Inhibition of the cyclin D1/E2F pathway by PCA-4230, a potent repressor ofcellular proliferation

1 Tight control of cellular growth is essential to ensure normal tissue pat terning and prevent pathological responses. Excessive vascular smooth muscl e cell (VSMC) proliferation is associated with the pathophysiology of ather osclerosis and restenosis post-angioplasty. Thus, drug targeting of patholo gical VSMC growth may be a suitable therapeutic intervention.in vascular pr oliferative diseases. 2 In the present study, we investigated the mechanisms underlying VSMC grow th arrest induced by the pharmacological agent PCA-4230. Addition of PCA-42 30 to cultured VSMCs blocked the induction of cyclin D1 and cyclin A expres sion normally seen in serum-restimulated cells. Moreover, PCA-4230 inhibite d cyclin-dependent kinase 2 (CDK2) activity and abrogated hyperphosphorylat ion of the retinoblastoma (Rb) gene product. Similarly, PCA-4230-dependent growth arrest of transformed cell lines correlated with reduced level of cy clin D1 protein and inhibition of CDK2 activity. Consistent with these find ings, PCA-4230 repressed serum-inducible cyclin A promoter activity, and ov erexpression of either cyclin D1 or E2F1 efficiently circumvented this inhi bitory effect. Importantly, adenovirus-mediated overexpression of E2F1 rest ored S-phase entry in PCA-4230-treated VSMCs, demonstrating that PCA-4230 r epresses cyclin A gene expression and VSMC growth via inhibition of the cyc lin D1/E2F pathway. 3 Because of its ability to inhibit the growth of human VSMCs and transform ed cell lines, future studies are warranted to assess whether PCA-4230 may be a suitable therapeutic intervention for the treatment of hyperproliferat ive disorders, including cardiovascular disease and cancer.