| Abstract: | The effect of proteasomal activity suppression induced by MG132, a synthetic proteasomal inhibitor of EGF-receptor complexes endocytosis in human epidermoid carcinoma A431 cell line, was studied. Using subcellular fractionation in 17% Percoll gradient, it was demonstrated that the addition of MG132 to the cells 15 min following stimulation of EGF endocytosis resulted in a slight accumulation of 125I-EGF in early endosomes, and in much more significant accumulation of the labeled growth factor in late endosomes/lysosomes, as compared to untreated cells. The release of 125I-EGF degradation products into the incubation medium was significantly (3-12-fold) inhibited in the presence of MG132. At the same time biochemical analysis has demonstrated that the EGF receptor itself is not a direct target of proteasomes, since it is revealed as a full-length protein with native mol. mass (170 kDa) in fractions of early and late endosomes and lysosomes. Possible mechanisms of the MG132 effect on intracellular processing of EGF-receptor complexes are discussed. |
