Disruption of CDK7 signaling leads to catastrophic chromosomal instability coupled with a loss of condensin-mediated chromatin compaction.

Chromatin organization is highly dynamic and modulates DNA replication, transcription, and chromosome segregation. Condensin is essential for chromosome assembly during mitosis and meiosis, as well as maintenance of chromosome structure during interphase. While it is well established that sustained condensin expression is necessary to ensure chromosome stability, the mechanisms that control its expression are not yet known. Herein, we report that disruption of cyclin-dependent kinase 7 (CDK7), the core catalytic subunit of CDK-activating kinase, leads to reduced transcription of several condensin subunits, including structural maintenance of chromosomes 2 (SMC2). Live and static microscopy revealed that inhibiting CDK7 signaling prolongs mitosis and induces chromatin bridge formation, DNA double-strand breaks, and abnormal nuclear features, all of which are indicative of mitotic catastrophe and chromosome instability. Affirming the importance of condensin regulation by CDK7, genetic suppression of the expression of SMC2, a core subunit of this complex, phenocopies CDK7 inhibition. Moreover, analysis of genome-wide chromatin conformation using Hi-C revealed that sustained activity of CDK7 is necessary to maintain chromatin sublooping, a function that is ascribed to condensin. Notably, the regulation of condensin subunit gene expression is independent of superenhancers. Together, these studies reveal a new role for CDK7 in sustaining chromatin configuration by ensuring the expression of condensin genes, including SMC2.

Maternal SMC2 is essential for embryonic development via participating chromosome condensation in mice.

During the oocyte growth, maturation and zygote development, chromatin structure keeps changing to regulate different nuclear activities. Here, we reported the role of SMC2, a core component of condensin complex, in oocyte and embryo development. Oocyte-specific conditional knockout of SMC2 caused female infertility. In the absence of SMC2, oocyte meiotic maturation and ovulation occurred normally, but chromosome condensation showed defects and DNA damages were accumulated in oocytes. The pronuclei were abnormally organized and micronuclei were frequently observed in fertilized eggs, their activity was impaired, and embryo development was arrested at the one-cell stage, suggesting that maternal SMC2 is essential for embryonic development.

The proteomic study of serially passaged human skin fibroblast cells uncovers down-regulation of the chromosome condensin complex proteins involved in replicative senescence.

Dermal fibroblast is one of the major constitutive cells of skin and plays a central role in skin senescence. The replicative senescence of fibroblasts may cause skin aging, bad wound healing, skin diseases and even cancer. In this study, a label-free quantitative proteomic approach was employed to analyzing the serial passaged human skin fibroblast (CCD-1079Sk) cells, resulting in 3371 proteins identified. Of which, 280 proteins were significantly changed in early passage (6 passages, P6), middle passage (12 passages, P12) and late passage (21 passages, P21), with a time-dependent decrease or increase tendency. Bioinformatic analysis demonstrated that the chromosome condensin complex, including structural maintenance of chromosomes protein 2 (SMC2) and structural maintenance of chromosomes protein 4 (SMC4), were down-regulated in the serially passaged fibroblast cells. The qRT-PCR and Western Blot experiments confirmed that the expression of these two proteins were significantly down-regulated in a time-dependent manner in the subculture of human skin fibroblasts (HSFb cells). In summary, we used serially passaged human skin fibroblast cells coupled with quantitative proteomic approach to profile the protein expression pattern in the temporal progress of replicative senescence in HSFb cells and revealed that the down-regulation of the chromosome condensin complex subunits, such as SMC2 and SMC4, may play an important role in the fibroblast senescence.

Identification of SMC2 and SMC4 as prognostic markers in breast cancer through bioinformatics analysis.

BACKGROUND: Breast cancer (BRCA) is one of the most common malignant tumors. The structural maintenance of chromosome (SMC) gene family has been shown to play an important role in human cancers. However, the role of SMC families in BRCA is unclear. This study aimed to explore the role and potential clinical value of whole SMCs in BRCA. METHODS: TIMER and UALCAN database were used to analysis the expression level. Genetic variations were analyzed by cBioPortal. Promoter methylation and protein level were analyzed by UCLCAN. GO and KEGG were analyzed by Metascape database. Prognostic value of SMCs was analyzed by Kaplan-Meier and multivariate cox regression analyses. Immune infiltration analysis was conducted by CIBERSORT. Immunotherapy outcome prediction was conducted by Cancer Immunome Atlas. Targeted drug therapy outcome prediction was taken by GDSC and R language. The cell viability was tested by CCK8 and migration was tested by wound healing assay. Xenograft model was used to investigate the in vivo role of SMC2. RESULTS: Expression levels of SMC1A, SMC2, SMC4, SMC5 and SMC6 mRNA were increased in BRCA tissues, and negatively correlated with promoter methylation. Overexpression of SMC2 and SMC4 was negatively correlated with survival. Function of SMCs family regulatory genes was mainly related to ATPase activity. Expression of most SMCs was negatively correlated with immunotherapy and drug therapy outcomes. Interfere SMC2 and SMC4 decreased IC50 values of 5-fluorouracil and oxaliplatin and inhibited the migration of MCF7 cells. Tumor growth and weights were significantly decreased in si-SMC2 groups. CONCLUSIONS: Combined bioinformatics and clinical specimen analysis verified SMC2 and SMC4 as independent prognostic factors in BRCA, suggesting their significance for the diagnosis and treatment of BRCA.

TDMPP activation of estrogen receptor 2a regulates smc2 and p53 signaling to interfere with liver development in zebrafish (Danio rerio).

Tris (2,6-dimethylphenyl) phosphate (TDMPP), a novel organic phosphorus flame retardant (OPFR), has been found to have estrogenic activity. Estrogens are critical in regulating various biological responses during liver development. However, the effects of TDMPP on zebrafish liver development remain largely unexplored. Here, we utilized a chemical genetic screening approach to assess the estrogenic effects of TDMPP on liver development and to elucidate the underlying molecular mechanism. Our findings revealed that zebrafish larvae exposed to environmentally relevant concentrations of TDMPP (0.05 and 0.5 µM) exhibited concentration-dependent liver impairments, including reduced liver size, histopathological changes, and hepatocyte apoptosis. In addition, E2 caused similar adverse effects to TDMPP, but the pharmacological blockade of estrogen synthesis alleviated the effects on liver development. Chemical inhibitors and morpholino knockdown assays indicated that the reduction of esr2a blocked TDMPP-induced liver impairments, which was further confirmed in the esr2a-/- mutant line. Subsequently, transcriptomic analysis showed that the estrogen receptor activated by TDMPP inhibited the expression of smc2, which was linked to the suppression of liver development through p53 activation. Consistently, overexpression of smc2 and inhibition of p53 evidently rescued hepatic damages induced by TDMPP. Taken together, the above findings identified esr2a, downstream smc2, and p53 as important regulators for the estrogenic effects of TDMPP on liver development. Our work fills crucial gaps in the current knowledge of TDMPP's hepatotoxicity, providing new insights into the adverse effects of TDMPP and the molecular mechanisms of action. These findings underscore the need for further ecological risk assessment and regulatory considerations.

SMC2 knockdown inhibits malignant progression of lung adenocarcinoma by upregulating BTG2 expression.

Lung adenocarcinoma (LUAD) is the most prevalent subtype of lung cancer worldwide. Structural maintenance of chromosomes 2 (SMC2) serves as a predictor of poor prognosis across various cancer types. This study aims to explore the role and underlying mechanisms of SMC2 in LUAD progression. The expression of SMC2 in LUAD tissues and its correlation with prognosis were analyzed by public databases. Knockdown of SMC2 was performed to assess the proliferation, migration and invasion ability of LUAD cells. Bulk RNA sequencing analysis identified enriched cellular pathways and remarkable upregulation of BTG anti-proliferation factor 2 (BTG2) expression after SMC2 knockdown in LUAD cells. Then, BTG2 was silenced to assess the malignant behavior of LUAD cells. Subcutaneous transplantation and intracranial tumor models of LUAD cells in BALB/c nude mice were established to assess the antineoplastic effect of SMC2 knockdown in vivo. Additionally, a lung metastasis model was created to evaluate the pro-metastatic effect of SMC2. Our findings indicated that SMC2 was upregulated in LUAD tissues and cell lines, with higher expression correlating with poor prognosis. SMC2 silencing suppressed the proliferation, migration and invasion ability of LUAD cells by upregulating BTG2 expression via p53 and inactivating ERK and AKT pathways. BTG2 silencing reversed the effects of SMC2 downregulation on malignant behaviors of LUAD cells and restored the phosphorylated ERK and AKT levels. Furthermore, SMC2 knockdown effectively prevented the formation of subcutaneous, intracranial and metastatic tumor in vivo, and upregulation of BTG2 expression after SMC2 knockdown was confirmed in tumor models. This study revealed that SMC2 knockdown restrained the malignant progression of LUAD through upregulation of BTG2 expression and inactivation of ERK and AKT pathways, and SMC2 could be a potential therapeutic target for LUAD treatment.

Functions of SMC2 in the Development of Zebrafish Liver.

SMC2 (structural maintenance of chromosomes 2) is the core subunit of condensins, which play a central role in chromosome organization and segregation. However, the functions of SMC2 in embryonic development remain poorly understood, due to the embryonic lethality of homozygous SMC2-/- mice. Herein, we explored the roles of SMC2 in the liver development of zebrafish. The depletion of SMC2, with the CRISPR/Cas9-dependent gene knockout approach, led to a small liver phenotype. The specification of hepatoblasts was unaffected. Mechanistically, extensive apoptosis occurred in the liver of SMC2 mutants, which was mainly associated with the activation of the p53-dependent apoptotic pathway. Moreover, an aberrant activation of a series of apoptotic pathways in SMC2 mutants was involved in the defective chromosome segregation and subsequent DNA damage. Therefore, our findings demonstrate that SMC2 is necessary for zebrafish liver development.

Intracellular Delivery of Anti-SMC2 Antibodies against Cancer Stem Cells.

Structural maintenance of chromosomes protein 2 (SMC2) is a central component of the condensin complex involved in DNA supercoiling, an essential process for embryonic stem cell survival. SMC2 over-expression has been related with tumorigenesis and cancer malignancy and its inhibition is regarded as a potential therapeutic strategy even though no drugs are currently available. Here, we propose to inhibit SMC2 by intracellular delivery of specific antibodies against the SMC2 protein. This strategy aims to reduce cancer malignancy by targeting cancer stem cells (CSC), the tumoral subpopulation responsible of tumor recurrence and metastasis. In order to prevent degradation and improve cellular internalization, anti-SMC2 antibodies (Ab-SMC2) were delivered by polymeric micelles (PM) based on Pluronic® F127 amphiphilic polymers. Importantly, scaffolding the Ab-SMC2 onto nanoparticles allowed its cellular internalization and highly increased its efficacy in terms of cytotoxicity and inhibition of tumorsphere formation in MDA-MB-231 and HCT116 breast and colon cancer cell lines, respectively. Moreover, in the case of the HCT116 cell line G1, cell-cycle arrest was also observed. In contrast, no effects from free Ab-SMC2 were detected in any case. Further, combination therapy of anti-SMC2 micelles with paclitaxel (PTX) and 5-Fluorouracil (5-FU) was also explored. For this, PTX and 5-FU were respectively loaded into an anti-SMC2 decorated PM. The efficacy of both encapsulated drugs was higher than their free forms in both the HCT116 and MDA-MB-231 cell lines. Remarkably, micelles loaded with Ab-SMC2 and PTX showed the highest efficacy in terms of inhibition of tumorsphere formation in HCT116 cells. Accordingly, our data clearly suggest an effective intracellular release of antibodies targeting SMC2 in these cell models and, further, strong cytotoxicity against CSC, alone and in combined treatments with Standard-of-Care drugs.

Cell cycle regulation of condensin Smc4.

The condensin complex is a conserved ATPase which promotes the compaction of chromatin during mitosis in eukaryotic cells. Condensin complexes have in addition been reported to contribute to interphase processes including sister chromatid cohesion. It is not understood how condensins specifically become competent to facilitate chromosome condensation in preparation for chromosome segregation in anaphase. Here we describe evidence that core condensin subunits are regulated at the level of protein stability in budding yeast. In particular, Smc2 and Smc4 abundance is cell cycle regulated, peaking at mitosis and falling to low levels in interphase. Smc4 degradation at the end of mitosis is dependent on the Anaphase Promoting Complex/Cyclosome and is mediated by the proteasome. Overproduction of Smc4 results in delayed decondensation, but has a limited ability to promote premature condensation in interphase. Unexpectedly, the Mad2 spindle checkpoint protein is required for mitotic Smc4 degradation. These studies have revealed the novel finding that condensin protein levels are cell cycle regulated and have identified the factors necessary for Smc4 proteolysis.

Mutational and expressional analysis of SMC2 gene in gastric and colorectal cancers with microsatellite instability.

Structural maintenance of chromosomes 2 (SMC2) gene encodes condensin complexes that are required for proper chromosome segregation and maintenance of chromosomal stability. Although cells with defective chromosome segregation become aneuploid and are prone to harbor chromosome instability, pathologic implications of SMC2 gene alterations are largely unknown. In a public database, we found that SMC2 gene had mononucleotide repeats that could be mutated in cancers with microsatellite instability (MSI). In this study, we analyzed these repeats in 32 gastric cancers (GC) with high MSI (MSI-H), 59 GC with low MSI (MSI-L)/stable MSI (MSS), 43 colorectal cancers (CRC) with MSI-H and 60 CRC with MSI-L/MSS by single-strand conformation polymorphism (SSCP) and DNA sequencing. We also analyzed SMC2 protein expression in GC and CRC tissues using immunohistochemistry. We found SMC2 frameshift mutations in two GC and two CRC that would result in truncation of SMC2. The mutations were detected exclusively in MSI-H cancers, but not in MSI-L/MSS cancers. Loss of SMC2 expression was observed in 22% of GC and 25% of CRC. Of note, all of the cancers with SMC2 frameshift mutations displayed loss of SMC2 expression. Also, both GC and CRC with MSI-H had significantly higher incidences in SMC2 frameshift mutations and loss of SMC2 expression than those with MSI-L/MSS. Our data indicate that SMC2 gene is altered by both frameshift mutation and loss of expression in GC and CRC with MSI-H, and suggest that SMC2 gene alterations might be involved in pathogenesis of these cancers.