Characterization of cis-acting element in renal NaPi-2 cotransporter mRNA that determines mRNA stability

Abstract

Hypophosphatemia leads to an increase in Na+-Pi cotransporter (NaPi-2) mRNA levels. This increase is posttranscriptional and correlates with a more stable transcript mediated by the terminal 698 nt of the NaPi-2 mRNA. A 71-nt binding element was identified with renal proteins from rats fed control and low-Pi (−Pi) diet. The binding of −Pi renal proteins to this transcript was increased compared with control proteins. The functionality of the ciselement was demonstrated by an in vitro degradation assay. −Pi renal proteins stabilized transcripts that included the cis element compared with control renal extracts. The full-length NaPi-2 transcript, but not control transcripts, was stabilized by −Pi extracts. Insertion of the binding element into green fluorescent protein (GFP) as a reporter gene decreased chimeric GFP mRNA levels in transfection experiments. Our results suggest that the protein-binding region of the NaPi-2 mRNA functions as a cis-acting instability element. In hypophosphatemia there is increased binding to the cis-acting element and subsequent stabilization of NaPi-2 mRNA.