Endocytosed epidermal growth factor (EGF) receptors contribute to the EGF-mediated growth arrest in A431 cells by inducing a sustained increase in p21/CIP1.
We investigated the ability of endocytosed activated epidermal growth factor receptors (EGFR) to induce expression of the cyclin-interacting protein p21/CIP1 in A431 cells. Transforming growth factor alpha (TGFalpha) and EGF both induced tyrosine phosphorylation, induction of p21/CIP1, and thereby inhibition of DNA synthesis. TGFalpha is released from the EGFR when the TGFalpha-EGFR complex encounters low pH upon endocytosis. Consistently, we found more rapid dephosphorylation of the EGFR and less induction of p21/CIP1 by TGFalpha than by EGF. This difference was abolished upon neutralizing endosomal pH by the carboxylic ionophore monensin or the proton ATPase inhibitor bafilomycin A1. When surface-bound TGFalpha was removed by acid stripping and endosomal pH was neutralized with bafilomycin A1, TGFalpha stimulated EGFR tyrosine phosphorylation, induced p21/CIP1, and inhibited DNA synthesis. This strongly suggests that p21/CIP1 can be induced by endocytosed, activated EGFR and that endocytosed EGFR can affect cell growth.
The National Hospital, The University of Oslo, Oslo, 0027, Norway.
E
E
Skarpen
L E
LE
Johannessen
K
K
Bjerk
H
H
Fasteng
T K
TK
Guren
B
B
Lindeman
G H
GH
Thoresen
T
T
Christoffersen
E
E
Stang
H S
HS
Huitfeldt
I H
IH
Madshus
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis; D004705:Endocytosis; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018942:Macrolides; D008856:Microscopy, Fluorescence; D008985:Monensin / Q000494:pharmacology; D010766:Phosphorylation; D013997:Time Factors; D016211:Transforming Growth Factor alpha / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000900:Anti-Bacterial Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D018942:Macrolides; D016211:Transforming Growth Factor alpha; D004815:Epidermal Growth Factor; C040929:bafilomycin A1; D004247:DNA; D008985:Monensin; D066246:ErbB Receptors; D017871:Calcium-Calmodulin-Dependent Protein Kinases