In response to DNA damage, cells initiate complex signalling cascades leading to growth arrest and DNA repair. The recruitment of 53BP1 to damaged sites requires the activation of the ubiquitination cascade controlled by the E3 ubiquitin ligases RNF8 and RNF168, and methylation of histone H4 on lysine 20. However, molecular events that regulate the accessibility of methylated histones, to allow the recruitment of 53BP1 to DNA breaks, are unclear. Here, we show that like 53BP1, the JMJD2A (also known as KDM4A) tandem tudor domain binds dimethylated histone H4K20; however, JMJD2A is degraded by the proteasome following the DNA damage in an RNF8‐dependent manner. We demonstrate that JMJD2A is ubiquitinated by RNF8 and RNF168. Moreover, ectopic expression of JMJD2A abrogates 53BP1 recruitment to DNA damage sites, indicating a role in antagonizing 53BP1 for methylated histone marks. The combined knockdown of JMJD2A and JMJD2B significantly rescued the ability of RNF8‐ and RNF168‐deficient cells to form 53BP1 foci. We propose that the RNF8‐dependent degradation of JMJD2A regulates DNA repair by controlling the recruitment of 53BP1 at DNA damage sites.

Background:The histone demethylase KDM4B is overexpressed in several tumor types and is oncogenic upon overexpression. Results: Kdm4b-EGFP recruits to DNA damage induced by laser micro-irradiation. Kdm4b-EGFP overexpression enhanced double-strand break repair and increased survival following ␥-irradiation. Conclusion: Kdm4b enhances the DNA damage response. Significance: Kdm4b overexpression may contribute to cytotoxic anti-cancer treatment resistance.

Polycomb protein histone methyltransferase, enhancer of Zeste homolog 2 (eZH2), is frequently overexpressed in human malignancy and is implicated in cancer cell proliferation and invasion. However, it is largely unknown whether eZH2 has a role in modulating the DNa damage response. Here, we show that polycomb repressive complex 2 (PrC2) is recruited to sites of DNa damage. this recruitment is independent of histone 2a variant X (H2aX) and the PI-3-related kinases atM and DNa-PKcs. We establish that ParP activity is required for retaining PrC2 at sites of DNa damage. Furthermore, depletion of eZH2 in cells decreases the efficiency of DSB repair and increases sensitivity of cells to gammairradiation. these data unravel a crucial role of PrC2 in determining cancer cellular sensitivity following DNa damage and suggest that therapeutic targeting of eZH2 activity might serve as a strategy for improving conventional chemotherapy in a given malignancy.

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The Jumonji D2 proteins (JMJD2/KDM4) function to demethylate di- and trimethylated (me2/3) histone 3 lysine 9 (H3K9me2/3) and H3K36me3. Knockout mouse models for Kdm4b and Kdm4d have not resulted in gross abnormalities, while mouse models for Kdm4a and Kdm4c have not been reported. However, the KDM4 subfamily of demethylases are overexpressed in several tumor types. Overexpression of KDM4 proteins alters transcription and chromatin remodeling, driving cellular proliferation, anchorage-independent growth, invasion, and migration. Increased proliferation occurs through KDM4-mediated modification of cell cycle timing, as well as through increased numbers of replication forks. Recent evidence also suggests that KDM4C overexpression contributes to the maintenance of a pluripotent state. Together these data suggest that overexpression of KDM4 proteins induces numerous oncogenic effects.

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), an oncogenic fusion gene protein that is characteristically found in a subset of anaplastic large cell lymphomas, promotes tumorigenesis through its functional and physical interactions with various biologically important proteins. The identification of these interacting proteins has proven to be useful to further our understanding of NPM-ALK-mediated tumorigenesis. For the first time, we performed a proteome-wide identification of NPM-ALK-binding proteins using tandem affinity purification and a highly sensitive mass spectrometric technique. Tandem affinity purification is a recently developed method that carries a lower background and higher sensitivity compared with the conventional immunoprecipitation-based protein purification protocols. The NPM-ALK gene was cloned into an HB-tagged vector and expressed in GP293 cells. Three independent experiments were performed and the reproducibility of the data was 68%. The vast majority of the previously reported NPM-ALK-binding proteins were detected. We also identified proteins that are involved in various cellular processes that were not previously described in association with NPM-ALK, such as MCM6 and MSH2 (DNA repair), Nup98 and importin 8 (subcellular protein transport), Stim1 (calcium signaling), 82Fip (RNA regulation), and BAG2 (proteosome degradation). We believe that these data highlight the functional diversity of NPM-ALK and provide new research directions for the study of the biology of this oncoprotein.

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In addition to their established role in repairing post-replicative DNA errors, DNA mismatch repair proteins contribute to cell cycle arrest and apoptosis in response to a wide range of exogenous DNA damage (e.g., alkylation-induced lesions). The role of DNA mismatch repair in response to ultraviolet-induced DNA damage has been historically controversial. Recent data, however, suggest that DNA mismatch repair proteins probably do not contribute to the removal of ultraviolet-induced DNA damage, but may be important in suppressing mutagenesis, effecting apoptosis, and suppressing tumorigenesis following exposure to ultraviolet radiation.