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Human facilitative glucose transporters. Isolation, functional characterization, and gene localization of cDNAs encoding an isoform (GLUT5) expressed in small intestine, kidney, muscle, and adipose tissue and an unusual glucose transporter pseudogene-like sequence (GLUT6).

Two novel facilitative glucose transporter-like cDNAs have been isolated from human small intestine and fetal skeletal muscle cDNA libraries by low stringency cross-hybridization with a fragment of the human erythrocyte/GLUT1 facilitative glucose transporter cDNA. One encodes a 501-amino acid facilitative glucose transporter, designated as the small intestine/GLUT5 isoform, having 41.7, 40.0, 38.7, and 41.6% identity with the previously described human erythrocyte/GLUT1, liver/GLUT2, brain/GLUT3, and muscle-fat/GLUT4 isoforms, respectively. GLUT5 mRNA is expressed at highest levels in small intestine and at much lower levels in kidney, skeletal muscle, and adipose tissue. Expression of in vitro synthesized human GLUT5 mRNA in Xenopus laevis oocytes indicates that the GLUT5 protein is a cytochalasin B-sensitive glucose carrier. The gene encoding the GLUT5 protein is located on the short arm of human chromosome 1. The second facilitative transporter-like cDNA sequence, designated GLUT6, is part of an 11-kilobase transcript that is expressed in all tissues examined. The sequence of a partial-length GLUT6 cDNA having an insert of 3.4 kilobase pairs revealed a region of 1.5 kilobase pairs that has 79.6% identity with the human brain/GLUT3 facilitative glucose transporter cDNA. However, because of the presence of multiple stop codons and frame shifts, this sequence cannot encode a functional glucose transporter protein. The region of facilitative glucose transporter nucleotide sequence homology in the GLUT6 transcript may have arisen by insertion of a reverse-transcribed GLUT3 transcript into the untranslated region of another gene. The GLUT6 gene is located on the long arm of human chromosome 5.

Adipose Tissue↗

A mutation in the protein S pseudogene is linked to protein S deficiency in a thrombophilic family.

Probands from 15 unrelated families with hereditary protein S deficiency type I, that is having a plasma total protein S concentration fifty percent of normal, were screened for abnormalities in their protein S genes by Southern analysis. Two probands were found to have a deviating DNA pattern with the restriction enzyme MspI. In the two patients the alteration concerned the disappearance of a MspI restriction site, CCGG, giving rise to an additional hybridizing MspI fragment. Analysis of relatives of both probands showed that in one family the mutation does not co-segregate with the phenotype of reduced plasma protein S. In the family of the other proband, however, complete linkage between the mutated gene pattern and the reduced total protein S concentration was found: 12 heterozygous relatives showed the additional MspI fragment but none of the investigated 26 normal members of the family. The mutation is shown to reside in the PS beta gene, the inactive protein S gene. The cause of type I protein S deficiency, a defect PS alpha gene has escaped detection by Southern analysis. No recombination has occurred between the PS alpha gene and the PS beta gene in 23 informative meioses. This suggests that the two protein S genes, located near the centromere of chromosome 3, are within 4 centiMorgan of each other.

Chromosome Mapping↗

Functional properties of proteins coded by three human alpha-interferon genes and a pseudogene.

We have characterized the functional properties of four highly purified recombinant human class I alpha-interferon subtypes whose biological activities have not been described previously. We selected biological and biochemical activities that may discriminate between different functions of these molecules. We found that the alpha subtypes could be discriminated only by antiviral-host range specificity and natural killer cell activation. Differences in their antiproliferative activity were cell line dependent. Competitive binding, antiproliferative activity in agar, enhancement of expression of HLA-ABC, elevation of 2'-5'-oligoadenylate synthetase levels and enhancement of phosphorylation of the Mr 69,000 protein kinase did not allow discrimination among the alpha I subtypes on the tested cell lines.

2',5'-Oligoadenylate Synthetase↗

Thiopurine methyltransferase pharmacogenetics. Cloning of human liver cDNA and a processed pseudogene on human chromosome 18q21.1.

Thiopurine methyltransferase (TPMT) is a genetically polymorphic enzyme that catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine. This genetic polymorphism is an important factor responsible for individual variation in thiopurine drug response. A cDNA for TPMT has been cloned from T84 human colon carcinoma cells. Northern blot analysis of multiple human tissues was performed with the T84 human colon carcinoma TPMT cDNA open reading frame (ORF) as a probe as one step toward understanding the molecular basis for the TPMT genetic polymorphism. Three mRNA species (approximately 1.4, 2.0, and 3.6 kb in length) were present in all tissues studied, including liver. However, none of these mRNAs matched the length of the 2.7 kb T84 TPMT cDNA. Therefore, it was important to clone a TPMT cDNA from a human drug-metabolizing organ such as the liver to determine whether its sequence matched that of the cDNA cloned from the T84 cell line. A human liver cDNA library was screened with the T84 TPMT cDNA ORF as a probe, and a 1.8 kb cDNA was isolated with a coding region sequence identical to that of the T84 TPMT cDNA. The TPMT cDNA ORF was then used to screen a human lymphocytes genomic DNA library in an attempt to clone the TPMT gene(s) in humans. Three intronless clones were isolated with identical ORF sequences that were 96% identical to that of the TPMT cDNA, but which contained multiple nucleotide substitutions and one deletion. The 3'- and 5'-flanking regions of one of the genomic DNA clones were sequenced.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗