Repo-man controls a protein phosphatase 1-dependent threshold for DNA damage checkpoint activation

The Role of CDCA2 in tumor genesis, prognosis and future treatments

The Cell Division Cycle Associated 2 (CDCA2) gene is responsible for encoding a targeting subunit of cell-cycle associated protein. CDCA2 plays a crucial role in various cellular processes, including chromosome segregation and decondensation, nuclear envelope reassembly, microtubule assembly, and DNA damage response. Additionally, CDCA2 is involved in multiple signaling pathways such as the PI3K/Akt pathway and p53 pathway. Undoubtedly, there exists a strong association between CDCA2 and cancer. Numerous studies have reported that elevated levels of CDCA2 are correlated with poor prognosis and several clinicopathological characteristics like tumor size and TNM stage across different types of cancer. Therefore, CDCA2 holds great potential as both a biomarker for diagnosis and a therapeutic target for interventions such as targeted therapies or immunotherapy. Given its promising prospects in scientific research and clinical applications, it is imperative for researchers to delve into the underlying mechanisms of CDCA2 and explore its utilization.

CAVPENET Peptide Inhibits Prostate Cancer Cells Proliferation and Migration through PP1γ-Dependent Inhibition of AKT Signaling

Protein phosphatase 1 (PP1) complexes have emerged as promising targets for anticancer therapies. The ability of peptides to mimic PP1-docking motifs, and so modulate interactions with regulatory factors, has enabled the creation of highly selective modulators of PP1-dependent cellular processes that promote tumor growth. The major objective of this study was to develop a novel bioactive cell-penetrating peptide (bioportide), which, by mimicking the PP1-binding motif of caveolin-1 (CAV1), would regulate PP1 activity, to hinder prostate cancer (PCa) progression. The designed bioportide, herein designated CAVPENET, and a scrambled homologue, were synthesized using microwave-assisted solid-phase methodologies and evaluated using PCa cell lines. Our findings indicate that CAVPENET successfully entered PCa cells to influence both viability and migration. This tumor suppressor activity of CAVPENET was attributed to inhibition of AKT signaling, a consequence of increased PP1γ activity. This led to the suppression of glycolytic metabolism and alteration in lipid metabolism, collectively representing the primary mechanism responsible for the anticancer properties of CAVPENET. Our results underscore the potential of the designed peptide as a novel therapy for PCa patients, setting the stage for further testing in more advanced models to fully realize its therapeutic promise.

Role of cell division cycle-associated proteins in regulating cell cycle and promoting tumor progression

The cell division cycle-associated protein (CDCA) family is important in regulating cell division. High CDCA expression is significantly linked to tumor development. This review summarizes clinical and basic studies on CDCAs conducted in recent decades. Furthermore, it systematically introduces the molecular expression and function, key mechanisms, cell cycle regulation, and roles of CDCAs in tumor development, cell proliferation, drug resistance, invasion, and metastasis. Additionally, it presents the latest research on tumor diagnosis, prognosis, and treatment targeting CDCAs. These findings are pivotal for further in-depth studies on the role of CDCAs in promoting tumor development and provide theoretical support for their application as new anti-tumor targets.

The eEF2 kinase coordinates the DNA damage response to cisplatin by supporting p53 activation

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) is a stress-responsive hub that inhibits the translation elongation factor eEF2, and consequently mRNA translation elongation, in response to hypoxia and nutrient deprivation. EEF2K is also involved in the response to DNA damage but its role in response to DNA crosslinks, as induced by cisplatin, is not known. Here we found that eEF2K is critical to mediate the cellular response to cisplatin. We uncovered that eEF2K deficient cells are more resistant to cisplatin treatment. Mechanistically, eEF2K deficiency blunts the activation of the DNA damage response associated ATM and ATR pathways, in turn preventing p53 activation and therefore compromising induction of cisplatin-induced apoptosis. We also report that loss of eEF2K delays the resolution of DNA damage triggered by cisplatin, suggesting that eEF2K contributes to DNA damage repair in response to cisplatin. In support of this, our data shows that eEF2K promotes the expression of the DNA repair protein ERCC1, critical for the repair of cisplatin-caused DNA damage. Finally, using Caenorhabditis elegans as an in vivo model, we find that deletion of efk-1, the worm eEF2K ortholog, mitigates the induction of germ cell death in response to cisplatin. Together, our data highlight that eEF2K represents an evolutionary conserved mediator of the DNA damage response to cisplatin which promotes p53 activation to induce cell death, or alternatively facilitates DNA repair, depending on the extent of DNA damage.

A pan-cancer analysis reveals the diagnostic and prognostic role of CDCA2 in low-grade glioma

BACKGROUND

Cell division cycle associated 2 (CDCA2), a member of the cell division cycle associated proteins (CDCA) family, is crucial in the regulation of cell mitosis and DNA repair. CDCA2 was extensively examined in our work to determine its role in a wide range of cancers.

METHODS

CDCA2 differential expression was studied in pan-cancer and in diverse molecular and immunological subgroups in this research. Additionally, the diagnostic and prognostic significance of CDCA2 in pan-cancer was also evaluated using receiver operating characteristic (ROC) and Kaplan-Meier (KM) curves. Prognostic value of CDCA2 in distinct clinical subgroups of lower grade glioma (LGG) was also investigated and a nomogram was constructed. Lastly, potential mechanisms of action of CDCA2 were interrogated including biological functions, ceRNA networks, m6A modification and immune infiltration.

RESULTS

CDCA2 is shown to be differentially expressed in a wide variety of cancers. Tumors are diagnosed and forecasted with a high degree of accuracy by CDCA2, and the quantity of expression CDCA2 is linked to the prognosis of many cancers. Additionally, the expression level of CDCA2 in various subgroups of LGG is also closely related to prognosis. The results of enrichment analyses reveal that CDCA2 is predominantly enriched in the cell cycle, mitosis, and DNA replication. Subsequently, hsa-miR-105-5p is predicted to target CDCA2. In addition, 4 lncRNAs were identified that may inhibit the hsa-miR-105-5p/CDCA2 axis in LGG. Meanwhile, CDCA2 expression is shown to be associated to m6A-related genes and levels of immune cell infiltration in LGG.

CONCLUSION

CDCA2 can serve as a novel biomarker for the diagnosis and prognosis in pan-cancer, especially in LGG. For the development of novel targeted therapies in LGG, it may be a potential molecular target. However, to be sure, we'll need to do additional biological experiments to back up our results from bioinformatic predictions.

The second half of mitosis and its implications in cancer biology

The nucleus undergoes dramatic structural and functional changes during cell division. With the entry into mitosis, in human cells the nuclear envelope breaks down, chromosomes rearrange into rod-like structures which are collected and segregated by the spindle apparatus. While these processes in the first half of mitosis have been intensively studied, much less is known about the second half of mitosis, when a functional nucleus reforms in each of the emerging cells. Here we review our current understanding of mitotic exit and nuclear reformation with spotlights on the links to cancer biology.

CDCA2 Promotes HCC Cells Development via AKT-mTOR Pathway

Background

Hepatocellular carcinoma (HCC) is a highly aggressive and solid malignancy with a poor prognosis. Cell division cycle associated 2 (CDCA2) is highly expressed in HCC and is considered to be closely related to the prognosis of patients with HCC. In this research, we aimed to investigate the function and potential mechanism of CDCA2 in HCC cells.

Methods

Gain- and loss-of-function experiments were conducted to determine the biological function of CDCA2 in HCC cells. Quantitative reverse transcription-polymerase chain reaction and western blot were utilized to examine the Messenger RNA (mRNA) and protein levels of CDCA2 in HCC cells. The malignant behaviors of HCC cells were analyzed by several biological experiments including cell viability, cell colony formation, and transwell assays. Western blot was also implemented to examine the expression of : AKT, protein kinase B and mTOR, mammalian target of rapamycin (AKT-mTOR) pathway related proteins and Cyclin D1.

Results

A significant increase of CDCA2 was observed in HCC cell lines. Upregulation of CDCA2 resulted in the enhancement of the growth, migration, and invasion of HCC cells. Inversely, depletion of CDCA2 displayed the opposite results. Furthermore, the protein levels of p-AKT, p-mTOR, and Cyclin D1 were elevated with CDCA2 upregulation and reduced with CDCA2 depletion in HCC cells.

Conclusion

Our observations revealed that CDCA2 promoted the malignant development of HCC cells, and AKT-mTOR pathway might involve in the underlying mechanism.

The MASTL-ENSA-PP2A/B55 axis modulates cisplatin resistance in oral squamous cell carcinoma

Platinum-based chemotherapy is the standard first-line treatment for oral squamous cell carcinoma (OSCC) that is inoperable, recurrent, or metastatic. Platinum sensitivity is a major determinant of patient survival in advanced OSCC. Here, we investigated the involvement of MASTL, a cell cycle kinase that mediates ENSA/ARPP19 phosphorylation and PP2A/B55 inhibition, in OSCC therapy. Interestingly, upregulation of MASTL and ENSA/ARPP19, and downregulation of PP2A/B55, were common in OSCC. MASTL expression was in association with poor patient survival. In established OSCC cell lines, upregulation of MASTL and ENSA, and downregulation of B55 genes, correlated with cisplatin resistance. We further confirmed that stable expression of MASTL in OSCC cells promoted cell survival and proliferation under cisplatin treatment, in an ENSA-dependent manner. Conversely, deletion of MASTL or ENSA, or overexpression of B55α, sensitized cisplatin response, consistent with increased DNA damage accumulation, signaling, and caspase activation. Moreover, GKI-1, the first-in-class small molecule inhibitor of MASTL kinase, phenocopied MASTL depletion in enhancing the outcome of cisplatin treatment in OSCC cells, at a dose substantially lower than that needed to disrupt mitotic entry. Finally, GKI-1 exhibited promising efficacy in a mouse tumor xenograft model, in conjunction with cisplatin therapy.

Cell division cycle associated 2 (CDCA2) upregulation promotes the progression of hepatocellular carcinoma in a p53-dependant manner

Background

Elevated expression and oncogenic functions of cell division cycle associated 2 (CDCA2), an important mitotic regulator, have been demonstrated in several cancer types, however their involvement in hepatocellular carcinoma (HCC) has not been elucidated, and the underlying molecular mechanism remains unclear. This study aims to determine the role of CDCA2 in HCC and the underlying molecular mechanism.

Methods

The expression of CDCA2 in HCC was studied in 40 pairs of frozen and 48 pairs of paraffin-embedded HCC samples and paracancerous normal samples by qRT-PCR and immunohistochemistry, respectively, and using The Cancer Genome Atlas (TCGA) datasets. The cellular function of CDCA2 was studied in vitro in the HepG2, Huh7 and SK-Hep1 HCC cell lines.

Results

We found significantly upregulated CDCA2 expression in HCC, which was correlated with higher clinical stage, tumor grade and Glypican-3 (+). High CDCA2 expression was correlated with worse overall survival. CDCA2 promoted the proliferation of HCC cells by promoting G1/S transition through the upregulation and activation of CCND1/CDK4/6 and CCNE1/CDK2, enhanced the clonogenic ability, inhibited apoptosis in a p53/p21-dependent manner by inhibiting the p38 MAPK pathway and activating the JNK/c-Jun pathway, and promoted the migration of p53-mutant Huh7 cells by activating the epithelial-mesenchymal transition. Targeting CDCA2 reduced the chemoresistance of HCC cells to cisplatin. CDCA2 expression was also regulated by cyclophilin J.

Conclusions

This study revealed elevated expression of CDCA2 in HCC, possibly as a result of p53 dysregulation, which was associated with worse prognosis of patients. We confirmed the oncogenic role of CDCA2 in HCC in vitro and revealed some of the underlying molecular mechanisms. This study indicated the potential value of CDCA2 as a future target for the treatment of HCC.

Identification of a 5-Nutrient Stress-Sensitive Gene Signature to Predict Survival for Colorectal Cancer

Background

The high heterogeneity and the complexity of the tumor microenvironment of colorectal cancer (CRC) have enhanced the difficulty of prognosis prediction based on conventional clinical indicators. Recent studies revealed that tumor cells could overcome various nutritional deficiencies by gene regulation and metabolic remodeling. However, whether differentially expressed genes (DEGs) in CRC cells under kinds of nutrient deficiency could be used to predict prognosis remained unveiled.

Methods

Three datasets (GSE70976, GSE13548, and GSE116087), in which colon cancer cells were, respectively, cultured in serum-free, glucose-free, or glutamine-free medium, were included to delineate the profiles of gene expression by nutrient stress. DEGs were figured out in three datasets, and gene functional analysis was performed. Survival analyses and Cox proportional hazards model were then used to identify nutrient stress sensitive genes in CRC datasets (GSE39582 and TCGA COAD). Then, a 5-gene signature was constructed and the risk scores were also calculated. Survival analyses, cox analyses, and nomogram were applied to predict the prognosis of patients with colorectal cancer. The effectiveness of the risk model was also tested.

Results

A total of 48 genes were found to be dysregulated in serum, glucose, or glutamine-deprived CRC cells, which were mainly enriched in cell cycle and endoplasmic reticulum stress pathways. After further analyses, 5 genes, MCM5, MCM6, CDCA2, GINS2, and SPC25, were identified to be differentially expressed in CRC and be related to prognosis of in CRC datasets. We used the above nutrient stress-sensitive genes to construct a risk scoring model. CRC samples in the datasets were divided into low-risk and high-risk groups. Data showed that higher risk scores were associated with better outcomes and risk scores decreased significantly with tumor procession. Moreover, the risk score could be used to predict the probability of survival based on nomogram.

Conclusions

The 5-nutrient stress-sensitive gene signature could act as an independent biomarker for survival prediction of CRC patients.

Protein post-translational modifications in the regulation of cancer hallmarks

Posttranslational modifications (PTMs) of proteins, the major mechanism of protein function regulation, play important roles in regulating a variety of cellular physiological and pathological processes. Although the classical PTMs, such as phosphorylation, acetylation, ubiquitination and methylation, have been well studied, the emergence of many new modifications, such as succinylation, hydroxybutyrylation, and lactylation, introduces a new layer to protein regulation, leaving much more to be explored and wide application prospects. In this review, we will provide a broad overview of the significant roles of PTMs in regulating human cancer hallmarks through selecting a diverse set of examples, and update the current advances in the therapeutic implications of these PTMs in human cancer.

Increased CDCA2 Level Was Related to Poor Prognosis in Hepatocellular Carcinoma and Associated With Up-Regulation of Immune Checkpoints

Background

Cell division cycle-associated protein 2 (CDCA2) is a member of cell cycle-related proteins. CDCA2 plays a role in the regulation of protein phosphatase 1(PP1) γ-dependent DNA damage response (DDR) and H3 phosphorylation. CDCA2 promotes the tumorigenesis and development of several types of cancers by promoting the proliferation of tumor cells. However, the relationship between CDCA2 expression and the clinicopathological characteristics of hepatocellular carcinoma (HCC) is unknown.

Methods

Gene expression information and clinical data were downloaded from The Cancer Genome Atlas (TCGA) database. The expression of CDCA2 and its correlation to clinical characteristics in HCC were analyzed. The expression level of CDCA2 was validated in HCC cell lines. The relationship between CDCA2 expression and the survival of patients with HCC was analyzed by using Kaplan–Meier method. The prognostic value of CDCA2 in HCC was estimated by Cox regression analysis. The expression difference of CDCA2 between HCC and normal tissues and its correlation to survival were verified in independent datasets. Gene set enrichment analysis (GSEA) was used to screen the CDCA2-related signaling pathways.

Results

Cell division cycle-associated protein 2 expression was upregulated in HCC tissues (p < 0.001) and increased CDCA2 was correlated to increased T stage, pathologic stage, histologic grade, and alpha-fetoprotein (AFP) level (p < 0.001). In addition, CDCA2 was overexpressed in HCC cell lines HepG2 and LM3. High CDCA2 expression level was associated with poor overall survival [hazard ratio (HR) = 1.69; 95% CI, 1.20–1.40, p = 0.003], disease specific survival (HR = 1.73; 95% CI, 1.11–2.71, p = 0.016), and progress free interval (HR = 1.74; 95% CI, 1.30–2.34, p < 0.001). Overexpression of CDCA2 and its correlation to poor survival in HCC were verified in Gene Expression Omnibus (GEO) datasets and Kaplan–Meier plotter database. Increased CDCA2 expression was associated with upregulation of PD-L1 (Spearman's coefficient = 0.207, p < 0.001), PD-L2 (Spearman coefficient's = 0.118, p < 0.05), and CTLA4 (Spearman's coefficient = 0.355, p < 0.001). GSEA showed that homologous recombination pathway, insulin signaling pathway, mitogen-activated protein kinase (MAPK) pathway, mismatch repair pathway, mechanistic target of rapamycin (mTOR) pathway, Notch pathway, T cell receptor pathway, toll like receptor pathway, and WNT pathway were enriched in CDCA2 high expression phenotype.

Conclusion

Cell division cycle-associated protein 2 may serve as an independent biomarker for poor prognosis in HCC and increased CDCA2 expression was associated with upregulation of immune checkpoints.

Cell Division Cycle-Associated Genes Are Potential Immune Regulators in Nasopharyngeal Carcinoma

Background

Cell division cycle-associated (CDCA) gene family is essential to cell cycle regulation. Numerous studies have illuminated that dysfunction of CDCA genes may not only lead to uncontrolled cell proliferation resulting in tumorigenesis but also influence immune cell infiltration in tumors. However, the role of the CDCA gene family on the prognosis and immune infiltration in nasopharyngeal carcinoma (NPC) remains to be unclear.

Methods

SBC human ceRNA array V1.0 was used to measure mRNA expression in three pairs of NPC tissues and nasopharyngitis tissues. The expression of CDCA8 was confirmed in an IHC microarray containing 130 NPC patients. Two external GEO cohorts were enrolled for further analysis. Prognosis analysis was performed using the Kaplan–Meier method. Gene set enrichment analysis (GSEA) was applied to explore the potential mechanism of CDCA genes in NPC. The relationship between CDCA gene family and immune infiltration in NPC was evaluated using the Xcell tool.

Results

CDCA genes were broadly upregulated in NPC tissues compared to nasopharyngitis tissues, and high expression of CDCA3/5/8 indicated worse prognosis in NPC. Besides cell cycle pathways, we found that CDCA3/5/8 were involved in multiple immune-related pathways. Overexpression of CDCA8 was strongly associated with less infiltration of CD8+ T cells and more infiltration of CD4+ Th1 cells and was negatively correlated with immune checkpoint blockade (ICB)-related genes.

Conclusion

CDCA gene family was upregulated in NPC, and their expressions were associated with adverse prognosis. High expression of CDCA8 was associated not only with poor prognosis, but also with less immune infiltration and downregulation of ICB-related genes in NPC.

Trichodysplasia spinulosa polyomavirus small T antigen synergistically modulates S6 protein translation and DNA damage response pathways to shape host cell environment

TSPyV is a viral agent linked to Trichodysplasia spinulosa, a disfiguring human skin disease which presents with hyperkeratotic spicule eruption in immunocompromised hosts. This proliferative disease state requires extensive modulation of the host cell environment. While the small T (sT) antigen of TSPyV has been postulated to cause widespread cellular perturbation, its specific substrates and their mechanistic connection are unclear. To identify the cellular substrates and pathways perturbed by TSPyV sT and propose a nuanced model that reconciles the multiple arms of TSPyV pathogenesis, changes in expression of several proteins and phospho-proteins in TSPyV sT expressing and TSPyV sT deletion mutant-expressing cell lysates were interrogated using Western blot assays. TSPyV sT expression exploits the DNA damage response pathway, by inducing hyperphosphorylation of ATM and 53BP1 and upregulation of BMI-1. Concurrently, sT dysregulates the S6 protein translation pathway via hyperphosphorylation of CDC2, p70 S6 kinase, S6, and PP1α. The S6^S244/247 and p-PP1α^T320 phospho-forms are points of overlap between the DDR and S6 networks. We propose a mechanistic rationale for previous reports positioning sT antigen as the key driver of TSPyV pathogenesis. We illuminate novel targets in the S6 and DDR pathways and recognize a potential synergy between these pathways. TSPyV may sensitize the cell to both unrestricted translation and genomic instability. This multi-pronged infection model may inform future therapeutic modalities against TSPyV and possibly other viruses with overlapping host substrates.

The Sm core components of small nuclear ribonucleoproteins promote homologous recombination repair

DNA Double strand breaks (DSBs) are highly hazardous to the cell, and are repaired predominantly via non-homologous end joining (NHEJ) and homologous recombination (HR). Using DSB-mimicking DNA templates, our proteomic studies identified a group of Sm core proteins of small nuclear ribonucleoproteins (snRNPs) as potential DSB-associated proteins. We further confirmed that these Sm proteins were recruited to laser-induced DNA damage sites, and co-localized with established DNA damage repair factors. Depletion of Sm-D3 or Sm-B induced accumulation of γ-H2AX, and impaired the repair efficiency of HR, but not NHEJ. Furthermore, disruption of Sm-D3 reduced the protein level of HR factors, especially RAD51 and CHK1, but caused no change in the expression of repair factors involved in NHEJ. Mechanistically, Sm-D3 proteins bound RAD51, suppressed the ubiquitination of RAD51, and mediated the stabilization of RAD51; Sm-D3 depletion particularly impacted the level of RAD51 and CHK1 on damaged chromatin. As such, our studies characterized a role of Sm proteins in HR repair, via a new mechanism that is distinct from their conventional functions in RNA processing and gene regulation, but consistent with their direct recruitment to DNA damage sites and association with repair factors.

Modulation of serine/threonine-protein phosphatase 1 (PP1) complexes: A promising approach in cancer treatment

Cancer is the second leading cause of death worldwide. Despite the availability of numerous therapeutic options, tumor heterogeneity and chemoresistance have limited the success of these treatments, and the development of effective anticancer therapies remains a major focus in oncology research. The serine/threonine-protein phosphatase 1 (PP1) and its complexes have been recognized as potential drug targets. Research on the modulation of PP1 complexes is currently at an early stage, but has immense potential. Chemically diverse compounds have been developed to disrupt or stabilize different PP1 complexes in various cancer types, with the objective of inhibiting disease progression. Beneficial results obtained in vitro now require further pre-clinical and clinical validation. In conclusion, the modulation of PP1 complexes seems to be a promising, albeit challenging, therapeutic strategy for cancer.

CDCA2 promotes tumorigenesis and induces radioresistance in oesophageal squamous cell carcinoma cells

Cell division cycle‑associated 2 (CDCA2) overexpression has been demonstrated to serve a significant role in tumorigenesis in certain types of cancer. Nevertheless, its role in tumour proliferation and radioresistance in oesophageal squamous cell carcinoma (ESCC) remains to be elucidated. Thus, the present study aimed to elucidate these roles. Data were downloaded from The Cancer Genome Atlas (TCGA) to compare the gene expression profiles. The expression of CDCA2 was higher in ESCC tissues compared with normal tissues. Gene set enrichment analysis was performed based on the ESCC cohorts in TCGA database. This demonstrated that higher expression of CDCA2 was significantly associated with the expression of related components of the cell cycle phase transition and G2/M phase transition pathways. Collectively, the results revealed that CDCA2 could serve as an underlying target to regulate tumour growth and radioresistance among patients with ESCC.

The roles of the cell division cycle-associated gene family in hepatocellular carcinoma

Background

The members of the cell division cycle-associated (CDCA) gene family are significant regulators of cell proliferation known to play key roles in various cancers. However, the function of CDCA genes in hepatocellular carcinoma (HCC) is unclear. The aim of this research was to clarify the roles of CDCA family members in HCC using bioinformatics analysis tools.

Methods

We studied data on the mRNA and protein expression of CDCA genes and survival in patients with HCC using the Oncomine, UALCAN, HPA, CCLE, LinkedOmics, cBioPortal, and Metascape databases.

Results

Significant overexpression of all CDCA members was found in HCC tissues. The expression levels of CDCAs were related to the tumor stage, and high expression levels were correlated with a low survival rate in patients with HCC. Also, we observed a high mutation rate (45%) of CDCAs in the HCC samples, which manifested as deep deletion, amplification, or increased mRNA expression. In the correlation analysis, we found that any 2 CDCA members were significantly positively correlated with each other. Cycle-related genes including AHCTF1, AKT1, BIRC5, CENPF, CENPL, and CENPQ were closely associated with CDCA gene alterations.

Conclusions

The findings of this study indicate that CDCAs may be potential therapeutic targets and prognostic indicators for patients with HCC.

A Nuclear Stress Pathway that Parallels Cytoplasmic Stress Granule Formation

Stress adaptation is exploited by cancer cells to survive and proliferate under adverse conditions. Survival pathways induced by stress are thus highly promising therapeutic targets. One key pathway involves formation of cytoplasmic stress granules, which regulate the location, stability, and translation of specific mRNAs. Here, we describe a transcriptional stress response that is triggered by similar stressors and characterized by accumulation of RepoMan (cell division cycle associated 2) at nuclear stress foci (nucSF). Formation of these structures is reversible, and they are distinct from known nuclear organelles and stress bodies. Immunofluorescence analysis revealed accumulation of heterochromatic markers, and increased association of RepoMan with the adenylate cyclase 2 (ADCY2) gene locus in stressed cells accompanied reduced levels of ADCY2 mRNA and protein. Quantitative comparison of the RepoMan interactome in stressed vs. unstressed cells identified condensin II as a nucSF factor, suggesting their functional association in the establishment and/or maintenance of these facultative heterochromatic domains.

A Comprehensive Analysis of Alterations in DNA Damage Repair Pathways Reveals a Potential Way to Enhance the Radio-Sensitivity of Esophageal Squamous Cell Cancer

Esophageal squamous cell cancer (ESCC) is a common malignancy with a poor 5-year overall survival in China. Altered DNA damage repair (DDR) pathways are associated with a predisposition to cancer and contribute to therapeutic response and resistance in cancers. However, alterations of DDR pathway genes in ESCC are still largely unknown. In this study, we employed genome sequencing data of 192 samples, comparative genomic hybridization data of 123 cases, and gene expression microarray data of 119 patients to firstly perform a comprehensive analysis of the gene alterations of 7 DDR pathways in ESCC. Gene mutations and copy number variations (CNVs) were observed in all 7 DDR pathways, and especially, CNVs were the dominant alteration types. Compared with other pathways, two DNA double-strand break (DSB) repair pathways homologous recombination (HR) and non-homologous end joining (NHEJ), carried significant gene mutations and CNVs especially gene amplifications. Most genes including RAD54B, NBS1, RAD51B, and PRKDC were significantly amplified and over-expressed in ESCC. Amplification and high expression of DSB repair pathway genes were associated with poorer overall survival. Gene set variation analysis further showed that DSB repair pathways were up-regulated in ESCC. Besides, we firstly demonstrated that combination of mirin and NU7441, two inhibitors for HR and NHEJ respectively, with ionizing radiation treatment significantly enhanced DSBs, reduced clonogenic cell survival, inhibited cell proliferation, and promoted cell apoptosis in ESCC cells with DSB pathway gene amplification. These findings suggest that DSB repair pathways were significantly altered in ESCC and inhibiting DSB repair pathways might enhance the radio-sensitivity of ESCC with DSB repair up-regulation.

Aurora B regulates PP1γ-Repo-Man interactions to maintain the chromosome condensation state

The mitotic kinase Aurora B regulates the condensation of chromatin into chromosomes by phosphorylating chromatin proteins during early mitosis, whereas the phosphatase PP1γ performs the opposite function. The roles of Aurora B and PP1γ must be tightly coordinated to maintain chromosomes at a high phosphorylation state, but the precise mechanisms regulating their function remain largely unclear. Here, mainly through immunofluorescence microscopy and co-immunoprecipitation assays, we find that dissociation of PP1γ from chromosomes is essential for maintaining chromosome phosphorylation. We uncover that PP1γ is recruited to mitotic chromosomes by its regulatory subunit Repo-Man in the absence of Aurora B activity and that Aurora B regulates dissociation of PP1γ by phosphorylating and disrupting PP1γ-Repo-Man interactions on chromatin. Overexpression of Repo-Man mutants that cannot be phosphorylated or inhibition of Aurora B kinase activity resulted in the retention of PP1γ on chromatin and prolonged the chromatin condensation process; a similar outcome was caused by the ectopic targeting of PP1γ to chromatin. Together, our findings reveal a novel regulation mechanism of chromatin condensation in which Aurora B counteracts PP1γ activity by releasing PP1γ from Repo-Man and may have important implications for understanding the regulations of dynamic structural changes of the chromosomes in mitosis.

ATM-associated signalling triggers the unfolded protein response and cell death in response to stress

Endoplasmic reticulum (ER) stress can be caused by perturbations in ER function resulting from the accumulation of unfolded/misfolded proteins in the ER lumen. Accumulating unfolded proteins trigger unfolded protein responses (UPRs) through activating three transmembrane sensors on the ER: IRE1α, PERK, and ATF6. The orchestrated action of these molecules upregulates genes encoding proteins involved in the downregulation of protein synthesis and acceleration of protein secretion. Ineffectiveness of these fail-safe mechanisms may lead to apoptosis. However, the molecular mechanisms upstream of the UPR are not fully understood. Here we show participation of ataxia telangiectasia mutated (ATM) in stress-induced apoptosis. Cytoplasmic ATM serves as a platform on which protein phosphatase 2A-dependent dephosphorylation of AKT activates glycogen synthase kinase 3β, thereby downregulating nascent polypeptide-associated complex α subunit and γ-taxilin, triggering UPRs and leading to mitochondria-dependent apoptosis. These results suggest an ATM/AKT-dependent cell death pathway triggered by various forms of stress.

Promiscuous Targeting of Cellular Proteins by Vpr Drives Systems-Level Proteomic Remodeling in HIV-1 Infection

HIV-1 encodes four “accessory proteins” (Vif, Vpr, Vpu, and Nef), dispensable for viral replication in vitro but essential for viral pathogenesis in vivo. Well characterized cellular targets have been associated with Vif, Vpu, and Nef, which counteract host restriction and promote viral replication. Conversely, although several substrates of Vpr have been described, their biological significance remains unclear. Here, we use complementary unbiased mass spectrometry-based approaches to demonstrate that Vpr is both necessary and sufficient for the DCAF1/DDB1/CUL4 E3 ubiquitin ligase-mediated degradation of at least 38 cellular proteins, causing systems-level changes to the cellular proteome. We therefore propose that promiscuous targeting of multiple host factors underpins complex Vpr-dependent cellular phenotypes and validate this in the case of G2/M cell cycle arrest. Our model explains how Vpr modulates so many cell biological processes and why the functional consequences of previously described Vpr targets, identified and studied in isolation, have proved elusive.

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HIV-1 Vpr is responsible for almost all proteomic changes in HIV-1-infected cells

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Vpr directly targets multiple nuclear proteins for degradation

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Vpr cellular phenotypes (e.g., cell cycle arrest) stem from broad substrate targeting

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Targeting of a few proteins is conserved across diverse primate lentiviral species

Polo-like kinase 1 (Plk1) is a positive regulator of DNA replication in the Xenopus in vitro system

Polo-like kinase 1 (Plk1) is a cell cycle kinase essential for mitosis progression, but also important for checkpoint recovery and adaptation in response to DNA damage and replication stress. However, although Plk1 is expressed in S phase, little is known about its function during unperturbed DNA replication. Using Xenopus laevis egg extracts, mimicking early embryonic replication, we demonstrate that Plk1 is simultaneously recruited to chromatin with pre-replication proteins where it accumulates throughout S phase. Further, we found that chromatin-bound Plk1 is phosphorylated on its activating site T201, which appears to be sensitive to dephosphorylation by protein phosphatase 2A. Extracts immunodepleted of Plk1 showed a decrease in DNA replication, rescued by wild type recombinant Plk1. Inversely, modest Plk1 overexpression accelerated DNA replication. Plk1 depletion led to an increase in Chk1 phosphorylation and to a decrease in Cdk2 activity, which strongly suggests that Plk1 could inhibit the ATR/Chk1-dependent intra-S phase checkpoint during normal S phase. In addition, we observed that phosphorylated Plk1 levels are high during the rapid, early cell cycles of Xenopus development but decrease after the mid-blastula transition when the cell cycle and the replication program slow down along with more active checkpoints. These data shed new light on the role of Plk1 as a positive regulating factor for DNA replication in early, rapidly dividing embryos.

CDCA2 acts as an oncogene and induces proliferation of clear cell renal cell carcinoma cells

Cell division cycle-associated 2 (CDCA2) plays an important role in regulating chromosome structure during mitosis. It is highly expressed in oral squamous cell carcinoma, neuroblastoma and lung adenocarcinoma, and its upregulation is positively associated with tumor progression. However, the expression, biological function and underlying mechanisms of the role of CDCA2 in clear cell renal cell carcinoma (ccRCC) remain poorly understood. In the present study, CDCA2 was demonstrated to be upregulated in ccRCC tissues compared with normal kidney tissue, where higher expression was generally associated with the degree of malignancy. Small interfering RNA-mediated knockdown of CDCA2 expression inhibited the viability and proliferation of 786-O and CAKI-1 cells, as measured by an MTT assay, colony formation assay and flow cytometry. Furthermore, western blot analysis suggested that CDCA2 regulates cell proliferation through the cell cycle-associated proteins cyclin D1 and cyclin dependent kinase 4, and the apoptotic protein Bcl-2. In conclusion, the present study indicated that CDCA2 may be an important factor in ccRCC progression and could be a potential therapeutic target in this disease.

The role of the CDCA gene family in ovarian cancer

Background

Ovarian cancer is a frequently-occurring reproductive system malignancy in females, which leads to an annual of over 100 thousand deaths worldwide.

Methods

The electronic databases, including GEPIA, ONCOMINE, Metascape, and Kaplan-Meier Plotter, were used to examine both survival and transcriptional data regarding the cell division cycle associated (CDCA) gene family among ovarian cancer patients.

Results

All CDCA genes expression levels were up-regulated in ovarian cancer tissues relative to those in non-carcinoma ovarian counterparts. Besides, CDCA5/7 expression levels were related to the late tumor stage. In addition, the Kaplan-Meier Plotter database was employed to carry out survival analysis, which suggested that ovarian cancer patients with increased CDCA2/3/5/7 expression levels had poor overall survival (OS) (P<0.05). Moreover, ovarian cancer patients that had up-regulated mRNA expression levels of CDCA2/5/8 had markedly reduced progression-free survival (PFS) (P<0.05); and up-regulated CDCA4 expression showed remarkable association with reduced post-progression survival (PPS) (P<0.05). Additionally, the following processes were affected by CDCA genes alterations, including R-HAS-2500257: resolution of sister chromatid cohesion; GO:0051301: cell division; CORUM: 1118: Chromosomal passenger complex (CPC, including CDCA8, INCENP, AURKB and BIRC5); CORUM: 127: NDC80 kinetochore complex; M129: PID PLK1 pathway; and GO: 0007080: mitotic metaphase plate congression, all of which were subjected to marked regulation since the alterations affected CDCA genes.

Conclusions

Up-regulated CDCA gene expression in ovarian cancer tissues probably played a crucial part in the occurrence of ovarian cancer. The up-regulated CDCA2/3/5/7 expression levels were used as the potential prognostic markers to improve the poor ovarian cancer survival and prognostic accuracy. Moreover, CDCA genes probably exerted their functions in tumorigenesis through the PLK1 pathway.

Analysis of the Expression of Cell Division Cycle-Associated Genes and Its Prognostic Significance in Human Lung Carcinoma: A Review of the Literature Databases

Background

Lung cancer (LC) has become the top cause responsible for cancer-related deaths. Cell division cycle-associated (CDCA) genes exert an important role in the life process. Dysregulation in the process of cell division may lead to malignancy.

Methods

Transcriptional data on CDCA gene family and patient survival data were examined for lung cancer (LC) patients from the GEPIA, Oncomine, cBioPortal, and Kaplan-Meier Plotter databases.

Results

CDCA1/2/3/4/5/7/8 expression levels were higher in lung adenocarcinoma tissues, and the CDCA1/2/3/4/5/6/7/8 expression levels were increased in squamous cell LC tissues compared with those in noncarcinoma lung tissues. The expression levels of CDCA1/2/3/4/5/8 showed correlation with tumor classification. The Kaplan-Meier Plotter database was employed to carry out survival analysis, indicating that increased CDCA1/2/3/4/5/6/7/8 expression levels were increased in squamous cell LC tissues compared with those in noncarcinoma lung tissues. The expression levels of P < 0.05). Only LC patients with increased CDCA3/4/5/8 expression were significantly related to lower post-progression survival (PPS) (P < 0.05). Only LC patients with increased CDCA gene family and patient survival data were examined for lung cancer (LC) patients from the GEPIA, Oncomine, cBioPortal, and Kaplan-Meier Plotter databases. CDCA8, INCENP, AURKB, and BIRC5); CORUM: 127: NDC80 kinetochore complex; M129: the PID PLK1 pathway; and GO: 0007080: mitotic metaphase plate congression, all of which were remarkably modulated since the alterations affected CDCA gene family and patient survival data were examined for lung cancer (LC) patients from the GEPIA, Oncomine, cBioPortal, and Kaplan-Meier Plotter databases.

Conclusions

Upregulated CDCA genes' expression levels in LC tissues probably play a crucial part in LC oncogenesis. The upregulated CDCA genes' expression levels are used as the potential prognostic markers to improve patient survival and the LC prognostic accuracy. CDCA genes probably exert their functions in tumorigenesis through the PLK1 pathway.CDCA gene family and patient survival data were examined for lung cancer (LC) patients from the GEPIA, Oncomine, cBioPortal, and Kaplan-Meier Plotter databases. CDCA gene family and patient survival data were examined for lung cancer (LC) patients from the GEPIA, Oncomine, cBioPortal, and Kaplan-Meier Plotter databases. CDCA gene family and patient survival data were examined for lung cancer (LC) patients from the GEPIA, Oncomine, cBioPortal, and Kaplan-Meier Plotter databases.

Co-regulation of the antagonistic RepoMan:Aurora-B pair in proliferating cells

Chromosome segregation during mitosis is antagonistically regulated by the Aurora-B kinase and RepoMan (recruits PP1 onto mitotic chromatin at anaphase)-associated phosphatases PP1/PP2A. Aurora B is overexpressed in many cancers but, surprisingly, this only rarely causes lethal aneuploidy. Here we show that RepoMan abundance is regulated by the same mechanisms that control Aurora B, including FOXM1-regulated expression and proteasomal degradation following ubiquitination by APC/C-CDH1 or SCF^FBXW7. The deregulation of these mechanisms can account for the balanced co-overexpression of Aurora B and RepoMan in many cancers, which limits chromosome segregation errors. In addition, Aurora B and RepoMan independently promote cancer cell proliferation by reducing checkpoint-­induced cell-cycle arrest during interphase. The co–up-regulation of RepoMan and Aurora B in tumors is inversely correlated with patient survival, underscoring its potential importance for tumor progression. Finally, we demonstrate that high RepoMan levels sensitize cancer cells to Aurora-B inhibitors. Hence, the co–up-regulation of RepoMan and Aurora B is associated with tumor aggressiveness but also exposes a vulnerable target for therapeutic intervention.

Systematic investigation of the prognostic value of cell division cycle-associated proteins for clear cell renal cell carcinoma patients

Aim: To explore the prognostic value of the cell division cycle-associated proteins (CDCA) family in clear cell renal cell carcinoma. Methods: Gene profiles were collected from the The Cancer Genome Atlas-Kidney Renal Clear Cell Carcinoma (TCGA-KIRC), the GSE29609 and GSE22541 datasets. Genetic alteration and DNA methylation data were downloaded from the cBioPortal and MethSurv. The functional enrichment data were analyzed by Metascape. Results: The mRNA expression of the CDCAs, except CBX2, was significantly increased in clear cell renal cell carcinoma patients. Genetic alterations might affect the expression of CDCAs, but promotor methylation does not affect CDCA gene expression. The overall expression of the CDCAs, according to the The Cancer Genome Atlas-KIRC database (hazard ratio [HR]: 2.18), the GSE29609 (HR: 6.08) and GSE22541 (HR: 6.73), was significantly associated with unfavorable overall survival. In addition, genes co-expressed with CDCAs (R² ≥0.3) were highly associated with cell division and the FOXM1 pathway. Conclusion: Our study demonstrated that the aberrant expression of CDCA gene family members plays an indispensable role in tumorigenesis.

Cell Cycle and DNA Repair Regulation in the Damage Response: Protein Phosphatases Take Over the Reins

Cells are constantly suffering genotoxic stresses that affect the integrity of our genetic material. Genotoxic insults must be repaired to avoid the loss or inappropriate transmission of the genetic information, a situation that could lead to the appearance of developmental abnormalities and tumorigenesis. To combat this threat, eukaryotic cells have evolved a set of sophisticated molecular mechanisms that are collectively known as the DNA damage response (DDR). This surveillance system controls several aspects of the cellular response, including the detection of lesions, a temporary cell cycle arrest, and the repair of the broken DNA. While the regulation of the DDR by numerous kinases has been well documented over the last decade, the complex roles of protein dephosphorylation have only recently begun to be investigated. Here, we review recent progress in the characterization of DDR-related protein phosphatases during the response to a DNA lesion, focusing mainly on their ability to modulate the DNA damage checkpoint and the repair of the damaged DNA. We also discuss their protein composition and structure, target specificity, and biochemical regulation along the different stages encompassed in the DDR. The compilation of this information will allow us to better comprehend the physiological significance of protein dephosphorylation in the maintenance of genome integrity and cell viability in response to genotoxic stress.

KRCC1: A potential therapeutic target in ovarian cancer

Using a systems biology approach to prioritize potential points of intervention in ovarian cancer, we identified the lysine rich coiled-coil 1 (KRCC1), as a potential target. High-grade serous ovarian cancer patient tumors and cells express significantly higher levels of KRCC1 which correlates with poor overall survival and chemoresistance. We demonstrate that KRCC1 is predominantly present in the chromatin-bound nuclear fraction, interacts with HDAC1, HDAC2, and with the serine-threonine phosphatase PP1CC. Silencing KRCC1 inhibits cellular plasticity, invasive properties, and potentiates apoptosis resulting in reduced tumor growth. These phenotypes are associated with increased acetylation of histones and with increased phosphorylation of H2AX and CHK1, suggesting the modulation of transcription and DNA damage that may be mediated by the action of HDAC and PP1CC, respectively. Hence, we address an urgent need to develop new targets in cancer.

Therapeutic Potential of the miRNA-ATM Axis in the Management of Tumor Radioresistance

The ataxia-telangiectasia mutated (ATM) protein kinase is widely known for its function as a chief mobilizer of the DNA damage response (DDR) upon DNA double-strand breaks. ATM orchestrates the DDR by modulating the expression of various miRNAs through several mechanisms. On the other hand, a set of miRNAs contribute to tight regulation of ATM by directly targeting the 3'-untranslated region of ATM mRNA. This review addresses the therapeutic application and molecular mechanisms that underlie the intricate interactions between miRNAs and ATM. It also describes therapeutic delivery of miRNAs in different environments such as hypoxic tumor microenvironments.

Phosphatase-dependent fluctuations in DNA-damage checkpoint activation at partially defective telomeres

Telomeres protect the ends of eukaryotic chromosomes, and telomere shortening causes irreversible cell-cycle arrest through activation of the DNA-damage checkpoint. In this study, we found that deletion of PPH3, encoding a 2A-like protein phosphatase, accelerated telomere-shortening-mediated senescence without affecting normal telomere length or the telomere erosion rate in Saccharomyces cerevisiae. Moreover, the loss of PPH3 increased sensitivity to telomere dysfunction. The detection of telomere abnormalities by DNA-damage sensors was not an all-or-none response, implying that Pph3 helps determine the border between normal and dysfunctional telomeres by suppressing premature activation of the DNA-damage checkpoint.

CDCA2 promotes the proliferation of colorectal cancer cells by activating the AKT/CCND1 pathway in vitro and in vivo

BACKGROUND

Cell division cycle associated 2 (CDCA2), upregulated in lung adenocarcinoma and oral squamous cell carcinoma, may be related to some malignant diseases. Nevertheless, its role in colorectal cancer (CRC) remains unknown.

METHODS

CDCA2 expression was analyzed using The Cancer Genome Atlas (TCGA), quantitative real-time PCR (qRT-PCR), and immunohistochemistry. The impact of CDCA2 on cell proliferation was analyzed via loss- or gain-of-function assays. Furthermore, gene set enrichment analysis was conducted to explore the potential mechanism of CDCA2 in CRC. Lastly, the expression levels of CCND1 and AKT were measured in CRC cell lines.

RESULTS

Our study revealed that CDCA2 expression was associated with tumor progression. Through loss- or gain-of-function assays, we found that upregulation of CDCA2 promoted the proliferation of DLD-1 cells, however, downregulation of CDCA2 in SW480 cells restrained proliferative capacity both in vitro and in vivo. The results of flow cytometry showed that CDCA2 promoted cell cycle progression via upregulation of CCND1 in CRC cell lines. In the following experiments, we found that CDCA2 regulated CCND1 expression through activating the PI3K/AKT pathway, and confirmed this using a specific PI3K inhibitor (LY294002).

CONCLUSIONS

This study demonstrates that overexpression of CDCA2 might target CCND1 to promote CRC cell proliferation and tumorigenesis through activation of the PI3K/AKT pathway.

SIRT7-mediated ATM deacetylation is essential for its deactivation and DNA damage repair

The activation of ataxia-telangiectasia mutated (ATM) upon DNA damage involves a cascade of reactions, including acetylation by TIP60 and autophosphorylation. However, how ATM is progressively deactivated after completing DNA damage repair remains obscure. Here, we report that sirtuin 7 (SIRT7)-mediated deacetylation is essential for dephosphorylation and deactivation of ATM. We show that SIRT7, a class III histone deacetylase, interacts with and deacetylates ATM in vitro and in vivo. In response to DNA damage, SIRT7 is mobilized onto chromatin and deacetylates ATM during the late stages of DNA damage response, when ATM is being gradually deactivated. Deacetylation of ATM by SIRT7 is prerequisite for its dephosphorylation by its phosphatase WIP1. Consequently, depletion of SIRT7 or acetylation-mimic mutation of ATM induces persistent ATM phosphorylation and activation, thus leading to impaired DNA damage repair. Together, our findings reveal a previously unidentified role of SIRT7 in regulating ATM activity and DNA damage repair.

Role of protein phosphatases PP1, PP2A, PP4 and Cdc14 in the DNA damage response

Maintenance of genome integrity is fundamental for cellular physiology. Our hereditary information encoded in the DNA is intrinsically susceptible to suffer variations, mostly due to the constant presence of endogenous and environmental genotoxic stresses. Genomic insults must be repaired to avoid loss or inappropriate transmission of the genetic information, a situation that could lead to the appearance of developmental anomalies and tumorigenesis. To safeguard our genome, cells have evolved a series of mechanisms collectively known as the DNA damage response (DDR). This surveillance system regulates multiple features of the cellular response, including the detection of the lesion, a transient cell cycle arrest and the restoration of the broken DNA molecule. While the role of multiple kinases in the DDR has been well documented over the last years, the intricate roles of protein dephosphorylation have only recently begun to be addressed. In this review, we have compiled recent information about the function of protein phosphatases PP1, PP2A, PP4 and Cdc14 in the DDR, focusing mainly on their capacity to regulate the DNA damage checkpoint and the repair mechanism encompassed in the restoration of a DNA lesion.

Phosphatase 1 Nuclear Targeting Subunit Mediates Recruitment and Function of Poly (ADP-Ribose) Polymerase 1 in DNA Repair

PARP, particularly PARP1, plays an essential role in the detection and repair of DNA single-strand breaks and double-strand breaks. PARP1 accumulates at DNA damage sites within seconds after DNA damage to catalyze the massive induction of substrate protein poly ADP-ribosylation (PARylation). However, the molecular mechanisms underlying the recruitment and activation of PARP1 in DNA repair are not fully understood. Here we show that phosphatase 1 nuclear targeting subunit 1 (PNUTS) is a robust binding partner of PARP1. Inhibition of PNUTS led to strong accumulation of endogenous DNA damage and sensitized the cellular response to a wide range of DNA-damaging agents, implicating PNUTS as an essential and multifaceted regulator of DNA repair. Recruitment of PNUTS to laser-induced DNA damage was similar to that of PARP1, and depletion or inhibition of PARP1 abrogated recruitment of PNUTS to sites of DNA damage. Conversely, PNUTS was required for efficient induction of substrate PARylation after DNA damage. PNUTS bound the BRCA1 C-terminal (BRCT) domain of PARP1 and was required for the recruitment of PARP1 to sites of DNA damage. Finally, depletion of PNUTS rendered cancer cells hypersensitive to PARP inhibition. Taken together, our study characterizes PNUTS as an essential partner of PARP1 in DNA repair and a potential drug target in cancer therapy. SIGNIFICANCE: These findings reveal PNUTS as an essential functional partner of PARP1 in DNA repair and suggest its inhibition as a potential therapeutic strategy in conjunction with DNA-damaging agents or PARP inhibitors.See related commentary by Murai and Pommier, p. 2460.

Chlamydia trachomatis Inhibits Homologous Recombination Repair of DNA Breaks by Interfering with PP2A Signaling

Cervical and ovarian cancers exhibit characteristic mutational signatures that are reminiscent of mutational processes, including defective homologous recombination (HR) repair. How these mutational processes are initiated during carcinogenesis is largely unclear. Chlamydia trachomatis infections are epidemiologically associated with cervical and ovarian cancers. Previously, we showed that C. trachomatis induces DNA double-strand breaks (DSBs) but suppresses Ataxia-telangiectasia mutated (ATM) activation and cell cycle checkpoints. The mechanisms by which ATM regulation is modulated and its consequences for the repair pathway in C. trachomatis-infected cells remain unknown. Here, we found that Chlamydia bacteria interfere with the usual response of PP2A to DSBs. As a result, PP2A activity remains high, as the level of inhibitory phosphorylation at Y307 remains unchanged following C. trachomatis-induced DSBs. Protein-protein interaction analysis revealed that C. trachomatis facilitates persistent interactions of PP2A with ATM, thus suppressing ATM activation. This correlated with a remarkable lack of homologous recombination (HR) repair in C. trachomatis-infected cells. Chemical inhibition of PP2A activity in infected cells released ATM from PP2A, resulting in ATM phosphorylation. Activated ATM was then recruited to DSBs and initiated downstream signaling, including phosphorylation of MRE11 and NBS1 and checkpoint kinase 2 (Chk2)-mediated activation of the G2/M cell cycle checkpoint in C. trachomatis-infected cells. Further, PP2A inhibition led to the restoration of C. trachomatis-suppressed HR DNA repair function. Taking the data together, this study revealed that C. trachomatis modulates PP2A signaling to suppress ATM activation to prevent cell cycle arrest, thus contributing to a deficient high-fidelity HR pathway and a conducive environment for mutagenesis.IMPORTANCEChlamydia trachomatis induces DNA double-strand breaks in host cells but simultaneously inhibits proper DNA damage response and repair mechanisms. This may render host cells prone to loss of genetic integrity and transformation. Here we show that C. trachomatis prevents activation of the key DNA damage response mediator ATM by preventing the release from PP2A, leading to a complete absence of homologous recombination repair in host cells.

Phosphatase 1 Nuclear Targeting Subunit (PNUTS) Regulates Aurora Kinases and Mitotic Progression

Mitotic progression is regulated largely by reversible phosphorylation events that are mediated by mitotic kinases and phosphatases. Protein phosphatase 1 (PP1) has been shown to play a crucial role in regulation of mitotic entry, progression, and exit. We previously observed, in Xenopus egg extracts, that phosphatase 1 nuclear targeting subunit (PPP1R10/PNUTS) acts as a mitotic regulator by negatively modulating PP1. This study investigates the role of PNUTS in mitotic progression in mammalian cells, and demonstrates that PNUTS expression is elevated in mitosis and depletion partially blocks mitotic entry. Cells that enter mitosis after PNUTS knockdown exhibit frequent chromosome mis-segregation. Aurora A/B kinase complexes and several kinetochore components are identified as PNUTS-associated proteins. PNUTS depletion suppresses the activation of Aurora A/B kinases, and disrupts the spatiotemporal regulation of the chromosomal passenger complex (CPC). PNUTS dynamically localizes to kinetochores, and is required for the activation of the spindle assembly checkpoint. Finally, PNUTS depletion sensitizes the tumor cell response to Aurora inhibition, suggesting that PNUTS is a potential drug target in combination anticancer therapy. IMPLICATIONS: Delineation of how PNUTS governs the mitotic activation and function of Aurora kinases will improve the understanding of the complex phospho-regulation in mitotic progression, and suggest new options to enhance the therapeutic efficacy of Aurora inhibitors.

A substrate-trapping strategy for protein phosphatase PP1 holoenzymes using hypoactive subunit fusions

The protein Ser/Thr phosphatase PP1 catalyzes an important fraction of protein dephosphorylation events and forms highly specific holoenzymes through an association with regulatory interactors of protein phosphatase one (RIPPOs). The functional characterization of individual PP1 holoenzymes is hampered by the lack of straightforward strategies for substrate mapping. Because efficient substrate recruitment often involves binding to both PP1 and its associated RIPPO, here we examined whether PP1-RIPPO fusions can be used to trap substrates for further analysis. Fusions of an hypoactive point mutant of PP1 and either of four tested RIPPOs accumulated in HEK293T cells with their associated substrates and were co-immunoprecipitated for subsequent identification of the substrates by immunoblotting or MS analysis. Hypoactive fusions were also used to study RIPPOs themselves as substrates for associated PP1. In contrast, substrate trapping was barely detected with active PP1-RIPPO fusions or with nonfused PP1 or RIPPO subunits. Our results suggest that hypoactive fusions of PP1 subunits represent an easy-to-use tool for substrate identification of individual holoenzymes.

Serine/threonine protein phosphatase 1 (PP1) controls growth and reproduction in Schistosoma japonicum

Schistosomiasis is a human parasitic disease caused by flatworms of the genus Schistosoma. Adult female schistosomes produce numerous eggs that are responsible for the pathogenesis and transmission of the disease, and the maturation of female gonads depends on the permanent pairing of females and males. Signaling protein kinases have been proven to control female gonad differentiation after pairing; however, little is known about the roles of protein phosphatases in the developmental and reproductive biology of schistosomes. Here we explored 3 genes encoding catalytic subunits of serine/threonine protein phosphatase 1 (PP1c) that were structurally and evolutionarily conserved in Schistosoma japonicum. In situ hybridization showed transcripts of 3 Sj-pp1c genes mainly localized in the reproductive organs and tissues. Triple knockdown of Sj-pp1c genes by RNA interference caused stunted growth and decreased pairing stability of worm pairs, as well as a remarkable reduction in cell proliferation activity and defects in reproductive maturation and fecundity. Transcriptomic analysis post-RNA interference suggested that Sj-pp1c genes are involved in controlling worm development and maturation mainly by regulating cell proliferation, eggshell synthesis, nutritional metabolism, cytoskeleton organization, and neural process. Our study provides the first insight into the fundamental contribution of Sj-PP1c to molecular mechanisms underlying the reproductive biology of schistosomes.-Zhao, L., Lu, Z., He, X., Mughal, M. N., Fang, R., Zhou, Y., Zhao, J., Gasser, R. B., Grevelding, C. G., Ye, Q., Hu, M. Serine/threonine protein phosphatase 1 (PP1) controls growth and reproduction in Schistosoma japonicum.

Role of Protein Phosphatase 1 and Inhibitor of Protein Phosphatase 1 in Nitric Oxide-Dependent Inhibition of the DNA Damage Response in Pancreatic β-Cells

Nitric oxide is produced at micromolar levels by pancreatic β-cells during exposure to proinflammatory cytokines. While classically viewed as damaging, nitric oxide also activates pathways that promote β-cell survival. We have shown that nitric oxide, in a cell type-selective manner, inhibits the DNA damage response (DDR) and, in doing so, protects β-cells from DNA damage-induced apoptosis. This study explores potential mechanisms by which nitric oxide inhibits DDR signaling. We show that inhibition of DDR signaling (measured by γH2AX formation and the phosphorylation of KAP1) is selective for nitric oxide, as other forms of reactive oxygen/nitrogen species do not impair DDR signaling. The kinetics and broad range of DDR substrates that are inhibited suggest that protein phosphatase activation may be one mechanism by which nitric oxide attenuates DDR signaling in β-cells. While protein phosphatase 1 (PP1) is a primary regulator of DDR signaling and an inhibitor of PP1 (IPP1) is selectively expressed only in β-cells, disruption of either IPP1 or PP1 does not modify the inhibitory actions of nitric oxide on DDR signaling in β-cells. These findings support a PP1-independent mechanism by which nitric oxide selectively impairs DDR signaling and protects β-cells from DNA damage-induced apoptosis.

Protein phosphatases at the nuclear envelope

The nuclear envelope (NE) is a unique topological structure formed by lipid membranes (Inner and Outer Membrane: IM and OM) interrupted by open channels (Nuclear Pore complexes). Besides its well-established structural role in providing a physical separation between the genome and the cytoplasm and regulating the exchanges between the two cellular compartments, it has become quite evident in recent years that the NE also represents a hub for localized signal transduction. Mechanical, stress, or mitogen signals reach the nucleus and trigger the activation of several pathways, many effectors of which are processed at the NE. Therefore, the concept of the NE acting just as a barrier needs to be expanded to embrace all the dynamic processes that are indeed associated with it. In this context, dynamic protein association and turnover coupled to reversible post-translational modifications of NE components can provide important clues on how this integrated cellular machinery functions as a whole. Reversible protein phosphorylation is the most used mechanism to control protein dynamics and association in cells. Keys to the reversibility of the system are protein phosphatases and the regulation of their activity in space and time. As the NE is clearly becoming an interesting compartment for the control and transduction of several signalling pathways, in this review we will focus on the role of Protein Phosphatases at the NE since the significance of this class of proteins in this context has been little explored.

Protein interactomes of protein phosphatase 2A B55 regulatory subunits reveal B55-mediated regulation of replication protein A under replication stress

The specific function of PP2A, a major serine/threonine phosphatase, is mediated by regulatory targeting subunits, such as members of the B55 family. Although implicated in cell division and other pathways, the specific substrates and functions of B55 targeting subunits are largely undefined. In this study we identified over 100 binding proteins of B55α and B55β in Xenopus egg extracts that are involved in metabolism, mitochondria function, molecular trafficking, cell division, cytoskeleton, DNA replication, DNA repair, and cell signaling. Among the B55α and B55β-associated proteins were numerous mitotic regulators, including many substrates of CDK1. Consistently, upregulation of B55α accelerated M-phase exit and inhibited M-phase entry. Moreover, specific substrates of CDK2, including factors of DNA replication and chromatin remodeling were identified within the interactomes of B55α and B55β, suggesting a role for these phosphatase subunits in DNA replication. In particular, we confirmed in human cells that B55α binds RPA and mediates the dephosphorylation of RPA2. The B55-RPA association is disrupted after replication stress, consistent with the induction of RPA2 phosphorylation. Thus, we report here a new mechanism that accounts for both how RPA phosphorylation is modulated by PP2A and how the phosphorylation of RPA2 is abruptly induced after replication stress.

Distinct expression of CDCA3, CDCA5, and CDCA8 leads to shorter relapse free survival in breast cancer patient

Breast cancer is a dangerous disease that results in high mortality rates for cancer patients. Many methods have been developed for the treatment and prevention of this disease. Determining the expression patterns of certain target genes in specific subtypes of breast cancer is important for developing new therapies for breast cancer. In the present study, we performed a holistic approach to screening the mRNA expression of six members of the cell division cycle-associated gene family (CDCA) with a focus on breast cancer using the Oncomine and The Cancer Cell Line Encyclopedia (CCLE) databases. Furthermore, Gene Expression-Based Outcome for Breast Cancer Online (GOBO) was also used to deeply mine the expression of each CDCA gene in clinical breast cancer tissue and breast cancer cell lines. Finally, the mRNA expression of the CDCA genes as related to breast cancer patient survival were analyzed using a Kaplan-Meier plot. CDCA3, CDCA5, and CDCA8 mRNA expression levels were significantly higher than the control sample in both clinical tumor sample and cancer cell lines. These highly expressed genes in the tumors of breast cancer patients dramatically reduced patient survival. The interaction network of CDCA3, CDCA5, and CDCA8 with their co-expressed genes also revealed that CDCA3 expression was highly correlated with cell cycle related genes such as CCNB2, CDC20, CDKN3, and CCNB1. CDCA5 expression was correlated with BUB1 and TRIP13, while CDCA8 expression was correlated with BUB1 and CCNB1. Altogether, these findings suggested CDCA3, CDCA5, and CDCA8 could have a high potency as targeted breast cancer therapies.

Protein phosphatase 1 and phosphatase 1 nuclear targeting subunit-dependent regulation of DNA-dependent protein kinase and non-homologous end joining

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) plays a key role in mediating non-homologous end joining (NHEJ), a major repair pathway for DNA double-strand breaks (DSBs). The activation, function and dynamics of DNA-PKcs is regulated largely by its reversible phosphorylation at numerous residues, many of which are targeted by DNA-PKcs itself. Interestingly, these DNA-PKcs phosphorylation sites function in a distinct, and sometimes opposing manner, suggesting that they are differentially regulated via complex actions of both kinases and phosphatases. In this study we identified several phosphatase subunits as potential DSB-associated proteins. In particular, protein phosphatase 1 (PP1) is recruited to a DSB-mimicking substrate in Xenopus egg extracts and sites of laser microirradiation in human cells. Depletion of PP1 impairs NHEJ in both Xenopus egg extracts and human cells. PP1 binds multiple motifs of DNA-PKcs, regulates DNA-PKcs phosphorylation, and is required for DNA-PKcs activation after DNA damage. Interestingly, phosphatase 1 nuclear targeting subunit (PNUTS), an inhibitory regulator of PP1, is also recruited to DNA damage sites to promote NHEJ. PNUTS associates with the DNA-PK complex and is required for DNA-PKcs phosphorylation at Ser-2056 and Thr-2609. Thus, PNUTS and PP1 together fine-tune the dynamic phosphorylation of DNA-PKcs after DNA damage to mediate NHEJ.

CDCA2 promotes lung adenocarcinoma cell proliferation and predicts poor survival in lung adenocarcinoma patients

Cell division cycle associated 2(CDCA2) is overexpressed in neuroblastoma and oral squamous cell carcinoma, and its overexpression positively correlates to tumor progression. However, the biological and clinical significance of CDCA2 in lung adenocarcinoma(LAC) has never been investigated. We determined the expression profile and clinical significance of CDCA2 using The Cancer Genome Atlas(TCGA) and tissue microarray(TMA). Furthermore, we explored the biological function of CDCA2 both in vitro and in vivo. A great upregulation of CDCA2 was observed in LAC tissues compared with adjacent normal tissues. Importantly, Cox regression analysis indicated that high level of CDCA2 was an independent risk factor for overall survival(OS) in LAC patients (TCGA: HR = 1.720, p = 0.004; TMA: HR = 1.971, p = 0.023). Inhibition of CDCA2 suppressed the proliferation of LAC cells via G1 phase arrest by downregulating cyclin E1(CCNE1), while overexpression of CDCA2 promoted LAC cells proliferation by upregulating CCNE1. Moreover, the oncogenic activity of CDCA2 was also confirmed in vivo. In conclusion, CDCA2 promotes proliferation of LAC cells and predicts poor prognosis in LAC patients. CDCA2 might play a significant role in LAC progression.

Paths from DNA damage and signaling to genome rearrangements via homologous recombination

DNA damage is a constant threat to genome integrity. DNA repair and damage signaling networks play a central role maintaining genome stability, suppressing tumorigenesis, and determining tumor response to common cancer chemotherapeutic agents and radiotherapy. DNA double-strand breaks (DSBs) are critical lesions induced by ionizing radiation and when replication forks encounter damage. DSBs can result in mutations and large-scale genome rearrangements reflecting mis-repair by non-homologous end joining or homologous recombination. Ionizing radiation induces genetic change immediately, and it also triggers delayed events weeks or even years after exposure, long after the initial damage has been repaired or diluted through cell division. This review covers DNA damage signaling and repair pathways and cell fate following genotoxic insult, including immediate and delayed genome instability and cell survival/cell death pathways.

Cell cycle-dependent regulation of Greatwall kinase by protein phosphatase 1 and regulatory subunit 3B

Greatwall (Gwl) kinase plays an essential role in the regulation of mitotic entry and progression. Mitotic activation of Gwl requires both cyclin-dependent kinase 1 (CDK1)-dependent phosphorylation and its autophosphorylation at an evolutionarily conserved serine residue near the carboxyl terminus (Ser-883 in Xenopus). In this study we show that Gwl associates with protein phosphatase 1 (PP1), particularly PP1γ, which mediates the dephosphorylation of Gwl Ser-883. Consistent with the mitotic activation of Gwl, its association with PP1 is disrupted in mitotic cells and egg extracts. During mitotic exit, PP1-dependent dephosphorylation of Gwl Ser-883 occurs prior to dephosphorylation of other mitotic substrates; replacing endogenous Gwl with a phosphomimetic S883E mutant blocks mitotic exit. Moreover, we identified PP1 regulatory subunit 3B (PPP1R3B) as a targeting subunit that can direct PP1 activity toward Gwl. PPP1R3B bridges PP1 and Gwl association and promotes Gwl Ser-883 dephosphorylation. Consistent with the cell cycle-dependent association of Gwl and PP1, Gwl and PPP1R3B dissociate in M phase. Interestingly, up-regulation of PPP1R3B facilitates mitotic exit and blocks mitotic entry. Thus, our study suggests PPP1R3B as a new cell cycle regulator that functions by governing Gwl dephosphorylation.