Altered phosphorylation of a 91-kDa protein in particulate fractions of rat kidney after protracted 1,25-dihydroxyvitamin D3 or estrogen treatment.
1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] treatment in vitamin D-deficient (-D) rats results in a dose-dependent decrease in phosphorylation of a 91-kDa protein (PP-D91) in particulate fractions of the kidney. This recently reported 1,25(OH)2D3 effect was examined in detail herein. In contrast to the pattern expected of a rapid signal transduction event, time course (4 h-7 days) experiments demonstrated that PP-D91 phosphorylation was not decreased until 3-5 days 1,25(OH)2D3 treatment, resulting in a 61 +/- 3% (P < 0.01, n = 3) decrease in PP-D91 phosphorylation by 7 days. These effects paralleled increases in plasma calcium from 9.3 +/- 0.6 to 13.9 +/- 0.7 mg/dl after 0 vs 7 days 1,25(OH)2D3 treatment, respectively. Subcellular fractionation demonstrated that the renal PP-D91 was predominantly localized and 1,25(OH)2D3-regulated in crude mitochondrial and microsomal fractions. Further, PP-D91 was present and 1,25(OH)2D3-regulated in enriched preparations of both proximal and distal renal tubule segments. Tissue distribution studies demonstrated that the PP-D91 was predominantly present and 1,25(OH)2D3 regulated in the kidney, although low levels of a vitamin D-independent phosphorylated band of similar size were observed in the lung and heart. In contrast to 1,25(OH)2D3, estradiol-17B treatment (1 mg/day x 7 day) significantly (P < 0.01) increased PP-D91 phosphorylation in kidney of both -D and +D rats (increased 118.5 +/- 10.6 and 81.9 +/- 6.3%, respectively). Phosphoamino acid analysis after PP-D91 phosphorylation, isolation, and proteolysis indicated that these hormones alter 32P incorporation into phosphoserine residues. In conclusion, the 1,25(OH)2D3 effect to reduce PP-D91 phosphorylation in particulate fractions of the rat kidney is a protracted, tissue-specific effect which parallels elevated plasma calcium levels in this model. Moreover, renal PP-D91 phosphorylation is differentially regulated by 1,25(OH)2D3 vs E2 treatment and occurs on phosphoserine residues. The parallel between decreased PP-D91 phosphorylation and 1,25(OH)2D3-induced hypercalcemia may suggest a role for PP-D91 in the renal response to hypervitaminosis D.
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Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
Siaw
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Cheung
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Walters
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D000818:Animals; D002117:Calcitriol / Q000172:deficiency / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D002458:Cell Fractionation; D004591:Electrophoresis, Polyacrylamide Gel; D004958:Estradiol / Q000494:pharmacology*; D007668:Kidney / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D019606:Phosphoamino Acids / Q000032:analysis; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism*; D010761:Phosphorus Radioisotopes / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D011374:Progesterone / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013739:Testosterone / Q000494:pharmacology; D014018:Tissue Distribution; D015431:Weight Loss
D019606:Phosphoamino Acids; D010750:Phosphoproteins; D010761:Phosphorus Radioisotopes; D010768:Phosphoserine; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D002117:Calcitriol; D002118:Calcium