Plasma vitamin D-binding protein (Gc-globulin): multiple tasks.
The transporter of vitamin D and its metabolites in blood has received increasing attention in recent years, and is recognized to be a member of a gene family that includes albumin and alpha-fetoprotein. Identical to the group specific component (Gc-globulin) of serum, the protein is a single-chain polypeptide constitutively synthesized in liver that circulates in amounts in far excess of normal vitamin D metabolite concentrations in blood. It plays the major role in the egress of endogenously synthesized vitamin D, from skin and appears to restrain D-sterols from too rapid/excessive cell entry. Along with plasma gelsolin, it comprises the plasma actin-scavenger system that facilitates removal of actin, liberated from lysed cells, by depolymerization and prevention of polymerization. Recently, the protein has been shown to behave as a co-chemotaxin specific for the complement peptide C5a, and its sialic acid-free form has been reported to play a role in macrophage activation. The latter functions strongly implicate its participation in inflammation responses. A unifying hypothesis might also suggest the protein to provide focal D-sterol delivery to cells that are important to the resolution of tissue injuries.
Haddad
J G
JG
University of Pennsylvania School of Medicine, Division of Endocrinology, Diabetes and Metabolism, Philadelphia 19104-6149, USA.
D000199:Actins / Q000378:metabolism; D000818:Animals; D002451:Cell Compartmentation; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism; D014018:Tissue Distribution; D014807:Vitamin D / Q000502:physiology*; D014809:Vitamin D-Binding Protein / Q000502:physiology*
D000199:Actins; D008840:Microfilament Proteins; D014809:Vitamin D-Binding Protein; D014807:Vitamin D