The role of Sp1 family members, the proximal GC-rich motifs, and the upstream enhancer region in the regulation of the human cell cycle inhibitor p21WAF-1/Cip1 gene promoter

Biochemistry. 2002 Oct 22;41(42):12771-84. doi: 10.1021/bi026141q.


In the present study we establish that specific members of the Sp1 family of transcription factors (Sp1 and Sp3) bind to all six GC-rich motifs (elements 1-6) present in the proximal promoter of the human cell cycle inhibitor p21(WAF-1/Cip1) gene. Competition analysis showed that Sp1 and Sp3 bound with high affinity to elements 1, 3, 4, and 5/6 and with lower affinity to element 2. Transfection experiments in the Sp1-deficient Drosophila SL2 cells established that Sp1 and Sp3 but not Sp2 are potent transactivators of the p21 promoter. Transactivation by Sp1 was compromised either by deletion of element 1 (-119/-114) or by using a truncated Sp1 form lacking the C-terminal regulatory domain D. Point mutagenesis of the -2325/+8 p21 promoter, targeting individual elements 1-6, showed that mutations in element 3 (-82/-77) caused a dramatic reduction (90%) in p21 promoter activity whereas mutations in other elements had a less severe effect. The mutations in element 3 abolished p21 promoter induction by upstream enhancer elements in HepG2 cells. Sp1, but not Sp3, mediated the transactivation of the p21 promoter by the TGFbeta signaling mediator Smad3 and Smad4 proteins whereas none of the individual mutations in elements 1-6 affected the transactivation of the p21 promoter by Smad proteins in HepG2 cells. Our results suggest that functional interactions between Sp1 family members bound to specific elements of the proximal promoter and factors bound to distal enhancer elements govern the hepatic activity of the human p21 promoter under basal or inducible conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5' Untranslated Regions / physiology*
  • Animals
  • Base Sequence
  • Binding Sites / genetics
  • COS Cells
  • Cell Line
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / genetics*
  • Cyclins / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • DNA-Binding Proteins / physiology
  • Drosophila / genetics
  • Enhancer Elements, Genetic / physiology*
  • GC Rich Sequence / physiology*
  • Gene Expression Regulation / physiology
  • Growth Inhibitors / genetics*
  • Growth Inhibitors / metabolism
  • Humans
  • Molecular Sequence Data
  • Multigene Family*
  • Promoter Regions, Genetic*
  • Protein Binding / genetics
  • Protein Structure, Tertiary / genetics
  • Rats
  • Sequence Deletion
  • Smad Proteins
  • Sp1 Transcription Factor / genetics
  • Sp1 Transcription Factor / metabolism
  • Sp1 Transcription Factor / physiology*
  • Sp3 Transcription Factor
  • Trans-Activators / metabolism
  • Trans-Activators / physiology
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transcription Factors / physiology
  • Transfection
  • Tumor Cells, Cultured


  • 5' Untranslated Regions
  • CDKN1A protein, human
  • Cdkn1a protein, rat
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • DNA-Binding Proteins
  • Growth Inhibitors
  • SP3 protein, human
  • Smad Proteins
  • Sp1 Transcription Factor
  • Sp3 protein, rat
  • Trans-Activators
  • Transcription Factors
  • Sp3 Transcription Factor