Smad4-independent regulation of p21/WAF1 by transforming growth factor-beta

Oncogene. 2004 Feb 5;23(5):1043-51. doi: 10.1038/sj.onc.1207222.


The transforming growth factor-beta (TGF-beta)-Smad signaling pathway inhibits the growth of human epithelial cells and plays a role in tumor suppression. The Smad4 gene is mutated or deleted in 50% of pancreatic cancers. In this study, the Smad4-null pancreatic cancer cell line BxPC-3 was transfected with either the Smad4 expression vector or the empty vector and incubated in the presence or absence of TGF-beta. The cells were analysed using a cDNA microarray, which included 2280 named genes to screen for target genes regulated by TGF-beta in either a Smad4-dependent or -independent manner. The microarray and subsequent quantitative RT-PCR analysis demonstrated that the Smad4-independent and -dependent signaling pathways driven by TGF-beta upregulated only one of the 2280 genes, respectively, suggesting that Smad4-independent signaling downstream of TGF-beta might be as widespread as Smad4-dependent signaling. In this study, we demonstrated that the cyclin-dependent kinase inhibitor p21/WAF1, which has been considered the major effector of the Smad-dependent growth inhibitory signal of TGF-beta, is upregulated in a Smad4-independent manner. The upregulation occurs through Smad2/3-dependent transcriptional activation of the p21/WAF1 promoter region. These results suggest a novel mechanism of gene regulation, that is, a novel signal mediator other than Smad4.

MeSH terms

  • Active Transport, Cell Nucleus / drug effects
  • Cell Division / drug effects
  • Cell Line, Tumor
  • Cell Nucleus / metabolism
  • Cells, Cultured
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / drug effects
  • Cyclins / genetics
  • Cyclins / metabolism*
  • DNA, Complementary / analysis
  • DNA-Binding Proteins / metabolism
  • Endoribonucleases
  • Enzyme Induction
  • Gene Deletion
  • Gene Expression Regulation / drug effects
  • Genes, Tumor Suppressor
  • Humans
  • Keratinocytes / metabolism
  • Oligonucleotide Array Sequence Analysis
  • Pancreatic Neoplasms / metabolism
  • Promoter Regions, Genetic
  • RNA, Messenger / metabolism
  • Signal Transduction
  • Smad2 Protein
  • Smad3 Protein
  • Trans-Activators / biosynthesis
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Transcriptional Activation
  • Transforming Growth Factor beta / pharmacology*


  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • DNA, Complementary
  • DNA-Binding Proteins
  • RNA, Messenger
  • SMAD2 protein, human
  • SMAD3 protein, human
  • Smad2 Protein
  • Smad3 Protein
  • Trans-Activators
  • Transforming Growth Factor beta
  • Endoribonucleases
  • DCP1A protein, human