Expression of cyclin-dependent kinase inhibitors in vascular disease

Arterial lesions in cardiovascular diseases are characterized by proliferation and migration of smooth muscle cells as well as deposition of connective tissue matrix. Factors that stimulate vascular smooth muscle cell (VSMC) proliferation are well described; however, the role of proteins that limit intimal hyperplasia is not well understood. To examine the function of Kip/Cip and INK cyclin-dependent kinase inhibitors (CKIs) in vascular diseases, the expression of p27(Kip1) and p16(INK) was examined in VSMCs in vitro and in porcine arteries and human atherosclerosis in vivo. Western blot and fluorescence activated cell-sorting analysis demonstrated that levels of p27(Kip1), but not p16(INK), increased during serum deprivation of primary VSMC cultures and caused G₁ arrest. p27(Kip1) inhibited Cdk2 activity, suggesting that Kip CKIs promote G₁ arrest in VSMCs by binding cyclin E/Cdk2. In porcine arteries, p27(Kip1), but not p16(INK), was constitutively expressed at low levels. Immediately after balloon injury, cell proliferation increased as p27(Kip1) levels declined. Three weeks after injury, p27(Kip1) was strongly expressed in intimal VSMCs when VSMC proliferation was 1 phase of the cell cycle.