Pdgf receptor expression and differential proliferation induced by
pdgf isoforms in human cultured bronchial smooth muscle.
Hirst, Stuart J., Peter J. Barnes, and Charles H. C. Twort.
Respiratory Research Laboratories, UMDS Department of Allergy and
Respiratory Medicine, St. Thomas' Hospital, LONDON SE1 7EH, UK and
Department of Thoracic Medicine, Royal Brompton National Heart and
Lung Institute, LONDON SW3 6LY, UK
APStracts 2:0168L, 1995.
The effect of recombinant PDGF isoforms (PDGF-AA, -BB and -AB) on
mitogenesis of human cultured airway smooth muscle (ASM) was examined
using the MTT reduction assay and [3H]thymidine incorporation.
Results were correlated with expression of PDGF receptor (PDGFR)
[alpha] and [beta] subunits in the absence and presence of fetal calf
serum (FCS). When FCS was absent PDGF-AB and -BB were potent
mitogens, while PDGF-AA was weakly mitogenic, evoking <20% of
the maximum response induced by the B-chain isoforms. When FCS (2.5%)
was present, all PDGF isoforms stimulated marked ASM proliferation
with similar efficacy and potency. Cross-competition binding analysis
in FCS-deprived cells revealed that ASM cells in culture express
mainly PDGFR[beta]. Preincubation with PDGF-AA or PDGFR[alpha]
neutralising anti-serum abolished PDGF-AA binding and decreased total
receptor number by _15%. The ratio of PDGFR [alpha]:[beta] subunits
was _1:8, supported by intense immunofluorescence staining for
PDGFR[beta] and weak staining for PDGFR[alpha]. In parallel studies
uptake of [3H]thymidine stimulated by PDGF-AA, but not PDGF-AB or
-BB, was inhibited by PDGFR[alpha] immobilisation. Western immunoblot
analysis confirmed expression of mature PDGFR[alpha] and [beta]
subunits in ASM cells. FCS did not cause any detectable increase in
PDGFR[alpha] expression or in PDGF-AA binding. These data support a
role for PDGFR[beta] mediating ASM mitogenesis during FCS-free
conditions, but in the presence of FCS both PDGFR[alpha] and [beta]
subunits are linked to mitogenesis. The enhanced mitogenicity of
PDGF-AA in the presence of FCS was independent of any detectable up
-regulation of PDGFR[alpha], suggesting that the inability of PDGF-AA
to promote mitogenesis in the absence of FCS is not simply due to
relative numbers of PDGFR[alpha] and PDGFR[beta].
Received 17 April 1995; accepted in final form 14 September 1995.
APS Manuscript Number L119-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95