摘要 : XLalphas, a variant of the stimulatory G protein alpha-subunit (Gsalpha), can mediate receptor-activated cAMP generation and, thus, mimic the actions of Gsalpha in transfected cells. However, it remains unknown whether XLalphas ca... 展开 XLalphas, a variant of the stimulatory G protein alpha-subunit (Gsalpha), can mediate receptor-activated cAMP generation and, thus, mimic the actions of Gsalpha in transfected cells. However, it remains unknown whether XLalphas can act in a similar manner in vivo. We have now generated mice with ectopic transgenic expression of rat XLalphas in the renal proximal tubule (rptXLalphas mice), where Gsalpha mediates most actions of PTH. Western blots and quantitative RT-PCR showed that, while Gsalpha and type-1 PTH receptor levels were unaltered, protein kinase A activity and 25-hydroxyvitamin D 1-alpha-hydroxylase (Cyp27b1) mRNA levels were significantly higher in renal proximal tubules of rptXLalphas 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 rptXLalphas mice compared to gender-matched controls. Serum calcium, phosphorus, and 1,25 dihydroxyvitamin D were within the normal range, but serum PTH was approximately 30% lower in rptXLalphas mice than in controls (152 +/- 16 vs. 222 +/- 41 pg/ml; P < 0.05). After crossing the rptXLalphas mice to mice with ablation of maternal Gnas exon 1 (E1(m-/+)), male offspring carrying both the XLalphas transgene and maternal Gnas exon 1 ablation (rptXLalphas/E1(m-/+)) were significantly less hypocalcemic than gender-matched E1(m-/+) littermates. Both E1(m-/+) and rptXLalphas/E1(m-/+) offspring had higher serum PTH than wild-type littermates, but the degree of secondary hyperparathyroidism tended to be lower in rptXLalphas/E1(m-/+) mice. Hence, transgenic XLalphas expression in the proximal tubule enhanced Gsalpha-mediated responses, indicating that XLalphas can mimic Gsalpha in vivo. 收起