Phorbol esters induce transient internalization without degradation of unoccupied epidermal growth factor receptors.
4 beta-Phorbol 12-myristate 13-acetate (PMA) treatment of KB cells at 37 degrees C rapidly induces a 50% reduction in epidermal growth factor (EGF) binding that is maximal by 30 min. EGF binding activity returns to the original value by 1 hr and remains constant for 2 hr thereafter. Using a polyclonal antibody directed against the cytoplasmic domain of the EGF receptor (EGF-R), we examined the fate of the receptor after PMA treatment. Immunofluorescent and electron microscopic localization of the EGF-R after PMA treatment demonstrated that about 50% of the receptor became internalized into endocytic vesicles (receptosomes) and Golgi-associated structures. Unlike EGF-induced internalization, PMA-induced internalization did not cause delivery of EGF-R to lysosomes or receptor degradation. Rather, receptor reappeared on the cell surface. No stimulation of EGF-R synthesis was observed after 1 hr of PMA treatment. Loss of cell surface binding correlated with the internalization of the EGF-R observed morphologically. A possible explanation for these observations is that PMA, an activator of protein kinase C, confers a signal sufficient for EGF-R clustering and internalization but not for transport to lysosomes.
Beguinot
L
L
Hanover
J A
JA
Ito
S
S
Richert
N D
ND
Willingham
M C
MC
Pastan
I
I
D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors; D006056:Golgi Apparatus / Q000378:metabolism; D006651:Histocytochemistry; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D010704:Phorbols; D011956:Receptors, Cell Surface; D004815:Epidermal Growth Factor; D011494:Protein Kinases; D066246:ErbB Receptors; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate