title: Review of current progress in the structure and function of Smad proteins.
abstract: OBJECTIVE
  To review the recent developments in the structure and function of Smad proteins.
  
  
  METHODS
  Both Chinese- and English-language literatures were searched using MEDLINE/CD-ROM (1997 - 2000) and the Index of Chinese-Language Literature (1997 - 2000).
  
  
  METHODS
  Data from published articles about TGF-beta signal transduction in recent domestic and foreign literature were selected.
  
  
  METHODS
  Data were mainly extracted from 22 articles which are listed in the reference section of this review.
  
  
  RESULTS
  Smad proteins mediate signal transduction induced by the TGF-beta superfamily. Based on their structural and functional properties, Smad proteins are divided into three groups. The first group, receptor-regulated Smads (R-Smads), are phosphorylated by activated type I receptors and form heteromeric complexes with the second group of Smads, common mediator Smads (Co-Smads). These Smad complexes translocate into the nucleus to influence gene transcription. Inhibitory Smads (I-Smads) are the third group and these antagonize the activity of R-Smads. In the nucleus, Smads can directly contact Smad-binding elements (SBE) in target gene promoters. Through interaction with different transcription factors, transcriptional co-activators or co-repressors, Smads elicit different effects in various cell types. The aberrance of Smad proteins has been noted in several human disorders such as fibrosis, hypertrophic scarring and cancer.
  
  
  CONCLUSIONS
  The structure of Smads determines their function as transcriptional factors which translocate signals from the cell surface to the nucleus where Smads regulate TGF-beta superfamily-dependent gene expression.
authors.affiliation: PLA Key Laboratory of Wound Repair, 304th Hospital, Beijing 100037, China. chenwei304@yahoo.com
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Fu
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Sheng
mesh_terms: D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology*; D006801:Humans; D015398:Signal Transduction; D051785:Smad Proteins; D015534:Trans-Activators / Q000737:chemistry* / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D051785:Smad Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta