Identification of aberrantly expressed F-box proteins in squamous-cell lung carcinoma

Downregulation of Splicing Factor PTBP1 Curtails FBXO5 Expression to Promote Cellular Senescence in Lung Adenocarcinoma

Polypyrimidine tract-binding protein 1 (PTBP1) plays an essential role in splicing and post-transcriptional regulation. Moreover, PTBP1 has been implicated as a causal factor in tumorigenesis. However, the involvement of PTBP1 in cellular senescence, a key biological process in aging and cancer suppression, remains to be clarified. Here, it is shown that PTBP1 is associated with the facilitation of tumor growth and the prognosis in lung adenocarcinoma (LUAD). PTBP1 exhibited significantly increased expression in various cancer types including LUAD and showed consistently decreased expression in multiple cellular senescence models. Suppression of PTBP1 induced cellular senescence in LUAD cells. In terms of molecular mechanisms, the silencing of PTBP1 enhanced the skipping of exon 3 in F-box protein 5 (FBXO5), resulting in the generation of a less stable RNA splice variant, FBXO5-S, which subsequently reduces the overall FBXO5 expression. Additionally, downregulation of FBXO5 was found to induce senescence in LUAD. Collectively, these findings illustrate that PTBP1 possesses an oncogenic function in LUAD through inhibiting senescence, and that targeting aberrant splicing mediated by PTBP1 has therapeutic potential in cancer treatment.

Fbxo45 facilitates the malignant progression of breast cancer by targeting Bim for ubiquitination and degradation

BACKGROUND

Breast cancer is one of the common malignancies in women. Evidence has demonstrated that FBXO45 plays a pivotal role in oncogenesis and progression. However, the role of FBXO45 in breast tumorigenesis remains elusive. Exploration of the regulatory mechanisms of FBXO45 in breast cancer development is pivotal for potential therapeutic interventions in patients with breast cancer.

METHODS

Hence, we used numerous approaches to explore the functions of FBXO45 and its underlaying mechanisms in breast cancer pathogenesis, including CCK-8 assay, EdU assay, colony formation analysis, apoptosis assay, RT-PCR, Western blotting, immunoprecipitation, ubiquitination assay, and cycloheximide chase assay.

RESULTS

We found that downregulation of FBXO45 inhibited cell proliferation, while upregulation of FBXO45 elevated cell proliferation in breast cancer. Silencing of FBXO45 induced cell apoptosis, whereas overexpression of FBXO45 inhibited cell apoptosis in breast cancer. Moreover, FBXO45 interacted with BIM and regulated its ubiquitination and degradation. Furthermore, knockdown of FBXO45 inhibited cell proliferation via regulation of BIM pathway. Notably, overexpression of FBXO45 facilitated tumor growth in mice. Strikingly, FBXO45 expression was associated with poor survival of breast cancer patients.

CONCLUSION

Our study could provide the rational for targeting FBXO45 to obtain benefit for breast cancer patients. Altogether, modulating FBXO45/Bim axis could be a promising strategy for breast cancer therapy.

FBXO5-mediated RNF183 degradation prevents endoplasmic reticulum stress-induced apoptosis and promotes colon cancer progression

Endoplasmic reticulum (ER) stress induces the unfolded protein response (UPR), and prolonged ER stress leads to cell apoptosis. Despite increasing research in this area, the underlying molecular mechanisms remain unclear. Here, we discover that ER stress upregulates the UPR signaling pathway while downregulating E2F target gene expression and inhibiting the G2/M phase transition. Prolonged ER stress decreases the mRNA levels of E2F2, which specifically regulates the expression of F-Box Protein 5(FBXO5), an F-box protein that functions as an inhibitor of the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase complex. Depletion of FBXO5 results in increased ER stress-induced apoptosis and decreased expression of proteins related to PERK/IRE1α/ATF6 signaling. Overexpression of FBXO5 wild-type (not its ΔF-box mutant) alleviates apoptosis and the expression of the C/EBP Homologous Protein (CHOP)/ATF. Mechanistically, we find that FBXO5 directly binds to and promotes the ubiquitin-dependent degradation of RNF183, which acts as a ubiquitin E3 ligase in regulating ER stress-induced apoptosis. Reversal of the apoptosis defects caused by FBXO5 deficiency in colorectal cancer cells can be achieved by knocking down RNF183 in FBXO5-deficient cells. Functionally, we observed significant upregulation of FBXO5 in colon cancer tissues, and its silencing suppresses tumor occurrence in vivo. Therefore, our study highlights the critical role of the FBXO5/RNF183 axis in ER stress regulation and identifies a potential therapeutic target for colon cancer treatment.

Identification of F-Box/SPRY Domain-Containing Protein 1 (FBXO45) as a Prognostic Biomarker for TMPRSS2-ERG-Positive Primary Prostate Cancers

BACKGROUND

F-box/SPRY domain-containing protein 1 (FBXO45) plays a crucial role in the regulation of apoptosis via the ubiquitylation and degradation of specific targets. Recent studies indicate the prognostic potential of FBXO45 in several cancers. However, its specific role in prostate carcinoma remains unclear.

METHODS

A systematic analysis of FBXO45 mRNA expression in PCA was performed using The Cancer Genome Atlas database and a publicly available Gene Expression Omnibus progression PCA cohort. Subsequently, FBXO45 protein expression was assessed via immunohistochemical analysis of a comprehensive tissue microarray cohort. The expression data were correlated with the clinicopathological parameters and biochemical-free survival. The immunohistochemical analyses were stratified according to the TMPRSS2-ERG rearrangement status. To assess the impact of FBXO45 knockdown on the tumour proliferation capacity of cells and metastatic potential, transfection with antisense-oligonucleotides was conducted within a cell culture model.

RESULTS

FBXO45 mRNA expression was associated with adverse clinicopathological parameters in the TCGA cohort and was enhanced throughout progression to distant metastasis. FBXO45 was associated with shortened biochemical-free survival, which was pronounced for the TMPRSS2-ERG-positive tumours. In vitro, FBXO45 knockdown led to a significant reduction in migration capacity in the PC3, DU145 and LNCaP cell cultures.

CONCLUSIONS

Comprehensive expression analysis and functional data suggest FBXO45 as a prognostic biomarker in PCA.

The E3 ligase subunit FBXO45 binds the interferon-λ receptor and promotes its degradation during influenza virus infection

Influenza remains a major public health challenge, as the viral infection activates multiple biological networks linked to altered host innate immunity. Following infection, IFN-λ, a ligand crucial for the resolution of viral infections, is known to bind to its cognate receptor, IFNLR1, in lung epithelia. However, little is known regarding the molecular expression and regulation of IFNLR1. Here, we show that IFNLR1 is a labile protein in human airway epithelia that is rapidly degraded after influenza infection. Using an unbiased proximal ligation biotin screen, we first identified that the Skp-Cullin-F box E3 ligase subunit, FBXO45, binds to IFNLR1. We demonstrate that FBXO45, induced in response to influenza infection, mediates IFNLR1 protein polyubiquitination and degradation through the ubiquitin-proteasome system by docking with its intracellular receptor domain. Furthermore, we found ectopically expressed FBXO45 and its silencing in cells differentially regulated both IFNLR1 protein stability and interferon-stimulated gene expression. Mutagenesis studies also indicated that expression of a K319R/K320R IFNLR1 variant in cells exhibited reduced polyubiquitination, yet greater stability and proteolytic resistance to FBXO45 and influenza-mediated receptor degradation. These results indicate that the IFN-λ-IFNLR1 receptor axis is tightly regulated by the Skp-Cullin-F box ubiquitin machinery, a pathway that may be exploited by influenza infection as a means to limit antiviral responses.

Fbxo45 promotes the malignant development of esophageal squamous cell carcinoma by targeting GGNBP2 for ubiquitination and degradation

Esophageal squamous cell carcinoma (ESCC) is one of the most common and deadly cancers. Fbxo45, a substrate recognition subunit of E3 ligase, is critically involved in tumorigenesis and tumor progression. However, the function of Fbxo45 and the underlying mechanisms have not been elucidated in ESCC. We used cellular and molecular methods to explore the molecular basis of Fbxo45-mediated ESCC development. We found that ectopic overexpression of Fbxo45 promoted the growth of Kyse-150, Kyse30 and ECA-109 cells and inhibited the apoptosis. Moreover, overexpression of Fbxo45 promoted the migration and invasion of ESCC cells. Consistently, knockdown of Fbxo45 exhibited the opposite effects on ESCC cells. Mechanistically, we observed that Fbxo45 binds to GGNBP2 via its SPRY domain and targets GGNBP2 for ubiquitination and degradation. GGNBP2 overexpression exhibited anticancer activity in ESCC cells. Furthermore, Fbxo45 exerted its functions by regulating GGNBP2 stability in ESCC cells. Notably, overexpression of Fbxo45 facilitated tumor growth in mice. Strikingly, Fbxo45 was highly expressed in ESCC tissues, and GGNBP2 had a lower expression in ESCC specimens. High expression of Fbxo45 and low expression of GGNBP2 were associated with poor prognosis in ESCC patients. Fbxo45 was negatively correlated with GGNBP2 expression in ESCC tissues. Therefore, Fbxo45 serves as an oncoprotein to promote ESCC tumorigenesis by targeting the stability of the tumor suppressor GGNBP2 in ESCC.

CACNA1C-AS2 inhibits cell proliferation and suppresses cell migration and invasion via targeting FBXO45 and PI3K/AKT/mTOR pathways in glioma

Glioma is the most common brain cancer with a poor prognosis, and its underlying molecular mechanisms still needs to be further explored. In the current study, we discovered that an antisense lncRNA, CACNA1C-AS2, suppressed growth, migration and invasion of glioma cells, suggesting that CACNA1C-AS2 functions as a tumor suppressor. Furthermore, we found that CACNA1C-AS2 negatively regulated Fbxo45 protein expression in glioma cells. Impressively, extensive experimental results revealed that Fbxo45 accelerated growth, migration and invasion of glioma cells. Clinically, increased Fbxo45 expression was observed in 75 human glioma tissue samples. Moreover, in vivo experiments also demonstrated that Fbxo45 overexpression enhanced tumor growth in mice. Especially, we further identified that Fbxo45 activated mTORC1 rather than mTORC2 through PI3K/AKT signaling to promote cell growth and motility in glioma cells. Rescue experiments also exhibited that CACNA1C-AS2 inhibited cell growth and motility partly through down-regulating Fbxo45 expression in glioma. Our results provide the novel insights into the critical role of CACNA1C-AS2/Fbxo45/mTOR axis involved in regulating glioma tumorigenesis and progression, and further indicate that CACNA1C-AS2 and Fbxo45 may be the potential biomarkers and therapeutic targets for glioma.

Identification of target and pathway of aspirin combined with Lipitor treatment in prostate cancer through integrated bioinformatics analysis

PURPOSE

Our previous studies have confirmed that aspirin combined with Lipitor inhibited the development of prostate cancer (PCa), but the mechanisms need to be comprehensively expounded. The study aims to screen out the hub genes of combination therapy and to explore their association with the pathogenesis and prognosis of PCa.

METHODS

Gene expressions were quantified by RNA sequencing (RNA-seq). Altered biological function, pathways of differentially expressed genes (DEGs), protein-protein interaction network, the filtering of hub genes, gene co-expression and the pathogenesis and prognosis were revealed by bioinformatics analysis. The correlation between hub gene expression and patient survival was validated by Kaplan-Meier. The effects of silent DNA replication and sister chromatid cohesion 1 (siDSCC1) combined with Lipitor and aspirin on DSCC1 expression, viability, invasion and migration of PCa cells were detected by qRT-PCR, Wound healing and transwell assays.

RESULTS

157 overlapped DEGs involved in FoxO, PI3K-Akt and p53 signaling pathways were identified. Ten hub genes (NEIL3, CDC7, DSCC1, CDC25C, PRIM1, MCM10, FBXO5, DTL, SERPINE1, EXO1) were verified to be correlated with the pathology and prognosis of PCa. DSCC1 silencing not only inhibited the viability, migration and invasion of PCa cells, but also strengthened the suppressing effects of Lipitor and aspirin alone or in combination on PCa cells.

CONCLUSION

The enrichment pathways and targets of Lipitor combined with aspirin in PCa are discovered, and DSCC1 silencing can potentiate the effect of Lipitor combined with aspirin in the treatment of PCa.

Prognostic Significance and Immunological Role of FBXO5 in Human Cancers: A Systematic Pan-Cancer Analysis

F-box protein 5 (FBXO5), an essential subunit of the ubiquitin protein ligase complex, is increasingly recognized to exhibit important biological effects in regulating tumor occurrence and progression. The present research was intended to systematically investigate the latent roles of FBXO5 in prognosis and immunological function across cancers. Pan-cancer analyses of FBXO5 were performed based upon publicly available online databases, mainly including the Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), UCSC Xena, cBioPortal, and ImmuCellAI, revealing the possible relationships between FBXO5 and prognosis, DNA methylation, tumor microenvironment (TME), infiltration of immune cells, immune-related genes, immune checkpoints, tumor mutation burden (TMB), and microsatellite instability (MSI). The results suggested that FBXO5 was expressed at a high level in numerous tumor cell lines with significant upregulation in most cancers as opposed to normal tissues. Of note, elevated expression of FBXO5 was significantly related to an unfavorable prognosis in many cancer types. Furthermore, DNA methylation and TME were confirmed to display evident correlation with the expression of FBXO5 in several malignancies. Moreover, FBXO5 expression was remarkably positively correlated with the levels of infiltrating Treg cells and Tcm cells in most tumors, but negatively correlated with tumor-infiltrating CD8⁺ T cells, NK/NKT cells, and Th2 cells. Meanwhile, FBXO5 was demonstrated to be co-expressed with the genes encoding immune activating and suppressive factors, chemokines, chemokine receptors, and major histocompatibility complex (MHC). Immune checkpoints, TMB, and MSI were also overtly associated with FBXO5 dysregulation among diverse kinds of cancers. Additionally, the enrichment analyses showed close relationships between FBXO5 expression and the processes related to cell cycle and immune inflammatory response. These findings provided a detailed comprehension of the oncogenic function of FBXO5. Because of its crucial roles in cancer immunity and tumorigenesis, FBXO5 may serve as a novel prognostic indicator and immunotherapeutic target for various malignancies.

Fbxo45 facilitates pancreatic carcinoma progression by targeting USP49 for ubiquitination and degradation

Fbxo45, a conserved F-box protein, comprises of an atypical SKP1, CUL1, F-box protein (SCF) ubiquitin ligase complex that promotes tumorigenesis and development. However, the biological function and molecular mechanisms of Fbxo45 involved in pancreatic carcinogenesis are ambiguous. We conducted several approaches, including transfection, coIP, real-time polymerase chain reaction (RT-PCR), Western blotting, ubiquitin assays, and animal studies, to explore the role of Fbxo45 in pancreatic cancer. Here, we report that USP49 stability is governed by Fbxo45-mediated ubiquitination and is enhanced by the absence of Fbxo45. Moreover, Fbxo45 binds to a short consensus sequence of USP49 through its SPRY domain. Furthermore, Fbxo45-mediated USP49 ubiquitination and degradation are enhanced by NEK6 kinase. Functionally, Fbxo45 increases cell viability and motility capacity by targeting USP49 in pancreatic cancer cells. Xenograft mouse experiments demonstrated that ectopic expression of Fbxo45 enhanced tumor growth in mice and that USP49 overexpression inhibited tumor growth in vivo. Notably, Fbxo45 expression was negatively associated with USP49 expression in pancreatic cancer tissues. Fbxo45 serves as an oncoprotein to facilitate pancreatic oncogenesis by regulating the stability of the tumor suppressor USP49 in pancreatic cancer.

Bioinformatics analysis identifying FBXO45 gene as a potential oncogene in esophageal cancer

BACKGROUND

F-box protein 45 (FBXO45) is a member of the F-box protein family, and is reportedly involved in the progression of many diseases. However, its role in esophageal cancer (ESCA) remains unclear.

METHODS

The expression, clinical characteristics, gene function, pathway, and correlation between the infiltration of different immune cells were analyzed using public data. The pan-cancer expression of FBXO45 was assessed using the TIMER2 database. The expression of FBXO45 in different tumor stages and histology subtypes were evaluated using the UALCAN database. The protein-protein interaction (PPI) network was constructed using the STRING database. Immune cell infiltration data were downloaded from the ImmuCellAI database.

RESULTS

The top 300 genes most positively correlated with FBXO45 were screened into the enrichment analysis. The functional enrichment results showed that FBXO45 was mainly associated with proteasomal protein catabolic process and the regulation of DNA metabolic processing in the biological process (BP) category; spindle, chromosomal region, and focal adhesion in the cellular component category; and ATPase activity and ubiquitin-protein transferase activity terms in the molecular function category. FBXO45 was overexpressed in ESCA and other cancer types. FBXO45 expression was positively associated with the infiltration levels of immunosuppressive cells, such as CD8+ (cluster of differentiation 8+) T cells and NK (natural killer cell) cells, in ESCA. MYCBP2 and SKP1 were most associated with FBXO45.

CONCLUSIONS

Our results suggested that FBXO45 is a potential oncogene in ESCA. Elevated FBXO45 expression indicates a relatively immunosuppressive microenvironment.

Elevated FBXO45 promotes liver tumorigenesis through enhancing IGF2BP1 ubiquitination and subsequent PLK1 upregulation

Dysregulation of tumor-relevant proteins may contribute to human hepatocellular carcinoma (HCC) tumorigenesis. FBXO45 is an E3 ubiquitin ligase that is frequently elevated expression in human HCC. However, it remains unknown whether FBXO45 is associated with hepatocarcinogenesis and how to treat HCC patients with high FBXO45 expression. Here, IHC and qPCR analysis revealed that FBXO45 protein and mRNA were highly expressed in 54.3% (57 of 105) and 52.2% (132 of 253) of the HCC tissue samples, respectively. Highly expressed FBXO45 promoted liver tumorigenesis in transgenic mice. Mechanistically, FBXO45 promoted IGF2BP1 ubiquitination at the Lys190 and Lys450 sites and subsequent activation, leading to the upregulation of PLK1 expression and the induction of cell proliferation and liver tumorigenesis in vitro and in vivo. PLK1 inhibition or IGF2BP1 knockdown significantly blocked FBXO45-driven liver tumorigenesis in FBXO45 transgenic mice, primary cells, and HCCs. Furthermore, IHC analysis on HCC tissue samples revealed a positive association between the hyperexpression of FBXO45 and PLK1/IGF2BP1, and both had positive relationship with poor survival in HCC patients. Thus, FBXO45 plays an important role in promoting liver tumorigenesis through IGF2BP1 ubiquitination and activation, and subsequent PLK1 upregulation, suggesting a new strategy for treating HCC by targeting FBXO45/IGF2BP1/PLK1 axis.

Downregulated F-Box/LRR-Repeat Protein 7 Facilitates Pancreatic Cancer Metastasis by Regulating Snail1 for Proteasomal Degradation

Pancreatic cancer (PCa) is one of the most aggressive lethal malignancies, and cancer metastasis is the major cause of PCa-associated death. F-box/LRR-repeat protein 7 (FBXL7) regulates cancer metastasis and the chemosensitivity of human pancreatic cancer. However, the clinical significance and biological role of FBXL7 in PCa have been rarely studied. In this study, we found that the expression of FBXL7 was down-regulated in PCa tissues compared with tumor-adjacent tissues, and the low expression of FBXL7 was positively associated with cancer metastasis. Functionally, overexpression of FBXL7 attenuated PANC1 cell invasion, whereas FBXL7 silencing promoted BxPC-3 cell invasion. Forced expression of FBXL7 upregulated the expression of epithelial markers (e.g., E-cadherin) and repressed the expression of mesenchymal markers (e.g., N-cadherin and Vimentin), indicating that FBXL7 negatively regulated the epithelial-mesenchymal transition (EMT) of PCa cells. Furthermore, we identified that FBXL7 repressed the expression of Snail1, a crucial transcription factor of EMT. Mechanistically, FBXL7 bound to Snail1 and promoted its ubiquitination and proteasomal degradation. In vivo studies demonstrated that FBXL7 inhibition promotes PCa metastasis. Taken together, our findings demonstrate that FBXL7 knockdown could efficiently enhance PCa metastasis by regulating Snail1-dependent EMT.

DNAJB9 suppresses the metastasis of triple-negative breast cancer by promoting FBXO45-mediated degradation of ZEB1

DNAJB9, a member of the heat shock protein 40 family, acts as a multifunctional player involved in the maintenance of their client proteins and cellular homeostasis. However, the mechanistic action of DNAJB9 in human malignancies is yet to be fully understood. In this study, we found that ectopic restoration of DNAJB9 inhibits the migration, invasion, in vivo metastasis, and lung colonization of triple-negative breast cancer (TNBC) cells. Mechanistically, DNAJB9 stabilizes FBXO45 protein by suppressing self-ubiquitination and reduces the abundance of ZEB1 by Lys48-linked polyubiquitination to inhibit the epithelial-mesenchymal transition (EMT) and metastasis. Clinically, the reduction of DNAJB9 expression, concomitant with decreased FBXO45 abundance in breast cancer tissues, correlates with poorer clinical outcomes of patients with breast cancer. Taken together, our results provide a novel insight into the metastasis of TNBC and define a promising therapeutic strategy for cancers with overactive ZEB1 by regulating the DNAJB9-FBXO45 signaling axis.

Dalhat M, Abdullah O, Kaleem M, Hosawi S, A Al-Abbasi F, Wu W, Choudhry H, Alhosin M. Targeting Post-Translational Modifications of the p73 Protein: A Promising Therapeutic Strategy for Tumors

The tumor suppressor p73 is a member of the p53 family and is expressed as different isoforms with opposing properties. The TAp73 isoforms act as tumor suppressors and have pro-apoptotic effects, whereas the ΔNp73 isoforms lack the N-terminus transactivation domain and behave as oncogenes. The TAp73 protein has a high degree of similarity with both p53 function and structure, and it induces the regulation of various genes involved in the cell cycle and apoptosis. Unlike those of the p53 gene, the mutations in the p73 gene are very rare in tumors. Cancer cells have developed several mechanisms to inhibit the activity and/or expression of p73, from the hypermethylation of its promoter to the modulation of the ratio between its pro- and anti-apoptotic isoforms. The p73 protein is also decorated by a panel of post-translational modifications, including phosphorylation, acetylation, ubiquitin proteasomal pathway modifications, and small ubiquitin-related modifier (SUMO)ylation, that regulate its transcriptional activity, subcellular localization, and stability. These modifications orchestrate the multiple anti-proliferative and pro-apoptotic functions of TAp73, thereby offering multiple promising candidates for targeted anti-cancer therapies. In this review, we summarize the current knowledge of the different pathways implicated in the regulation of TAp73 at the post-translational level. This review also highlights the growing importance of targeting the post-translational modifications of TAp73 as a promising antitumor strategy, regardless of p53 status.

Regulation of Epithelial-Mesenchymal Plasticity by the E3 Ubiquitin-Ligases in Cancer

The epithelial-mesenchymal plasticity (EMP) is a process by which epithelial cells acquire the ability to dynamically switch between epithelial and mesenchymal phenotypic cellular states. Epithelial cell plasticity in the context of an epithelial-to-mesenchymal transition (EMT) confers increased cell motility, invasiveness and the ability to disseminate to distant sites and form metastasis. The modulation of molecularly defined targets involved in this process has become an attractive therapeutic strategy against cancer. Protein degradation carried out by ubiquitination has gained attention as it can selectively degrade proteins of interest. In the ubiquitination reaction, the E3 ubiquitin-ligases are responsible for the specific binding of ubiquitin to a small subset of target proteins, and are considered promising anticancer drug targets. In this review, we summarize the role of the E3 ubiquitin-ligases that control targeted protein degradation in cancer-EMT, and we highlight the potential use of the E3 ubiquitin-ligases as drug targets for the development of small-molecule drugs against cancer.

FBXO45 is a potential therapeutic target for cancer therapy

FBXO protein 45 (FBXO45), a substrate-recognition subunit of E3 ligases, has been characterised to have pivotal roles in many human diseases, including nervous system diseases, inflammatory diseases and human malignancies. In this article, we describe the expression of FBXO45 in several types of human tumour specimens and highlight the downstream substrates of FBXO45. Moreover, the biological functions of FBXO45 in the regulation of proliferation, apoptosis, the cell cycle and metastasis are mentioned. Furthermore, we describe that the expression level of FBXO45 is regulated by several upstream factors such as miR-27a, Hey1, m6A and the lncRNA RP11. As FBXO45 has a critical role in tumorigenesis and progression, FBXO45 might be a novel therapeutic target for cancer treatment.

Skp2 in the ubiquitin-proteasome system: A comprehensive review

The ubiquitin-proteasome system (UPS) is a complex process that regulates protein stability and activity by the sequential actions of E1, E2 and E3 enzymes to influence diverse aspects of eukaryotic cells. However, due to the diversity of proteins in cells, substrate selection is a highly critical part of the process. As a key player in UPS, E3 ubiquitin ligases recruit substrates for ubiquitination specifically. Among them, RING E3 ubiquitin ligases which are the most abundant E3 ubiquitin ligases contribute to diverse cellular processes. The multisubunit cullin-RING ligases (CRLs) are the largest family of RING E3 ubiquitin ligases with tremendous plasticity in substrate specificity and regulate a vast array of cellular functions. The F-box protein Skp2 is a component of CRL1 (the prototype of CRLs) which is expressed in many tissues and participates in multiple cellular functions such as cell proliferation, metabolism, and tumorigenesis by contributing to the ubiquitination and subsequent degradation of several specific tumor suppressors. Most importantly, Skp2 plays a pivotal role in a plethora of cancer-associated signaling pathways. It enhances cell growth, accelerates cell cycle progression, promotes migration and invasion, and inhibits cell apoptosis among others. Hence, targeting Skp2 may represent a novel and attractive strategy for the treatment of different human cancers overexpressing this oncogene. In this review article, we summarized the known roles of Skp2 both in health and disease states in relation to the UPS.

An upstream open reading frame regulates vasculogenic mimicry of glioma via ZNRD1-AS1/miR-499a-5p/ELF1/EMI1 pathway

Increasing evidence has suggested that gliomas can supply blood through vasculogenic mimicry. In this study, the expression and function of ZNRD1‐AS1‐144aa‐uORF (144aa‐uORF) and some non‐coding RNAs in gliomas were assessed. Real‐time quantitative PCR or Western blot was used to discover the expression of 144aa‐uORF, ZNRD1‐AS1, miR‐499a‐5p, ELF1 and EMI1 in gliomas. In addition, RIP and RNA pull‐down assays were applied to explore the interrelationship between 144aa‐uORF and ZNRD1‐AS1. The role of the 144aa‐uORF\ZNRD1‐AS1\miR‐499a‐5p\ELF1\EMI1 axis in vasculogenic mimicry formation of gliomas was analysed. This study illustrates the reduced expression of the 144aa‐uORF in glioma tissues and cells. Up‐regulation of 144aa‐uORF inhibits proliferation, migration, invasion and vasculogenic mimicry formation within glioma cells. The up‐regulated 144aa‐uORF can increase the degradation of ZNRD1‐AS1 through the nonsense‐mediated RNA decay (NMD) pathway. Knockdown of ZNRD1‐AS1 inhibits vasculogenic mimicry in glioma cells by modulating miR‐499a‐5p. At the same time, miR‐499a‐5p is down‐regulated and has a tumour‐suppressive effect in gliomas. In addition, ZNRD1‐AS1 serves as a competitive endogenous RNA (ceRNA) and regulates the expression of ELF1 by binding to miR‐499a‐5p. Notably, ELF1 binds to the promoter region of EMI1 and up‐regulates EMI1 expression, while simultaneously promoting vasculogenic mimicry in glioma cells. This study suggests that the 144aa‐uORF\ZNRD1‐AS1\miR‐499a‐5p\ELF1\EMI1 axis takes key part in regulating the formation of vasculogenic mimicry in gliomas and may provide a potential target for glioma treatment.

FBXO25 Promotes Cutaneous Squamous Cell Carcinoma Growth and Metastasis through Cyclin D1

FBPs are components of the SCF protein E3 ubiquitin ligase and can specifically bind to substrates and thereby regulate multiple tumor behaviors. However, the role of FBPs, FBXO25 in particular, in cutaneous squamous cell carcinoma (cSCC) has not been explored yet. In this study, we found FBXO25 to be highly expressed in cSCC in mice and in vitro, whereas it was significantly less expressed in normal keratinocytes. Stable silencing of FBXO25 in SCC13 cells led to reduced tumor growth, and the knockdown of FBXO25 was accompanied by downregulation of cyclin D1. Correspondingly, stable overexpression of cyclin D1 in FBXO25-deficient SCC13 tumors increased tumor growth, supporting the hypothesis that FBXO25 promotes cSCC growth and metastasis through cyclin D1. Moreover, we found FBXO25 and cyclin D1 interaction to be facilitated through the repressor (Oct-1) of cyclin D1. Our data indicate that Oct-1 interacts directly with FBXO25 and undergoes downregulation, consequently stabilizing cyclin D1 and promoting tumor growth and metastasis.

Emerging roles of F-box proteins in cancer drug resistance

Chemotherapy continues to be a major treatment strategy for various human malignancies. However, the frequent emergence of chemoresistance compromises chemotherapy efficacy leading to poor prognosis. Thus, overcoming drug resistance is pivotal to achieve enhanced therapy efficacy in various cancers. Although increased evidence has revealed that reduced drug uptake, increased drug efflux, drug target protein alterations, drug sequestration in organelles, enhanced drug metabolism, impaired DNA repair systems, and anti-apoptotic mechanisms, are critically involved in drug resistance, the detailed resistance mechanisms have not been fully elucidated in distinct cancers. Recently, F-box protein (FBPs), key subunits in Skp1-Cullin1-F-box protein (SCF) E3 ligase complexes, have been found to play critical roles in carcinogenesis, tumor progression, and drug resistance through degradation of their downstream substrates. Therefore, in this review, we describe the functions of FBPs that are involved in drug resistance and discuss how FBPs contribute to the development of cancer drug resistance. Furthermore, we propose that targeting FBPs might be a promising strategy to overcome drug resistance and achieve better treatment outcome in cancer patients. Lastly, we state the limitations and challenges of using FBPs to overcome chemotherapeutic drug resistance in various cancers.

Acidic leucine-rich nuclear phosphoprotein-32A expression contributes to adverse outcome in acute myeloid leukemia

Background

Acidic leucine-rich nuclear phosphoprotein-32A (ANP32A) is a novel regulator of histone H3 acetylation and promotes leukemogenesis in acute myeloid leukemia (AML). However, its prognostic value in AML remains unclear.

Methods

In this study, we evaluated the prognostic significance of ANP32A expression using two independent large cohorts of cytogenetically normal AML (CN-AML) patients. Multivariable analysis in CN-AML group was also presented. Based on the ANP32A expression, its related genes, dysregulation of pathways, interaction network analysis between microRNAs and target genes, as well as methylation analysis were performed to unveil the complex functions behind ANP32A.

Results

Here we demonstrated overexpression of ANP32A was notably associated with unfavorable outcome in two independent cohorts of CN-AML patients (OS: P=0.012, EFS: P=0.005, n=185; OS: P=0.041, n=232), as well as in European Leukemia Net (ELN) Intermediate-I group (OS: P=0.018, EFS: P=0.045, n=115), National Comprehensive Cancer Network (NCCN) Intermediate Risk AML group (OS: P=0.048, EFS: P=0.039, n=225), and non-M3 AML group (OS: P=0.034, EFS: P=0.011, n=435). Multivariable analysis further validated ANP32A as a high-risk factor in CN-AML group. Multi-omics analysis presented overexpression of ANP32A was associated with aberrant expression of oncogenes and tumor suppressor, up/down-regulation of metabolic and immune-related pathways, dysregulation of microRNAs, and hypomethylation on CpG island and 1st Exon regions.

Conclusions

We proved ANP32A as a novel, potential unfavorable prognosticator and therapeutic target for AML.

Emerging role of F-box proteins in the regulation of epithelial-mesenchymal transition and stem cells in human cancers

Emerging evidence shows that epithelial-mesenchymal transition (EMT) plays a crucial role in tumor invasion, metastasis, cancer stem cells, and drug resistance. Data obtained thus far have revealed that F-box proteins are critically involved in the regulation of the EMT process and stem cell differentiation in human cancers. In this review, we will briefly describe the role of EMT and stem cells in cell metastasis and drug resistance. We will also highlight how numerous F-box proteins govern the EMT process and stem cell survival by controlling their downstream targets. Additionally, we will discuss whether F-box proteins involved in drug resistance are associated with EMT and cancer stem cells. Targeting these F-box proteins might be a potential therapeutic strategy to reverse EMT and inhibit cancer stem cells and thus overcome drug resistance in human cancers.