Studies on the action of apoptosis inducing factor derived from bovine colostrum

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We found a cell-growth inhibiting factor in partially purified fraction from bovine colostrum using an ion-exchange chromatography. The factor induced apoptosis in mouse LM fibroblasts. It is well known that bovine colostrum contains IGF-I,so we measured IGF-I concentrations of the fraction. The fraction contained about 500ng/mg protein of IGF-I.Then, effects of IGF-I on cell proliferation were determined using three cell lines, LM,L6, and Balb/c 3T3 cells. To our surprise, IGF-I induced cell death of LM cells, while it stimulated proliferation of L6 and Balb/c 3T3 cells in low FCS condition. Herbimycin A,a tyrosine kinase inhibitor, inhibited cell death induced by IGF-I in LM cells.These data suggests that IGF-I induces cell death of LM cells and the action involves activation of tyrosine kinase.