Human Na(+)-myo-inositol cotransporter gene: alternate splicing generates diverse transcripts.
Na(+)-myo-inositol cotransport activity generally maintains millimolar intracellular concentrations of myo-inositol and specifically promotes transepithelial myo-inositol transport in kidney, intestine, retina, and choroid plexus. Glucose-induced, tissue-specific myo-inositol depletion and impaired Na(+)-myo-inositol cotransport activity are implicated in the pathogenesis of diabetic complications, a process modeled in vitro in cultured human retinal pigment epithelium (RPE) cells. To explore this process at the molecular level, a human RPE cDNA library was screened with a canine Na(+)-dependent myo-inositol cotransporter (SMIT) cDNA. Overlapping cDNAs spanning 3569 nt were cloned. The resulting cDNA sequence contained a 2154-nt open reading frame, 97% identical to the canine SMIT amino acid sequence. Genomic clones containing SMIT exons suggested that the cDNA is derived from at least five exons. Hypertonic stress induced a time-dependent increase, initially in a 16-kb transcript and subsequently in 11.5-, 9.8-, 8.5-, 3.8-, and approximately 1.2-kb SMIT transcripts, that was ascribed to alternate exon splicing using exon-specific probes and direct cDNA sequencing. The human SMIT gene is a complex multiexon transcriptional unit that by alternate exon splicing generates multiple SMIT transcripts that accumulate differentially in response to hypertonic stress.
Porcellati
F
F
Department of Internal Medicine, University of Michigan Medical School, Ann Arbor 48109, USA.
Hlaing
T
T
Togawa
M
M
Stevens
M J
MJ
Larkin
D D
DD
Hosaka
Y
Y
Glover
T W
TW
Henry
D N
DN
Greene
D A
DA
Killen
P D
PD
D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004285:Dogs; D005091:Exons / Q000235:genetics; D006360:Heat-Shock Proteins / Q000235:genetics*; D006801:Humans; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D012313:RNA / Q000235:genetics; D027981:Symporters; D014158:Transcription, Genetic / Q000235:genetics*
D002352:Carrier Proteins; D018076:DNA, Complementary; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D027981:Symporters; C073884:SLC5A3 protein, human; D012313:RNA