Protracted 1,25-dihydroxyvitamin D treatment stimulates multiple calmodulin binding proteins in rat kidney

Previous studies demonstrated that 1,25-dihydroxyvitamin D [1,25-(OH)2D] treatment in vivo stimulates [125I]calmodulin (CaM) binding to several proteins (detected by [125I]CaM gel overlay) in cytosol preparations from rat kidney. This study establishes the sizes of the principal stimulated forms and physiological aspects of their stimulation by the hormone. Densitometric analysis of the 1,25-(OH)2D-stimulated [125I]CaM binding activities demonstrated induction of two major bands, M(r) = 110 +/- 2.4 and 94 +/- 1.2 K. This analysis also revealed induction of a previously existing band at 150 +/- 2.7 K and induction of a 74 +/- 1.1 K band. 1,25-(OH)2D-induction of the [125I]CaM binding activities (CaMBP-Ds) was observed in both vitamin D-deficient and normal vitamin D-sufficient rats. The [125I]CaM binding activities were abolished by incubation with 1000-fold excess CaM, but not calbindin-D28, troponin C, parvalbumin, or alpha-lactalbumin. 1,25-(OH)2D induction of the [125I]CaM binding activities exhibited a graded dose response at 5-100 ng/day, and 5-7 days treatment was required for strong induction. The [125I]CaM binding activities in the kidney exhibited differential subcellular distributions: 150 K CaMBPs were present in crude preparations of nuclei, microsomes, and mitochondria; a 110 K CaMBP was present in the microsomal preparation; and the 94 and 74 K CaMBPs were restricted to the cytosol. 1,25-(OH)2D treatment resulted in the induction of the microsomal 110 K CaMBP and possibly the nuclear (but not in mitochondrial or microsomal) 150 K CaMBPs. In conclusion, there are at least four 1,25-(OH)2D-induced [125I]CaM binding activities in the rat kidney, with some variations in subcellular distribution. Moreover, their pattern of induction suggests that 1,25-(OH)2D regulation of the [125I]CaM binding activities is not a part of the immediate 1,25-(OH)2D signal transduction pathway, but rather may result from altered genomic activity after hormone treatment.