Abstract 20709: The Parathyroid Hormone-related Peptide (PTHrP) Induces Arterial Vascular Smooth Muscle Cell Proliferation and Neointima Formation via a Skp2 and C-myc Dependent Pathway.
Parathyroid hormone-related protein (PTHrP) contains a classical bipartite nuclear localization signal. Nuclear targeting of PTHrP is associated with proliferation of arterial vascular smooth muscle cells (VSMC). In the arterial wall, PTHrP is markedly upregulated in response to angioplasty, and is associated with arterial re-stenosis. Overexpression exacerbates arterial re-stenosis, and, conversely, knockout of the PTHrP gene is associated with decreased VSMC proliferation in vivo. In arterial smooth muscle, the cell cycle inhibitor, p27, plays a central role in developing neointima formation. P27 expression is rapidly decreased after angioplasty, and replacement of p27 after angioplasty markedly reduces neointima development. We have shown that PTHrP overexpression leads to p27 downregulation, mostly through increased proteosomal degradation. Here, we determined the molecular mechanisms through which PTHrP targets p27 for degradation. PTHrP overexpression in VSMC was associated with an upregulation of Skp2 and c-myc (or Myc), two critical regulators of p27 stability and neointima formation. In VSMC overexpressing PTHrP, normalization of Skp2 or c-myc using siRNA knockdown normalized cell cycle progression and p27 expression. These data indicate that both, Skp2 and c-myc, mediate of the p27 loss and induced proliferation by PTHrP in VSMC. Well known target genes of c-myc, involved in p27 stability, were also upregulated in VSMC overexpressing PTHrP, suggesting a critical role of c-myc in p27 downregulation by PTHrP. These include Cullin 1, cdc25a, Cks1 and cdk7. Further, c-myc promoter activity was increased by an 8 fold in VSMC overexpressing PTHrP. In primary VSMC, overexpression of PTHrP led to increased cell cycle progression, increased c-myc expression and decreased p27 expression. Conversely, knockdown of PTHrP in primary VSMC from floxed-PTHrP mice, using adenoviral delivery of the Cre-recombinase, led to a significant cell cycle arrest and p27 upregulation. Collectively, these data describe for the first time the role of PTHrP in the regulation of Skp2 and c-myc in VSMC. Therefore, this new “PTHrP-Skp2-c-myc” axis is a potential target for therapeutic manipulation of the arterial response to injury.
- © 2010 by American Heart Association, Inc.