Autosomal dominant hypercalciuria in a mouse model due to a mutation of the epithelial calcium channel, TRPV5

Contains fulltext : 118040.pdf (publisher's version ) (Open Access)Hypercalciuria is a major cause of nephrolithiasis, and is a common and complex disorder involving genetic and environmental factors. Identification of genetic factors for monogenic forms of hypercalciuria is hampered by the limited availability of large families, and to facilitate such studies, we screened for hypercalciuria in mice from an N-ethyl-N-nitrosourea mutagenesis programme. We identified a mouse with autosomal dominant hypercalciuria (HCALC1). Linkage studies mapped the Hcalc1 locus to a 11.94 Mb region on chromosome 6 containing the transient receptor potential cation channel, subfamily V, members 5 (Trpv5) and 6 (Trpv6) genes. DNA sequence analysis of coding regions, intron-exon boundaries and promoters of Trpv5 and Trpv6 identified a novel T to C transition in codon 682 of TRPV5, mutating a conserved serine to a proline (S682P). Compared to wild-type littermates, heterozygous (Trpv5(682P/+)) and homozygous (Trpv5(682P/682P)) mutant mice had hypercalciuria, polyuria, hyperphosphaturia and a more acidic urine, and approximately 10% of males developed tubulointerstitial nephritis. Trpv5(682P/682P) mice also had normal plasma parathyroid hormone but increased 1,25-dihydroxyvitamin D(3) concentrations without increased bone resorption, consistent with a renal defect for the hypercalciuria. Expression of the S682P mutation in human embryonic kidney cells revealed that TRPV5-S682P-expressing cells had a lower baseline intracellular calcium concentration than wild-type TRPV5-expressing cells, suggesting an altered calcium permeability. Immunohistological studies revealed a selective decrease in TRPV5-expression from the renal distal convoluted tubules of Trpv5(682P/+) and Trpv5(682P/682P) mice consistent with a trafficking defect. In addition, Trpv5(682P/682P) mice had a reduction in renal expression of the intracellular calcium-binding protein, calbindin-D(28K), consistent with a specific defect in TRPV5-mediated renal calcium reabsorption. Thus, our findings indicate that the TRPV5 S682P mutant is functionally significant and study of HCALC1, a novel model for autosomal dominant hypercalciuria, may help further our understanding of renal calcium reabsorption and hypercalciuria

Myc targets Cks1 to provoke the suppression of p27Kip1, proliferation and lymphomagenesis

Reduced levels of the cyclin-dependent kinase inhibitor p27Kip1 connote poor prognosis in cancer. In human Burkitt lymphoma and in precancerous B cells and lymphomas arising in Eμ-Myc transgenic mice, p27Kip1 expression is markedly reduced. We show that the transcription of the Cks1 component of the SCFSkp2 complex that is necessary for p27Kip1 ubiquitylation and degradation is induced by Myc. Further, Cks1 expression is elevated in precancerous Eμ-Myc B cells, and high levels of Cks1 are also a hallmark of Eμ-Myc lymphoma and of human Burkitt lymphoma. Finally, loss of Cks1 in Eμ-Myc B cells elevates p27Kip1 levels, reduces proliferation and markedly delays lymphoma development and dissemination of disease. Therefore, Myc suppresses p27Kip1 expression, accelerates cell proliferation and promotes tumorigenesis at least in part through its ability to selectively induce Cks1