K. Page et al., Characterization of a rac1 signaling pathway to cyclin D-1 expression in airway smooth muscle cells, J BIOL CHEM, 274(31), 1999, pp. 22065-22071
We examined the importance of the Rho family GTPase Rad for cyclin D-1 prom
oter transcriptional activation in bovine tracheal myocytes. Overexpression
of active Rad induced transcription from the cyclin D-1 promoter, whereas
platelet-derived growth factor (PDGF)-induced transcription was inhibited b
y a dominant-negative allele of Rad, suggesting that Rad functions as an up
stream activator of cyclin D-1 in this system. Rad forms part of the NADPH
oxidase complex that generates reactive oxygen species such as H2O2. PDGF s
timulated a substantial increase in intracellular reactive oxygen species,
as measured by the fluorescence of dichlorofluorescein-loaded cells, and th
is was blocked by the glutathione peroxidase mimetic ebselen. Pretreatment
with ebselen, catalase, and the flavoprotein inhibitor diphenylene iodonium
each attenuated PDGF- and Rac1-mediated cyclin D-1 promoter activation, wh
ile having no effect on the induction of cyclin D-1 by mitogen-activated pr
otein kinase/extracellular signal-regulated kinase (ERK) kinase-1 (MEK1), t
he upstream activator of ERKs. Antioxidant treatment also inhibited PDGF-in
duced cyclin D-1 protein expression and DNA synthesis. Overexpression of an
N-terminal fragment of p67(phox), a component of NADPH oxidase which inter
acts with Rad, attenuated PDGF-indueed cyclin D-1 promoter activity, wherea
s overexpression of the wild-type p67 did not. Finally, Rad was neither req
uired nor sufficient for ERK activation. Taken together, these data suggest
a model by which two distinct signaling pathways, the ERK and Rad pathways
, positively regulate cyclin D-1 and smooth muscle growth.