TY - JOUR
T1 - Binding of extracellular maspin to β1 integrins inhibits vascular smooth muscle cell migration
AU - Bass, Rosemary
AU - Wagstaff, Laura
AU - Ravenhill, Lorna
AU - Ellis, Vincent
PY - 2009/10/2
Y1 - 2009/10/2
N2 - Maspin is a serpin that has multiple effects on cell behavior, including inhibition of migration. How maspin mediates these diverse effects remains unclear, as it is devoid of protease inhibitory activity. We have previously shown that maspin rapidly inhibits the migration of vascular smooth muscle cells (VSMC), suggesting the involvement of direct interactions with cell surface proteins. Here, using immunofluorescence microscopy, we demonstrate that maspin binds specifically to the surface of VSMC in the dedifferentiated, but not the differentiated, phenotype. Ligand blotting of VSMC lysates revealed the presence of several maspin-binding proteins, with a protein of 150 kDa differentially expressed between the two VSMC phenotypes. Western blotting suggested that this protein was the ß1 integrin subunit, and subsequently both a3ß1 and a5ß1, but not avß3, were shown to associate with maspin by coimmunoprecipitation. Specific binding of these integrins was also observed using maspin-affinity chromatography, using HT1080 cell lysates. Direct binding of maspin to a5ß1 was confirmed using a recombinant a5ß1-Fc fusion protein. Using conformation-dependent anti-ß1 antibodies, maspin binding to VSMC was found to lead to a decrease in the activation status of the integrin. The functional involvement of a5ß1 in mediating the effect of maspin was established by the inhibition of migration of CHO cells overexpressing human a5 integrin, but not those lacking a5 expression. Our observations suggest that maspin engages in specific interactions with a limited number of integrins on VSMC, leading to their inactivation, and that these interactions are responsible for the effects of maspin in the pericellular environment.
AB - Maspin is a serpin that has multiple effects on cell behavior, including inhibition of migration. How maspin mediates these diverse effects remains unclear, as it is devoid of protease inhibitory activity. We have previously shown that maspin rapidly inhibits the migration of vascular smooth muscle cells (VSMC), suggesting the involvement of direct interactions with cell surface proteins. Here, using immunofluorescence microscopy, we demonstrate that maspin binds specifically to the surface of VSMC in the dedifferentiated, but not the differentiated, phenotype. Ligand blotting of VSMC lysates revealed the presence of several maspin-binding proteins, with a protein of 150 kDa differentially expressed between the two VSMC phenotypes. Western blotting suggested that this protein was the ß1 integrin subunit, and subsequently both a3ß1 and a5ß1, but not avß3, were shown to associate with maspin by coimmunoprecipitation. Specific binding of these integrins was also observed using maspin-affinity chromatography, using HT1080 cell lysates. Direct binding of maspin to a5ß1 was confirmed using a recombinant a5ß1-Fc fusion protein. Using conformation-dependent anti-ß1 antibodies, maspin binding to VSMC was found to lead to a decrease in the activation status of the integrin. The functional involvement of a5ß1 in mediating the effect of maspin was established by the inhibition of migration of CHO cells overexpressing human a5 integrin, but not those lacking a5 expression. Our observations suggest that maspin engages in specific interactions with a limited number of integrins on VSMC, leading to their inactivation, and that these interactions are responsible for the effects of maspin in the pericellular environment.
U2 - 10.1074/jbc.M109.038919
DO - 10.1074/jbc.M109.038919
M3 - Article
VL - 284
SP - 27712
EP - 27720
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 40
ER -