Scaffold protein FHL2 facilitates MDM2-mediated degradation of IER3 to regulate proliferation of cervical cancer cells

Oncogene. 2016 Sep 29;35(39):5106-18. doi: 10.1038/onc.2016.54. Epub 2016 Mar 14.


The expression of immediate early response 3 (IER3), a protein with a short half-life, is rapidly induced by various cellular stimuli. We recently reported that IER3 induces the apoptosis of cervical cancer cells and that its expression is downregulated in patients with cervical cancer. However, the molecular mechanism involved in the rapid degradation of IER3 remains unknown. Here, we demonstrate that MDM2 is an E3 ligase that interacts with IER3 and promotes its ubiquitination, followed by proteasomal degradation. Polyubiquitination of the conserved lysine 60 of IER3 is essential for its degradation. In addition, four and a half LIM domains protein 2 (FHL2) binds to both IER3 and MDM2, allowing for efficient MDM2-mediated IER3 degradation by facilitating an association between MDM2 and IER3. Moreover, IER3 induces cell cycle arrest in cervical cancer cells and its activity is further enhanced in cells in which FHL2 or MDM2 was silenced, thereby preventing IER3 degradation. The E6 and E7 oncoproteins of human papilloma virus 18 regulated IER3 expression. FHL2 expression was significantly higher in the squamous epithelium of cervical carcinoma tissues than in non-cancerous cervical tissues, whereas cervical carcinoma expression of IER3 was downregulated in this region. Thus, we determined the molecular mechanism responsible for IER3 degradation, involving a ternary complex of IER3, MDM2 and FHL2, which may contribute to cervical tumor growth. Furthermore, we demonstrated that FHL2 serves as a scaffold for E3 ligase and its substrate during the ubiquitination reaction, a function that has not been previously reported for this protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis Regulatory Proteins / genetics*
  • Cell Proliferation / genetics
  • DNA-Binding Proteins / genetics
  • Female
  • Gene Expression Regulation, Neoplastic
  • HeLa Cells
  • Human papillomavirus 18 / genetics
  • Human papillomavirus 18 / pathogenicity
  • Humans
  • LIM-Homeodomain Proteins / genetics*
  • Membrane Proteins / genetics*
  • Muscle Proteins / genetics*
  • Oncogene Proteins, Viral / genetics
  • Proteasome Endopeptidase Complex / genetics
  • Proteolysis
  • Proto-Oncogene Proteins c-mdm2 / genetics*
  • Transcription Factors / genetics*
  • Ubiquitination
  • Uterine Cervical Neoplasms / genetics*
  • Uterine Cervical Neoplasms / pathology
  • Uterine Cervical Neoplasms / virology


  • Apoptosis Regulatory Proteins
  • DNA-Binding Proteins
  • E6 protein, Human papillomavirus type 18
  • E7 protein, Human papillomavirus type 18
  • FHL2 protein, human
  • IER3 protein, human
  • LIM-Homeodomain Proteins
  • Membrane Proteins
  • Muscle Proteins
  • Oncogene Proteins, Viral
  • Transcription Factors
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2
  • Proteasome Endopeptidase Complex