AJP - Endocrinology and Metabolism, Vol 260, Issue 5 E794-E800, Copyright © 1991 by American Physiological Society
Vitamin D independence of small calcium-binding proteins in nonclassical target tissues
M. R. Walters, M. E. Bruns, R. M. Carter and P. C. Riggle
Department of Physiology, Tulane Medical School, New Orleans, Louisiana 70112.
The presence and regulation of Ca-binding proteins (CaBPs) were
investigated in newly identified 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]
target tissues. 45Ca(2+)-blot analysis of proteins in normal rats yielded a
45Ca2+ band comigrating with authentic calmodulin. Additionally, a
parvalbumin-like band (mol mass = 15.4 +/- 0.3 kDa) was prominent in
prostate, and a strong unidentified 45Ca2+ band was always evident in the
testis (mol mass = 23.5 +/- 0.7 kDa). Lung, bladder, and especially
prostate demonstrated 45Ca2+ bands comigrating with the intestinal vitamin
D-related CaBP (CaBP-D9K; mol mass = 10.9 +/- 0.5 kDa). Most tissues
(including testis, heart, and lung) exhibited low levels of a 45Ca2+ band
comigrating with the renal CaBP-D28K (mol mass = 28.3 +/- 0.4 kDa).
Importantly, 45Ca2+ binding to all detectable CaBPs was unchanged in these
four tissues in vitamin D-deficient rats, despite substantial
downregulation of the intestinal CaBP-D9K and renal CaBP-D28K. Neither
immunoblot analysis (rabbit anti-rat renal CaBP-D28K) nor Northern analysis
(rat brain CaBP-D28K cDNA) provided evidence for coidentity of the 28-kDa
45Ca2+ band with the CaBP-D28K. Conversely, immunoblot analysis of lung,
but not prostate, cytosol provided evidence for specific
immunocross-reactivity to rabbit anti-rat intestinal CaBP-D9K. Immunoblot
analysis of the 9-kDa CaBP in lung further confirmed its vitamin D
independence. In conclusion, the vitamin D independence of the CaBPs in
these putative new 1,25(OH)2D3 targets suggests the absence of an
obligatory relationship between 1,25(OH)2D3 effects and CaBP induction
therein.(ABSTRACT TRUNCATED AT 250 WORDS)
