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Regulation of tenascin-C, a vascular smooth muscle cell survival factor that interacts with the alpha v beta 3 integrin to promote epidermal growth factor receptor phosphorylation and growth.

Jones PL, Crack J, Rabinovitch M - J. Cell Biol. (1997)

Bottom Line: 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 beta 3 integrins replicates the effect of TN-C on EGF-R clustering and tyrosine phosphorylation.Conversely, suppression of MMPs downregulates TN-C and induces apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Division of Cardiovascular Research, Research Institute, The Hospital for Sick Children, University of Toronto, Ontario, Canada.

ABSTRACT
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 matrix metalloproteinase (MMP) inhibitor (GM6001) suppresses SMC TN-C expression on native collagen, whereas denatured collagen promotes TN-C expression in a beta 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 alpha v beta 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 beta 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 beta 3 integrin ligands in type I collagen. In turn, alpha v beta 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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Hypothetical model for the  regulation and function of tenascin-C  in vascular smooth muscle cells. (A)  Vascular smooth muscle cells attach  and spread on native type I collagen  using β1 integrins. Under serum-free  conditions, the cells withdraw from the  cell cycle and become quiescent. (B)  Degradation of native type I collagen  by matrix metalloproteinases (MMPs)  leads to the exposure of cryptic RGD  sites that preferentially bind β3 subunit–containing integrins. In turn, occupancy and activation of β3 integrins  signals the production of TN-C. (C) Incorporation of multivalent TN-C protein into the underlying substrate leads  to further aggregation and activation  of β3-containing integrins (αvβ3), and to  the accumulation of tyrosine-phosphorylated (Tyr-P) signaling molecules and  actin into a focal adhesion complex  (FAC). Note that even in the absence  of the EGF ligand, the TN-C–dependent reorganization of the cytoskeleton leads to clustering of actin-associated EGF-Rs. (D) Addition of EGF  ligand to clustered EGF-Rs results in  rapid and substantial tyrosine phosphorylation of the EGF-R and activation of downstream pathways culminating in the generation of nuclear  signals leading to cell proliferation.
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Figure 9: Hypothetical model for the regulation and function of tenascin-C in vascular smooth muscle cells. (A) Vascular smooth muscle cells attach and spread on native type I collagen using β1 integrins. Under serum-free conditions, the cells withdraw from the cell cycle and become quiescent. (B) Degradation of native type I collagen by matrix metalloproteinases (MMPs) leads to the exposure of cryptic RGD sites that preferentially bind β3 subunit–containing integrins. In turn, occupancy and activation of β3 integrins signals the production of TN-C. (C) Incorporation of multivalent TN-C protein into the underlying substrate leads to further aggregation and activation of β3-containing integrins (αvβ3), and to the accumulation of tyrosine-phosphorylated (Tyr-P) signaling molecules and actin into a focal adhesion complex (FAC). Note that even in the absence of the EGF ligand, the TN-C–dependent reorganization of the cytoskeleton leads to clustering of actin-associated EGF-Rs. (D) Addition of EGF ligand to clustered EGF-Rs results in rapid and substantial tyrosine phosphorylation of the EGF-R and activation of downstream pathways culminating in the generation of nuclear signals leading to cell proliferation.

Mentions: A number of studies have described the induction of TN-C in remodeling vascular tissues, where it has been functionally linked to SMC proliferation (Hedin et al., 1991; Hahn et al., 1995; Chen et al., 1996; Jones and Rabinovitch, 1996; Jones et al., 1997). However, remarkably little was known about the nature of the factors that determine its expression in these tissues or the mechanism by which TN-C supports SMC growth. In this study, we demonstrate that MMPs positively regulate TN-C protein expression and that the mechanism likely involves exposure of cryptic β3 integrin–binding sites in type I collagen. We also show that TN-C rescues SMCs from apoptosis and promotes EGF-dependent SMC survival through interactions with the αvβ3 integrin receptor, which modulates cell shape and EGF-dependent tyrosine phosphorylation. These studies therefore provide new evidence to show how remodeling of the extracellular microenvironment by ECM-degrading proteinases may influence integrin growth factor receptor signaling functions and thus cell behavior. Fig. 9 shows a hypothetical model for the regulation and function of TN-C in SMCs based on our findings.


Regulation of tenascin-C, a vascular smooth muscle cell survival factor that interacts with the alpha v beta 3 integrin to promote epidermal growth factor receptor phosphorylation and growth.

Jones PL, Crack J, Rabinovitch M - J. Cell Biol. (1997)

Hypothetical model for the  regulation and function of tenascin-C  in vascular smooth muscle cells. (A)  Vascular smooth muscle cells attach  and spread on native type I collagen  using β1 integrins. Under serum-free  conditions, the cells withdraw from the  cell cycle and become quiescent. (B)  Degradation of native type I collagen  by matrix metalloproteinases (MMPs)  leads to the exposure of cryptic RGD  sites that preferentially bind β3 subunit–containing integrins. In turn, occupancy and activation of β3 integrins  signals the production of TN-C. (C) Incorporation of multivalent TN-C protein into the underlying substrate leads  to further aggregation and activation  of β3-containing integrins (αvβ3), and to  the accumulation of tyrosine-phosphorylated (Tyr-P) signaling molecules and  actin into a focal adhesion complex  (FAC). Note that even in the absence  of the EGF ligand, the TN-C–dependent reorganization of the cytoskeleton leads to clustering of actin-associated EGF-Rs. (D) Addition of EGF  ligand to clustered EGF-Rs results in  rapid and substantial tyrosine phosphorylation of the EGF-R and activation of downstream pathways culminating in the generation of nuclear  signals leading to cell proliferation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139818&req=5

Figure 9: Hypothetical model for the regulation and function of tenascin-C in vascular smooth muscle cells. (A) Vascular smooth muscle cells attach and spread on native type I collagen using β1 integrins. Under serum-free conditions, the cells withdraw from the cell cycle and become quiescent. (B) Degradation of native type I collagen by matrix metalloproteinases (MMPs) leads to the exposure of cryptic RGD sites that preferentially bind β3 subunit–containing integrins. In turn, occupancy and activation of β3 integrins signals the production of TN-C. (C) Incorporation of multivalent TN-C protein into the underlying substrate leads to further aggregation and activation of β3-containing integrins (αvβ3), and to the accumulation of tyrosine-phosphorylated (Tyr-P) signaling molecules and actin into a focal adhesion complex (FAC). Note that even in the absence of the EGF ligand, the TN-C–dependent reorganization of the cytoskeleton leads to clustering of actin-associated EGF-Rs. (D) Addition of EGF ligand to clustered EGF-Rs results in rapid and substantial tyrosine phosphorylation of the EGF-R and activation of downstream pathways culminating in the generation of nuclear signals leading to cell proliferation.
Mentions: A number of studies have described the induction of TN-C in remodeling vascular tissues, where it has been functionally linked to SMC proliferation (Hedin et al., 1991; Hahn et al., 1995; Chen et al., 1996; Jones and Rabinovitch, 1996; Jones et al., 1997). However, remarkably little was known about the nature of the factors that determine its expression in these tissues or the mechanism by which TN-C supports SMC growth. In this study, we demonstrate that MMPs positively regulate TN-C protein expression and that the mechanism likely involves exposure of cryptic β3 integrin–binding sites in type I collagen. We also show that TN-C rescues SMCs from apoptosis and promotes EGF-dependent SMC survival through interactions with the αvβ3 integrin receptor, which modulates cell shape and EGF-dependent tyrosine phosphorylation. These studies therefore provide new evidence to show how remodeling of the extracellular microenvironment by ECM-degrading proteinases may influence integrin growth factor receptor signaling functions and thus cell behavior. Fig. 9 shows a hypothetical model for the regulation and function of TN-C in SMCs based on our findings.

Bottom Line: 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 beta 3 integrins replicates the effect of TN-C on EGF-R clustering and tyrosine phosphorylation.Conversely, suppression of MMPs downregulates TN-C and induces apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Division of Cardiovascular Research, Research Institute, The Hospital for Sick Children, University of Toronto, Ontario, Canada.

ABSTRACT
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 matrix metalloproteinase (MMP) inhibitor (GM6001) suppresses SMC TN-C expression on native collagen, whereas denatured collagen promotes TN-C expression in a beta 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 alpha v beta 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 beta 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 beta 3 integrin ligands in type I collagen. In turn, alpha v beta 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.

Show MeSH
Related in: MedlinePlus