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Vascular smooth muscle cell growth arrest on blockade of thrombospondin-1 requires p21(Cip1/WAF1)
1Department of Medicine (Cardiology), St. Elizabeth's Medical Center, Tufts University School of Medicine, Boston, Massachusetts 02135, USA.
Abstract:
Abnormal proliferation of vascular smooth muscle cells (VSMCs) is thought to play an important role in the pathogenesis of atherosclerosis and restenosis. Previous studies have implicated the extracellular matrix protein thrombospondin-1 (TSP1) in mitogen-dependent proliferation of VSMCs. In this study, we investigated the molecular mechanisms involved in TSP1-mediated regulation of VSMC growth. Neutralizing A4.1 anti-TSP1 antibody inhibited the activity of the G(1)/S cyclin-dependent kinase 2 (cdk2) and blocked the induction of S-phase entry, which normally occurs in serum-stimulated VSMCs. This growth-inhibitory effect was associated with a marked induction of p21(Cip1/WAF1) (p21) expression in A4.1-treated VSMCs. Moreover, addition of A4.1 antibody to VSMCs markedly increased the level of p21 bound to cdk2. Thus growth arrest on antibody blockade of TSP1 may be mediated by the cdk inhibitory protein p21. Consistent with this notion, anti-TSP1 antibody inhibited [(3)H]-thymidine incorporation in wild-type but not in p21-deficient mouse embryonic fibroblasts (MEFs). Together, these data suggest that p21 plays an important role in TSP1-mediated control of cellular proliferation.
Insights
Thrombospondin-1 (TSP1) regulates vascular smooth muscle cell (VSMC) proliferation. Blocking TSP1 with an antibody increases p21 expression, inhibiting cell growth, suggesting p21 mediates TSP1
Area of Science:
- Vascular biology
- Cell cycle regulation
- Molecular mechanisms of disease
Background:
- Vascular smooth muscle cell (VSMC) proliferation is key in atherosclerosis and restenosis.
- Thrombospondin-1 (TSP1), an extracellular matrix protein, is implicated in VSMC mitogenesis.
Purpose of the Study:
- To elucidate the molecular mechanisms of TSP1-mediated VSMC growth regulation.
- To investigate the role of p21 in TSP1-dependent VSMC proliferation.
Main Methods:
- Used neutralizing anti-TSP1 antibody (A4.1) to study VSMC proliferation.
- Assessed cyclin-dependent kinase 2 (cdk2) activity and S-phase entry.
- Measured p21(Cip1/WAF1) (p21) expression and its binding to cdk2.
- Utilized p21-deficient mouse embryonic fibroblasts (MEFs) for validation.
Main Results:
- Anti-TSP1 antibody inhibited cdk2 activity and S-phase entry in VSMCs.
- TSP1 blockade led to increased p21 expression and its binding to cdk2.
- Anti-TSP1 antibody reduced [(3)H]-thymidine incorporation in wild-type MEFs but not in p21-deficient MEFs.
Conclusions:
- TSP1 blockade induces VSMC growth arrest, potentially mediated by the cyclin-dependent kinase inhibitor p21.
- p21 plays a crucial role in TSP1-dependent control of cellular proliferation.
- Findings offer insights into therapeutic strategies for vascular proliferative diseases.