title: RRM2 regulates Bcl-2 in head and neck and lung cancers: a potential target for cancer therapy.
abstract: OBJECTIVE
  Ribonucleotide reductase subunit M2 (RRM2) plays an active role in tumor progression. Recently, we reported that depletion of RRM2 by systemic delivery of a nanoparticle carrying RRM2-specific siRNA suppresses head and neck tumor growth. The aim of this study is to clarify the underlying mechanism by which RRM2 depletion inhibits tumor growth.
  
  
  METHODS
  siRNA-mediated gene silencing was carried out to downregulate RRM2. Immunoblotting, reverse-transcriptase PCR, confocal microscopy, tissue fractionation, gene overexpression and knockdown were employed to analyze critical apoptosis signaling. Conventional immunohistochemistry and quantum dot-based immunofluorescence were applied to detect RRM2 and Bcl2 expression and localization in tissue samples from patients and mice.
  
  
  RESULTS
  Knockdown of RRM2 led to apoptosis through the intrinsic pathway in head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) cell lines. We showed that Bcl-2 is a key determinant controlling apoptosis, both in vitro and in vivo, and that RRM2 depletion significantly reduces Bcl-2 protein expression. We observed that RRM2 regulates Bcl-2 protein stability, with RRM2 suppression leading to increased Bcl-2 degradation, and identified their colocalization in HNSCC and NSCLC cells. In a total of 50 specimens each from patients with HNSCC and NSCLC, we identified the colocalization of Bcl-2 and RRM2 and found a significant positive correlation between their expression in HNSCC (R = 0.98; P < 0.0001) and NSCLC (R = 0.92; P < 0.0001) tumor tissues.
  
  
  CONCLUSIONS
  Our novel findings add to the knowledge of RRM2 in regulating expression of the antiapoptotic protein Bcl-2 and reveal a critical link between RRM2 and Bcl-2 in apoptosis signaling.
authors.affiliation: Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University, Atlanta, GA 30322, USA.
authors.forename: Mohammad Aminur
authors.initials: MA
authors.lastname: Rahman
authors.forename: A R M Ruhul
authors.initials: AR
authors.lastname: Amin
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Wang
authors.forename: Lydia
authors.initials: L
authors.lastname: Koenig
authors.forename: Sreenivas
authors.initials: S
authors.lastname: Nannapaneni
authors.forename: Zhengjia
authors.initials: Z
authors.lastname: Chen
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Wang
authors.forename: Gabriel
authors.initials: G
authors.lastname: Sica
authors.forename: Xingming
authors.initials: X
authors.lastname: Deng
authors.forename: Zhuo Georgia
authors.initials: ZG
authors.lastname: Chen
authors.forename: Dong M
authors.initials: DM
authors.lastname: Shin
mesh_terms: D017209:Apoptosis / Q000235:genetics; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism; D012262:Ribonucleoside Diphosphate Reductase / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D000077195:Squamous Cell Carcinoma of Head and Neck; D014158:Transcription, Genetic; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C000606368:Trp73 protein, mouse; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C093713:ribonucleotide reductase M2; D012262:Ribonucleoside Diphosphate Reductase; D051057:Proto-Oncogene Proteins c-akt