[The endocytosis of the epidermal growth factor (EGF) in EGF-dependent cells of the HC11 mouse mammary epithelium line].

Mouse epithelial mammary cell line HC11, expressing about 30 thousands receptors for epidermal growth factor (EGF) per cell, is a physiological target for this growth factor. It is found that EGF behaves as a strong mitogen for HC11 cells: EGF (10 ng/ml) produced more than a 6-fold increase in 14C-thymidine incorporation into DNA of the cells, while 10% serum stimulated only a 2.5-fold increase, compared to control. It was shown that about 60-80% of surface-bound 125I-EGF were internalized within the first 5 min upon stimulation of endocytosis, regardless of cultivation conditions. However, the serum and EGF affected on later steps of endocytosis in different way. A prolonged presence of EGF in the growth medium before the experiment led lo a significant increase in transition of internalized 125I-EGF from light to heavy endosomes. At the same time, I 0 % serum caused a dramatic decrease if the rate of 125I-EGF degradation, which was resulted in accumulation of un-degraded growth factor in lysosomes. However, serum did not influence the earlier steps of endocytosis. A conclusion has been made that it is the efficiency of EGF transition from light to heavy endosomes (which means sorting of EGF-receptor complexes for degradative pathway) that is regulated by EGF-dependent manner in HC11 cells.