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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
POSTER ABSTRACTSHep G2 Catabolism of a and a' Subunits, from 7S Soy Globulin, is Correlated with their Up-Regulation of LDL- Receptors
Manzoni C., Lovati M.R., Gianazza E. and Sirtori C.R.
Institute of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133 Milan, Italy
The catabolism of isolated soy globulins, added to the culture medium of human hepatoma cells (Hep G2), was analyzed by two-dimensional electrophoresis. In parallel, the ability of the a and a' subunits from 7S soy globulin, versus the whole 7S and 11S globulins, to up-regulate lipoprotein uptake and degradation in the same cell line was investigated. This experiment was carried out in an attempt to identify peptide components responsible for the enhanced expression of LDL-receptors following 24h incubation with soy globulins (Lovati et al., J Nutr 122, 1971, 1992; Lovati et al. 1996 in press). After addition of the globulins, simple protein staining did not show marked changes in the overall pattern of cellular extracts. With immunodetection, intact 7S components were observed, both free in the culture medium and bound to the cell surface; inside the cells, the a + a' subunits in their native forms disappeared completely, whereas most of the B chains was unaffected or barely reduced in size. Conversely, largely unmodified soybean proteins were detected in a lysate of 11 S globulin-treated cells. Incubation of Hep G2 cells with purified a + a' from 7S markedly increased uptake and degradation of 125I-LDL, added to the culture medium, whereas the B chains were ineffective; 7S globulin itself was more active than 11S in this assay. It is suggested that the ability to cause a specific biological effect should be produced by peptides arising by proteolysis and this correlates in fact, in our test system, with the kinetics and/or the extent of the catabolism of individual components within the cells. Further studies should assess whether this process occurs 'in vivo' and is responsible of LDL-receptor modulation as previously shown in blood monocytes of hypercholesterolemic type II patients, after soy protein diet.
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