RNF168 cooperates with RNF8 to mediate FOXM1 ubiquitination and degradation in breast cancer epirubicin treatment

The Emerging Role of the Histone H2AK13/15 Ubiquitination: Mechanisms of Writing, Reading, and Erasing in DNA Damage Repair and Disease

Histone modifications serve as molecular switches controlling critical cellular processes. The ubiquitination of histone H2A at lysines 13 and 15 (H2AK13/15ub) is a crucial epigenetic modification that coordinates DNA repair and genome stability during the DNA damage response (DDR). This epigenetic mark is dynamically regulated by three functional protein groups: "writer" enzymes (e.g., E3 ubiquitin ligase RNF168 that catalyzes H2AK13/15ub formation), "reader" proteins (including 53BP1 and BRCA1-BARD1 that recognize the mark to guide DNA repair), and "eraser" deubiquitinases (such as USP3 and USP16 that remove the modification). Dysregulation of the precisely coordinated network of H2AK13/15ub is strongly associated with various diseases, including RIDDLE syndrome, neurodegenerative disorders, immune deficiencies, and breast cancer. This review systematically analyzes the dynamic regulation of H2AK13/15ub in DDR and explores its therapeutic potential for disease intervention.

The Role of the Fox Gene in Breast Cancer Progression

Forkhead box (FOX) genes are a family of transcription factors that participate in many biological activities, from early embryogenesis to the formation of organs, and from regulation of glucose metabolism to regulation of longevity. Given the extensive influence in the multicellular process, FOX family proteins are responsible for the progression of many types of cancers, especially lung cancer, breast cancer, prostate cancer, and other cancers. Breast cancer is the most common cancer among women, and 2.3 million women were diagnosed in 2020. So, various drugs targeting the FOX signaling pathway have been developed to inhibit breast cancer progression. While the role of the FOX family gene in cancer development has not received enough attention, discovering more potential drugs targeting the FOX signaling pathway is urgently demanded. Here, we review the main members in the FOX gene family and summarize their signaling pathway, including the regulation of the FOX genes and their effects on breast cancer progression. We hope this review will emphasize the understanding of the role of the FOX gene in breast cancer and inspire the discovery of effective anti-breast cancer medicines targeting the FOX gene in the future.

ABL1-mediated phosphorylation promotes FOXM1-related tumorigenicity by Increasing FOXM1 stability

The transcription factor FOXM1, which plays critical roles in cell cycle progression and tumorigenesis, is highly expressed in rapidly proliferating cells and various tumor tissues, and high FOXM1 expression is related to a poor prognosis. However, the mechanism responsible for FOXM1 dysregulation is not fully understood. Here, we show that ABL1, a nonreceptor tyrosine kinase, contributes to the high expression of FOXM1 and FOXM1-dependent tumor development. Mechanistically, ABL1 directly binds FOXM1 and mediates FOXM1 phosphorylation at multiple tyrosine (Y) residues. Among these phospho-Y sites, pY575 is indispensable for FOXM1 stability as phosphorylation at this site protects FOXM1 from ubiquitin-proteasomal degradation. The interaction of FOXM1 with CDH1, a coactivator of the E3 ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C), which is responsible for FOXM1 degradation, is significantly inhibited by Y575 phosphorylation. The phospho-deficient FOXM1(Y575F) mutant exhibited increased ubiquitination, a shortened half-life, and consequently a substantially decreased abundance. Compared to wild-type cells, a homozygous Cr-Y575F cell line expressing endogenous FOXM1(Y575F) that was generated by CRISPR/Cas9 showed obviously delayed mitosis progression, impeded colony formation and inhibited xenotransplanted tumor growth. Overall, our study demonstrates that ABL1 kinase is involved in high FOXM1 expression, providing clear evidence that ABL1 may act as a therapeutic target for the treatment of tumors with high FOXM1 expression.

Crosstalk between SUMOylation and other post-translational modifications in breast cancer

Breast cancer represents the most prevalent tumor type and a foremost cause of mortality among women globally. The complex pathophysiological processes of breast cancer tumorigenesis and progression are regulated by protein post-translational modifications (PTMs), which are triggered by different carcinogenic factors and signaling pathways, with small ubiquitin-like modifier (SUMOylation) emerging as a particularly pivotal player in this context. Recent studies have demonstrated that SUMOylation does not act alone, but interacts with other PTMs, such as phosphorylation, ubiquitination, acetylation, and methylation, thereby leading to the regulation of various pathological activities in breast cancer. This review explores novel and existing mechanisms of crosstalk between SUMOylation and other PTMs. Typically, SUMOylation is regulated by phosphorylation to exert feedback control, while also modulates subsequent ubiquitination, acetylation, or methylation. The crosstalk pairs in promoting or inhibiting breast cancer are protein-specific and site-specific. In mechanism, alterations in amino acid side chain charges, protein conformations, or the occupation of specific sites at specific domains or sites underlie the complex crosstalk. In summary, this review centers on elucidating the crosstalk between SUMOylation and other PTMs in breast cancer oncogenesis and progression and discuss the molecular mechanisms contributing to these interactions, offering insights into their potential applications in facilitating novel treatments for breast cancer.

MiR-3677-3p promotes development and sorafenib resistance of hepatitis B-related hepatocellular carcinoma by inhibiting FOXM1 ubiquitination

Being encoded by hepatitis B, hepatitis B X (HBx) protein plays crucial roles in hepatitis B-related hepatocellular carcinoma (HCC) occurrence, development, and metastasis. miRNAs also function in the progression of hepatitis B-related HCC. Hence, the objective of this study was to explore the impacts of miR-3677-3p on tumor progression and sorafenib resistance in hepatitis B-related HCC and the related underlying mechanisms. Our research revealed that miR-3677-3p and FOXM1 was up-regulated and FBXO31 was down-regulated in HBV+ HCC cells and tumor tissues from nude mice. After miR-3677-3p overexpression, cell proliferative, invasive, and migrating potentials and stemness-related protein (CD133, EpCAM, and OCT4) levels were enhanced, and cell apoptosis was reduced in Huh7 + HBx/SR cells and HepG2.2.15/SR cells. Besides, miR-3677-3p promoted the drug resistance of Huh7 + HBx/SR cells and HepG2.2.15/SR cells to sorafenib and lifted IC50. In vivo experiments, miR-3677-3p down-regulation suppressed the tumor growth in the hepatitis B HCC nude mouse models. Mechanistically, miR-3677-3p targeted and negatively-regulated FBXO31 and FBXO31 could enrich FOXM1 protein. miR-3677-3p down-regulation or FBXO31 overexpression promoted the ubiquitylation of FOXM1. In a word, miR-3677-3p bound to FBXO31 and inhibited FBXO31 expression, thus curtailing the ubiquitylation degradation of FOXM1, contributing to HCC development and sorafenib resistance.

RNF112-mediated FOXM1 ubiquitination suppresses the proliferation and invasion of gastric cancer

Forkhead box M1 (FOXM1) plays a critical role in development physiologically and tumorigenesis pathologically. However, insufficient efforts have been dedicated to exploring the regulation, in particular the degradation of FOXM1. Here, the ON-TARGETplus siRNA library targeting E3 ligases was used to screen potential candidates to repress FOXM1. Of note, mechanism study revealed that RNF112 directly ubiquitinates FOXM1 in gastric cancer, resulting in a decreased FOXM1 transcriptional network and suppressing the proliferation and invasion of gastric cancer. Interestingly, the well-established small-molecule compound RCM-1 significantly enhanced the interaction between RNF112 and FOXM1, which further promoted FOXM1 ubiquitination and subsequently exerted promising anticancer effects in vitro and in vivo. Altogether, we demonstrate that RNF112 suppresses gastric cancer progression by ubiquitinating FOXM1 and highlight the RNF112/FOXM1 axis serves as both prognosis biomarker and therapeutic target in gastric cancer.

Emerging Roles of RNF168 in Tumor Progression

RING finger protein 168 (RNF168) is an E3 ubiquitin ligase with the RING finger domain. It is an important protein contributing to the DNA double-strand damage repair pathway. Recent studies have found that RNF168 is significantly implicated in the occurrence and development of various cancers. Additionally, RNF168 contributes to the drug resistance of tumor cells by enhancing their DNA repair ability or regulating the degradation of target proteins. This paper summarizes and prospects the research progress of the structure and main functions of RNF168, especially its roles and the underlying mechanisms in tumorigenesis.

Targeting CSC-related transcription factors by E3 ubiquitin ligases for cancer therapy

Evidence has revealed that transcription factors play essential roles in regulation of multiple cellular processes, including cell proliferation, metastasis, EMT, cancer stem cells and chemoresistance. Dysregulated expression levels of transcription factors contribute to tumorigenesis and malignant progression. The expression of transcription factors is tightly governed by several signaling pathways, noncoding RNAs and E3 ubiquitin ligases. Cancer stem cells (CSCs) have been validated in regulation of tumor metastasis, reoccurrence and chemoresistance in human cancer. Transcription factors have been verified to participate in regulation of CSC formation, including Oct4, SOX2, KLF4, c-Myc, Nanog, GATA, SALL4, Bmi-1, OLIG2, POU3F2 and FOX proteins. In this review article, we will describe the critical role of CSC-related transcription factors. We will further discuss which E3 ligases regulate the degradation of these CSC-related transcription factors and their underlying mechanisms. We also mentioned the functions and mechanisms of EMT-associated transcription factors such as ZEB1, ZEB2, Snail, Slug, Twist1 and Twist2. Furthermore, we highlight the therapeutic potential via targeting E3 ubiquitin ligases for modulation of these transcription factors.

c-FLIP promotes drug resistance in non-small-cell lung cancer cells via upregulating FoxM1 expression

The forkhead box M1 (FoxM1) protein, a transcription factor, plays critical roles in regulating tumor growth and drug resistance, while cellular FLICE-inhibitory protein (c-FLIP), an anti-apoptotic regulator, is involved in the ubiquitin-proteasome pathway. In this study, we investigated the effects of c-FLIP on the expression and ubiquitination levels of FoxM1 along with drug susceptibility in non-small-cell lung cancer (NSCLC) cells. We first showed that the expression levels of FoxM1 and c-FLIP were increased and positively correlated (R2 = 0.1106, P < 0.0001) in 90 NSCLC samples. The survival data from prognostic analysis demonstrated that high expression of c-FLIP and/or FoxM1 was related to poor prognosis in NSCLC patients and that the combination of FoxM1 and c-FLIP could be a more precise prognostic biomarker than either alone. Then, we explored the functions of c-FLIP/FoxM1 in drug resistance in NSCLC cell lines and a xenograft mouse model in vivo. We showed that c-FLIP stabilized FoxM1 by inhibiting its ubiquitination, thus upregulated the expression of FoxM1 at post-transcriptional level. In addition, a positive feedback loop composed of FoxM1, β-catenin and p65 also participated in c-FLIP-FoxM1 axis. We revealed that c-FLIP promoted the resistance of NSCLC cells to thiostrepton and osimertinib by upregulating FoxM1. Taken together, these results reveal a new mechanism by which c-FLIP regulates FoxM1 and the function of this interaction in the development of thiostrepton and osimertinib resistance. This study provides experimental evidence for the potential therapeutic benefit of targeting the c-FLIP-FoxM1 axis for lung cancer treatment.

TRIM56 Reduces Radiosensitization of Human Glioblastoma by Regulating FOXM1-Mediated DNA Repair

Recurrent glioblastoma is characterized by resistance to radiotherapy or chemotherapy. In this study, we investigated the role of TRIM56 in radiosensitization and its potential underlying molecular mechanism. TRIM56 expression levels were measured in glioblastoma tissues and cell lines by immunohistochemical staining, western blot, and qRT-PCR. MTT assay, colony formation assay, and TUNEL assay were used to investigate the effect of TRIM56 on cell viability, cell proliferation, and cell apoptosis. Co-immunoprecipitation was used to clarify the interaction between TRIM56 and FOXM1. Finally, tumor xenograft experiments were performed to analyze the effect of TRIM56 on tumor growth in vivo. The expression of TRIM56 was significantly increased in glioblastoma tissues and cell lines and its expression was associated with poor prognosis of patients with glioblastoma. Moreover, TRIM56 reduced the radiosensitivity of glioblastoma cells and promoted DNA repairment. Mechanistically, TRIM56 promoted FOXM1 protein level, enhanced the stability of FOXM1 by de-ubiquitination, and promoted DNA damage repair through FOXM1 in glioblastoma cells. TRIM56 could reduce the radiosensitivity of glioblastoma in vivo. TRIM56 may suppress the radiosensitization of human glioblastoma by regulating FOXM1-mediated DNA repair. Targeting the TRIM56 may be an effective method to reverse radiotherapy-resistant in glioblastoma recurrent.

New answers to the old RIDDLE: RNF168 and the DNA damage response pathway

The chromatin-based DNA damage response pathway is tightly orchestrated by histone post-translational modifications, including histone H2A ubiquitination. Ubiquitination plays an integral role in regulating cellular processes including DNA damage signaling and repair. The ubiquitin E3 ligase RNF168 is essential in assembling a cohort of DNA repair proteins at the damaged chromatin via its enzymatic activity. RNF168 ubiquitinates histone H2A(X) at the N terminus and generates a specific docking scaffold for ubiquitin-binding motif-containing proteins. The regulation of RNF168 at damaged chromatin and the mechanistic implication in the recruitment of DNA repair proteins to the damaged sites remain an area of active investigation. Here, we review the function and regulation of RNF168 in the context of ubiquitin-mediated DNA damage signaling and repair. We will also discuss the unanswered questions that require further investigation and how understanding RNF168 targeting specificity could benefit the therapeutic development for cancer treatment.

USP28 facilitates pancreatic cancer progression through activation of Wnt/β-catenin pathway via stabilising FOXM1

Ubiquitination is an important post-translational modification that can be reversed by a family of enzymes called deubiquitinating enzymes (DUBs). Ubiquitin-specific protease 28 (USP28), a member of the DUBs family, functions as a potential tumour promoter in various cancers. However, the biological function and clinical significance of USP28 in pancreatic cancer (PC) are still unclear. Here, we showed that PC tumours had higher USP28 expression compared with that of normal pancreatic tissues, and high USP28 level was significantly correlated with malignant phenotype and shorter survival in patients with PC. Overexpression of USP28 accelerated PC cell growth, whereas USP28 knockdown impaired PC cell growth both in vitro and in vivo. Further, we found that USP28 promoted PC cell growth by facilitating cell cycle progression and inhibiting apoptosis. Mechanistically, USP28 deubiquitinated and stabilised FOXM1, a critical mediator of Wnt/β-catenin signalling. USP28-mediated stabilisation of FOXM1 significantly promoted nucleus β-catenin trans-activation, which in turn led to the activation of the Wnt/β-catenin pathway. Finally, restoration of FOXM1 expression abolished the anti-tumour effects of USP28-silencing. Thus, USP28 contributes to PC pathogenesis through enhancing the FOXM1-mediated Wnt/β-catenin signalling, and could be a potential diagnostic and therapeutic target for PC cases.

Nuclear localisation of Aurora-A: its regulation and significance for Aurora-A functions in cancer

The Aurora-A kinase regulates cell division, by controlling centrosome biology and spindle assembly. Cancer cells often display elevated levels of the kinase, due to amplification of the gene locus, increased transcription or post-translational modifications. Several inhibitors of Aurora-A activity have been developed as anti-cancer agents and are under evaluation in clinical trials. Although the well-known mitotic roles of Aurora-A point at chromosomal instability, a hallmark of cancer, as a major link between Aurora-A overexpression and disease, recent evidence highlights the existence of non-mitotic functions of potential relevance. Here we focus on a nuclear-localised fraction of Aurora-A with oncogenic roles. Interestingly, this pool would identify not only non-mitotic, but also kinase-independent functions of the kinase. We review existing data in the literature and databases, examining potential links between Aurora-A stabilisation and localisation, and discuss them in the perspective of a more effective targeting of Aurora-A in cancer therapy.

RNF168 promotes RHOC degradation by ubiquitination to restrain gastric cancer progression via decreasing HDAC1 expression

Gastric cancer (GC) is the most common cancer worldwide. Although advances in the treatments, the oncogenic mechanisms are still largely unknown. RNF168 (ring-finger nuclear factor 168) is an important regulator of DNA double-strand break (DSB) repair, and its defects have been involved in the pathogenesis of a number of human diseases including cancer. However, its effects on GC are still unclear. In the study, we demonstrated that RNF168 expression was remarkably down-regulated in human GC tissues, and its low expression showed worse overall survival rate in GC patients. Importantly, we here reported that RNF168 directly interacted with Ras homolog gene family member C (RHOC) and induced its ubiquitination to promote RHOC degradation. RHOC exhibited higher expression in human GC tissues, and its knockdown significantly restrained cell proliferation, migration and invasion in GC cell lines. Moreover, RHOC knockdown led to a significant reduction in GC tumor growth in a xenograft mouse model. Additionally, histone deacetylase 1 (HDAC1) was found to be markedly decreased in GC cells with RHOC knockdown. Intriguingly, RHOC suppression-ameliorated proliferative and migratory ability in GC cells were significantly diminished by HDAC1 over-expression. Our in vivo studies finally confirmed that RHOC inhibition dramatically reduced the lung metastasis in nude mice. Collectively, all our results demonstrated that RNF168 directly interacted with RHOC to induce its degradation via promoting its ubiquitination, contributing to the inhibition of cell proliferation and metastasis in GC through decreasing HDAC1. Thus, targeting RNF168/RHOC/HDAC1 axis might be promising to develop effective therapies for GC treatment.

FOXM1 and Cancer: Faulty Cellular Signaling Derails Homeostasis

Forkhead box transcription factor, FOXM1 is implicated in several cellular processes such as proliferation, cell cycle progression, cell differentiation, DNA damage repair, tissue homeostasis, angiogenesis, apoptosis, and redox signaling. In addition to being a boon for the normal functioning of a cell, FOXM1 turns out to be a bane by manifesting in several disease scenarios including cancer. It has been given an oncogenic status based on several evidences indicating its role in tumor development and progression. FOXM1 is highly expressed in several cancers and has also been implicated in poor prognosis. A comprehensive understanding of various aspects of this molecule has revealed its role in angiogenesis, invasion, migration, self- renewal and drug resistance. In this review, we attempt to understand various mechanisms underlying FOXM1 gene and protein regulation in cancer including the different signaling pathways, post-transcriptional and post-translational modifications. Identifying crucial molecules associated with these processes can aid in the development of potential pharmacological approaches to curb FOXM1 mediated tumorigenesis.

RNF168 is highly expressed in esophageal squamous cell carcinoma and contributes to the malignant behaviors in association with the Wnt/β-catenin signaling pathway

E3 ubiquitin ligase RING finger protein 168 (RNF168) is one of the key proteins in DNA damage repair. Abnormal expression of RNF168 has recently been found in some tumors. However, the role of RNF168 in the development of esophageal squamous cell carcinoma (ESCC) has not been fully elucidated. Here we report that expression of RNF168 in esophageal squamous cell carcinoma is increased with respect to normal esophageal epithelial tissue. Notably, in ESCC patients, increased RNF168 expression was associated with tumor stage and depth of invasion. Knockdown of the RNF168 gene inhibited proliferation of esophageal cancer cells, promoted cell apoptosis, and interfered with cell movement, ultimately inhibiting tumor xenograft growth. Mechanistic studies showed that RNF168 influenced the malignant behavior of esophageal cancer cells by regulating the Wnt/ β-catenin signaling pathway. In addition, RNF168 expression was positively correlated with wingless-type MMTV integration site family member 3A (WNT3A) expression, and high expression of RNF168 and WNT3A predicted a low survival rate. In conclusion, our findings highlight the important role of RNF168 in ESCC tumorigenesis and provide new biomarkers and therapeutic targets for the treatment of ESCC.

Identification of the potential roles of ring finger protein 8 in TP53-mutant breast cancer

Breast cancer is one of the malignant tumors with the highest mortality rate. With the development of precise treatment technology for cancer, numerous molecular targets have been identified and applied in the treatment of diseases. The present study investigated the potential role of ring finger protein 8 (RNF8) in TP53-mutant breast cancer and explored its possible mechanisms of action through a combination of bioinformatics techniques and cell biology. The results revealed that significantly different genes were expressed in RNF8-knockout mice sequencing data compared with in the control group in the presence of TP53 mutations. Downregulated genes were significantly enriched in several pathways of cell proliferation and apoptosis regulation, development and transcription regulation, while upregulated genes were mainly enriched in immune response-associated signaling pathways. Therefore, the consensus genes of the major signaling pathways were further analyzed, revealing that among patients with TP53 wild-type breast cancer, the prognosis of patients with low expression levels of fibroblast growth factor receptor 1, LIM homeobox 2 and EPH receptor B2 was improved compared with that of patients with high expression levels, while among patients with TP53-mutant breast cancer, there was no significant difference in survival status. In addition, among patients with TP53-mutant breast cancer, the prognosis of patients with high BR serine/threonine kinase 1 expression was significantly improved compared with that in patients with low expression. Finally, cell biology experiments demonstrated that in TP53-mutant breast cancer cells (HCC1937), inhibition of RNF8 significantly inhibited the proliferation of TP53-mutant HCC1937 cells and promoted their apoptosis. The present findings may enrich the understanding of the role of RNF8 and indicated that RNF8 may be used as a potential molecular target in TP53-mutant breast cancer, which may lead to the development of clinical treatment strategies.

USP22 positively modulates ERα action via its deubiquitinase activity in breast cancer

Estrogen receptor α (ERα) is the crucial factor in ERα-positive breast cancer progression. Endocrine therapies targeting ERα signaling is one of the widely used therapeutic strategies for breast cancer. However, a large number of the patients become refractory to therapy. Abnormal expression of ERα co-regulator facilitates breast cancer development and tendency of endocrine resistance. Thus, it is necessary to discover the novel co-regulators modulating ERα action. Here, we demonstrate that histone deubiquitinase USP22 is highly expressed in breast cancer samples compared with that in the benign tissue, and high expression of USP22 was significantly associated with poorer overall survival in BCa samples. Moreover, USP22 associates with ERα to be involved in maintenance of ERα stability. USP22 enhances ERα-induced transactivation. We further provide the evidence that USP22 is recruited together with ERα to cis-regulatory elements of ERα target gene. USP22 promotes cell growth even under hypoxia condition and with the treatment of ERα antagonist in breast cancer cells. Importantly, the deubiquitination activity of USP22 is required for its functions on maintenance of ERα stability, thereby enhancing ERα action and conferring endocrine resistance in breast cancer.

FOXM1 Deubiquitination by USP21 Regulates Cell Cycle Progression and Paclitaxel Sensitivity in Basal-like Breast Cancer

The transcription factor FOXM1 contributes to cell cycle progression and is significantly upregulated in basal-like breast cancer (BLBC). Despite its importance in normal and cancer cell cycles, we lack a complete understanding of mechanisms that regulate FOXM1. We identified USP21 in an RNAi-based screen for deubiquitinases that control FOXM1 abundance. USP21 increases the stability of FOXM1, and USP21 binds and deubiquitinates FOXM1 in vivo and in vitro, indicating a direct enzyme-substrate relationship. Depleting USP21 downregulates the FOXM1 transcriptional network and causes a signifi-cant delay in cell cycle progression. Significantly, USP21 depletion sensitized BLBC cell lines and mouse xenograft tumors to paclitaxel, an anti-mitotic, frontline therapy in BLBC treatment. USP21 is the most frequently amplified deubiquitinase in BLBC patient tumors, and its amplification co-occurs with the upregulation of FOXM1 protein. Altogether, these data suggest a role for USP21 in the proliferation and potentially treatment of FOXM1-high, USP21-high BLBC.

The cell cycle transcription factor FOXM1 is activated in basal-like breast cancer (BLBC) and associated with therapeutic resistance and poor patient outcomes. Arceci et al. show USP21 antagonizes FOXM1 degradation, thereby promoting proliferation and paclitaxel resistance. USP21 is catalytically active and recurrently overexpressed in BLBC, representing a potential therapeutic target.

A Cdh1-FoxM1-Apc axis controls muscle development and regeneration

Forkhead box M1 (FoxM1) transcriptional factor has a principal role in regulating cell proliferation, self-renewal, and tumorigenesis. However, whether FoxM1 regulates endogenous muscle development and regeneration remains unclear. Here we found that loss of FoxM1 in muscle satellite cells (SCs) resulted in muscle atrophy and defective muscle regeneration. FoxM1 functioned as a direct transcription activator of adenomatous polyposis coli (Apc), preventing hyperactivation of wnt/β-catenin signaling during muscle regeneration. FoxM1 overexpression in SCs promoted myogenesis but impaired muscle regeneration as a result of spontaneous activation and exhaustion of SCs by transcriptional regulation of Cyclin B1 (Ccnb1). The E3 ubiquitin ligase Cdh1 (also termed Fzr1) was required for FoxM1 ubiquitylation and subsequent degradation. Loss of Cdh1 promoted quiescent SCs to enter into the cell cycle and the SC pool was depleted by serial muscle injuries. Haploinsufficiency of FoxM1 ameliorated muscle regeneration of Cdh1 knock-out mice. These data demonstrate that the Cdh1–FoxM1–Apc axis functions as a key regulator of muscle development and regeneration.

CBP mediated DOT1L acetylation confers DOT1L stability and promotes cancer metastasis

Background and Aim: DOT1L regulates various genes involved in cancer onset and progression by catalyzing H3K79 methylation, but how DOT1L activity itself is regulated is unclear. Here, we aimed to identify specific DOT1L post-translational modifications that might regulate DOT1L activity and thus impact on colorectal cancer (CRC) progression. Methods: We conducted affinity purification and mass spectrometry to explore DOT1L post-translational modifications. We then established transwell migration and invasion assays to specifically investigate the role of DOT1L(K358) acetylation on CRC cellular behavior in vitro and a bioluminescence imaging approach to determine the role of DOT1L(K358) acetylation in CRC metastasis in vivo. We performed chromatin immunoprecipitation to identify DOT1L acetylation-controlled target genes. Finally, we used immunohistochemical staining of human tissue arrays to examine the relevance of DOT1L(K358) acetylation in CRC progression and metastasis and the correlation between DOT1L acetylation and CBP. Results: We found that CBP mediates DOT1L K358 acetylation in human colon cancer cells and positively correlates with CRC stages. Mechanistically, DOT1L acetylation confers DOT1L stability by preventing the binding of RNF8 to DOT1L and subsequent proteasomal degradation, but does not affect its enzyme activity. Once stabilized, DOT1L can catalyze the H3K79 methylation of genes involved in epithelial-mesenchymal transition, including SNAIL and ZEB1. An acetylation mimic DOT1L mutant (Q358) could induce a cancer-like phenotype in vitro, characterized by metastasis and invasion. Finally, DOT1L(K358) acetylation correlated with CRC progression and a poor survival rate as well as with high CBP expression. Conclusions: DOT1L acetylation by CBP drives CRC progression and metastasis. Targeting DOT1L deacetylation signaling is a potential therapeutic strategy for DOT1L-driven cancers.

METase/lncRNA HULC/FoxM1 reduced cisplatin resistance in gastric cancer by suppressing autophagy

BACKGROUND

Autophagy plays an important role in regulating cisplatin (CDDP) resistance in gastric cancer cells. However, the underlying mechanism of methioninase (METase) in the regulation of autophagy and CDDP resistance of gastric cancer cells is still not clear.

MATERIALS AND METHODS

Western blot was used to detect the levels of autophagy-related proteins, multidrug-resistant 1 (MDR-1), and FoxM1 protein. LncRNA HULC was detected by qRT-PCR. Cell viability was detected using CCK-8 assay. The interaction between lncRNA HULC and FoxM1 was confirmed by RNA pull-down and RIP assay.

RESULTS

Lentiviral vector carrying METase (LV-METase) suppressed autophagy and CDDP resistance of drug-resistant gastric cancer cells. LncRNA HULC was significantly downregulated in drug-resistant gastric cancer cells transfected with LV-METase. Besides, we found that lncRNA HULC interacted with FoxM1. In addition, METase suppressed autophagy to reduce CDDP resistance of drug-resistant gastric cancer cells through regulating HULC/FoxM1, and interfering HULC suppressed autophagy to reduce CDDP resistance of drug-resistant gastric cancer cells through regulating FoxM1. Finally, interfering HULC inhibited tumor growth in vivo.

CONCLUSION

METase suppressed autophagy to reduce CDDP resistance of drug-resistant gastric cancer cells through regulating HULC/FoxM1 pathway.

UCHL3 promotes pancreatic cancer progression and chemo-resistance through FOXM1 stabilization

The dysregulation of deubiquitinating enzymes has been reported to be important in the development of many human cancers, including pancreatic cancer. However, the precise role and potential mechanism of action of the deubiquitinating enzyme UCHL3 in pancreatic cancer progression and chemo-resistance, are poorly elucidated. In the current study, the consequences of UCHL3 knockdown in pancreatic cancer cells were evaluated via cell viability and colony formation assays. In vivo experiments were also conducted to confirm the effect of UCHL3 and FOXM1 depletion on tumor growth in nude mouse xenograft models. Cell migration and invasion were assessed by wound-healing and transwell assays, respectively. Co-immunoprecipitation (co-IP) and in vitro deubiquitination assays were performed to investigate the interactions between UCHL3 and FOXM1. Immunohistochemical (IHC) staining was utilized to examine the expression of UCHL3 and FOXM1 in pancreatic cancer tissues. Our results demonstrate that UCHL3 deubiquitinated and stabilized FOXM1, thereby potentiating proliferation, migration, and invasion of pancreatic cancer cells. Furthermore, knockdown of UCHL3 increased FOXM1 ubiquitination, which enhanced FOXM1 turnover and promoted pancreatic cancer cells' sensitivity to gemcitabine. High UCHL3 expression was positively associated with FOXM1 expression level in pancreatic cancer patient samples. Collectively, our study established the UCHL3-FOXM1 axis as a pivotal driver of pancreatic cancer progression and gemcitabine resistance and provided evidence for the potential therapeutic benefit of targeting the UCHL3-FOXM1 axis for pancreatic cancer treatment.

FOXM1 modulates 5-fluorouracil sensitivity in cholangiocarcinoma through thymidylate synthase (TYMS): implications of FOXM1-TYMS axis uncoupling in 5-FU resistance

Fluorouracil (5-FU) is the first-line chemotherapeutic drug for cholangiocarcinoma (CCA), but its efficacy has been compromised by the development of resistance. Development of 5-FU resistance is associated with elevated expression of its cellular target, thymidylate synthase (TYMS). E2F1 transcription factor has previously been shown to modulate the expression of FOXM1 and TYMS. Immunohistochemical (IHC) analysis revealed a strong correlated upregulation of FOXM1 (78%) and TYMS (48%) expression at the protein levels in CCA tissues. In agreement, RT-qPCR and western blot analyses of four human CCA cell lines at the baseline level and in response to high doses of 5-FU revealed good correlations between FOXM1 and TYMS expression in the CCA cell lines tested, except for the highly 5-FU-resistant HuCCA cells. Consistently, siRNA-mediated knockdown of FOXM1 reduced the clonogenicity and TYMS expression in the relatively sensitive KKU-D131 but not in the highly resistant HuCCA cells. Interestingly, silencing of TYMS sensitized both KKU-D131 and HuCCA to 5-FU treatment, suggesting that resistance to very high levels of 5-FU is due to the inability of the genotoxic sensor FOXM1 to modulate TYMS expression. Consistently, ChIP analysis revealed that FOXM1 binds efficiently to the TYMS promoter and modulates TYMS expression at the promoter level upon 5-FU treatment in KKU-D131 but not in HuCCA cells. In addition, E2F1 expression did not correlate with either FOXM1 or TYMS expression and E2F1 depletion has no effects on the clonogenicity and TYMS expression in the CCA cells. In conclusion, our data show that FOXM1 regulates TYMS expression to modulate 5-FU resistance in CCA and that severe 5-FU resistance can be caused by the uncoupling of the regulation of TYMS by FOXM1. Our findings suggest that the FOXM1–TYMS axis can be a novel diagnostic, predictive and prognostic marker as well as a therapeutic target for CCA.

Regulation of the master regulator FOXM1 in cancer

FOXM1 (forkhead box protein M1) is a critical proliferation-associated transcription factor that is widely spatiotemporally expressed during the cell cycle. It is closely involved with the processes of cell proliferation, self-renewal, and tumorigenesis. In most human cancers, FOXM1 is overexpressed, and this indicates a poor prognosis for cancer patients. FOXM1 maintains cancer hallmarks by regulating the expression of target genes at the transcriptional level. Due to its potential role as molecular target in cancer therapy, FOXM1 was named the Molecule of the Year in 2010. However, the mechanism of FOXM1 dysregulation remains indistinct. A comprehensive understanding of FOXM1 regulation will provide novel insight for cancer and other diseases in which FOXM1 plays a major role. Here, we summarize the transcriptional regulation, post-transcriptional regulation and post-translational modifications of FOXM1, which will provide extremely important implications for novel strategies targeting FOXM1.

The FOXO3-FOXM1 axis: A key cancer drug target and a modulator of cancer drug resistance

The FOXO3 and FOXM1 forkhead box transcription factors, functioning downstream of the essential PI3K-Akt, Ras-ERK and JNK/p38MAPK signalling cascades, are crucial for cell proliferation, differentiation, cell survival, senescence, DNA damage repair and cell cycle control. The development of resistance to both conventional and newly emerged molecularly targeted therapies is a major challenge confronting current cancer treatment in the clinic. Intriguingly, the mechanisms of resistance to ‘classical’ cytotoxic chemotherapeutics and to molecularly targeted therapies are invariably linked to deregulated signalling through the FOXO3 and FOXM1 transcription factors. This is owing to the involvement of FOXO3 and FOXM1 in the regulation of genes linked to crucial drug action-related cellular processes, including stem cell renewal, DNA repair, cell survival, drug efflux, and deregulated mitosis. A better understanding of the mechanisms regulating the FOXO3-FOXM1 axis, as well as their downstream transcriptional targets and functions, may render these proteins reliable and early diagnostic/prognostic factors as well as crucial therapeutic targets for cancer treatment and importantly, for overcoming chemotherapeutic drug resistance.

Retroviral insertional mutagenesis implicates E3 ubiquitin ligase RNF168 in the control of cell proliferation and survival

The E3 ubiquitin ligase RNF168 is a ring finger protein that has previously been identified to play an important regulatory role in the repair of double-strand DNA breaks.  In the present study, an unbiased forward genetics functional screen in mouse granulocyte/ macrophage progenitor cell line FDCP1 has identified E3 ubiquitin ligase RNF168 as a key regulator of cell survival and proliferation. Our data indicate that RNF168 is an important component of the mechanisms controlling cell fate, not only in human and mouse haematopoietic growth factor-dependent cells, but also in the human breast epithelial cell line MCF-7. These observations therefore suggest that RNF168 provides a connection to key pathways controlling cell fate, potentially through interaction with PML nuclear bodies and/or epigenetic control of gene expression. Our study is the first to demonstrate a critical role for RNF168 in the in the mechanisms regulating cell proliferation and survival, in addition to its well-established role in DNA repair.

Identification of candidate genes related to pancreatic cancer based on analysis of gene co-expression and protein-protein interaction network

Pancreatic cancer (PC) is one of the most common causes of cancer mortality worldwide. As the genetic mechanism of this complex disease is not uncovered clearly, identification of related genes of PC is of great significance that could provide new insights into gene function as well as potential therapy targets. In this study, we performed an integrated network method to discover PC candidate genes based on known PC related genes. Utilizing the subnetwork extraction algorithm with gene co-expression profiles and protein-protein interaction data, we obtained the integrated network comprising of the known PC related genes (denoted as seed genes) and the putative genes (denoted as linker genes). We then prioritized the linker genes based on their network information and inferred six key genes (KRT19, BARD1, MST1R, S100A14, LGALS1 and RNF168) as candidate genes of PC. Further analysis indicated that all of these genes have been reported as pancreatic cancer associated genes. Finally, we developed an expression signature using these six key genes which significantly stratified PC patients according to overall survival (Logrank p = 0.003) and was validated on an independent clinical cohort (Logrank p = 0.03). Overall, the identified six genes might offer helpful prognostic stratification information and be suitable to transfer to clinical use in PC patients.

USP5 promotes tumorigenesis and progression of pancreatic cancer by stabilizing FoxM1 protein

Increased ubiquitin-specific protease 5 (USP5) has been associated with tumorigenesis of malignancy including glioblastoma, melanoma and hepatocellular carcinoma. However, the role of USP5 in tumorigenesis of pancreatic ductal adenocarcinoma (PDAC) has not been studied yet. In this study, we demonstrated that USP5 was significantly upregulated in a panel of PDAC cell lines and correlated with FoxM1 protein expression. USP5 knockdown inhibited proliferation of PANC-1 and SW1990, two PDAC cell lines. In the mouse xenografted pancreatic tumor model, suppression of USP5 significantly decreased tumor growth, correlated with down regulation of FoxM1. Additionally, we found that overexpression of USP5 stabilized the FoxM1 protein in PDAC cells. Overexpression of USP5 extended the half-life of FoxM1. Knockdown of USP5 in PANC-1 cells decreased FoxM1 protein level while the proteasome inhibitor MG-132 treatment restored FoxM1 expression. We also found that endogenous USP5 was coimmunoprecipitated with an endogenous FoxM1 from PANC-1 cells while FoxM1 was also coimmunoprecipitated with USP5. Furthermore, we also confirmed that USP5 regulated proliferation of PDAC via FoxM1 by rescuing the inhibitory effect of USP5 knockdown with ectopic expression of FoxM1 in USP5-depleted cells. Taken together, our study demonstrates that USP5 plays a critical role in tumorigenesis and progression of pancreatic cancer by stabilizing FoxM1 protein, and provides a rationale for USP5 being a potential therapeutic approach against PDAC.