Road to the crossroads of life and death: linking sister chromatid cohesion and separation to aneuploidy, apoptosis and cancer

Identification of common factors among fibrosarcoma, rhabdomyosarcoma, and osteosarcoma by network analysis

Sarcoma cancers are uncommon malignant tumors, and there are many subgroups, including fibrosarcoma (FS), which mainly affects middle-aged and older adults in deep soft tissues. Rhabdomyosarcoma (RMS), on the other hand, is the most common soft-tissue sarcoma in children and is located in the head and neck area. Osteosarcomas (OS) is the predominant form of primary bone cancer among young adults, primarily resulting from sporadically random mutations. This frequently results in the dissemination of cancer cells to the lungs, commonly known as metastasis. Mesodermal cells are the origin of sarcoma cancers. In this study, a rather radical approach has been applied. Instead of comparing homogenous cancer types, we focus on three main subtypes of sarcoma: fibrosarcoma, rhabdomyosarcoma, and osteosarcoma, and compare their gene expression with normal cell groups to identify the differentially expressed genes (DEGs). Next, by applying protein-protein interaction (PPI) network analysis, we determine the hub genes and crucial factors, such as transcription factors (TFs), affected by these types of cancer. Our findings indicate a modification in a range of pathways associated with cell cycle, extracellular matrix, and DNA repair in these three malignancies. Results showed that fibrosarcoma (FS), rhabdomyosarcoma (RMS), and osteosarcoma (OS) had 653, 1270, and 2823 differentially expressed genes (DEGs), respectively. Interestingly, there were 24 DEGs common to all three types. Network analysis showed that the fibrosarcoma network had two sub-networks identified in FS that contributed to the catabolic process of collagen via the G-protein coupled receptor signaling pathway. The rhabdomyosarcoma network included nine sub-networks associated with cell division, extracellular matrix organization, mRNA splicing via spliceosome, and others. The osteosarcoma network has 13 sub-networks, including mRNA splicing, sister chromatid cohesion, DNA repair, etc. In conclusion, the common DEGs identified in this study have been shown to play significant and multiple roles in various other cancers based on the literature review, indicating their significance.

Recurrent Germline Variant in RAD21 Predisposes Children to Lymphoblastic Leukemia or Lymphoma

Somatic loss of function mutations in cohesin genes are frequently associated with various cancer types, while cohesin disruption in the germline causes cohesinopathies such as Cornelia-de-Lange syndrome (CdLS). Here, we present the discovery of a recurrent heterozygous RAD21 germline aberration at amino acid position 298 (p.P298S/A) identified in three children with lymphoblastic leukemia or lymphoma in a total dataset of 482 pediatric cancer patients. While RAD21 p.P298S/A did not disrupt the formation of the cohesin complex, it altered RAD21 gene expression, DNA damage response and primary patient fibroblasts showed increased G2/M arrest after irradiation and Mitomycin-C treatment. Subsequent single-cell RNA-sequencing analysis of healthy human bone marrow confirmed the upregulation of distinct cohesin gene patterns during hematopoiesis, highlighting the importance of RAD21 expression within proliferating B- and T-cells. Our clinical and functional data therefore suggest that RAD21 germline variants can predispose to childhood lymphoblastic leukemia or lymphoma without displaying a CdLS phenotype.

miR-122 Inhibits the Cervical Cancer Development by Targeting the Oncogene RAD21

Cervical cancer (CC) is one of the most frequently diagnosed tumors in female. miR-122 has been proved to be dominant in CC. The particular role of miR-122 in CC is unclear. Thus, we attempted to investigate the prognostic role of miR-122 in CC. We used the database of Kaplan-Meier curve plot. Growth and apoptosis of C33A cells were detected by CCK-8, colony formation assay, transwell assays and flow cytometry analysis. The target gene of miR-122 was identified using bioinformatics, q-PCR, western blot and luciferase assay. It showed that CC patients with overexpression of miR-122 have a better prognosis in the Kaplan-Meier plot database analysis. Overexpressed miR-122 inhibited the malignant growth and induced apoptosis of CC. miR-122 targeting of RAD21 cohesin complex component (RAD21) was identified using bioinformatics, Q-PCR, western blot and luciferase assay analyses. Moreover, we found miR-122 conduct its functions via RAD21 via the PI3K/AKT signaling pathway. Importantly, overexpression of RAD21 restored the roles of miR-122 in CC. Our data suggested that miR-122 could block malignant growth and promoted apoptosis by targeting RAD21 in CC. Our finding indicates miR-122 could potentially participate in the pathogenesis and be a biomarker or the potential therapeutic target of CC.

Cohesin subunit RAD21: From biology to disease

RAD21 (also known as KIAA0078, NXP1, HR21, Mcd1, Scc1, and hereafter called RAD21), an essential gene, encodes a DNA double-strand break (DSB) repair protein that is evolutionarily conserved in all eukaryotes from budding yeast to humans. RAD21 protein is a structural component of the highly conserved cohesin complex consisting of RAD21, SMC1a, SMC3, and SCC3 [STAG1 (SA1) and STAG2 (SA2) in metazoans] proteins, involved in sister chromatid cohesion. This function is essential for proper chromosome segregation, post-replicative DNA repair, and prevention of inappropriate recombination between repetitive regions. In interphase, cohesin also functions in the control of gene expression by binding to numerous sites within the genome. In addition to playing roles in the normal cell cycle and DNA DSB repair, RAD21 is also linked to the apoptotic pathways. Germline heterozygous or homozygous missense mutations in RAD21 have been associated with human genetic disorders, including developmental diseases such as Cornelia de Lange syndrome (CdLS) and chronic intestinal pseudo-obstruction (CIPO) called Mungan syndrome, respectively, and collectively termed as cohesinopathies. Somatic mutations and amplification of the RAD21 have also been widely reported in both human solid and hematopoietic tumors. Considering the role of RAD21 in a broad range of cellular processes that are hot spots in neoplasm, it is not surprising that the deregulation of RAD21 has been increasingly evident in human cancers. Herein, we review the biology of RAD21 and the cellular processes that this important protein regulates and discuss the significance of RAD21 deregulation in cancer and cohesinopathies.

Nanoscale dynamics of centromere nucleosomes and the critical roles of CENP-A

In the absence of a functioning centromere, chromosome segregation becomes aberrant, leading to an increased rate of aneuploidy. The highly specific recognition of centromeres by kinetochores suggests that specific structural characteristics define this region, however, the structural details and mechanism underlying this recognition remains a matter of intense investigation. To address this, high-speed atomic force microscopy was used for direct visualization of the spontaneous dynamics of CENP-A nucleosomes at the sub-second time scale. We report that CENP-A nucleosomes change conformation spontaneously and reversibly, utilizing two major pathways: unwrapping, and looping of the DNA; enabling core transfer between neighboring DNA substrates. Along with these nucleosome dynamics we observed that CENP-A stabilizes the histone core against dissociating to histone subunits upon unwrapping DNA, unique from H3 cores which are only capable of such plasticity in the presence of remodeling factors. These findings have implications for the dynamics and integrity of nucleosomes at the centromere.

Dysfunction of Sister Chromatids Separation Promotes Progression of Hepatocellular Carcinoma According to Analysis of Gene Expression Profiling

Despite studying the various molecular mechanisms of hepatocellular carcinoma (HCC), effective drugs and biomarkers in HCC therapy are still scarce. The present study was designed to investigate dysregulated pathways, novel biomarkers and therapeutic targets for HCC. The gene expression dataset of GSE14520, which included 362 tumor and their paired non-tumor tissues of HCC, was extracted for processing by the Robust multi-array average (RMA) algorithm in the R environment. SAM methods were leveraged to identify differentially expressed genes (DEGs). Functional analysis of DEGs was performed using DAVID. The GeneMania and Cytohubba were used to construct the PPI network. To avoid individual bias, GSEA and survival analysis were employed to verify the results. The results of these analyses indicated that separation of sister chromatids was the most aberrant phase in the progression of HCC, and the most frequently involved genes, EZH2, GINS1, TPX2, CENPF, and BUB1B, require further study to be used as drug targets or biomarkers in diagnosis and treatment of HCC.

The Expression of Cohesin Subunit SA2 Predicts Breast Cancer Survival

Cohesin is one of the main regulators of sister chromatid separation during the metaphase/anaphase transition. It is a multiprotein complex consisting of 4 core subunits, one of those being the SA2 subunit. SA2 plays the final role in dismantling the cohesion complex from the sister chromatids and also functions in DNA double-strand break repair and gene regulation. There is increasing evidence regarding the involvement of both overexpression and underexpression of cohesin in cancer. Here, we present expression patterns of SA2 in different types of human breast tissue, and the prognostic analysis in the material from breast cancer patients with long-term follow-up. SA2 immunoexpression was evaluated in benign, precancerous, and malignant breast tissue, and was classified into low-intensity or high-intensity groups. The DNA content was determined by image cytometry on breast cancer cell imprints. Prognostic analyses were based on 445 breast cancer patients with upto 20 years' follow-up. SA2 immunoexpression was equally high in both benign and precancerous breast tissue. Instead, 72% of the invasive breast cancers showed deficient SA2 expression. These patients were also associated with an unfavorable outcome as indicated by a 1.6-fold risk of breast cancer death (P=0.0208). The majority (75%) of the patients with low SA2 expression were alive 6.0 years after the diagnosis, whereas the majority of the patients with high SA2 expression survived 17.6 years after the diagnosis. No statistically significant association could be detected between SA2 immunoexpression and DNA aneuploidy. Our results and previous literature indicate that decreased SA2 immunoexpression is associated with malignant breast disease and a particularly unfavorable course of disease.

Of Rings and Rods: Regulating Cohesin Entrapment of DNA to Generate Intra- and Intermolecular Tethers

The clinical relevance of cohesin in DNA repair, tumorigenesis, and severe birth defects continues to fuel efforts in understanding cohesin structure, regulation, and enzymology. Early models depicting huge cohesin rings that entrap two DNA segments within a single lumen are fading into obscurity based on contradictory findings, but elucidating cohesin structure amid a myriad of functions remains challenging. Due in large part to integrated uses of a wide range of methodologies, recent advances are beginning to cast light into the depths that previously cloaked cohesin structure. Additional efforts similarly provide new insights into cohesin enzymology: specifically, the discoveries of ATP-dependent transitions that promote cohesin binding and release from DNA. In combination, these efforts posit a new model that cohesin exists primarily as a relatively flattened structure that entraps only a single DNA molecule and that subsequent ATP hydrolysis, acetylation, and oligomeric assembly tether together individual DNA segments.

Enhanced expression of cohesin loading factor NIPBL confers poor prognosis and chemotherapy resistance in non-small cell lung cancer

BACKGROUND

NIPBL, the sister chromatid cohesion 2 (SCC2) human homolog, is a cohesin loading factor which is essential for deposition of cohesin onto the sister chromatid. Recent studies have shown that NIPBL contribute to sister chromatid cohesion and plays a critical role in development, DNA repair, and gene regulation. In this study, we measured the expression of NIPBL in clinical non-small cell lung cancer specimens, and determined its effects on cellular processes and chemosensitivity in vitro.

METHODS

NIPBL immunohistochemistry was performed on 123 lung adenocarcinoma samples. Through knockdown of NIPBL protein expression, non-small cell lung cancer cell lines were used to test the potential involvement of NIPBL silencing on cell proliferation, migration, invasion, and apoptosis. Chemosensitivity was assessed with clonogenic assays, and chromatin immunoprecipitation assays were performed to analyze the relationship between NIPBL and signal transducers and activators of transcription 3 (STAT3).

RESULTS

Immunohistochemical analysis showed that high expression of NIPBL was strongly correlated with poor prognosis, tumor differentiation, and lymph node metastasis. Survival analysis further indicated that NIPBL expression was a potential prognostic factor for non-small cell lung cancer. Knockdown of NIPBL in non-small cell lung cancer cell lines significantly reduced cellular proliferation, migration, and invasion, and enhanced cellular apoptosis and sensitivity to cisplatin, paclitaxel, and gemcitabine hydrochloride. NIPBL bound to the promoter region of the STAT3 gene, directly regulating the expression of STAT3.

CONCLUSIONS

These data suggested that NIPBL played a significant role in lung carcinogenesis. NIPBL expression conferred poor prognosis and resistance to chemotherapy in non-small cell lung cancer, suggesting that NIPBL may be a novel therapeutic target.

MMTV-Espl1 transgenic mice develop aneuploid, estrogen receptor alpha (ERα)-positive mammary adenocarcinomas

Separase, a protease encoded by the ESPL1 gene, cleaves the chromosomal cohesin during mitosis. Separase protein and transcripts are overexpressed in a wide range of human cancers (Meyer et al., Clin Cancer Res 2009; 15: 2703-2710). To investigate the physiological consequence of Separase overexpression in animals, we have generated a transgenic MMTVEspl1 mouse model that overexpresses Separase protein in the mammary glands. MMTV-Espl1 mice in a C57BL/6 genetic background develop aggressive, highly aneuploid, and estrogen receptor alpha positive (ERα+) mammary adenocarcinomas with an 80% penetrance. The mammary tumors caused by overexpression of Separase, alone or combined with p53 heterozygosity, in mammary epithelium mimic several aspects of the most aggressive forms of human breast cancer, including high levels of genetic instability, cell cycle defects, poor differentiation, distant metastasis, and metaplasia. Histopathologically, MMTV-Espl1 tumors are highly heterogeneous showing features of both luminal as well as basal subtypes of breast cancers, with aggressive disease phenotype. In addition to aneuploidy, Separase overexpression results in chromosomal instability (CIN) including premature chromatid separation (PCS), lagging chromosomes, anaphase bridges, micronuclei, centrosome amplification, multi nucleated cells, gradual accumulation of DNA damage, and progressive loss of tumor suppressors p53 and cadherin gene loci. These results suggest that Separase overexpressing mammary cells are not only susceptible to chromosomal missegregation-induced aneuploidy but also other genetic instabilities including DNA damage and loss of key tumor suppressor gene loci, which in combination can initiate tumorigenesis and disease progression.

Sister chromatid cohesion defects are associated with chromosome instability in Hodgkin lymphoma cells

Background

Chromosome instability manifests as an abnormal chromosome complement and is a pathogenic event in cancer. Although a correlation between abnormal chromosome numbers and cancer exist, the underlying mechanisms that cause chromosome instability are poorly understood. Recent data suggests that aberrant sister chromatid cohesion causes chromosome instability and thus contributes to the development of cancer. Cohesion normally functions by tethering nascently synthesized chromatids together to prevent premature segregation and thus chromosome instability. Although the prevalence of aberrant cohesion has been reported for some solid tumors, its prevalence within liquid tumors is unknown. Consequently, the current study was undertaken to evaluate aberrant cohesion within Hodgkin lymphoma, a lymphoid malignancy that frequently exhibits chromosome instability.

Methods

Using established cytogenetic techniques, the prevalence of chromosome instability and aberrant cohesion was examined within mitotic spreads generated from five commonly employed Hodgkin lymphoma cell lines (L-1236, KM-H2, L-428, L-540 and HDLM-2) and a lymphocyte control. Indirect immunofluorescence and Western blot analyses were performed to evaluate the localization and expression of six critical proteins involved in the regulation of sister chromatid cohesion.

Results

We first confirmed that all five Hodgkin lymphoma cell lines exhibited chromosome instability relative to the lymphocyte control. We then determined that each Hodgkin lymphoma cell line exhibited cohesion defects that were subsequently classified into mild, moderate or severe categories. Surprisingly, ~50% of the mitotic spreads generated from L-540 and HDLM-2 harbored cohesion defects. To gain mechanistic insight into the underlying cause of the aberrant cohesion we examined the localization and expression of six critical proteins involved in cohesion. Although all proteins produced the expected nuclear localization pattern, striking differences in RAD21 expression was observed: RAD21 expression was lowest in L-540 and highest within HDLM-2.

Conclusion

We conclude that aberrant cohesion is a common feature of all five Hodgkin lymphoma cell lines evaluated. We further conclude that aberrant RAD21 expression is a strong candidate to underlie aberrant cohesion, chromosome instability and contribute to the development of the disease. Our findings support a growing body of evidence suggesting that cohesion defects and aberrant RAD21 expression are pathogenic events that contribute to tumor development.

Characterization of the interaction between the cohesin subunits Rad21 and SA1/2

The cohesin complex is responsible for the fidelity of chromosomal segregation during mitosis. It consists of four core subunits, namely Rad21/Mcd1/Scc1, Smc1, Smc3, and one of the yeast Scc3 orthologs SA1 or SA2. Sister chromatid cohesion is generated during DNA replication and maintained until the onset of anaphase. Among the many proposed models of the cohesin complex, the 'core' cohesin subunits Smc1, Smc3, and Rad21 are almost universally displayed as tripartite ring. However, other than its supportive role in the cohesin ring, little is known about the fourth core subunit SA1/SA2. To gain deeper insight into the function of SA1/SA2 in the cohesin complex, we have mapped the interactive regions of SA2 and Rad21 in vitro and ex vivo. Whereas SA2 interacts with Rad21 through a broad region (301-750 aa), Rad21 binds to SA proteins through two SA-binding motifs on Rad21, namely N-terminal (NT) and middle part (MP) SA-binding motif, located at 60-81 aa of the N-terminus and 383-392 aa of the MP of Rad21, respectively. The MP SA-binding motif is a 10 amino acid, α-helical motif. Deletion of these 10 amino acids or mutation of three conserved amino acids (L(385), F(389), and T(390)) in this α-helical motif significantly hinders Rad21 from physically interacting with SA1/2. Besides the MP SA-binding motif, the NT SA-binding motif is also important for SA1/2 interaction. Although mutations on both SA-binding motifs disrupt Rad21-SA1/2 interaction, they had no apparent effect on the Smc1-Smc3-Rad21 interaction. However, the Rad21-Rad21 dimerization was reduced by the mutations, indicating potential involvement of the two SA-binding motifs in the formation of the two-ring handcuff for chromosomal cohesion. Furthermore, mutant Rad21 proteins failed to significantly rescue precocious chromosome separation caused by depletion of endogenous Rad21 in mitotic cells, further indicating the physiological significance of the two SA-binding motifs of Rad21.

Chromosomal instability, aneuploidy and routine high-resolution DNA content analysis in oral cancer risk evaluation

Carcinogen exposure of the oral cavity is thought to create an extensive 'field cancerization'. According to this model, a very early precursor of oral cancer is a patch of normal-appearing mucosa in which stem cells share genetic/genomic aberrations. These precancerous fields then become clinically visible as white and red lesions (leuko- and erythro-plakias), which represent the vast majority of the oral potentially malignant disorders. This review focuses on aneuploidy (where it is from) and on biomarkers associated with DNA aneuploidy in oral mucosa and oral potentially malignant disorders, as detected by DNA image and flow cytometry. Data from the literature strongly support the association of DNA ploidy with dysplasia. However, work is still needed to prove the clinical value of DNA ploidy in large-scale prospective studies. Using high-resolution DNA flow cytometry with fresh/frozen material and the degree of DNA aneuploidy (DNA Index) might improve the prediction of risk of oral cancer development.

The dark side of cohesin: the carcinogenic point of view

Genome instability is a hallmark of cancer cells and how it arises is still not completely understood. Correct chromosome segregation is a pre-requisite for preserving genome integrity. Cohesin helps to ensure faithful chromosome segregation during cell cycle, however, much evidence regarding its functions have come to light over the last few years and suggest that cohesin plays multiple roles in the maintenance of genome stability. Here we review our rapidly increasing knowledge on the involvement of cohesin pathway in genome stability and cancer.

Separase loss of function cooperates with the loss of p53 in the initiation and progression of T- and B-cell lymphoma, leukemia and aneuploidy in mice

Background

Cohesin protease Separase plays a key role in faithful segregation of sister chromatids by cleaving the cohesin complex at the metaphase to anaphase transition. Homozygous deletion of ESPL1 gene that encodes Separase protein results in embryonic lethality in mice and Separase overexpression lead to aneuploidy and tumorigenesis. However, the effect of Separase haploinsufficiency has not been thoroughly investigated.

Methodology/Principal Findings

Here we examined the effect of ESPL1 heterozygosity using a hypomorphic mouse model that has reduced germline Separase activity. We report that while ESPL1 mutant (ESPL1 ^+/hyp) mice have a normal phenotype, in the absence of p53, these mice develop spontaneous T- and B-cell lymphomas, and leukemia with a significantly shortened latency as compared to p53 null mice. The ESPL1 hypomorphic, p53 heterozygous transgenic mice (ESPL1^+/hyp, p53^+/−) also show a significantly reduced life span with an altered tumor spectrum of carcinomas and sarcomas compared to p53^+/− mice alone. Furthermore, ESPL1^+/hyp, p53^−/− mice display significantly higher levels of genetic instability and aneuploidy in normal cells, as indicated by the abnormal metaphase counts and SKY analysis of primary splenocytes.

Conclusions/Significance

Our results indicate that reduced levels of Separase act synergistically with loss of p53 in the initiation and progression of B- and T- cell lymphomas, which is aided by increased chromosomal missegregation and accumulation of genomic instability. ESPL1^+/hyp, p53^−/− mice provide a new animal model for mechanistic study of aggressive lymphoma and also for preclinical evaluation of new agents for its therapy.

Rad51C is essential for embryonic development and haploinsufficiency causes increased DNA damage sensitivity and genomic instability

Homologous recombination is essential for repair of DNA interstrand cross-links and double-strand breaks. The Rad51C protein is one of the five Rad51 paralogs in vertebrates implicated in homologous recombination. A previously described hamster cell mutant defective in Rad51C (CL-V4B) showed increased sensitivity to DNA damaging agents and displayed genomic instability. Here, we identified a splice donor mutation at position +5 of intron 5 of the Rad51C gene in this mutant, and generated mice harboring an analogous base pair alteration. Rad51C(splice) heterozygous animals are viable and do not display any phenotypic abnormalities, however homozygous Rad51C(splice) embryos die during early development (E8.5). Detailed analysis of two CL-V4B revertants, V4B-MR1 and V4B-MR2, that have reduced levels of full-length Rad51C transcript when compared to wild type hamster cells, showed increased sensitivity to mitomycin C (MMC) in clonogenic survival, suggesting haploinsufficiency of Rad51C. Similarly, mouse Rad51C(splice/neo) heterozygous ES cells also displayed increased MMC sensitivity. Moreover, in both hamster revertants, Rad51C haploinsufficiency gives rise to increased frequencies of spontaneous and MMC-induced chromosomal aberrations, impaired sister chromatid cohesion and reduced cloning efficiency. These results imply that adequate expression of Rad51C in mammalian cells is essential for maintaining genomic stability and sister chromatid cohesion to prevent malignant transformation.