Sp1 inhibits proliferation and induces apoptosis in vascular smooth muscle cells by repressing p21WAF1/Cip1 transcription and cyclin D1-Cdk4-p21WAF1/Cip1 complex formation.
Atherosclerosis and restenosis are common vascular disorders that involve excess proliferation of smooth muscle cells (SMCs) in the artery wall. In this study we demonstrate the anti-mitogenic, pro-apoptotic role of the zinc finger transcription factor Sp1 in vascular SMCs and define the underlying molecular mechanism via its capacity to repress the expression of the cyclin-dependent kinase inhibitor p21WAF1/Cip1 at the level of transcription, mRNA, and protein. SMC proliferation inducible by a dominant-negative mutant form of Sp1 was abrogated by antisense strategies targeting p21WAF1/Cip1. Conversely, antisense p21WAF1/Cip1 induced apoptosis in SMCs overexpressing dominant-negative-Sp1. p21WAF1/Cip1 overexpression alone stimulated proliferation and inhibited apoptosis. Sp1 down-regulated p21WAF1/Cip1 expression in SMCs. Sp1 blocked assembly of cyclin D1-Cdk4-p21WAF1/Cip1 complex formation whose integrity is critical for G1->S transition. Moreover, Rb phosphorylation, which lies immediately downstream of the cyclin D1-Cdk4-p21WAF1/Cip1 complex, was blocked either by Sp1 overexpression or antisense p21WAF1/Cip1. These findings, using complementary approaches, demonstrate the inverse relationship between Sp1 and p21WAF1/Cip1 in SMCs and the capacity of Sp1 to regulate SMC proliferation and apoptosis via its repression of p21WAF1/Cip1.
Kavurma
Mary M
MM
Center for Vascular Research, Department of Pathology, The University of New South Wales, and Prince of Wales Hospital, Sydney 2052, Australia.
Khachigian
Levon M
LM
D000818:Animals; D017209:Apoptosis; D001158:Arteries / Q000378:metabolism; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D015536:Down-Regulation; D004730:Endothelium, Vascular / Q000166:cytology*; D005047:Etoposide / Q000494:pharmacology; D005799:Genes, Dominant; D009154:Mutation; D032389:Myocytes, Smooth Muscle / Q000473:pathology*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011921:Rats, Inbred WKY; D016160:Retinoblastoma Protein / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D014158:Transcription, Genetic; D016335:Zinc Fingers
C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D019384:Nucleic Acid Synthesis Inhibitors; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D016329:Sp1 Transcription Factor; D019938:Cyclin D1; D005047:Etoposide; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D001973:Bromodeoxyuridine