Previous studies demonstrated that 1,25-dihydroxyvitamin D [1,25-(OH)(
2)D] treatment in vivo stimulates [I-125]calmodulin (CaM) binding to s
everal proteins (detected by [I-125]CaM gel overlay) in cytosol prepar
ations from rat kidney. This study establishes the sizes of the princi
pal stimulated forms and physiological aspects of their stimulation by
the hormone. Densitometric analysis of the 1,25-(OH)(2)D-stimulated [
I-125]CaM binding activities demonstrated induction of two major bands
, M(r) = 110 +/- 2.4 and 94 +/- 1.2 K. This analysis also revealed ind
uction of a previously existing band at 150 +/- 2.7 K and induction of
a 74 +/- 1.1 K band. 1,25-(OH)(2)D-induction of the [I-125]CaM bindin
g activities (CaMBP-Ds) was observed in both vitamin D-deficient and n
ormal vitamin D-sufficient rats. The [I-125]CaM binding activities wer
e abolished by incubation with 1000-fold excess CaM, but not calbindin
-D28, troponin C, parvalbumin, or alpha-lactalbumin. 1,25-(OH)(2)D ind
uction of the [I-125]CaM binding activities exhibited a graded dose re
sponse at 5-100 ng/day, and 5-7 days treatment was required for strong
induction. The [I-125]CaM binding activities in the kidney exhibited
differential subcellular distributions: 150 K CaMBPs were present in c
rude preparations of nuclei, microsomes, and mitochondria; a 110 K CaM
BP was present in the microsomal preparation; and the 94 and 74 K CaMB
Ps were restricted to the cytosol. 1,25-(OH)(2)D 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)(2)D-induced [I-125]CaM binding activ
ities in the rat kidney, with some variations in subcellular distribut
ion. Moreover, their pattern of induction suggests that 1,25-(OH)(2)D
regulation of the [I-125]CaM binding activities is not a part of the i
mmediate 1,25-(OH)(2)D signal transduction pathway, but rather may res
ult from altered genomic activity after hormone treatment.