The F-box protein, FBXO7 is required to maintain chromosome stability in humans

E3 ubiquitin ligases and their therapeutic potential in disease Management

Ubiquitination is a vital post-translational modification that regulates protein stability and various cellular processes through the addition of ubiquitin molecules. Central to this process are E3 ubiquitin ligases, which determine the specificity of ubiquitination by coordinating the attachment of ubiquitin to target proteins, influencing their degradation, localization, and activity. E3 ubiquitin ligases are involved in numerous cellular pathways, including DNA repair, cell proliferation, and immune responses. Dysregulation of E3 ubiquitin ligases is often associated with cancer, contributing to tumor progression and resistance to therapies. The development of targeted protein degraders, such as proteolysis-targeting chimeras (PROTACs), represents a significant advancement in drug discovery, leveraging the specificity of E3 ubiquitin ligases to selectively eliminate pathogenic proteins. However, challenges remain in translating this knowledge into effective therapies, including issues related to tissue-specific targeting and off-target effects. The limitations also include a limited understanding of ligase-substrate interactions that includes both the identification of novel E3 ligases and their substrates, as well as understanding the dynamic, context-dependent nature of these interactions, which can vary across tissue types or disease states This review emphasizes the therapeutic potential of E3 ubiquitin ligases, exploring their diverse roles in disease, their contribution to targeted degradation strategies while highlighting the need for further research to overcome current limitations and enhance therapeutic efficacy.

Loss of EMI1 compromises chromosome stability and is associated with cellular transformation in colonic epithelial cell contexts

BACKGROUND

Colorectal cancer (CRC) is still a leading cause of cancer deaths worldwide. Thus, identifying the aberrant genes and proteins underlying disease pathogenesis is critical to improve early detection methods and develop novel therapeutic strategies. Chromosome instability (CIN), or ongoing changes in chromosome complements, is a predominant form of genome instability. It is a driver of genetic heterogeneity found in ~85% of CRCs. Although CIN contributes to CRC pathogenesis, the molecular determinants underlying CIN remain poorly understood. Recently, EMI1, an F-box protein, was identified as a candidate CIN gene. In this study, we sought to determine the impact reduced EMI1 expression has on CIN and cellular transformation.

METHODS

Coupling siRNA-based silencing and CRISPR/Cas9 knockout clones with quantitative imaging microscopy we evaluated the impact reduced EMI1 expression has on CIN and cellular transformation in four colonic epithelial cell contexts.

RESULTS

Quantitative imaging microscopy data revealed that reduced EMI1 expression induces increases in CIN phenotypes in both transient (siRNA) and constitutive (CRISPR/Cas9) cell models that are associated with increases in DNA damage and cellular transformation phenotypes in long-term studies.

CONCLUSIONS

This study determined that reduced EMI1 expression induces CIN and promotes cellular transformation, which is consistent with a role in early CRC development.

Recent advances in CRISPR-Cas systems for colorectal cancer research and therapeutics

INTRODUCTION

Colon cancer, ranked as the fourth leading global cause of cancer death, exhibits a complex progression marked by genetic variations. Over the past decade, the utilization of diverse CRISPR systems has propelled accelerated research into colorectal cancer (CRC) treatment.

AREAS COVERED

CRISPR/Cas9, a key player in this research, identifies new oncogenes, tumor suppressor genes (TSGs), and drug-resistance genes. Additionally, it facilitates the construction of experimental models, conducts genome-wide library screening, and develops new therapeutic targets, especially for targeted knockout in vivo or molecular targeted drug delivery, contributing to personalized treatments and significantly enhancing the care of colon cancer patients. In this review, we provide insights into the mechanism of the CRISPR/Cas9 system, offering a comprehensive exploration of its applications in CRC, spanning screening, modeling, gene functions, diagnosis, and gene therapy. While acknowledging its transformative potential, the article  highlights the challenges and limitations of CRISPR systems.

EXPERT OPINION

The application of CRISPR/Cas9 in CRC research provides a promising avenue for personalized treatments. Its potential for identifying key genes and enabling experimental models and genome-wide screening enhances patient care. This review underscores the significance of CRISPR-Cas9 gene editing technology across basic research, diagnosis, and the treatment landscape of colon cancer.

FBXO7 ubiquitinates PRMT1 to suppress serine synthesis and tumor growth in hepatocellular carcinoma

Cancer cells are often addicted to serine synthesis to support growth. How serine synthesis is regulated in cancer is not well understood. We recently demonstrated protein arginine methyltransferase 1 (PRMT1) is upregulated in hepatocellular carcinoma (HCC) to methylate and activate phosphoglycerate dehydrogenase (PHGDH), thereby promoting serine synthesis. However, the mechanisms underlying PRMT1 upregulation and regulation of PRMT1-PHGDH axis remain unclear. Here, we show the E3 ubiquitin ligase F-box-only protein 7 (FBXO7) inhibits serine synthesis in HCC by binding PRMT1, inducing lysine 37 ubiquitination, and promoting proteosomal degradation of PRMT1. FBXO7-mediated PRMT1 downregulation cripples PHGDH arginine methylation and activation, resulting in impaired serine synthesis, accumulation of reactive oxygen species (ROS), and inhibition of HCC cell growth. Notably, FBXO7 is significantly downregulated in human HCC tissues, and inversely associated with PRMT1 protein and PHGDH methylation level. Overall, our study provides mechanistic insights into the regulation of cancer serine synthesis by FBXO7-PRMT1-PHGDH axis, and will facilitate the development of serine-targeting strategies for cancer therapy.

Evaluating Chromosome Instability and Genotoxicity Through Single Cell Quantitative Imaging Microscopy

Across eukaryotes, genome stability is essential for normal cell function, physiology, and species survival. Aberrant expression of key genes or exposure to genotoxic agents can have detrimental effects on genome stability and contribute to the development of various diseases, including cancer. Chromosome instability (CIN), or ongoing changes in chromosome complements, is a frequent form of genome instability observed in cancer and is a driver of genetic and cell-to-cell heterogeneity that can be rapidly detected and quantitatively assessed using surrogate markers of CIN. For example, single cell quantitative imaging microscopy (QuantIM) can be used to simultaneously identify changes in nuclear areas and micronucleus formation. While changes in nuclear areas are often associated with large-scale changes in chromosome complements (i.e., ploidy), micronuclei are small extra-nuclear bodies found outside the primary nucleus that have previously been employed as a measure of genotoxicity of test compounds. Here, we present a facile QuantIM approach that allows for the rapid assessment and quantification of CIN associated phenotypes and genotoxicity. First, we provide protocols to optimize and execute CIN and genotoxicity assays. Secondly, we present the critical imaging settings, optimization steps, downstream statistical analyses, and data visualization strategies employed to obtain high quality and robust data. These approaches can be easily applied to assess the prevalence of CIN associated phenotypes and genotoxic stress for a myriad of experimental and clinical contexts ranging from direct tests to large-scale screens of various genetic contexts (i.e., aberrant gene expression) or chemical compounds. In summary, this QuantIM approach facilitates the identification of novel CIN genes and/or genotoxic agents that will provide greater insight into the aberrant genes and pathways underlying CIN and genotoxicity.

FBXO7 Confers Mesenchymal Properties and Chemoresistance in Glioblastoma by Controlling Rbfox2-Mediated Alternative Splicing

Mesenchymal glioblastoma (GBM) is highly resistant to radio-and chemotherapy and correlates with worse survival outcomes in GBM patients; however, the underlying mechanism determining the mesenchymal phenotype remains largely unclear. Herein, it is revealed that FBXO7, a substrate-recognition component of the SCF complex implicated in the pathogenesis of Parkinson's disease, confers mesenchymal properties and chemoresistance in GBM by controlling Rbfox2-mediated alternative splicing. Specifically, FBXO7 ubiquitinates Rbfox2 Lys249 through K63-linked ubiquitin chains upon arginine dimethylation at Arg341 and Arg441 by PRMT5, leading to Rbfox2 stabilization. FBXO7 controls Rbfox2-mediated splicing of mesenchymal genes, including FoxM1, Mta1, and Postn. FBXO7-induced exon Va inclusion of FoxM1 promotes FoxM1 phosphorylation by MEK1 and nuclear translocation, thereby upregulates CD44, CD9, and ID1 levels, resulting in GBM stem cell self-renewal and mesenchymal transformation. Moreover, FBXO7 is stabilized by temozolomide, and FBXO7 depletion sensitizes tumor xenografts in mice to chemotherapy. The findings demonstrate that the FBXO7-Rbfox2 axis-mediated splicing contributes to mesenchymal transformation and tumorigenesis, and targeting FBXO7 represents a potential strategy for GBM treatment.

Aberrant HMGA2 Expression Sustains Genome Instability That Promotes Metastasis and Therapeutic Resistance in Colorectal Cancer

Colorectal cancer (CRC) is one of the most lethal cancers worldwide, accounting for nearly ~10% of all cancer diagnoses and deaths. Current therapeutic approaches have considerably increased survival for patients diagnosed at early stages; however, ~20% of CRC patients are diagnosed with late-stage, metastatic CRC, where 5-year survival rates drop to 6–13% and treatment options are limited. Genome instability is an enabling hallmark of cancer that confers increased acquisition of genetic alterations, mutations, copy number variations and chromosomal rearrangements. In that regard, research has shown a clear association between genome instability and CRC, as the accumulation of aberrations in cancer-related genes provides subpopulations of cells with several advantages, such as increased proliferation rates, metastatic potential and therapeutic resistance. Although numerous genes have been associated with CRC, few have been validated as predictive biomarkers of metastasis or therapeutic resistance. A growing body of evidence suggests a member of the High-Mobility Group A (HMGA) gene family, HMGA2, is a potential biomarker of metastatic spread and therapeutic resistance. HMGA2 is expressed in embryonic tissues and is frequently upregulated in aggressively growing cancers, including CRC. As an architectural, non-histone chromatin binding factor, it initiates chromatin decompaction to facilitate transcriptional regulation. HMGA2 maintains the capacity for stem cell renewal in embryonic and cancer tissues and is a known promoter of epithelial-to-mesenchymal transition in tumor cells. This review will focus on the known molecular mechanisms by which HMGA2 exerts genome protective functions that contribute to cancer cell survival and chemoresistance in CRC.

Reduced SKP2 Expression Adversely Impacts Genome Stability and Promotes Cellular Transformation in Colonic Epithelial Cells

Despite the high morbidity and mortality rates associated with colorectal cancer (CRC), the underlying molecular mechanisms driving CRC development remain largely uncharacterized. Chromosome instability (CIN), or ongoing changes in chromosome complements, occurs in ~85% of CRCs and is a proposed driver of cancer development, as the genomic changes imparted by CIN enable the acquisition of karyotypes that are favorable for cellular transformation and the classic hallmarks of cancer. Despite these associations, the aberrant genes and proteins driving CIN remain elusive. SKP2 encodes an F-box protein, a variable subunit of the SKP1-CUL1-F-box (SCF) complex that selectively targets proteins for polyubiquitylation and degradation. Recent data have identified the core SCF complex components (SKP1, CUL1, and RBX1) as CIN genes; however, the impact reduced SKP2 expression has on CIN, cellular transformation, and oncogenesis remains unknown. Using both short- small interfering RNA (siRNA) and long-term (CRISPR/Cas9) approaches, we demonstrate that diminished SKP2 expression induces CIN in both malignant and non-malignant colonic epithelial cell contexts. Moreover, temporal assays reveal that reduced SKP2 expression promotes cellular transformation, as demonstrated by enhanced anchorage-independent growth. Collectively, these data identify SKP2 as a novel CIN gene in clinically relevant models and highlight its potential pathogenic role in CRC development.

A Comprehensive Assessment of Genetic and Epigenetic Alterations Identifies Frequent Variations Impacting Six Prototypic SCF Complex Members

The SKP1, CUL1, F-box protein (SCF) complex represents a family of 69 E3 ubiquitin ligases that poly-ubiquitinate protein substrates marking them for proteolytic degradation via the 26S proteasome. Established SCF complex targets include transcription factors, oncoproteins and tumor suppressors that modulate cell cycle activity and mitotic fidelity. Accordingly, genetic and epigenetic alterations involving SCF complex member genes are expected to adversely impact target regulation and contribute to disease etiology. To gain novel insight into cancer pathogenesis, we determined the prevalence of genetic and epigenetic alterations in six prototypic SCF complex member genes (SKP1, CUL1, RBX1, SKP2, FBXW7 and FBXO5) from patient datasets extracted from The Cancer Genome Atlas (TCGA). Collectively, ~45% of observed SCF complex member mutations are predicted to impact complex structure and/or function in 10 solid tumor types. In addition, the distribution of encoded alterations suggest SCF complex members may exhibit either tumor suppressor or oncogenic mutational profiles in a cancer type dependent manner. Further bioinformatic analyses reveal the potential functional implications of encoded alterations arising from missense mutations by examining predicted deleterious mutations with available crystal structures. The SCF complex also exhibits frequent copy number alterations in a variety of cancer types that generally correspond with mRNA expression levels. Finally, we note that SCF complex member genes are differentially methylated across cancer types, which may effectively phenocopy gene copy number alterations. Collectively, these data show that SCF complex member genes are frequently altered at the genetic and epigenetic levels in many cancer types, which will adversely impact the normal targeting and timely destruction of protein substrates, which may contribute to the development and progression of an extensive array of cancer types.