Tumor suppressor roles of CENP-E and Nsl1 in Drosophila epithelial tissues

Centromeres in cancer: Unraveling the link between chromosomal instability and tumorigenesis

Centromeres are critical structures involved in chromosome segregation, maintaining genomic stability, and facilitating the accurate transmission of genetic information. They are key in coordinating the assembly and help keep the correct structure, location, and function of the kinetochore, a proteinaceous structure vital for ensuring proper chromosome segregation during cell division. Abnormalities in centromere structure can lead to aneuploidy or chromosomal instability, which have been implicated in various diseases, including cancer. Accordingly, abnormalities in centromeres, such as structural rearrangements and dysregulation of centromere-associated proteins, disrupt gene function, leading to uncontrolled cell growth and tumor progression. For instance, altered expression of CENP-A, CENP-E, and others such as BUB1, BUBR1, MAD1, and INCENP, have been shown to ascribe to centromere over-amplification, chromosome missegregation, aneuploidy, and chromosomal instability; this, in turn, can culminate in tumor progression. These centromere abnormalities also promoted tumor heterogeneity by generating genetically diverse cell populations within tumors. Advanced techniques like fluorescence in situ hybridization (FISH) and chromosomal microarray analysis are crucial for detecting centromere abnormalities, enabling accurate cancer classification and tailored treatment strategies. Researchers are exploring strategies to disrupt centromere-associated proteins for targeted cancer therapies. Thus, this review explores centromere abnormalities in cancer, their molecular mechanisms, diagnostic implications, and therapeutic targeting. It aims to advance our understanding of centromeres' role in cancer and develop advanced diagnostic tools and targeted therapies for improved cancer management and treatment.

N6-methyladenosine writer METTL16-mediated alternative splicing and translation control are essential for murine spermatogenesis

BACKGROUND

The mitosis-to-meiosis switch during spermatogenesis requires dynamic changes in gene expression. However, the regulation of meiotic transcriptional and post-transcriptional machinery during this transition remains elusive.

RESULTS

We report that methyltransferase-like protein 16 (METTL16), an N6-methyladenosine (m6A) writer, is required for mitosis-to-meiosis transition during spermatogenesis. Germline conditional knockout of Mettl16 in male mice impairs spermatogonial differentiation and meiosis initiation. Mechanistically, METTL16 interacts with splicing factors to regulate the alternative splicing of meiosis-related genes such as Stag3. Ribosome profiling reveals that the translation efficiency of many meiotic genes is dysregulated in METTL16-deficient testes. m6A-sequencing shows that ablation of METTL16 causes upregulation of the m6A-enriched transcripts and downregulation of the m6A-depleted transcripts, similar to Meioc and/or Ythdc2 mutants. Further in vivo and in vitro experiments demonstrate that the methyltransferase activity site (PP185-186AA) of METTL16 is necessary for spermatogenesis.

CONCLUSIONS

Our findings support a molecular model wherein the m6A writer METTL16-mediated alternative splicing and translation efficiency regulation are required to control the mitosis-to-meiosis germ cell fate decision in mice, with implications for understanding meiosis-related male fertility disorders.

Kinesin-7 CENP-E in tumorigenesis: Chromosome instability, spindle assembly checkpoint, and applications

Kinesin motors are a large family of molecular motors that walk along microtubules to fulfill many roles in intracellular transport, microtubule organization, and chromosome alignment. Kinesin-7 CENP-E (Centromere protein E) is a chromosome scaffold-associated protein that is located in the corona layer of centromeres, which participates in kinetochore-microtubule attachment, chromosome alignment, and spindle assembly checkpoint. Over the past 3 decades, CENP-E has attracted great interest as a promising new mitotic target for cancer therapy and drug development. In this review, we describe expression patterns of CENP-E in multiple tumors and highlight the functions of CENP-E in cancer cell proliferation. We summarize recent advances in structural domains, roles, and functions of CENP-E in cell division. Notably, we describe the dual functions of CENP-E in inhibiting and promoting tumorigenesis. We summarize the mechanisms by which CENP-E affects tumorigenesis through chromosome instability and spindle assembly checkpoints. Finally, we overview and summarize the CENP-E-specific inhibitors, mechanisms of drug resistances and their applications.

Polar Chromosomes-Challenges of a Risky Path

The process of chromosome congression and alignment is at the core of mitotic fidelity. In this review, we discuss distinct spatial routes that the chromosomes take to align during prometaphase, which are characterized by distinct biomolecular requirements. Peripheral polar chromosomes are an intriguing case as their alignment depends on the activity of kinetochore motors, polar ejection forces, and a transition from lateral to end-on attachments to microtubules, all of which can result in the delayed alignment of these chromosomes. Due to their undesirable position close to and often behind the spindle pole, these chromosomes may be particularly prone to the formation of erroneous kinetochore-microtubule interactions, such as merotelic attachments. To prevent such errors, the cell employs intricate mechanisms to preposition the spindle poles with respect to chromosomes, ensure the formation of end-on attachments in restricted spindle regions, repair faulty attachments by error correction mechanisms, and delay segregation by the spindle assembly checkpoint. Despite this protective machinery, there are several ways in which polar chromosomes can fail in alignment, mis-segregate, and lead to aneuploidy. In agreement with this, polar chromosomes are present in certain tumors and may even be involved in the process of tumorigenesis.

Proteostasis failure and mitochondrial dysfunction leads to aneuploidy-induced senescence

Aneuploidy, an unbalanced number of chromosomes, is highly deleterious at the cellular level and leads to senescence, a stress-induced response characterized by permanent cell-cycle arrest and a well-defined associated secretory phenotype. Here, we use a Drosophila epithelial model to delineate the pathway that leads to the induction of senescence as a consequence of the acquisition of an aneuploid karyotype. Whereas aneuploidy induces, as a result of gene dosage imbalance, proteotoxic stress and activation of the major protein quality control mechanisms, near-saturation functioning of autophagy leads to compromised mitophagy, accumulation of dysfunctional mitochondria, and the production of radical oxygen species (ROS). We uncovered a role of c-Jun N-terminal kinase (JNK) in driving senescence as a consequence of dysfunctional mitochondria and ROS. We show that activation of the major protein quality control mechanisms and mitophagy dampens the deleterious effects of aneuploidy, and we identify a role of senescence in proteostasis and compensatory proliferation for tissue repair.

Loss of the spectraplakin gene Short stop induces a DNA damage response in Drosophila epithelia

Epithelia are an eminent tissue type and a common driver of tumorigenesis, requiring continual precision in cell division to maintain tissue structure and genome integrity. Mitotic defects often trigger apoptosis, impairing cell viability as a tradeoff for tumor suppression. Identifying conditions that lead to cell death and understanding the mechanisms behind this response are therefore of considerable importance. Here we investigated how epithelia of the Drosophila wing disc respond to loss of Short stop (Shot), a cytoskeletal crosslinking spectraplakin protein that we previously found to control mitotic spindle assembly and chromosome dynamics. In contrast to other known spindle-regulating genes, Shot knockdown induces apoptosis in the absence of Jun kinase (JNK) activation, but instead leads to elevated levels of active p38 kinase. Shot loss leads to double-strand break (DSB) DNA damage, and the apoptotic response is exacerbated by concomitant loss of p53. DSB accumulation is increased by suppression of the spindle assembly checkpoint, suggesting this effect results from chromosome damage during error-prone mitoses. Consistent with DSB induction, we found that the DNA damage and stress response genes, Growth arrest and DNA damage (GADD45) and Apoptosis signal-regulating kinase 1 (Ask1), are transcriptionally upregulated as part of the shot-induced apoptotic response. Finally, co-depletion of Shot and GADD45 induced significantly higher rates of chromosome segregation errors in cultured cells and suppressed shot-induced mitotic arrest. Our results demonstrate that epithelia are capable of mounting molecularly distinct responses to loss of different spindle-associated genes and underscore the importance of proper cytoskeletal organization in tissue homeostasis.

The Tubulin Code in Mitosis and Cancer

The “tubulin code” combines different α/β-tubulin isotypes with several post-translational modifications (PTMs) to generate microtubule diversity in cells. During cell division, specific microtubule populations in the mitotic spindle are differentially modified, but only recently, the functional significance of the tubulin code, with particular emphasis on the role specified by tubulin PTMs, started to be elucidated. This is the case of α-tubulin detyrosination, which was shown to guide chromosomes during congression to the metaphase plate and allow the discrimination of mitotic errors, whose correction is required to prevent chromosomal instability—a hallmark of human cancers implicated in tumor evolution and metastasis. Although alterations in the expression of certain tubulin isotypes and associated PTMs have been reported in human cancers, it remains unclear whether and how the tubulin code has any functional implications for cancer cell properties. Here, we review the role of the tubulin code in chromosome segregation during mitosis and how it impacts cancer cell properties. In this context, we discuss the existence of an emerging “cancer tubulin code” and the respective implications for diagnostic, prognostic and therapeutic purposes.

Ruminal transcript abundance of the centromere-associated protein E gene may influence residual feed intake in beef steers

A better understanding regarding the mechanisms by which the rumen processes feed may assist us in identifying animals with superior feed efficiency. Studies to evaluate the gene expression of rumen tissue have previously been performed to analyze their relationship with feed efficiency. Continuing this research is critical to determine whether the expression of the genes identified is associated with feed efficiency in additional populations of beef cattle to ensure that they are robust across breed and environment. A previous rumen-transcriptome study on Hereford × Angus steers identified 122 differentially expressed genes (P_FDR  < 0.05) associated with residual feed intake (RFI), a measure of feed efficiency. The purpose of our study was to test the most divergent, up- and down-regulated genes in the rumen tissue of an unrelated population of Hereford × Angus steers that included two contemporary groups. A total of 13 genes were evaluated by quantitative real-time PCR. The centromere-associated protein E (CENPE) gene was expressed in lower concentrations in the rumen epithelium of steers in the more efficient (low RFI) group in both contemporary groups of animals, which was the same as the previous study. In addition, CENPE, a gene involved in chromosome alignment during mitosis, has also been associated with growth traits in cattle and pigs. There was no relationship between the expression of the other 12 genes tested with RFI in the population of steers in this study, which illustrates the importance of validating gene expression data in additional populations.

Aneuploidy in intestinal stem cells promotes gut dysplasia in Drosophila

Aneuploidy is associated with different human diseases including cancer. However, different cell types appear to respond differently to aneuploidy, either by promoting tumorigenesis or causing cell death. We set out to study the behavior of adult Drosophila melanogaster intestinal stem cells (ISCs) after induction of chromosome missegregation either by abrogation of the spindle assembly checkpoint or through kinetochore disruption or centrosome amplification. These conditions induce moderate levels of aneuploidy in ISCs, and we find no evidence of apoptosis. Instead, we observe a significant accumulation of ISCs associated with increased stem cell proliferation and an excess of enteroendocrine cells. Moreover, aneuploidy causes up-regulation of the JNK pathway throughout the posterior midgut, and specific inhibition of JNK signaling in ISCs is sufficient to prevent dysplasia. Our findings highlight the importance of understanding the behavior of different stem cell populations to aneuploidy and how these can act as reservoirs for genomic alterations that can lead to tissue pathologies.

Mechanisms of Chromosome Congression during Mitosis

Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.

Whole-Genome Resequencing of Holstein Bulls for Indel Discovery and Identification of Genes Associated with Milk Composition Traits in Dairy Cattle

The use of whole-genome resequencing to obtain more information on genetic variation could produce a range of benefits for the dairy cattle industry, especially with regard to increasing milk production and improving milk composition. In this study, we sequenced the genomes of eight Holstein bulls from four half- or full-sib families, with high and low estimated breeding values (EBVs) of milk protein percentage and fat percentage at an average effective depth of 10×, using Illumina sequencing. Over 0.9 million nonredundant short insertions and deletions (indels) [1–49 base pairs (bp)] were obtained. Among them, 3,625 indels that were polymorphic between the high and low groups of bulls were revealed and subjected to further analysis. The vast majority (76.67%) of these indels were novel. Follow-up validation assays confirmed that most (70%) of the randomly selected indels represented true variations. The indels that were polymorphic between the two groups were annotated based on the cattle genome sequence assembly (UMD3.1.69); as a result, nearly 1,137 of them were found to be located within 767 annotated genes, only 5 (0.138%) of which were located in exons. Then, by integrated analysis of the 767 genes with known quantitative trait loci (QTL); significant single-nucleotide polymorphisms (SNPs) previously identified by genome-wide association studies (GWASs) to be associated with bovine milk protein and fat traits; and the well-known pathways involved in protein, fat synthesis, and metabolism, we identified a total of 11 promising candidate genes potentially affecting milk composition traits. These were FCGR2B, CENPE, RETSAT, ACSBG2, NFKB2, TBC1D1, NLK, MAP3K1, SLC30A2, ANGPT1 and UGDH. Our findings provide a basis for further study and reveal key genes for milk composition traits in dairy cattle.

Mitotic catastrophe and cancer drug resistance: A link that must to be broken

An increased tendency of genomic alterations during the life cycle of cells leads to genomic instability, which is a major driving force for tumorigenesis. A considerable fraction of tumor cells are tetraploid or aneuploid, which renders them intrinsically susceptible to mitotic aberrations, and hence, are particularly sensitive to the induction of mitotic catastrophe. Resistance to cell death is also closely linked to genomic instability, as it enables malignant cells to expand even in a stressful environment. Currently it is known that cells can die via multiple mechanisms. Mitotic catastrophe represents a step preceding apoptosis or necrosis, depending on the expression and/or proper function of several proteins. Mitotic catastrophe was proposed to be an onco-suppressive mechanism and the evasion of mitotic catastrophe constitutes one of the gateways to cancer development. Thus, stimulation of mitotic catastrophe appears to be a promising strategy in cancer treatment. Indeed, several chemotherapeutic drugs are currently used at concentrations that induce apoptosis irrespective of the cell cycle phase, yet are very efficient at triggering mitotic catastrophe at lower doses, significantly limiting side effects. In the present review we summarize current data concerning the role of mitotic catastrophe in cancer drug resistance and discuss novel strategies to break this link.

Oncogenic STRAP functions as a novel negative regulator of E-cadherin and p21(Cip1) by modulating the transcription factor Sp1

We have previously reported the identification of a novel WD-domain protein, STRAP that plays a role in maintenance of mesenchymal morphology by regulating E-cadherin and that enhances tumorigenicity partly by downregulating CDK inhibitor p21(Cip1). However, the functional mechanism of regulation of E-cadherin and p21(Cip1) by STRAP is unknown. Here, we have employed STRAP knock out and knockdown cell models (mouse embryonic fibroblast, human cancer cell lines) to show how STRAP downregulates E-cadherin and p21(Cip1) by abrogating the binding of Sp1 to its consensus binding sites. Moreover, ChIP assays suggest that STRAP recruits HDAC1 to Sp1 binding sites in p21(Cip1) promoter. Interestingly, loss of STRAP can stabilize Sp1 by repressing its ubiquitination in G1 phase, resulting in an enhanced expression of p21(Cip1) by >4.5-fold and cell cycle arrest. Using Bioinformatics and Microarray analyses, we have observed that 87% mouse genes downregulated by STRAP have conserved Sp1 binding sites. In NSCLC, the expression levels of STRAP inversely correlated with that of Sp1 (60%). These results suggest a novel mechanism of regulation of E-cadherin and p21(Cip1) by STRAP by modulating Sp1-dependent transcription, and higher expression of STRAP in lung cancer may contribute to downregulation of E-cadherin and p21(Cip1) and to tumor progression.

Epithelial cell division: keeping aneuploidy levels in check

Aneuploidy is deleterious at the cellular and organismal level and can promote tumorigenesis. Two new studies in Drosophila imaginal discs underscore the cellular and tissue-wide mechanisms that prevent the accumulation of aneuploid cells in symmetrically dividing epithelial tissues upon changes in centrosome number.

Consequences of Aneuploidy in Cancer: Transcriptome and Beyond

Cancer cells differ from normal healthy cells in multiple aspects ranging from altered cellular signaling through metabolic changes to aberrant chromosome content, so called aneuploidy. The large-scale changes in copy numbers of chromosomes or large chromosomal regions due to aneuploidy alter significantly the gene expression, as several hundreds of genes are gained or lost. Comparison of quantitative genome, transcriptome and proteome data enables dissection of the molecular causes that underlie the gene expression changes observed in cancer cells and provides a new perspective on the molecular consequences of aneuploidy. Here, we will map to what degree aneuploidy affects the expression of genes located on the affected chromosomes. We will also address the effects of aneuploidy on global gene expression in cancer cells as well as whether and how it may contribute to the physiology of cancer cells.