HJURP is recruited to double-strand break sites and facilitates DNA repair by promoting chromatin reorganization.

HJURP is overexpressed in several cancer types and strongly correlates with patient survival. However, the mechanistic basis underlying the association of HJURP with cancer aggressiveness is not well understood. HJURP promotes the loading of the histone H3 variant, CENP-A, at the centromeric chromatin, epigenetically defining the centromeres and supporting proper chromosome segregation. In addition, HJURP is associated with DNA repair but its function in this process is still scarcely explored. Here, we demonstrate that HJURP is recruited to DSBs through a mechanism requiring chromatin PARylation and promotes epigenetic alterations that favor the execution of DNA repair. Incorporation of HJURP at DSBs promotes turnover of H3K9me3 and HP1, facilitating DNA damage signaling and DSB repair. Moreover, HJURP overexpression in glioma cell lines also affected global structure of heterochromatin independently of DNA damage induction, promoting genome-wide reorganization and assisting DNA damage response. HJURP overexpression therefore extensively alters DNA damage signaling and DSB repair, and also increases radioresistance of glioma cells. Importantly, HJURP expression levels in tumors are also associated with poor response of patients to radiation. Thus, our results enlarge the understanding of HJURP involvement in DNA repair and highlight it as a promising target for the development of adjuvant therapies that sensitize tumor cells to irradiation.

The Roles of Histone Post-Translational Modifications in the Formation and Function of a Mitotic Chromosome.

During mitosis, many cellular structures are organized to segregate the replicated genome to the daughter cells. Chromatin is condensed to shape a mitotic chromosome. A multiprotein complex known as kinetochore is organized on a specific region of each chromosome, the centromere, which is defined by the presence of a histone H3 variant called CENP-A. The cytoskeleton is re-arranged to give rise to the mitotic spindle that binds to kinetochores and leads to the movement of chromosomes. How chromatin regulates different activities during mitosis is not well known. The role of histone post-translational modifications (HPTMs) in mitosis has been recently revealed. Specific HPTMs participate in local compaction during chromosome condensation. On the other hand, HPTMs are involved in CENP-A incorporation in the centromere region, an essential activity to maintain centromere identity. HPTMs also participate in the formation of regulatory protein complexes, such as the chromosomal passenger complex (CPC) and the spindle assembly checkpoint (SAC). Finally, we discuss how HPTMs can be modified by environmental factors and the possible consequences on chromosome segregation and genome stability.

HJURP knockdown disrupts clonogenic capacity and increases radiation-induced cell death of glioblastoma cells.

The Holliday Junction-Recognition Protein (HJURP) was reported as overexpressed in several cancers and also strongly correlated with poor prognosis of patients, especially in glioblastoma (GBM), the most common and deadly type of primary brain tumor. HJURP is responsible for loading the histone H3 variant-the Centromeric Protein A (CENP-A)-at the centromeres in a cell cycle-regulated manner, being required for proper chromosome segregation. Here we investigated HJURP association with survival and radioresistance of different GBM cell lines. HJURP knockdown compromised the clonogenic capacity and severely impaired survival of five distinct GBM cells, while nontumor astrocytes were not affected. U251MG cells showed a robust cell cycle arrest in G2/M phases followed by a drastic increment in cell death after HJURP silencing, while U138MG and U343MG cell lines presented augmented senescence with a comparable increase in cell death. Importantly, we verified that the impact on cell cycle dynamics and clonogenic survival were associated with loss CENP-A at the centromeres. Moreover, radiation resistance was also impacted by HJURP modulation in several GBM cell lines. U87MG, T98G, U138MG, and U343MG cells were all sensitized to ionizing radiation after HJURP reduction. These data reinforce the requirement of HJURP for proliferative capacity and radioresistance of tumor cells, underlining its potential as a promising therapeutic target for GBM.

A comprehensive study of epigenetic alterations in hepatocellular carcinoma identifies potential therapeutic targets.

BACKGROUND & AIMS: A causal link has recently been established between epigenetic alterations and hepatocarcinogenesis, indicating that epigenetic inhibition may have therapeutic potential. We aimed to identify and target epigenetic modifiers that show molecular alterations in hepatocellular carcinoma (HCC). METHODS: We studied the molecular-clinical correlations of epigenetic modifiers including bromodomains, histone acetyltransferases, lysine methyltransferases and lysine demethylases in HCC using The Cancer Genome Atlas (TCGA) data of 365 patients with HCC. The therapeutic potential of epigenetic inhibitors was evaluated in vitro and in vivo. RNA sequencing analysis and its correlation with expression and clinical data in the TCGA dataset were used to identify expression programs normalized by Jumonji lysine demethylase (JmjC) inhibitors. RESULTS: Genetic alterations, aberrant expression, and correlation between tumor expression and poor patient prognosis of epigenetic enzymes are common events in HCC. Epigenetic inhibitors that target bromodomain (JQ-1), lysine methyltransferases (BIX-1294 and LLY-507) and JmjC lysine demethylases (JIB-04, GSK-J4 and SD-70) reduce HCC aggressiveness. The pan-JmjC inhibitor JIB-04 had a potent antitumor effect in tumor bearing mice. HCC cells treated with JmjC inhibitors showed overlapping changes in expression programs related with inhibition of cell proliferation and induction of cell death. JmjC inhibition reverses an aggressive HCC gene expression program that is also altered in patients with HCC. Several genes downregulated by JmjC inhibitors are highly expressed in tumor vs. non-tumor parenchyma, and their high expression correlates with a poor prognosis. We identified and validated a 4-gene expression prognostic signature consisting of CENPA, KIF20A, PLK1, and NCAPG. CONCLUSIONS: The epigenetic alterations identified in HCC can be used to predict prognosis and to define a subgroup of high-risk patients that would potentially benefit from JmjC inhibitor therapy. LAY SUMMARY: In this study, we found that mutations and changes in expression of epigenetic modifiers are common events in human hepatocellular carcinoma, leading to an aggressive gene expression program and poor clinical prognosis. The transcriptional program can be reversed by pharmacological inhibition of Jumonji enzymes. This inhibition blocks hepatocellular carcinoma progression, providing a novel potential therapeutic strategy.

Concurrent Duplication of Drosophila Cid and Cenp-C Genes Resulted in Accelerated Evolution and Male Germline-Biased Expression of the New Copies.

Despite their essential role in the process of chromosome segregation in eukaryotes, kinetochore proteins are highly diverse across species, being lost, duplicated, created, or diversified during evolution. Based on comparative genomics, the duplication of the inner kinetochore proteins CenH3 and Cenp-C, which are interdependent in their roles of establishing centromere identity and function, can be said to be rare in animals. Surprisingly, the Drosophila CenH3 homolog Cid underwent four independent duplication events during evolution. Particularly interesting are the highly diverged Cid1 and Cid5 paralogs of the Drosophila subgenus, which are probably present in over one thousand species. Given that CenH3 and Cenp-C likely co-evolve as a functional unit, we investigated the molecular evolution of Cenp-C in species of Drosophila. We report yet another Cid duplication (leading to Cid6) within the Drosophila subgenus and show that not only Cid, but also Cenp-C is duplicated in the entire subgenus. The Cenp-C paralogs, which we named Cenp-C1 and Cenp-C2, are highly divergent. Both Cenp-C1 and Cenp-C2 retain key motifs involved in centromere localization and function, while some functional motifs are conserved in an alternate manner between the paralogs. Interestingly, both Cid5 and Cenp-C2 are male germline-biased and evolved adaptively. However, it is currently unclear if the paralogs subfunctionalized or if the new copies acquired a new function. Our findings point towards a specific inner kinetochore composition in a specific context (i.e., spermatogenesis), which could prove valuable for the understanding of how the extensive kinetochore diversity is related to essential cellular functions.