Calbindin-D9K Gene Expression in the Lung of the Rat. Absence of Regulation by 1,25-dihydroxyvitamin D3 and Estrogen

Calbindin-D9K (CaBP9K) is classically considered to be the molecular expression of 1,25-dihydroxyvitamin D3. The hormone is known to regulate the rat CaBP9K gene in duodenal tissue at transcriptional and posttranscriptional levels. This study shows that the CaBP9K gene is expressed in the rat lung, and that this expression is probably not vitamin D- or estrogen-dependent. The CaBP9K gene is not expressed in alveolar macrophages, but CaBP9K messenger RNA (mRNA) was localized by in situ hybridization in alveolar epithelial cells. CaBP9K mRNA was detected as early as the 20th day of gestation. The quantity of CaBP9K mRNA gradually increased during growth, from 1-77 days after birth, whereas the CaBP9K concentration dramatically increased from day 19 to day 20 of gestation. Vitamin D-deficient male rats (8 weeks old) were given a single injection of 1,25-dihydroxyvitamin D3 (650 pmol/100 g body wt) and killed 1 h and 24 h after injection. The hormonal treatment resulted in a rise in duodenal CaBP9K mRNA, but no significant change in lung extracted CaBP9K mRNA. Mature ovariectomized rats were injected with 17 beta-estradiol (0.5 microgram/100 g body wt) and killed 24, 48, and 72 h later. The CaBP9K mRNA concentration in the uterus was markedly dependent on estrogen; that of the lung was not. The factors regulating the CaBP9K gene expression in the lung remain to be determined.