title: Transgenic overexpression of the extra-large Gsα variant XLαs enhances Gsα-mediated responses in the mouse renal proximal tubule in vivo.
abstract: XLαs, a variant of the stimulatory G protein α-subunit (Gsα), can mediate receptor-activated cAMP generation and, thus, mimic the actions of Gsα in transfected cells. However, it remains unknown whether XLαs can act in a similar manner in vivo. We have now generated mice with ectopic transgenic expression of rat XLαs in the renal proximal tubule (rptXLαs mice), where Gsα mediates most actions of PTH. Western blots and quantitative RT-PCR showed that, while Gsα and type-1 PTH receptor levels were unaltered, protein kinase A activity and 25-hydroxyvitamin D 1-α-hydroxylase (Cyp27b1) mRNA levels were significantly higher in renal proximal tubules of rptXLαs mice than wild-type littermates. Immunohistochemical analysis of kidney sections showed that the sodium-phosphate cotransporter type 2a was modestly reduced in brush border membranes of male rptXLαs mice compared to gender-matched controls. Serum calcium, phosphorus, and 1,25 dihydroxyvitamin D were within the normal range, but serum PTH was ∼30% lower in rptXLαs mice than in controls (152 ± 16 vs. 222 ± 41 pg/ml; P < 0.05). After crossing the rptXLαs mice to mice with ablation of maternal Gnas exon 1 (E1(m-/+)), male offspring carrying both the XLαs transgene and maternal Gnas exon 1 ablation (rptXLαs/E1(m-/+)) were significantly less hypocalcemic than gender-matched E1(m-/+) littermates. Both E1(m-/+) and rptXLαs/E1(m-/+) offspring had higher serum PTH than wild-type littermates, but the degree of secondary hyperparathyroidism tended to be lower in rptXLαs/E1(m-/+) mice. Hence, transgenic XLαs expression in the proximal tubule enhanced Gsα-mediated responses, indicating that XLαs can mimic Gsα in vivo.
authors.affiliation: Endocrine Unit, Department of Medicine, Massachusetts General Hospital, 50 Blossom Street, Thier 10, Boston, Massachusetts 02114, USA.
authors.forename: Zun
authors.initials: Z
authors.lastname: Liu
authors.forename: Hiroko
authors.initials: H
authors.lastname: Segawa
authors.forename: Cumhur
authors.initials: C
authors.lastname: Aydin
authors.forename: Monica
authors.initials: M
authors.lastname: Reyes
authors.forename: Reinhold G
authors.initials: RG
authors.lastname: Erben
authors.forename: Lee S
authors.initials: LS
authors.lastname: Weinstein
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.forename: Vladimir
authors.initials: V
authors.lastname: Marshansky
authors.forename: Leopold F
authors.initials: LF
authors.lastname: Fröhlich
authors.forename: Murat
authors.initials: M
authors.lastname: Bastepe
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D051379:Mice; D016133:Polymerase Chain Reaction; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D019205:GTP-Binding Protein alpha Subunits, Gs