Transcription of the sodium/myo-inositol cotransporter gene is regulated by multiple tonicity-responsive enhancers spread over 50 kilobase pairs in the 5'-flanking region.
The sodium/myo-inositol cotransporter is a plasma membrane protein responsible for concentrative cellular accumulation of myo-inositol in a variety of tissues. When cells in kidney and brain are exposed to a hyperosmolar salt condition (hypertonicity) due to the operation of urinary concentration mechanism and pathological conditions, respectively, they survive the stress of hypertonicity by raising the cellular concentration of myo-inositol. Transcription of the sodium/myo-inositol cotransporter gene is markedly stimulated in response to hypertonicity, leading to an increase in the activity of the cotransporter, which in turn drives the osmoprotective accumulation of myo-inositol. To understand the molecular mechanisms by which hypertonicity stimulates transcription, we analyzed the 5'-flanking region of the cotransporter gene for cis-acting regulatory sequences. We identified five tonicity-responsive enhancers that are scattered over 50 kilobase pairs. All the enhancers are variations of the same type of enhancer interacting with the transcription factor named tonicity-responsive enhancer binding protein. In vivo methylation experiments demonstrated that exposure of cells to hypertonicity increases the binding of tonicity-responsive enhancer binding protein to the enhancer sites, indicating that all of these enhancers are involved in the transcriptional stimulation. We conclude that the sodium/myo-inositol cotransporter gene is regulated by a large region (approximately 50 kilobase pairs) upstream of the gene.
Division of Nephrology, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
J S
JS
Rim
M G
MG
Atta
S C
SC
Dahl
G T
GT
Berry
J S
JS
Handler
H M
HM
Kwon
D000818:Animals; D001483:Base Sequence; D001692:Biological Transport / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000502:physiology; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005786:Gene Expression Regulation / Q000235:genetics*; D017930:Genes, Reporter; D006360:Heat-Shock Proteins / Q000235:genetics*; D006982:Hypertonic Solutions / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D027981:Symporters; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics*; D014162:Transfection / Q000235:genetics
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D006982:Hypertonic Solutions; D008565:Membrane Proteins; D027981:Symporters; D014157:Transcription Factors; C073884:SLC5A3 protein, human; D007294:Inositol