Calbindin28kDa and calmodulin are hyperabundant in XXXX dental enamel cells. Identification of the protein phosphatase calcineurin as a principal calmodulin target and of a secretion-related role for calbindin28kDa.

@entity14855 @entity1133 @entity1219 @entity460 @entity35 @entity214
Enamel cells are likely to experience heavy demands for intracellular @entity460 homeostasis during the secretion and hypermineralization of dental enamel. Here, the two major high-affinity @entity460 -binding proteins in @entity35 enamel epithelium were identified as calbindin28kDa and calmodulin, using a microscale approach. Both proteins were hyperabundant, totalling up to 2% of the soluble protein and surpassing the amounts in cerebellum, the benchmark tissue. Calbindin28kDa and calmodulin accounted for 26% of the total @entity460 -binding capacity in enamel cell cytosol, under near physiological conditions. Numerous calmodulin-binding proteins were detected with an overlay assay, indicating that calmodulin has multiple major targets in enamel cells. The @entity460 /calmodulin-regulated protein phosphatase, calcineurin, was identified as a principal calmodulin target constituting 0.1% of the soluble protein. Calmodulin and calcineurin were expressed constitutively, implying continued heavy usage of @entity460 /calmodulin-based and phosphorylation-based signalling events throughout enamel cell development. Calbindin28kDa, in contrast, was expressed at fourfold higher levels in secretion-phase cells than during the @entity460 -intensive hypermineralization phase, unexpectedly pointing to an important role associated with secretion. Supporting this notion, immunoblots revealed that 33% of total ( @entity214 -soluble) calbindin28kDa was in the particulate fraction and predominantly associated with the Triton-insoluble cytoskeleton. Solubilisation of cytoskeletal calbindin28kDa required high concentrations of @entity1219 or @entity1133 , indicating the existence of a high-affinity target ligand. The unusual abundance of calmodulin, calbindin28kDa and @entity14855 demonstrated here provides the first molecular evidence that enamal cells possess a strong capability for intracellular @entity460 homeostasis. Since none of these proteins was up-regulated during enamel hypermineralization, it appears that other @entity460 -binding proteins are primarily involved in the putative transcellular passage of @entity460 .
