Molecular mechanism of regulation of the calcium‐binding protein calbindin‐D 9k ,and its physiological role(s) in mammals: a review of current research

•  Introduction •  Phenotype of CaBP‐9k knockout mouse •  Uterine expression and regulation of CaBP‐9k •  Placental expression and regulation of CaBP‐9k•  Duodenal and renal expression and regulation of CaBP‐9k •  Pituitary expression and regulation of CaBP‐9k •  Transcriptional regulation of CaBP‐9k •  ConclusionsAbstract Calbindin‐D 9k (CaBP‐9k) is a cytosolic calcium‐binding protein that is expressed in a variety of tissues, such as uterus, placenta, intestine, kidney, pituitary gland and bone. At present, the precise role(s) of CaBP‐9k remains to be clarified. CaBP‐9k‐null mice are normal, which indicates that other calcium‐transporter genes can compensate for the lack CaBP‐9k. Uterine CaBP‐9k has been shown to be involved in the regulation of myometrial activity by intracellular calcium. In the uterus and placenta, CaBP‐9k expression is regulated by the sex steroid hormones oestrogen (E2) and progesterone (P4). Intestinal CaBP‐9k is involved in intestinal calcium absorption, and is regulated at the transcriptional and post‐transcriptional levels by 1,25‐dihydroxyvitamin D3, the hormonal form of vitamin D. Thus, evidence to date suggests that CaBP‐9k may be regulated in a tissue‐specific manner. In this review, we will summarize current data on the molecular mechanism of regulation of CaBP‐9k in mammals, including recent research data generated in our laboratories.