Transcriptional regulation of the human NaPi-IIb cotransporter by EGF in Caco-2 cells involves c-myb.
The type IIb sodium-phosphate (NaP(i)-IIb) cotransporter mediates intestinal phosphate absorption. Previous work in our laboratory has shown that EGF inhibited NaP(i)-IIb cotransporter expression through transcriptional regulation. To understand this regulation, progressively shorter human NaP(i)-IIb promoter constructs were used to define the EGF response region, and gel mobility shift assays (GMSAs) were used to characterize DNA-protein interactions. Promoter analysis determined that the EGF response region was located between -784 and -729 base pair (bp) of the promoter. GMSAs and overexpression studies revealed an interaction between this promoter region and c-myb transcription factor. Inhibition of EGF receptor activation restored promoter function. Further studies suggested that MAPK, PKC, and/or PKA pathways are involved in this regulation. In conclusion, these studies suggest that EGF decreases human NaP(i)-IIb gene expression by modifying the c-myb protein such that it inhibits transcriptional activation. We further conclude that this downregulation of promoter function is mediated by EGF-activated PKC/PKA and MAPK pathways. This is the first study that demonstrates involvement of c-myb in the regulation of intestinal nutrient absorption.
Xu
Hua
H
Department of Pediatrics, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA.
Inouye
Michael
M
Hines
Eric R
ER
Collins
James F
JF
Ghishan
Fayez K
FK
D001483:Base Sequence / Q000235:genetics; D015153:Blotting, Western; D018938:Caco-2 Cells; D004247:DNA / Q000235:genetics / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000502:physiology*; D066246:ErbB Receptors / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology; D009687:Nuclear Proteins / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D020598:Proto-Oncogene Proteins c-myb / Q000502:physiology*; D011799:Quinazolines; D015398:Signal Transduction / Q000502:physiology; D050608:Sodium-Phosphate Cotransporter Proteins; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D027981:Symporters / Q000235:genetics*; D014158:Transcription, Genetic / Q000502:physiology*; D020032:Tyrphostins / Q000494:pharmacology
D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D020598:Proto-Oncogene Proteins c-myb; D011799:Quinazolines; C493557:SLC34A2 protein, human; D050608:Sodium-Phosphate Cotransporter Proteins; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D027981:Symporters; D020032:Tyrphostins; C101044:RTKI cpd; D004815:Epidermal Growth Factor; D004247:DNA; D066246:ErbB Receptors