RRM2 regulates Bcl-2 in head and neck and lung cancers: a potential target for cancer therapy
Purpose: 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 performed to downregulate RRM2. Immunoblotting, RT-PCR, confocal microscopy, tissue fractionation, gene overexpression and knockdown were employed to analyze critical apoptosis signaling. Conventional immunohistochemistry (IHC) and quantum dot-based IHF 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 demonstrated 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 co-localization in HNSCC and NSCLC cells. In a total of 50 specimens each from HNSCC and NSCLC patients, we identified the co-localization 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.
Conclusion: Our novel findings add to the knowledge of RRM2 in regulating expression of the anti-apoptotic protein Bcl-2 and reveal a critical link between RRM2 and Bcl-2 in apoptosis signaling.
Rahman MA, Amin AR, Wang D, Koenig L, Nannapaneni S, Chen Z, Wang Z, Sica G, Deng X, Chen ZG, Shin DM. RRM2 regulates Bcl-2 in head and neck and lung cancers: a potential target for cancer therapy. Clinical Cancer Research. 2013 Jul 1;19(13):3416-28. doi: 10.1158/1078-0432.CCR-13-0073.