title: A functional SNP in the MDM2 promoter mediates E2F1 affinity to modulate cyclin D1 expression in tumor cell proliferation.
abstract: BACKGROUND
  The MDM2 oncogene, a negative regulator of p53, has a functional polymorphism in the promoter region (SNP309) that is associated with multiple kinds of cancers including non-melanoma skin cancer. SNP309 has been shown to associate with accelerated tumor formation by increasing the affinity of the transcriptional activator Sp1. It remains unknown whether there are other factors involved in the regulation of MDM2 transcription through a trans-regulatory mechanism.
  
  
  METHODS
  In this study, SNP309 was verified to be associated with overexpression of MDM2 in tumor cells. Bioinformatics predicts that the T to G substitution at SNP309 generates a stronger E2F1 binding site, which was confirmed by ChIP and luciferase assays.
  
  
  RESULTS
  E2F1 knockdown downregulates the expression of MDM2, which confirms that E2F1 is a functional upstream regulator. Furthermore, tumor cells with the GG genotype exhibited a higher proliferation rate than TT, correlating with cyclin D1 expression. E2F1 depletion significantly inhibits the proliferation capacity and downregulates cyclin D1 expression, especially in GG genotype skin fibroblasts. Notably, E2F1 siRNA effects could be rescued by cyclin D1 overexpression.
  
  
  CONCLUSIONS
  Taken together, a novel modulator E2F1 was identified as regulating MDM2 expression dependent on SNP309 and further mediates cyclin D1 expression and tumor cell proliferation. E2F1 might act as an important factor for SNP309 serving as a rate-limiting event in carcinogenesis.
authors.affiliation: Department of Dermatology, No.1 Hospital of China Medical University, Shenyang, China E-mail : chundihe@hotmail.com.
authors.forename: Zhen-Hai
authors.initials: ZH
authors.lastname: Yang
authors.forename: Chun-Lin
authors.initials: CL
authors.lastname: Zhou
authors.forename: Hong
authors.initials: H
authors.lastname: Zhu
authors.forename: Jiu-Hong
authors.initials: JH
authors.lastname: Li
authors.forename: Chun-Di
authors.initials: CD
authors.lastname: He
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000235:genetics*; D019938:Cyclin D1 / Q000235:genetics*; D050687:E2F1 Transcription Factor / Q000235:genetics*; D005347:Fibroblasts / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D006801:Humans; D011401:Promoter Regions, Genetic / Q000235:genetics; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics*; D012878:Skin Neoplasms / Q000235:genetics*
chemical_list: C530104:CCND1 protein, human; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D019938:Cyclin D1; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2