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Children's Foundation Research Center of Memphis at Le Bonheur Children's Medical Center, University of Tennessee Health Science Center, Memphis, Tennessee 38103
Dietary lipid
acutely upregulates apolipoprotein (apo) A-IV expression by sevenfold
at the pretranslational level in neonatal swine jejunum. To determine
the mechanism of this regulation, two-day-old female swine received
intraduodenal infusions of low- and high-triacylglycerol (TG)
isocaloric diets for 24 h. Nuclear runoff assay confirmed apo A-IV
gene transcriptional regulation by the high-TG diet. Footprinting
analysis using the swine apo A-IV proximal promoter sequence (+14 to
246 bp) demonstrated three regions protected by the low-TG extracts.
Of these three motifs, only ACCTTC showed 100% homology to the human
sequence and was further studied. EMSA was performed using probes
containing wild-type (WT) and mutant (M) motifs. A shift was noted with
the low-TG nuclear extracts with the WT probe but not with the M probe. Excess unlabeled free WT probe competed out the shift, whereas the M
probe did not. No significant shift occurred with either probe using
high-TG extracts. These results suggest that a repressor protein binds
to the ACCTTC motif and becomes unbound during lipid absorption,
allowing transcriptional activation of the apo A-IV gene in newborn
swine small intestine.
DNAse I DNA protection assay; electrophoretic mobility shift assay; gene transcription; nuclear runoff assay; small intestine
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