Molecular cloning of two rat Na+/Pi cotransporters: evidence for differential tissue expression of transcripts.
Recently, Na+/Pi cotransport activity has been demonstrated in rat liver hepatocytes. Here, we report the isolation of two Na+/Pi cotransporter cDNAs (RNaPi-1a and RNaPi-1b) from a rat liver cDNA library. The two cDNAs have the same coding but different 5'-untranslated regions. The rat cDNAs encode a polypeptide of 465 amino acids, having 62% and 66% identity with the rabbit NaPi-1 and human kidney Na+/Pi cotransporter, respectively. Northern blot analysis showed that a RNaPi-1a--specific probe detected two major transcripts (2.3 and 1.8 kb), whereas a RNaPi-1b--specific probe hybridized with one transcript (1.8 kb) in rat kidney, liver, and hepatocytes in primary culture. Rat liver expressed much higher levels of RNaPi-1a than RNaPi-1b, whereas the converse was true for rat kidney. Low levels of RNaPi-1 mRNAs were also detected in rat heart, brain, and skeletal muscle. These findings indicate that there are at least two isoforms of RNaPi-1 transcripts expressed in liver and kidney and that the levels of expression of the RNaPi-1a and RNaPi-1b may be controlled by tissue-specific factors.
Li
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H
Department of Pharmacology, Medical College of Ohio, Toledo 43614, USA.
Xie
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008099:Liver / Q000737:chemistry* / Q000166:cytology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis* / Q000235:genetics; D011817:Rabbits; D051381:Rats; D016914:Ribonuclease H; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D027981:Symporters
D002352:Carrier Proteins; D018076:DNA, Complementary; D012333:RNA, Messenger; C493546:SLC17A1 protein, human; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D027981:Symporters; D016914:Ribonuclease H