Current understanding of the molecular actions of vitamin D.
The important reactions that occur to the vitamin D molecule and the important reactions involved in the expression of the final active form of vitamin D are reviewed in a critical manner. After an overview of the metabolism of vitamin D to its active form and to its metabolic degradation products, the molecular understanding of the 1alpha-hydroxylation reaction and the 24-hydroxylation reaction of the vitamin D hormone is presented. Furthermore, the role of vitamin D in maintenance of serum calcium is reviewed at the physiological level and at the molecular level whenever possible. Of particular importance is the regulation of the parathyroid gland by the vitamin D hormone. A third section describes the known molecular events involved in the action of 1alpha,25-dihydroxyvitamin D3 on its target cells. This includes reviewing what is now known concerning the overall mechanism of transcriptional regulation by vitamin D. It describes the vitamin D receptors that have been cloned and identified and describes the coactivators and retinoid X receptors required for the function of vitamin D in its genomic actions. The presence of receptor in previously uncharted target organs of vitamin D action has led to a study of the possible function of vitamin D in these organs. A good example of a new function described for 1alpha,25-dihydroxyvitamin D3 is that found in the parathyroid gland. This is also true for the role of vitamin D hormone in skin, the immune system, a possible role in the pancreas, i.e., in the islet cells, and a possible role in female reproduction. This review also raises the intriguing question of whether vitamin D plays an important role in embryonic development, since vitamin D deficiency does not prohibit development, nor does vitamin D receptor knockout. The final section reviews some interesting analogs of the vitamin D hormone and their possible uses. The review ends with possible ideas with regard to future directions of vitamin D drug design.
Jones
G
G
Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
Strugnell
S A
SA
DeLuca
H F
HF
D000595:Amino Acid Sequence; D000818:Animals; D002116:Calcitonin / Q000502:physiology; D002118:Calcium / Q000502:physiology; D015195:Drug Design; D006801:Humans; D006900:Hydroxylation; D008969:Molecular Sequence Data; D010280:Parathyroid Glands / Q000502:physiology; D018167:Receptors, Calcitriol / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000502:physiology; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000502:physiology; D014807:Vitamin D / Q000378:metabolism / Q000502:physiology*
D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014807:Vitamin D; D002116:Calcitonin; D002118:Calcium