Partial purification and characterization of a growth factor present in goat's colostrum. Similarities with platelet-derived growth factor

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Abstract
A factor in goat''s colostrum which stimulates DNA synthesis and cell proliferation in Swiss 3T3 fibroblasts was purified .apprx. 350-fold by a sequence of acid precipitation, cation-exchange chromatography and gel filtration. The growth factor is a highly basic, heat stable (100.degree. C for 5 min) polypeptide with MW .apprx. 35,000. The polypeptide resists denaturation by guanidinium chloride or urea but is totally inactivated by treatment with reducing agents. The factor, which is termed colostric basis growth factor (CBGF), inhibits the binding of 125I-labeled epidermal growth factor (125I-EGF) to Swiss 3T3 fibroblasts but does not inhibit 125I-EGF binding to epidermoid A431 [human carcinoma] cells. CBGF interacts synergistically with plasma in stimulating DNA synthesis in quiescent Swiss 3T3 cells. The chemical and biological properties of CBGF are thus very similar to the properties reported for the human platelet-derived growth factor. Although high concentrations of CBGF are present in the colostrum of goats, cows, and sheep, the milk of these species contains little or no factor. The origin and possible functions of CBGF are unknown.