Down-regulation of L-type Ca2+ channel transcript levels by 1,25-dihyroxyvitamin D3. Osteoblastic cells express L-type alpha1C Ca2+ channel isoforms.
Osteoblast Ca2+ channels play a fundamental role in controlling intracellular and systemic Ca2+ homeostasis. A reverse transcription-polymerase chain reaction strategy was used to determine the molecular identity of voltage-sensitive calcium channels present in ROS 17/2.8 osteosarcoma cells. The amino acid sequences encoded by the two resultant PCR products matched the alpha1C-a and the alpha1C-d isoforms. The ability of 1, 25-dihydroxyvitamin D3 (1,25(OH)2D3) and structural analogs to modulate expression of voltage-sensitive calcium channel mRNA transcripts was then investigated. ROS 17/2.8 cells were cultured for 48 h in the presence of either 1,25(OH)2D3,1,24-dihydroxy-22-ene-24-cyclopropyl D3 (analog BT) or 25-hydroxy-16-ene-23-yne-D3 (analog AT), and the levels of mRNA encoding alpha1C were quantitated using a competitive reverse transcription-polymerase chain reaction assay. We found that 1, 25(OH)2D3 and analog BT reduced steady state levels of alpha1C mRNA. Conversely, the Ca2+-mobilizing analog AT did not alter steady state levels of voltage-sensitive calcium channel mRNA. Since analog BT, but not analog AT, binds and transcriptionally activates the nuclear receptor for 1,25(OH)2D3, these findings suggest that the down-regulation of voltage-sensitive calcium channel mRNA levels may involve the nuclear receptor.
Meszaros
J G
JG
Department of Basic Sciences, University of Texas Dental Branch, Houston, Texas 77030, USA. farachca@bite.db.uth.tmc.edu
Karin
N J
NJ
Akanbi
K
K
Farach-Carson
M C
MC
D000595:Amino Acid Sequence; D000818:Animals; D002117:Calcitriol / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000235:genetics*; D015536:Down-Regulation; D018507:Gene Expression Regulation, Developmental; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D012886:Skull / Q000378:metabolism; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D012333:RNA, Messenger; D002117:Calcitriol; D002118:Calcium