A Receptor-Specific Function for Notch2 in Mediating Vascular Smooth Muscle Cell Growth Arrest Through p27kip1
Rationale: Deregulated vascular smooth muscle cell (VSMC) proliferation contributes to multiple vascular pathologies, and Notch signaling regulates VSMC phenotype.
Objective: Previous work focused on Notch1 and Notch3 in VSMC during vascular disease; however, the role of Notch2 is unknown. Because injured murine carotid arteries display increased Notch2 in VSMC as compared to uninjured arteries, we sought to understand the impact of Notch2 signaling in VSMC.
Methods and Results: In human primary VSMC, Jagged-1 (Jag-1) significantly reduced proliferation through specific activation of Notch2. Increased levels of p27kip1 were observed downstream of Jag-1/Notch2 signaling, and required for cell cycle exit. Jag-1 activation of Notch resulted in increased phosphorylation on serine 10, decreased ubiquitination and prolonged half-life of p27kip1. Jag-1/Notch2 signaling robustly decreased S-phase kinase associated protein (Skp2), an F-box protein that degrades p27kip1 during G1. Over expression of Skp2 prior to Notch activation by Jag-1 suppressed the induction of p27kip1. Additionally, increased Notch2 andp27kip1 expression was co-localized to the non-proliferative zone of injured arteries as indicated by co-staining with proliferating cell nuclear antigen (PCNA), whereas Notch3 was expressed throughout normal and injured arteries, suggesting Notch2 may negatively regulate lesion formation.
Conclusions: We propose a receptor specific function for Notch2 in regulating Jag-1-induced p27kip1 expression and growth arrest in VSMC. During vascular remodeling, co-localization of Notch2 and p27kip1to the non-proliferating region supports a model where Notch2 activation may negatively regulate VSMC proliferation to lessen the severity of the lesion. Thus Notch2 is a potential target for control of VSMC hyperplasia.
- Received February 27, 2013.
- Revision received August 20, 2013.
- Accepted August 21, 2013.