[Compartmentalization dynamics of the epidermal growth factor in A431 cells]

Dynamics of compartmentalization of epidermal growth factor (EGF) in human carcinoma A431 cells during the first hour after initiation of endocytosis was examined by methods of the organelle fractionation on a 20% Percoll gradient and of the microfluorimetric visualization of endocytosis of rhodamine-labeled EGF (EGF-R). EGF was revealed in small vesicles localized in the peripheral region of cytoplasm in a few minutes after endocytosis initiation. During centrifugation in Percoll these vesicles (endosomes), with an average density of 1.038 g/ml, were seen co-sedimented with Golgi membranes. By one hour after initiation of endocytosis, EGF-R was accumulated in perinuclear zone, in a trans-Golgi region, as numerous big luminous centres that were apparently MB-endosomes and had the same density in Percoll as did small peripheral endosomes. Such centres appeared in several cells already within 5-10 minutes. In A431 cells EGF did not reach lysosomes within 60 minutes, because no accumulation of 125I-EGF was shown in lysosome corresponding regions of Percoll gradient (average density 1.070 g/ml).