Immunoselection of cDNAs to avian intestinal calcium binding protein 28K and a novel calmodulin-like protein: assessment of mRNA regulation by the vitamin D hormone.

Calcium's role in a variety of cellular processes has been well documented. The storage, distribution, and delivery of calcium are regulated by a family of binding proteins including troponin C, calmodulin, parvalbumin, and vitamin D dependent calcium binding protein (CaBP-28), all of which have evolved from a common ancestral gene. To evaluate vitamin D regulation of gene transcription, a CaBP-28 cDNA (767 base pairs) was isolated from a chicken intestine lambda gt11 library utilizing a polyvalent CaBP-28 antibody as a probe. Coincident with the identification of the CaBP-28 cDNA, a group of cDNAs also was isolated (with the anti-CaBP-28 antibody) that demonstrated 84% nucleotide homology and 99% deduced amino acid homology with chicken brain calmodulin (CaM). This new CaM-like cDNA was named neoCaM. There is little nucleotide homology between the CaBP-28 cDNA and neoCaM. The CaBP-28 cDNA hybridizes with three transcripts of 2000, 2900, and 3300 bases which are dramatically induced by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], while the neoCaM cDNA recognizes three distinct (from CaBP-28) transcripts. Two of these mRNAs are 1400 and 1800 bases as described for brain CaM, but another larger 4000-base transcript is detected with neoCaM. Neither the CaM nor the neoCaM transcript reveals any modulation by 1,25(OH)2D3. Herein, we discuss the possible significance of not only the isolation of both cDNAs with a single antibody but also the relation of neoCaM to other well-characterized CaM cDNAs.

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