysis using a probe prepared from the bovine cDNA. GLUT4 mRNA was detected in skeletal muscle, heart, and adipose t issue, but not in liver, kidney, lung, brain, or spleen. Such a distri bution is essentially the same as in humans and rodents, suggesting th at GLUT4 is an insulin-responsive glucose transporter in cattle.