1,25-Dihydroxyvitamin D3 affects the synthesis, phosphorylation and in vitro calmodulin binding of myoblast cytoskeletal proteins.

Incubation of chick embryo myoblasts with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] (10(-10) M, 24 h), markedly stimulated the incorporation of [3H]leucine into total cytoskeletal proteins and this effect was abolished when the sterol treatment was performed in the presence of cycloheximide or actinomycin D. 1,25(OH)2D3 selectively stimulated the de novo synthesis of several proteins with apparent molecular masses (isoelectric points) of 220 kDa (6.1 and 9.7), 150 kDa (7.5), 110 kDa (7.2), 68 kDa (9.5, 7.5 and 4.5), 50 kDa (8.5), 44 kDa (6.3), 27 kDa (7.8) and 15 kDa (5.5). Labelling of proteins with [125I]calmodulin after their separation on SDS-polyacrylamide gels showed that 1,25(OH)2D3-dependent protein of 110 kDa is the major calmodulin-binding component of myoblasts cytoskeleton. In addition, the sterol increased the phosphorylation of several cytoskeletal proteins including that of 110 and 15 kDa whose synthesis potentiates.