Vitamin D3 differentially regulates parathyroid hormone/parathyroid hormone-related peptide receptor expression in bone and cartilage
Norio Amizuka, … , Hidehiro Ozawa, John H. White
Norio Amizuka, … , Hidehiro Ozawa, John H. White
Published February 1, 1999
Citation Information: J Clin Invest. 1999;103(3):373-381. https://doi.org/10.1172/JCI3265.
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Article

Vitamin D3 differentially regulates parathyroid hormone/parathyroid hormone-related peptide receptor expression in bone and cartilage

Abstract

Transcription of the mouse parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR) gene is controlled by promoters P1 and P2. We performed transcript-specific in situ hybridization and found that P2 is the predominant promoter controlling PTHR gene expression in bone and cartilage. Treatment with 1α,25-dihydroxyvitamin D3 (D3) in vivo specifically downregulated P2-specific transcripts in osteoblasts, but not in chondrocytes, under conditions where it enhanced bone resorption. Treatment of the osteoblastic cell line MC3T3-E1 with D3 in vitro reduced expression of both P2-specific transcripts and PTHR protein. This effect was not blocked by cycloheximide, indicating that D3 inhibits PTHR expression by downregulating transcription of the P2 promoter. A similar inhibitory effect of D3 was not observed in the chondrocytic cell line CFK2. Gene-transfer experiments showed that P2, but not P1, is active in both MC3T3-E1 and CFK2 cells, and that D3 specifically inhibited P2 promoter activity in MC3T3-E1, but not in CFK2 cells. Inhibition of P2 activity by D3 required promoter sequences lying more that 1.6 kb upstream of the P2 transcription start site. Thus, the P2 promoter controls PTHR gene expression in both osteoblasts and chondrocytes. D3 downregulates PTHR gene transcription in a cell-specific manner by inhibiting P2 promoter activity in osteoblasts, but not in chondrocytes.

Authors

Norio Amizuka, Mei Yee Kwan, David Goltzman, Hidehiro Ozawa, John H. White

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Figure 2

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Downregulation of PTHR gene expression in vivo and in vitro by D3. Expre...
Downregulation of PTHR gene expression in vivo and in vitro by D3. Expression of the PTHR gene (a) was detected by RT-PCR as described in Methods. At 25 cycles of amplification, PCR products in control (–) MC3T3-E1 cells and in tibiae are more abundant than those observed after D3 treatment (+). At 40 cycles of amplification, no differences were observed between the PTHR PCR products obtained from control and D3-treated cells. RT-PCR for GAPDH at 20 cycles revealed the same level of gene expression from both control and D3-treated MC3T3-E1 cells and mouse tibiae (b). Arrows in a and b denote the positions of the PCR products of the PTHR and GAPDH genes respectively. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; PTHR, parathyroid hormone receptor; RT, reverse transcription.