Urokinase receptor primes cells to proliferate in response to epidermal growth factor.
Epidermal growth factor (EGF) expresses mitogenic activity by a mechanism that requires the EGF receptor (EGFR). We report that murine embryonic fibroblasts (MEFs) proliferate in response to EGF only when these cells express the urokinase receptor (uPAR). EGFR expression was equivalent in uPAR-/- and uPAR+/+ MEFs. In response to EGF, these cells demonstrated equivalent overall EGFR tyrosine phosphorylation and ERK/MAP kinase activation; however, phosphorylation of Tyr-845 in the EGFR, which has been implicated in cell growth, was substantially decreased in uPAR-/- MEFs. STAT5b activation also was decreased. As Tyr-845 is a c-Src target, we overexpressed c-Src in uPAR-/- MEFs and rescued EGF mitogenic activity. Rescue also was achieved by expressing murine but not human uPAR, suggesting a role for autocrine uPAR cell-signaling. In MDA-MB 231 breast cancer cells, EGF mitogenic activity was blocked by uPAR gene silencing, with antibodies that block uPA-binding to uPAR, and with a synthetic peptide that disrupts uPAR-dependent cell signaling. Again, c-Src overexpression rescued the mitogenic activity of EGF. We conclude that uPAR-dependent cell-signaling may prime cells to proliferate in response to EGF by promoting Tyr-845 phosphorylation and STAT5b activation. The importance of this pathway depends on the c-Src level in the cell.
Jo
M
M
Department of Pathology, University of California San Diego, La Jolla, CA, USA.
Thomas
K S
KS
Takimoto
S
S
Gaultier
A
A
Hsieh
E H
EH
Lester
R D
RD
Gonias
S L
SL
D000818:Animals; D019898:Autocrine Communication; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D010958:Plasminogen / Q000378:metabolism; D011485:Protein Binding; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000502:physiology*; D055293:Receptors, Urokinase Plasminogen Activator; D050799:STAT5 Transcription Factor / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
C524898:PLAUR protein, human; C524899:Plaur protein, mouse; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D050799:STAT5 Transcription Factor; C494095:STAT5B protein, human; D014443:Tyrosine; D004815:Epidermal Growth Factor; D010958:Plasminogen; D066246:ErbB Receptors; D016392:Proto-Oncogene Proteins pp60(c-src); D020928:Mitogen-Activated Protein Kinases; D014568:Urokinase-Type Plasminogen Activator