Ay. Karpova et al., MEK1 IS REQUIRED FOR PDGF-INDUCED ERK ACTIVATION AND DNA-SYNTHESIS INTRACHEAL MYOCYTES, American journal of physiology. Lung cellular and molecular physiology, 16(3), 1997, pp. 558-565
We tested whether activation of mitogen-activated protein kinase/extra
cellular signal-regulated kinase kinase-1 (MEK1) is required and suffi
cient for extracellular signal-regulated kinase (ERK) activation in ai
rway smooth muscle cells. First, we transiently cotransfected bovine t
racheal myocytes with an epitope-tagged ERK2 and a dominant-negative o
r a constitutively active form of the gene encoding MEK1 and assessed
ERK2 activation by in vitro phosphorylation assay. Expression of the d
ominant-negative MEK1 inhibited platelet-derived growth factor (PDGF)-
induced ERK2 activation, whereas expression of the constitutively acti
ve MEK1 induced ERK2 activation, suggesting that MEK1 is required and
sufficient for ERK activation in these cells. Next, we assessed the ef
fect of PD-98059, a synthetic MEK inhibitor, on PDGF-induced MEK1 and
ERK activation. PD-98059 (10 mu M) inhibited MEK1 and ERK activation,
confirming that MEK1 is required for ERK activation in bovine tracheal
myocytes. PD-98059 had no effect on Src or Raf-1 activity, evidence t
hat PD-98059 is a specific inhibitor of MEK in this system. Finally, P
D-98059 reduced PDGF-induced [H-3]thymidine incorporation in a concent
ration-dependent manner, suggesting that catalytic activation of MEK1
and ERKs is required for DNA synthesis. We conclude that MEK1 is requi
red for PDGF-induced ERK activation in bovine tracheal myocytes and th
at MEK1 and ERKs are required for PDGF-induced DNA synthesis in these
cells.