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v
3 Integrin to Promote
Epidermal Growth Factor Receptor Phosphorylation and Growth
Division of Cardiovascular Research, Research Institute, The Hospital for Sick Children and Departments of Pediatrics,
Pathology, and Medicine, University of Toronto, Toronto, Ontario, Canada M5G 1X8
Tenascin-C (TN-C) is induced in pulmonary
vascular disease, where it colocalizes with proliferating
smooth muscle cells (SMCs) and epidermal growth factor (EGF). Furthermore, cultured SMCs require TN-C
for EGF-dependent growth on type I collagen. In this study, we explore the regulation and function of TN-C
in SMCs. We show that a matix metalloproteinase
(MMP) inhibitor (GM6001) suppresses SMC TN-C
expression on native collagen, whereas denatured collagen promotes TN-C expression in a
3 integrin-
dependent manner, independent of MMPs. Floating
type I collagen gel also suppresses SMC MMP activity
and TN-C protein synthesis and induces apoptosis, in
the presence of EGF. Addition of exogenous TN-C to
SMCs on floating collagen, or to SMCs treated with
GM6001, restores the EGF growth response and "rescues" cells from apoptosis. The mechanism by which
TN-C facilitates EGF-dependent survival and growth
was then investigated. We show that TN-C interactions with
v
3 integrins modify SMC shape, and EGF-
dependent growth. These features are associated with
redistribution of filamentous actin to focal adhesion
complexes, which colocalize with clusters of EGF-Rs,
tyrosine-phosphorylated proteins, and increased activation of EGF-Rs after addition of EGF. Cross-linking
SMC
3 integrins replicates the effect of TN-C on
EGF-R clustering and tyrosine phosphorylation. Together, these studies represent a functional paradigm
for ECM-dependent cell survival whereby MMPs upregulate TN-C by generating
3 integrin ligands in type
I collagen. In turn,
v
3 interactions with TN-C alter
SMC shape and increase EGF-R clustering and EGF-dependent growth. Conversely, suppression of MMPs
downregulates TN-C and induces apoptosis.
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