Regulation of intracellular protein degradation by insulin and growth factors.

Protein breakdown in many cell lines is inhibited by growth factors. The response is specific, rapid and additive only at suboptimal concentrations. Transformed cells are typically more sensitive to growth factors than nontransformed cells while the effectiveness of growth factors in human fibroblasts is diminished with senescence. Bovine colostrum has been shown to be an extremely rich source of growth factors as compared to serum.