Kinetic analysis of epidermal growth factor endocytosis in rat hepatocytes. Effects of diabetes.
In the present study we followed the different steps of epidermal growth factor receptor (EGF-R) endocytosis in freshly isolated rat hepatocytes. Hepatocytes exhibit two classes of surface EGF receptors consisting of approximately 5,000 high-affinity sites (Kd = 15 pM) and 166,000 low-affinity sites (Kd = 670 pM). Binding of labeled EGF to hepatocytes permeabilized by digitonin shows that 75% of the total EGF-R are localized at the cell surface. At 37 degrees C, hepatocytes continuously internalized and degraded EGF in spite of a down-regulation of cell surface receptors. The internalization rate constants measured as a function of a range 125I-EGF concentrations (0.01 - 5 nM) involving various degrees of EGF-R occupancy show superimposable curves. This indicates that the specific internalization rate of EGF-R complex is independent of receptor occupancy. Streptozotocin-induced diabetes reduces the number of low-affinity EGF-R to 50,000 and produces a complete loss of high-affinity sites. The dynamics of 125I-EGF endocytosis show that diabetic hepatocytes fail to down-regulate the surface EGF-R efficiently although the constant rate of internalization is not modified. Decreased down-regulation of EGF-R together with enhanced EGF endocytosis suggest a greater efficiency in EGF-R recycling in diabetic rat hepatocytes.
Dahmane
A
A
Laboratoire de Biochimie, Faculté de Pharmacie, Université Paris-Sud, Châtenay-Malabry, France.
Gil
S
S
Bréhier
A
A
Davy
J
J
Féger
J
J
D000818:Animals; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D015536:Down-Regulation; D004705:Endocytosis; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013311:Streptozocin
D007457:Iodine Radioisotopes; D013311:Streptozocin; D004815:Epidermal Growth Factor; D066246:ErbB Receptors