ß-TrCP1 facilitates cell cycle checkpoint activation, DNA repair, and cell survival through ablation of ß-TrCP2 in response to genotoxic stress.

F-box proteins ß-TrCP1 and ß-TrCP2 are paralogs present in the human genome. They control several cellular processes including cell cycle and DNA damage signaling. Moreover, it is reported that they facilitate DNA damage-induced accumulation of p53 by directing proteasomal degradation of MDM2, a protein that promotes p53 degradation. However, the individual roles of ß-TrCP1 and ß-TrCP2 in the genotoxic stress-induced activation of cell cycle checkpoints and DNA damage repair remain largely unknown. Here, using biochemical, molecular biology, flow cytometric, and immunofluorescence techniques, we show that ß-TrCP1 and ß-TrCP2 communicate during genotoxic stress. We found that expression levels of ß-TrCP1 are significantly increased while levels of ß-TrCP2 are markedly decreased upon induction of genotoxic stress. Further, our results revealed that DNA damage-induced activation of ATM kinase plays an important role in maintaining the reciprocal expression levels of ß-TrCP1 and ß-TrCP2 via the phosphorylation of ß-TrCP1 at Ser158. Phosphorylated ß-TrCP1 potently promotes the proteasomal degradation of ß-TrCP2 and MDM2, resulting in the activation of p53. Additionally, ß-TrCP1 impedes MDM2 accumulation via abrogation of its lysine 63-linked polyubiquitination by ß-TrCP2. Thus, ß-TrCP1 helps to arrest cells at the G2/M phase of the cell cycle and promotes DNA repair upon DNA damage through attenuation of ß-TrCP2. Collectively, our findings elucidate an intriguing posttranslational regulatory mechanism of these two paralogs under genotoxic stress and revealed ß-TrCP1 as a key player in maintaining the genome integrity through the attenuation of ß-TrCP2 levels in response to genotoxic stress.

Feedback-regulated transcriptional repression of FBXO31 by c-Myc triggers ovarian cancer tumorigenesis.

FBXO31, a member of F-box protein family, has been shown to play an important role in preventing tumorigenesis by preserving genomic stability during cell proliferation as well as upon genotoxic stress. Inactivation of FBXO31 due to loss of heterozygosity is associated with various cancers, including ovarian cancer, one of the deadliest forms of gynecological cancers. However, the role and regulation of FBXO31 in ovarian cancer remained elusive. Here, using biochemical and molecular biology techniques, we show that c-Myc suppresses the mRNA levels of FBXO31 in ovarian cancer. Chromatin immunoprecipitation experiment showed that c-Myc is recruited to the promoter region of FBXO31 and prevents FBXO31 mRNA synthesis. In contrast, FBXO31 maintains the c-Myc expression at an optimum through proteasome pathway. FBXO31 interacts with and facilitates the polyubiquitination of c-Myc through the SCF complex and thereby inhibits ovarian cancer growth both in vitro and in vivo. Moreover, FBXO31-mediated proteasomal degradation of c-Myc is unique. Unlike other negative regulators, FBXO31 recognizes c-Myc in phosphorylation independent manner to direct its degradation. Further, expression levels analysis revealed that c-Myc and FBXO31 share a converse correlation of expression in ovarian cancer cell lines and patient samples. We observed an increase in the expression levels of c-Myc with a concomitant decrease in the levels of FBXO31 in higher grades of ovarian cancer patient samples. In conclusion, our study demonstrated that oncogene c-Myc impairs the tumor-suppressive functions of FBXO31 to promote ovarian cancer progression, and therefore c-Myc-FBXO31 axis can be explored to develop better cancer therapy.

Histone ubiquitination: Role in genome integrity and chromatin organization.

Maintenance of genome integrity is a precise but tedious and complex job for the cell. Several post-translational modifications (PTMs) play vital roles in maintaining the genome integrity. Although ubiquitination is one of the most crucial PTMs, which regulates the localization and stability of the nonhistone proteins in various cellular and developmental processes, ubiquitination of the histones is a pivotal epigenetic event critically regulating chromatin architecture. In addition to genome integrity, importance of ubiquitination of core histones (H2A, H2A, H3, and H4) and linker histone (H1) have been reported in several cellular processes. However, the complex interplay of histone ubiquitination and other PTMs, as well as the intricate chromatin architecture and dynamics, pose a significant challenge to unravel how histone ubiquitination safeguards genome stability. Therefore, further studies are needed to elucidate the interactions between histone ubiquitination and other PTMs, and their role in preserving genome integrity. Here, we review all types of histone ubiquitinations known till date in maintaining genomic integrity during transcription, replication, cell cycle, and DNA damage response processes. In addition, we have also discussed the role of histone ubiquitination in regulating other histone PTMs emphasizing methylation and acetylation as well as their potential implications in chromatin architecture. Further, we have also discussed the involvement of deubiquitination enzymes (DUBs) in controlling histone ubiquitination in modulating cellular processes.

FBXW10: a male-biased E3 ligase in liver cancer.

Two recent studies, by Lin et al. and Liu et al., unveiled the pivotal role of F-box and WD repeat domain containing 10 (FBXW10)-mediated ubiquitination and activation of oncogenic signaling as the primary driver behind the higher prevalence of hepatocellular carcinoma (HCC) in men. These discoveries shed light on underlying mechanisms of sex-biased cancer and provide a promising roadmap for both basic and clinical research.

FBXW2 suppresses breast tumorigenesis by targeting AKT-Moesin-SKP2 axis.

Oncogene Moesin plays critical role in initiation, progression, and metastasis of multiple cancers. It exerts oncogenic activity due to its high-level expression as well as posttranslational modification in cancer. However, factors responsible for its high-level expression remain elusive. In this study, we identified positive as well as negative regulators of Moesin. Our study reveals that Moesin is a cellular target of F-box protein FBXW2. We showed that FBXW2 suppresses breast cancer progression through directing proteasomal degradation of Moesin. In contrast, AKT kinase plays an important role in oncogenic function of Moesin by protecting it from FBXW2-mediated proteasomal degradation. Mechanistically, AKT phosphorylates Moesin at Thr-558 and thereby prevents its degradation by FBXW2 via weakening the association between FBXW2 and Moesin. Further, accumulated Moesin prevents FBXW2-mediated degradation of oncogene SKP2, showing that Moesin functions as an upstream regulator of oncogene SKP2. In turn, SKP2 stabilizes Moesin by directing its non-degradable form of polyubiquitination and therefore AKT-Moesin-SKP2 oncogenic axis plays crucial role in breast cancer progression. Collectively, our study reveals that FBXW2 functions as a tumor suppressor in breast cancer by restricting AKT-Moesin-SKP2 axis. Thus, AKT-Moesin-SKP2 axis may be explored for the development of therapeutics for cancer treatment.

An innate pathogen sensing strategy involving ubiquitination of bacterial surface proteins.

Sensing of pathogens by ubiquitination is a critical arm of cellular immunity. However, universal ubiquitination targets on microbes remain unidentified. Here, using in vitro, ex vivo, and in vivo studies, we identify the first protein-based ubiquitination substrates on phylogenetically diverse bacteria by unveiling a strategy that uses recognition of degron-like motifs. Such motifs form a new class of intra-cytosolic pathogen-associated molecular patterns (PAMPs). Their incorporation enabled recognition of nonubiquitin targets by host ubiquitin ligases. We find that SCFFBW7 E3 ligase, supported by the regulatory kinase, glycogen synthase kinase 3ß, is crucial for effective pathogen detection and clearance. This provides a mechanistic explanation for enhanced risk of infections in patients with chronic lymphocytic leukemia bearing mutations in F-box and WD repeat domain containing 7 protein. We conclude that exploitation of this generic pathogen sensing strategy allows conservation of host resources and boosts antimicrobial immunity.

Ezrin gone rogue in cancer progression and metastasis: An enticing therapeutic target.

Cancer metastasis is the primary cause of morbidity and mortality in cancer as it remains the most complicated, devastating, and enigmatic aspect of cancer. Several decades of extensive research have identified several key players closely associated with metastasis. Among these players, cytoskeletal linker Ezrin (the founding member of the ERM (Ezrin-Radixin-Moesin) family) was identified as a critical promoter of metastasis in pediatric cancers in the early 21st century. Ezrin was discovered 40 years ago as a aminor component of intestinal epithelial microvillus core protein, which is enriched in actin-containing cell surface structures. It controls gastric acid secretion and plays diverse physiological roles including maintaining cell polarity, regulating cell adhesion, cell motility and morphogenesis. Extensive research for more than two decades evinces that Ezrin is frequently dysregulated in several human cancers. Overexpression, altered subcellular localization and/or aberrant activation of Ezrin are closely associated with higher metastatic incidence and patient mortality, thereby justifying Ezrin as a valuable prognostic biomarker in cancer. Ezrin plays multifaceted role in multiple aspects of cancer, with its significant contribution in the complex metastatic cascade, through reorganizing the cytoskeleton and deregulating various cellular signaling pathways. Current preclinical studies using genetic and/or pharmacological approaches reveal that inactivation of Ezrin results in significant inhibition of Ezrin-mediated tumor growth and metastasis as well as increase in the sensitivity of cancer cells to various chemotherapeutic drugs. In this review, we discuss the recent advances illuminating the molecular mechanisms responsible for Ezrin dysregulation in cancer and its pleiotropic role in cancer progression and metastasis. We also highlight its potential as a prognostic biomarker and therapeutic target in various cancers. More importantly, we put forward some potential questions, which we strongly believe, will stimulate both basic and translational research to better understand Ezrin-mediated malignancy, ultimately leading to the development of Ezrin-targeted cancer therapy for the betterment of human life.

Damsel in distress calling on her knights: Illuminating the pioneering role of E3 ubiquitin ligases in guarding the genome integrity.

The maintenance of genomic integrity is of utmost importance for the organisms to survive and to accurately inherit traits to their progenies. Any kind of DNA damage either due to defect in DNA duplication and/ or uncontrolled cell division or intracellular insults or environment radiation can result in gene mutation, chromosomal aberration and ultimately genomic instability, which may cause several diseases including cancers. Therefore, cells have evolved machineries for the surveillance of genomic integrity. Enormous exciting studies in the past indicate that ubiquitination (a posttranslational modification of proteins) plays a crucial role in maintaining the genomic integrity by diverse ways. In fact, various E3 ubiquitin ligases catalyse ubiquitination of key proteins to control their central role during cell cycle, DNA damage response (DDR) and DNA repair. Some E3 ligases promote genomic instability while others prevent it, deregulation of both of which leads to several malignancies. In this review, we consolidate the recent findings wherein the role of ubiquitination in conferring genome integrity is highlighted. We also discuss the latest discoveries on the mechanisms utilized by various E3 ligases to preserve genomic stability, with a focus on their actions during cell cycle progression and different types of DNA damage response as well as repair pathways.

Keep your eyes peeled for long noncoding RNAs: Explaining their boundless role in cancer metastasis, drug resistance, and clinical application.

Cancer metastasis and drug resistance are two major obstacles in the treatment of cancer and therefore, the leading cause of cancer-associated mortalities worldwide. Hence, an in-depth understanding of these processes and identification of the underlying key players could help design a better therapeutic regimen to treat cancer. Earlier thought to be merely transcriptional junk and having passive or secondary function, recent advances in the genomic research have unravelled that long noncoding RNAs (lncRNAs) play pivotal roles in diverse physiological as well as pathological processes including cancer metastasis and drug resistance. LncRNAs can regulate various steps of the complex metastatic cascade such as epithelial-mesenchymal transition (EMT), invasion, migration and metastatic colonization, and also affect the sensitivity of cancer cells to various chemotherapeutic drugs. A substantial body of literature for more than a decade of research evince that lncRNAs can regulate gene expression at different levels such as epigenetic, transcriptional, posttranscriptional, translational and posttranslational levels, depending on their subcellular localization and through their ability to interact with DNA, RNA and proteins. In this review, we mainly focus on how lncRNAs affect cancer metastasis by modulating expression of key metastasis-associated genes at various levels of gene regulation. We also discuss how lncRNAs confer cancer cells either sensitivity or resistance to various chemo-therapeutic drugs via different mechanisms. Finally, we highlight the immense potential of lncRNAs as prognostic and diagnostic biomarkers as well as therapeutic targets in cancer.

Co-operative binding of SKP1, Cullin1 and Cullin7 to FBXW8 results in Cullin1-SKP1-FBXW8-Cullin7 functional complex formation that monitors cellular function of ß-TrCP1.

F-box protein FBXW8 is known to interact with scaffolding protein Cullin1 and Cullin7 to form SCF (SKP1, Cullin and F-box protein) complex. However, detail understanding about the importance of both Cullins for SCF-FBXW8 complex formation as well as its ubiquitin ligase activity remains elusive. Here, we show that, through in vitro and in vivo studies, Cullin1 and Cullin7 increase each other's binding to FBXW8 synergistically. Interestingly, absence of either Cullin results in abrogation of binding of other Cullin to FBXW8. Binding of SKP1 to FBXW8 also increases in the presence of both the Cullins. Thus, SKP1, Cullin1 and Cullin7 are essential to form Cullin1-SKP1-FBXW8-Cullin7 functional ubiquitin ligase complex. Further, using computational, mutational and biochemical analysis, we found that Cullin1 binds to N-terminus of FBXW8 through SKP1 while Cullin7 associates with C-terminus of FBXW8 to form Cullin1-SKP1-FBXW8-Cullin7 functional complex in a cooperative manner. Results showed that Cullin1-SKP1-FBXW8-Cullin7 complex plays a key role in maintaining the basal level expression of ß-TrCP1. Moreover, Cullin1-SKP1-FBXW8-Cullin7 complex promotes cell migration by activating ß-catenin via directing proteasomal degradation of ß-TrCP1. Overall, our study reveals the intriguing molecular mechanism of assembly of SKP1, Cullin1, Cullin7 and FBXW8 to form Cullin1-SKP1-FBXW8-Cullin7 functional complex that control the function of ß-TrCP1.