Transcriptional regulation and chromosomal assignment of the mammalian calbindin-D28k gene

To determine whether 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] regulates transcription of the rat renal calbindin-D28k gene, the rate of calbindin-D28k mRNA synthesis was measured directly in nuclei using the in vitro nuclear transcription assay. Nuclei were prepared from kidneys of vitamin D-deficient rats at various times after a single ip injection of 1,25-(OH)2D3, and transcription was allowed to proceed in vitro in the presence of [32P]UTP for 30 min at 29 C, at which time the incorporation of UTP into trichloroacetic acid-precipitable material was optimal. Incorporation of UTP was decreased by 64.6% by alpha-amanitin, which selectively inhibits polymerase II. Purified [32P]RNA was analyzed for newly synthesized calbindin-D-28k gene transcripts by hybridization to calbindin-D28k cDNA immobilized on nitrocellulose filters. Using this assay we found that the first significant increase in calbindin-D28k gene transcription occurred at 1 h, and the peak of transcriptional activity occurred at 2 h. Within 12 h of 1,25-(OH)2D3 treatment, calbindin-D28k gene transcription returned to control levels. Using Northern blot analysis, a significant increase in calbindin-D RNA was first observed 2 h after hormone administration, reaching a maximum at 12 h. Renal calbindin-D28k protein levels are significantly increased by 3 h and reach a maximum value 48 h after hormone administration. Our results suggest that the early increase in renal calbindin-D28k may be due to transcriptional regulation. The long time lag between transcription and the peak of calbindin mRNA and calbindin protein accumulation may reflect the involvement of post-transcriptional mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)