Checkpoint kinase CHk2 controls renal CYp27b1 expression, calcitriol formation, and calcium-phosphate metabolism

Abstract

© Springer-Verlag Berlin Heidelberg 2014. Checkpoint kinase 2 (Chk2) is the main effector kinase of ataxia telangiectasia mutated (ATM) and responsible for cell cycle regulation. ATM signaling has been shown to upregulate interferon-regulating factor-1 (IRF-1), a transcription factor also expressed in the kidney. Calcitriol (1,25 (OH)2D3), a major regulator of mineral metabolism, is generated by 25-hydroxyvitamin D 1α-hydroxylase in the kidney. Since 25-hydroxyvitamin D 1α-hydroxylase expression is enhanced by IRF-1, the present study explored the role of Chk2 for calcitriol formation and mineral metabolism. Chk2- deficient mice (chk2−/−) were compared to wild-type mice (chk2+/+). Transcript levels of renal 25-hydroxyvitamin D 1α-hydroxylase, Chk2, and IRF-1 were determined by RTPCR; Klotho expression by Western blotting; bone density by μCT analysis; serum or plasma 1,25 (OH)2D3, PTH, and Cterminal FGF23 concentrations by immunoassays; and serum, fecal, and urinary calcium and phosphate concentrations by photometry. The renal expression of IRF-1 and 25- hydroxyvitamin D 1α-hydroxylase as well as serum 1,25 (OH)2D3 and FGF23 levels were significantly lower in chk2−/− mice compared to chk2+/+ mice. Plasma PTH was not different between the genotypes. Renal calcium and phosphate excretion were significantly higher in chk2−/− mice than in chk2+/+ mice despite hypophosphatemia and normocalcemia. Bone density was not different between the genotypes. We conclude that Chk2 regulates renal 25- hydroxyvitamin D 1α-hydroxylase expression thereby impacting on calcium and phosphate metabolism.