ALTERED PHOSPHORYLATION OF A 91-KDA PROTEIN IN PARTICULATE FRACTIONS OF RAT-KIDNEY AFTER PROTRACTED 1,25-DIHYDROXYVITAMIN D-3 OR ESTROGEN-TREATMENT

1,25-Dihydroxyvitamin D-3 [1,25(OH)(2)D-3] treatment in vitamin D-defi cient (-D) rats results in a dose-dependent decrease in phosphorylatio n of a 91-kDa protein (PP-D91) in particulate fractions of the kidney, This recently reported 1,25(OH)(2)D-8 effect was examined in detail h erein, In contrast to the pattern expected of a rapid signal transduct ion event, time course (4 h-7 days) experiments demonstrated that PP-D 91 phosphorylation was not decreased until 3-5 days 1,25(OH)(2)D-3 tre atment, resulting in a 61 +/- 3% (P < 0.01, n = 3) decrease in PP-D91 phosphorylation by 7 days, These effects paralleled increases in plasm a calcium from 9.3 +/- 0.6 to 13.9 +/- 0.7 mg/dl after 0 vs 7 days 1,2 5(OH)(2)D-3 treatment, respectively, Subcellular fractionation demonst rated that the renal PP-D91 was predominantly localized and 1,25(OH)(2 )D-3-regulated in elude mitochondrial and microsomal fractions, Furthe r, PP-D(9)1 was present and 1,25(OH)(2)D-3-regulated in enriched prepa rations of both proximal and distal renal tubule segments, Tissue dist ribution studies demonstrated that the PP-D91 was predominantly presen t and 1,25(OH)(2)D-3 regulated in the kidney, although low levels of a vitamin D-independent phosphorylated band of similar size were observ ed in the lung and heart, In contrast to 1,25(OH)(2)D-3, estradiol-17B treatment (1 mg/day x 7 day) significantly (P < 0.01) increased PP-D9 1 phosphorylation in kidney of both -D and +D rats (increased 118.5 +/ - 10.6 and 81.9 +/- 6.3%, respectively), Phosphoamino acid analysis af ter PP-D91 phosphorylation, isolation, and proteolysis indicated that these hormones alter P-32 incorporation into phosphoserine residues, I n conclusion, the 1,25(OH)(2)D-3 effect to reduce PP-D91 phosphorylati on 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 regul ated by 1,25(OH)(2)D-3 vs E-2 treatment and occurs on phosphoserine re sidues, The parallel between decreased PP-D91 phosphorylation and 1,25 (OH)(2)D-3-induced hypercalcemia may suggest a role for PP-D91 in the renal response to hypervitaminosis D. (C) 1997 Academic Press.