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Down‐regulation of Ca 2+ ‐Activated K + Channel K Ca 3.1 in mouse preosteoblast cells treated with vitamin D receptor agonists
Author(s) -
Kito Hiroaki,
Endo Kyoko,
kajikuri Junko,
Ohya Susumu
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.01964
Subject(s) - calcitriol receptor , chemistry , calcitriol , medicine , endocrinology , microbiology and biotechnology , bone tissue , trpv6 , calcium metabolism , calcium , receptor , vitamin d and neurology , biology , biochemistry , anatomy , organic chemistry
Background Bone tissue is a dynamic and living organ, constantly renewed through the process of bone remodeling. The intricate balance between bone‐forming and bone‐resorbing activity is vital for maintenance of bone homeostasis. Vitamin D (VD) plays pivotal roles in calcium homeostasis, mineral metabolism, and bone development indirectly via control calcium absorption in the intestine and reabsorption in the kidney. However, several in vitro studies showed that VD can directly suppress the cell proliferation of mouse osteoblasts. The direct effect of VD receptor (VDR) in osteoblasts is poorly understood. The intermediate‐conductance Ca 2+ ‐activated K + channel K Ca 3.1 regulates intracellular Ca 2+ signaling and is associated with cell proliferation in various non‐excitable cells including preosteoblasts. In this study, we examined the effects of treatments with VDR agonists on the expression and activity of K Ca 3.1 in mouse preosteoblast MC3T3‐E1 cells. Methods Intracellular Ca 2+ changes were measured in MC3T3‐E1 cells by Ca 2+ indicator, fura‐2/AM. Cell viability was measured by a WST‐1 assay. MC3T3‐E1 cells were transiently transfected with HDAC2, Fra‐1, and VDR Silencer Select pre‐designed siRNAs using a Lipofectamine RNAiMAX reagent. The Silencer Select negative control No.1 siRNA was used as a control. Results Treatments with calcitriol, a VDR agonist, for 48 h markedly decreased the expression levels of K Ca 3.1 transcripts and proteins in MC3T3‐E1 cells, resulting in the significant inhibition of Ca 2+ rises induced by DCEBIO, a specific K Ca 3.1 activator. Treatments with calcitriol also significantly decreased the expression of several transcriptional regulators of K Ca 3.1 such as histone deacetylase 2 (HDAC2) and Fra‐1 composed of activation protein 1. In addition, the pharmacological blockade of HDAC with vorinostat, a pan‐HDAC inhibitor, significantly decreased the expression of K Ca 3.1. The knockdown of Fra‐1 using siRNA decreased the expression of K Ca 3.1 mRNA without the suppression of HDAC2 mRNA. The knockdown of VDR also recovered the expression of K Ca 3.1, HDAC2 and Fra‐1 in calcitriol‐treated MC3T3‐E1 cells. Conclusion Our results suggest that K Ca 3.1 is a new downstream target of VDR signaling and the down‐regulation of K Ca 3.1 through the transcriptional repression of K Ca 3.1 contribute, at least partly, to the antiproliferative effects of VDR agonists in mouse pre‐osteoblasts.