Sp1 inhibits proliferation and induces apoptosis in vascular smooth muscle cells by repressing p21WAF1/Cip1 transcription and cyclin D1-Cdk4-p21WAF1/Cip1 complex formation

J Biol Chem. 2003 Aug 29;278(35):32537-43. doi: 10.1074/jbc.M305650200. Epub 2003 Jun 9.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Arteries / metabolism
  • Blotting, Western
  • Bromodeoxyuridine / pharmacology
  • CDC2-CDC28 Kinases*
  • Cell Cycle
  • Cell Division
  • Cell Line
  • Cells, Cultured
  • Cyclin D1 / metabolism*
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinase 4
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclin-Dependent Kinases / metabolism*
  • Cyclins / metabolism*
  • Down-Regulation
  • Endothelium, Vascular / cytology*
  • Etoposide / pharmacology
  • Genes, Dominant
  • Mutation
  • Myocytes, Smooth Muscle / pathology*
  • Nucleic Acid Synthesis Inhibitors / pharmacology
  • Oligonucleotides, Antisense / pharmacology
  • Phosphorylation
  • Plasmids / metabolism
  • Precipitin Tests
  • Promoter Regions, Genetic
  • Protein Binding
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins*
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Inbred WKY
  • Retinoblastoma Protein / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sp1 Transcription Factor / genetics
  • Sp1 Transcription Factor / metabolism
  • Sp1 Transcription Factor / physiology*
  • Time Factors
  • Transcription, Genetic*
  • Zinc Fingers


  • Cdkn1a protein, rat
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Nucleic Acid Synthesis Inhibitors
  • Oligonucleotides, Antisense
  • Proto-Oncogene Proteins
  • RNA, Messenger
  • Retinoblastoma Protein
  • Sp1 Transcription Factor
  • Cyclin D1
  • Etoposide
  • Protein-Serine-Threonine Kinases
  • CDC2-CDC28 Kinases
  • Cdk2 protein, rat
  • Cdk4 protein, rat
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinase 4
  • Cyclin-Dependent Kinases
  • Bromodeoxyuridine