title: Alternative transcripts of rat slc19a1: defective sorting and inefficient expression of alternative splicing products--an addendum.
abstract: Recently, we have reported about the existence and cloning of alternative transcripts of the solute carrier 19a1 in rat liver and kidney, and have explained their origin from tissue specific promoters and by alternative splicing [DNA Seq. 2005, 16(1), 1-6]. The variant open reading frames (ORFs) of these transcripts were now expressed as fusion proteins with an N-terminal GFP. Transfection of HPCT-1E3 hepatocytoma cells as well as the MDCK kidney epithelial cell line with the GFP-fusion of the major splicing form containing 12 transmembrane domains (TMD) resulted in a strong fluorescence at the plasma membrane, which was stable over at least 3 days. Expression of GFP alone gave a comparable overall fluorescence intensity, although, staining was distributed evenly throughout the cells. Fusions of GFP with the shorter ORFs of all alternative slc19a1 transcripts containing 6-7 predicted TMD were expressed less efficiently and not sorted to the plasma membrane. Instead, these proteins accumulated in intracellular granules, and were, apparently, degraded. Hence, it is unlikely that these minor splicing forms are directly involved in solute transport across the plasma membrane.
authors.affiliation: Pharmacy and Toxicology, Faculty of Veterinary Medicine, An den Tierkliniken 15, University of Leipzig, Institute of Pharmacology, Leipzig, 04103, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Schrader
authors.forename: Carsten
authors.initials: C
authors.lastname: Kneuer
authors.forename: Hamid M
authors.initials: HM
authors.lastname: Said
authors.forename: Walther
authors.initials: W
authors.lastname: Honscha
mesh_terms: D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D015870:Gene Expression; D026901:Membrane Transport Proteins / Q000235:genetics*; D015778:Minor Histocompatibility Antigens; D020033:Protein Isoforms / Q000235:genetics* / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats; D058978:Reduced Folate Carrier Protein
chemical_list: D026901:Membrane Transport Proteins; D015778:Minor Histocompatibility Antigens; D020033:Protein Isoforms; D058978:Reduced Folate Carrier Protein; C043408:Slc19a1 protein, rat