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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
POSTER ABSTRACTS7S Globulin from Soybean is Metabo-lized in Human Cell Cultures by a Specific Uptake and Degradation System
Lovati MR., Manzoni C. and Sirtori C.R.
Institute of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133 Milan, Italy
In previous reports (Lovati et al., J Nutr 122, 1971, 1992: Lovati et al. 1996 in press), we described the stimulatory effect of 7S one of the major storage globulins from soybean, on the low density lipoprotein (LDL)-receptor mediated pathway in cell cultures. We have now examined the biological fate of the 7S globulin in hepatoma cell line (Hep G2) and in human skin fibroblasts (HSF) to gain further insights into the 7S globulin cell processing, the final effect of which appears to be an enhanced expression of LDL-receptors. The ability of 7S globulin to bind, be internalized and degraded by both cell types was investigated in different experimental conditions. In all cases, specific uptake (binding +internalization) and degradation of the 125 I-7S globulin were curvilinear functions of substrate concentrations at 37oC. The two processes were saturated at a concentration around 80 m g/ml, at which an up-regulation of LDL-receptor has been previously described. The specific uptake of the 125 I-7S globulin at 37oC was a curvilinear function of time, and reached equilibrium after 6 and 12 h in HSF and Hep G2, respectively. Binding experiments, carried out at 4oC in Hep G2 cells, showed a specific and saturable association of the 7S globulin to the membrane. Linear Scatchard analysis demonstrated a single population of binding sites. The amount of 7S globulin bound at saturation (Bmax) is about 2.73 mg/ml with a apparent Kd of 21 mM, assuming 175 kDa for 7S globulin MW. SDS-PAGE of Hep G2 membrane proteins incubated with 125I-7S globulin revealed a specific interaction of 7S globulin with cell protein component/s with MW between 14 and 21kDa. Further studies should therefore be done, to ascertain whether this interaction is directly or indirectly related to the observed stimulation of the LDL-receptors.
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