p160 Bcr mediates platelet-derived growth factor activation of extracellular signal-regulated kinase in vascular smooth muscle cells.
BACKGROUND
The human Bcr gene was originally identified by its presence in the chimeric Bcr/Abl oncogene, which is causative for chronic myeloblastic leukemia. Because Bcr encodes a serine/threonine protein kinase, we studied its kinase activity and determined the role of Bcr in the PDGF signaling pathway to ERK1/2 activation and DNA synthesis in rat aortic smooth muscle cells (RASMCs).


RESULTS
In RASMCs, platelet-derived growth factor-BB (PDGF) stimulated Bcr kinase activity, with a maximum at 1 minute. Because phosphatidylinositol 3'-kinase (PI3-K) is essential for Bcr/Abl leukemogenesis, we evaluated the role of mouse PDGF-beta-receptor binding sites for PI3-K (Y708, Y719) and for phospholipase C-gamma (Y977, Y989) in PDGF-mediated Bcr kinase activation. The mutant PDGF receptor Y708F/Y719F but not Y977F/Y989F showed significantly reduced Bcr kinase activity. To determine the role of Bcr in PDGF-mediated signal transduction events leading to ERK1/2 and its downstream Elk1 transcription activation, wild-type (WT) and kinase-negative (KN) Bcr were transiently expressed in RASMCs. Bcr WT enhanced, whereas Bcr KN inhibited, PDGF-stimulated ERK1/2 and Elk1 transcriptional activity. Overexpression of Bcr also enhanced PDGF-induced Ras/Raf-1 activity and DNA synthesis, but this regulation is independent of the kinase activity of Bcr. Finally, we found that Bcr expression was increased in the neointimal layer after balloon injury of rat carotid artery.


CONCLUSIONS
These results demonstrated the importance of Bcr in PDGF-mediated events, such as activation of Ras, Raf-1, ERK1/2, and Elk1, and stimulation of DNA synthesis.
Che
W
W
Center for Cardiovascular Research, University of Rochester, Rochester, NY, USA.
Abe
J
J
Yoshizumi
M
M
Huang
Q
Q
Glassman
M
M
Ohta
S
S
Melaragno
M G
MG
Poppa
V
V
Yan
C
C
Lerner-Marmarosh
N
N
Zhang
C
C
Wu
Y
Y
Arlinghaus
R
R
Berk
B C
BC
D000818:Animals; D001011:Aorta; D016466:CHO Cells; D002339:Carotid Arteries / Q000378:metabolism; D002478:Cells, Cultured; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051562:Proto-Oncogene Proteins c-bcr; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D017479:Receptors, Platelet-Derived Growth Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D017539:Tunica Intima / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
D015513:Oncogene Proteins; D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D004247:DNA; D011505:Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor; C496613:BCR protein, human; D051562:Proto-Oncogene Proteins c-bcr; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins