Atherosclerosis is a 'response-to-injury' process associated with chronic inflammation, tissue repair and a considerable cell turnover. These growth-related processes are controlled by the 'cell cycle clock' which is composed of cyclin-dependent kinases (Cdks), their activating subunits, the cyclins, and by inhibitors of Cdks (Ckis). P27 is a Cki which associates with cyclin A-Cdk2, cyclin D-Cdk4 and with cyclin E (CE)-Cdk2 complexes thereby abrogating their catalytic activity leading to potent inhibition of late G1 to S-phase transition. Furthermore, TGF-beta 1 mRNA and immunoreactivity are locally increased in atherosclerotic lesions. Since TGF-beta 1 growth suppressive function in the late G1 phase may be mediated by p27, blocking the catalytic activity of CE-Cdk2 complexes, via the stimulation of TGF-beta-RI and TGF-beta-RII, we investigated the topographical association between TGF-beta-RI, TGF-beta-RII, p27(Kip1) and CE by immunohistochemistry in coronary artery segments without atherosclerosis and carotid atheromatous plaques of 11 patients undergoing carotid endarterectomy. P27-immunoreactivity was present in 11/11 atherosclerotic (92.7 +/- 3.3% of the cells) and 5/5 control (80.9 +/- 3.7% of the cells; P < 0.002 versus control) specimens and localized to nuclei of macrophages (CD68-positive), vascular smooth muscle cells (alpha-actin positive), T-lymphocytes (CD3-positive) as well as to the nuclei of endothelial cells. In the atherosclerotic tissue, TGF-beta-RI and TGF-beta-RII-immunoreactivity was present in 11/11 specimens and localized to inflammatory cells and to cells with VSMC-like-morphology. TGF-beta-RI-immunoreactivity was present in 87.4 +/- 5.3% (controls 75.3 +/- 7.48%; n.s.) and TGF-beta-RII-immunoreactivity was present in 83.7 +/- 6.8% (controls 39.5 +/- 7.3%; P<0.002) of the cells. Double immunolabeling, and investigation of serial sections revealed co-expression of TGF-beta-RI and TGF-beta-RII in virtually all cells positive for P27. In the atherosclerotic specimens, CE-immunoreactivity was present in all specimens in macrophages (CD68-positive), vascular smooth muscle cells (alpha-actin positive) and in endothelial cells in 12.58 +/- 13.58% of the nuclei whereas in the controls CE staining was restricted to 0.19 +/- 0.43% of the cells (P < 0.001). Importantly, as shown by immunofluorescent double-labeling, we found cells expressing P27 that were simultaneously positive for CE. In summary, the present study provides evidence that TGF-beta 1 present in human atherosclerotic tissue may mediate its growth suppressive activity also by p27, blocking the activity of CE-Cdk2 complexes. Quantitative analysis revealed that TGF-beta-RII, p27 and CE are concordantly upregulated in the atherosclerotic tissue with chronic inflammation, supporting the view that TGF-beta 1, p27 and CE may play an important role in the processes associated with chronic inflammation and cell turnover in advanced human atherosclerotic plaques. Taken together, these results provide a possible link between the chronic inflammation associated with advanced atherosclerosis, the effects of extracellular growth factors and cell cycle control. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.
