Y. Moz et al., Protein-RNA interactions determine the stability of the renal NaPi-2 cotransporter mRNA and its translation in hypophosphatemic rats, J BIOL CHEM, 274(36), 1999, pp. 25266-25272
Hypophosphatemia leads to an increase in type II Na+ dependent inorganic ph
osphate cotransporter (NaPi-2) mRNA and protein levels in the kidney and in
creases renal phosphate reabsorption. Nuclear transcript run-on experiments
showed that the effect of a low phosphate diet was post-transcriptional. I
n an in vitro degradation assay, renal proteins from hypophosphatemic rats
stabilized the NaPi-2 transcript g-fold compared with control rats and this
was dependent upon an intact NaPi-2 3'-untranslated region (UTR), To deter
mine an effect of hypophosphatemia upon NaPi-a protein synthesis, the incor
poration of injected [S-35]methionine into renal proteins was studied in vi
vo, Hypophosphatemia leads to increased [S-35]methionine incorporation only
into NaPi-2 protein. The effect of hypophosphatemia on translation was stu
died in an in vitro translation assay, where hypophosphatemic renal protein
s led to increased translation of NaPi-2 and other transcripts. NaPi-2 RNA
interaction with cytosolic proteins was studied by UV cross-linking and Nor
thwestern gels. Hypophosphatemic proteins led to increased binding of renal
cytosolic proteins to the 5'-UTR of NaPi-2 mRNA. Therefore, hypophosphatem
ia increases NaPi-2 gene expression post-transcriptionally, which correlate
s with a more stable transcript mediated by the 3'-UTR, and an increase in
NaPi-2 translation involving protein binding to the 5'-UTR. These findings
show that phosphate regulates gene expression by affecting protein-RNA inte
ractions in vivo.