Fbxo45-mediated degradation of the tumor-suppressor Par-4 regulates cancer cell survival

The FBXO45-GEF-H1 Axis Controls Germinal Center Formation and B-cell Lymphomagenesis

SIGNIFICANCE

We describe the identification of a previously unrecognized ubiquitin ligase-substrate (FBXO45-GEF-H1) regulatory axis that plays an important role in germinal center formation and pathogenesis of common BCLs. These studies reveal novel insights linking dysregulated ubiquitin-mediated control to exploitable vulnerabilities and novel therapeutic strategies for these cancers.

FBXO45 restricts HIV-1 replication by inducing SQSTM1/p62-mediated autophagic degradation of Tat

As a key regulator of human immunodeficiency virus type 1 (HIV-1) transcription, Tat plays an essential role in viral replication and latency, making it a promising target for designing viral control strategies. Identifying host factors that modulate Tat and exploring the underlying mechanisms will benefit our understanding of HIV-1 transcriptional regulation and provide valuable insights into Tat-based therapeutic strategies. Here, by employing the TurboID approach, we discovered high-affinity binding between FBXO45 and Tat. Our findings demonstrate that FBXO45 negatively regulates Tat by promoting Tat ubiquitination and directing it to autophagic degradation. Autophagic degradation of Tat has been reported, but the specific underlying mechanisms remain unidentified. We elucidated this issue by providing evidence that FBXO45-mediated Tat polyubiquitination is an essential prerequisite for this process. Silencing of FBXO45 leads to a deficiency of autophagy receptor SQSTM1/p62 to bind and facilitate the autophagic degradation of Tat. Our results further underscore the crosstalk between post-translational modifications of Tat by demonstrating that the phosphorylation site of the Tat S62 residue is required for ubiquitination induced by FBXO45. Furthermore, in the context of the regulation of HIV-1, FBXO45 inhibits viral replication and maintains the latency of HIV-1 by suppressing viral transcription. Importantly, FBXO45 overexpression significantly attenuated viral rebound after antiretroviral therapy withdrawal. In summary, our findings suggest a novel role for FBXO45 in regulating HIV-1 replication by inducing the ubiquitination and SQSTM1/p62-dependent autophagic degradation of Tat. Considering the indispensable role of Tat in the regulation of HIV-1 replication and reactivation, FBXO45 may be a potential target for therapeutic intervention against HIV-1.IMPORTANCEHIV-1 Tat plays an indispensable role in regulating viral transcription and is a promising target for achieving a functional cure for AIDS. Identifying the host factors that modulate Tat expression could benefit the development of anti-HIV-1 strategies targeting Tat. Using TurboID assay, we identified a significant interaction between FBXO45 and Tat. Functionally, FBXO45 ubiquitinates and directs Tat for SQSTM1/p62-mediated autophagic degradation, thereby effectively restricting HIV-1 replication and maintaining HIV-1 latency by suppressing Tat-dependent viral transcription. These findings uncover a novel role for FBXO45 in regulating Tat and broaden our understanding of the host mechanisms involved in Tat processing.

Loss of Fbxo45 in AT2 cells leads to insufficient histone supply and initiates lung adenocarcinoma

Dysregulation of histone supply is implicated in various cancers, including lung adenocarcinoma (LUAD), although the underlying mechanisms remain poorly understood. Here, we demonstrate that knockout of Fbxo45 in mouse alveolar epithelial type 2 (AT2) cells leads to spontaneous LUAD. Our findings reveal that FBXO45 is a novel cell-cycle-regulated protein that is degraded upon phosphorylation by CDK1 during the S/G2 phase. During the S phase or DNA damage repair, FBXO45 binds to UPF1 and recruits the phosphatase PPP6C, thereby inhibiting UPF1 phosphorylation. This process is crucial for preventing the degradation of replication-dependent (RD) histone mRNAs and ensuring an adequate histone supply. In the absence of FBXO45, the impaired interaction between PPP6C and UPF1 results in sustained hyperphosphorylation of UPF1 throughout the cell cycle, leading to an insufficient histone supply, chromatin relaxation, genomic instability, and an increased rate of gene mutations, ultimately culminating in malignant transformation. Notably, analysis of clinical LUAD specimens confirms a positive correlation between the loss of FBXO45 and genomic instability, which is consistent with our findings in the mouse model. These results highlight the critical role of FBXO45 as a genomic guardian in coordinating histone supply and DNA replication, providing valuable insights into potential therapeutic targets and strategies for the treatment of LUAD.

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.

Inhibitors Targeting the F-BOX Proteins

F-box proteins are involved in multiple cellular processes through ubiquitylation and consequent degradation of targeted substrates. Any significant mutation in F-box protein-mediated proteolysis can cause human malformations. The various cellular processes F-box proteins involved include cell proliferation, apoptosis, invasion, angiogenesis, and metastasis. To target F-box proteins and their associated signaling pathways for cancer treatment, researchers have developed thousands of F-box inhibitors. The most advanced inhibitor of FBW7, NVD-BK M120, is a powerful P13 kinase inhibitor that has been proven to bring about apoptosis in cancerous human lung cells by disrupting levels of the protein known as MCL1. Moreover, F-box Inhibitors have demonstrated their efficacy for treating certain cancers through targeting particular mutated proteins. This paper explores the key studies on how F-box proteins act and their contribution to malignancy development, which fabricates an in-depth perception of inhibitors targeting the F-box proteins and their signaling pathways that eventually isolate the most promising approach to anti-cancer treatments.

The Antitumor Potential of λ-Carrageenan Oligosaccharides on Gastric Carcinoma by Immunomodulation

Gastric carcinoma is a frequently detected malignancy worldwide, while its mainstream drugs usually result in some adverse reactions, including immunosuppression. λ-carrageenan oligosaccharides (COS) have attracted increasing attention as potential anticancer agents due to their ability to enhance immune function. Our current work assessed the antitumor mechanism of λ-COS using BGC-823 cells. Our findings indicated that λ-COS alone did not have a significant impact on BGC-823 cells in vitro; however, it was effective in inhibiting tumor growth in vivo. When THP-1 cells were pre-incubated with λ-COS and used to condition the medium, BGC-823 cells in vitro displayed a concentration-dependent induction of cell apoptosis, nuclear damage, and the collapse of mitochondrial transmembrane potential. These findings suggested that the antineoplastic effect of λ-COS was primarily due to its immunoenhancement property. Treatment with λ-COS was found to significantly enhance the phagocytic capability of macrophages, increase the secretion of TNF-α and IFN-γ, and improve the indexes of spleen and thymus in BALB/c mice. In addition, λ-COS was found to inhibit the growth of BGC-823-derived tumors in vitro by activating the Par-4 signaling pathway, which may be stimulated by the combination of TNF-α and IFN-γ. When used in combination with 5-FU, λ-COS demonstrated enhanced anti-gastric carcinoma activity and improved the immunosuppression induced by 5-FU alone. These findings suggested that λ-COS could be used as an immune-modulating agent for chemotherapy.

Enhancing the Conformational Stability of the cl-Par-4 Tumor Suppressor via Site-Directed Mutagenesis

Intrinsically disordered proteins play important roles in cell signaling, and dysregulation of these proteins is associated with several diseases. Prostate apoptosis response-4 (Par-4), an approximately 40 kilodalton proapoptotic tumor suppressor, is a predominantly intrinsically disordered protein whose downregulation has been observed in various cancers. The caspase-cleaved fragment of Par-4 (cl-Par-4) is active and plays a role in tumor suppression by inhibiting cell survival pathways. Here, we employed site-directed mutagenesis to create a cl-Par-4 point mutant (D313K). The expressed and purified D313K protein was characterized using biophysical techniques, and the results were compared to that of the wild-type (WT). We have previously demonstrated that WT cl-Par-4 attains a stable, compact, and helical conformation in the presence of a high level of salt at physiological pH. Here, we show that the D313K protein attains a similar conformation as the WT in the presence of salt, but at an approximately two times lower salt concentration. This establishes that the substitution of a basic residue for an acidic residue at position 313 alleviates inter-helical charge repulsion between dimer partners and helps to stabilize the structural conformation.

An optimized protocol to detect protein ubiquitination and activation by ubiquitination assay in vivo and CCK-8 assay

E3 ubiquitin ligases play a role in protein degradation, cellular localization, and activation, and their dysregulation is associated with human diseases. Here, we present a protocol to detect IGF2BP1 ubiquitination and activation by an E3 ubiquitin ligase FBXO45. We describe steps for preparing cells and transfecting plasmids. We detail the use of western blot to detect IGF2BP1 ubiquitination and a Cell Counting Kit-8 (CCK-8) assay to detect IGF2BP1 activation. This protocol is applicable to other proteins of interest. For complete details on the use and execution of this protocol, please refer to Lin et al. (2021).¹.

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.

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.

Fbxo45-mediated NP-STEP46 degradation via K6-linked ubiquitination sustains ERK activity in lung cancer

Lung cancer is one of the most threatening malignant tumors to human health. Epidermal growth factor receptor (EGFR)‐targeted therapy is a common and essential means for the clinical treatment of lung cancer. However, drug resistance has always affected the therapeutic effect and survival rate in non‐small cell lung cancer (NSCLC). Tumor heterogeneity is a significant reason, yielding various drug resistance mechanisms, such as EGFR‐dependent or ‐independent extracellular signal‐regulated kinase 1 and/or 2 (ERK1/2) activation in NSCLC. To examine whether this aberrant activation of ERK1/2 is related to the loss of function of its specific phosphatase, a series of in vitro and in vivo assays were performed. We found that F‐box/SPRY domain‐containing protein 1 (Fbxo45) induces ubiquitination of NP‐STEP₄₆, an active form of striatal‐enriched protein tyrosine phosphatase, with a K6‐linked poly‐ubiquitin chain. This ubiquitination led to proteasome degradation in the nucleus, which then sustains the aberrant level of phosphorylated‐ERK (pERK) and promotes tumor growth of NSCLC. Fbxo45 silencing can significantly inhibit cell proliferation and tumor growth. Moreover, NSCLC cells with silenced Fbxo45 showed great sensitivity to the EGFR tyrosine kinase inhibitor (TKI) afatinib. Here, we first report this critical pERK maintenance mechanism, which might be independent of the upstream kinase activity in NSCLC. We propose that inhibiting Fbxo45 may combat the issue of drug resistance in NSCLC patients, especially combining with EGFR‐TKI therapy.

E3 ubiquitin ligase RBX1 drives the metastasis of triple negative breast cancer through a FBXO45-TWIST1-dependent degradation mechanism

Triple-negative breast cancer (TNBC) patients are at high risk of recurrence and metastasis in the early stages, although receiving standard treatment. However, the underlying mechanism of TNBC remains unclear. Here, the critical effect of E3 ubiquitin ligase RBX1 in the metastasis of TNBC was reported for the first time. We discovered that RBX1 expression was evidently raised in the tissues of TNBC. Our clinical research displayed that high RBX1 expression was markedly related to poor distant invasion and survival. Functional analysis exhibited that RBX1 facilitated metastasis of TNBC cells through increasing EMT. Furthermore, we demonstrated that RBX1 knockdown increased the levels of the Twist family bHLH transcription factor 1 (TWIST1), is a significant regulator in the EMT process in some cancers. It can be observed an evident positive correlation between the TWIST1 and RBX1 levels, further confirming that EMT induced by RBX1 in TNBC cells is determined by TWIST1. Mechanistically, RBX1 modulates the expression of TWIST1 via modulating FBXO45, directly binding to FBXO45, and facilitating its degradation and ubiquitination. Briefly, our findings confirm that RBX1 is probably a new biomarker of TNBC carcinogenesis, thus suggesting that targeting the RBX1/FBXO45/TWIST1 axis may be an underlying strategy for TNBC treatment.

Anti-cancer function of microRNA-30e is mediated by negative regulation of HELLPAR, a noncoding macroRNA, and genes involved in ubiquitination and cell cycle progression in prostate cancer

Prostate cancer (PCa) progression relies on androgen receptor (AR) function, making AR a top candidate for PCa therapy. However, development of drug resistance is common, which eventually leads to development of castration‐resistant PCa. This warrants a better understanding of the pathophysiology of PCa that facilitates the aberrant activation of key signaling pathways including AR. MicroRNAs (miRNAs) function as regulators of cancer progression as they modulate various cellular processes. Here, we demonstrate a multidimensional function of miR‐30e through the regulation of genes involved in various signaling pathways. We noted loss of miR‐30e expression in prostate tumors, which, when restored, led to cell cycle arrest, induction of apoptosis, improved drug sensitivity of PCa cells and reduced tumor progression in xenograft models. We show that experimental upregulation of miR‐30e reduces expression of mRNAs including AR, FBXO45, SRSF7 and MYBL2 and a novel long noncoding RNA (lncRNA) HELLPAR, which are involved in cell cycle, apoptosis and ubiquitination, and the effects could be rescued by inhibition of miR‐30e expression. RNA immunoprecipitation analysis confirmed direct interactions between miR‐30e and its RNA targets. We noted a newly identified reciprocal relationship between miR‐30e and HELLPAR, as inhibition of HELLPAR improved stabilization of miR‐30e. Transcriptome profiling and quantitative real‐time PCR (qRT‐PCR) validation of miR‐30e‐expressing PCa cells showed differential expression of genes involved in cell cycle progression, apoptosis and ubiquitination, which supports our in vitro study. This study demonstrates an integrated function of miR‐30e on dysregulation of miRNA/lncRNA/mRNA axes that may have diagnostic and therapeutic significance in aggressive PCa.

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.

Comprehensive Analysis of Expression, Prognostic Value, and Immune Infiltration for Ubiquitination-Related FBXOs in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most refractory human malignancies. F-box only proteins (FBXO) are the core components of SKP1-cullin 1-F-box E3 ubiquitin ligase, which have been reported to play crucial roles in tumor initiation and progression via ubiquitination-mediated proteasomal degradation. However, the clinical implications and biological functions of FBXOs in PDAC have not been fully clarified. Herein we perform a comprehensive analysis for the clinical values and functional roles of FBXOs in PDAC using different public databases. We found that FBXO1 (CCNF), FBXO20 (LMO7), FBXO22, FBXO28, FBXO32, and FBXO45 (designated six-FBXOs) were robustly upregulated in PDAC tissues, which predicted an adverse prognosis of PDAC patients. There was a significant correlation between the expression levels of six-FBXOs and the clinicopathological features in PDAC. The transcriptional levels of six-FBXOs were subjected to the influence of promoter methylation levels. There were more than 40% genetic alterations and mutations of six-FBXOs, which affected the clinical outcome of PDAC patients. Furthermore, the expression of six-FBXOs was associated with immune infiltrations and activated status, including B cells, CD8⁺ T cells, CD4⁺ T cells, NK cells, macrophages, and dendritic cells. The functional prediction revealed that the six-FBXOs were involved in ubiquitination-related pathways and other vital signaling pathways, such as p53, PI3K/Akt, and Hippo pathway. Therefore, six-FBXOs are the promising prognostic biomarkers or potential targets for PDAC diagnosis and treatment.

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.

A Novel miRNA-mRNA Axis Involves in Regulating Transcriptional Disorders in Pancreatic Adenocarcinoma

Background

Currently, there is still a lack of understanding about the mechanism and therapeutic targets of pancreatic adenocarcinoma (PAAD). The potential of miRNA-mRNA networks for the identification of regulatory mechanisms involved in PAAD development remains unexplored.

Methods

We compared differentially expressed miRNAs (DEMIs) and differentially expressed genes (DEGs) in PAAD and normal tissues from the Gene Expression Omnibus (GEO) database. Transcription factors (TFs) were obtained from FunRich. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of DEGs and DEMIs were implemented using Database for Annotation, Visualization and Integrated Discovery (DAVID). Then, key miRNAs and targeted mRNAs were identified by assessment of their expression and prognosis in UALCAN and Kaplan-Meier plotters. In the last step, the candidate miRNA-mRNA selected was confirmed by real-time quantitative polymerase chain reaction (qRT-PCR).

Results

We distinguished 62 significant DEMIs, 1314 upregulated DEGs, and 1110 downregulated DEGs. The top 10 TFs were identified. In total, there were 160 hub genes obtained by intersecting the set of 2224 predicted targets with the set of significant DEGs. And we selected 8 key miRNAs. Furthermore, low expression of miR-455-3p in PAAD tissue was closely connected with poor prognosis, and only 5 target mRNAs were predicted to be increased in PAAD tissue with poor prognosis. Therefore, a novel miRNA-hub gene regulatory network in PAAD was constructed. Finally, in vitro experiments indicated that miR-455-3p expression was decreased in PAAD sample. HOXC4, DLG4, DYNLL1 and FBXO45 were validated by qRT-PCR as highly probable targets of miR-455-3p.

Conclusion

A novel miRNA-mRNA axis has been discovered that may be involved in the regulation of transcriptional disorders and affected the survival of PAAD patients, which would provide a novel strategy for the treatment of PAAD.

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.

Systematic analysis of the expression and prognosis relevance of FBXO family reveals the significance of FBXO1 in human breast cancer

Background

Breast cancer (BC) remains a prevalent and common form of cancer with high heterogeneity. Making efforts to explore novel molecular biomarkers and serve as potential disease indicators, which is essential to effectively enhance the prognosis and individualized treatment of BC. FBXO proteins act as the core component of E3 ubiquitin ligase, which play essential regulators roles in multiple cellular processes. Recently, research has indicated that FBXOs also play significant roles in cancer development. However, the molecular functions of these family members in BC have not been fully elucidated.

Methods

In this research, we investigated the expression data, survival relevance and mutation situation of 10 FBXO members (FBXO1, 2, 5, 6, 16, 17, 22, 28, 31 and 45) in patients with BC from the Oncomine, GEPIA, HPA, Kaplan–Meier Plotter, UALCAN and cBioPortal databases. The high transcriptional levels of FBXO1 in different subtypes of BC were verified by immunohistochemical staining and the specific mutations of FBXO1 were obtained from COSMIC database. Top 10 genes with the highest correlation to FBXO1 were identified through cBioPortal and COXPRESdb tools. Additionally, functional enrichment analysis, PPI network and survival relevance of FBXO1 and co-expressed genes in BC were obtained from DAVID, STRING, UCSC Xena, GEPIA, bc-GenExMiner and Kaplan–Meier Plotter databases. FBXO1 siRNAs were transfected into MCF-7 and MDA-MB-231 cell lines. Expression of FBXO1 in BC cell lines was detected by western-blot and RT-qPCR. Cell proliferation was detected by using CCK-8 kit and colony formation assay. Cell migration was detected by wound‐healing and transwell migration assay.

Results

We found that FBXO2, FBXO6, FBXO16 and FBXO17 were potential favorable prognostic factors for BC. FBXO1, FBXO5, FBXO22, FBXO28, FBXO31 and FBXO45 may be the independent poor prognostic factors for BC. All of them were correlated to clinicopathological staging. Moreover, knockdown of FBXO1 in MCF7 and MDA-MB-231 cell lines resulted in decreased cell proliferation and migration in vitro. We identified that FBXO1 was an excellent molecular biomarker and therapeutic target for different molecular typing of BC.

Conclusion

This study implies that FBXO1, FBXO2, FBXO5, FBXO6, FBXO16, FBXO17, FBXO22, FBXO28, FBXO31 and FBXO45 genes are potential clinical targets and prognostic biomarkers for patients with different molecular typing of BC. In addition, the overexpression of FBXO1 is always found in breast cancer and predicts disadvantageous prognosis, implicating it could as an appealing therapeutic target for breast cancer patients.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

Prostate apoptosis response-4 and tumor suppression: it's not just about apoptosis anymore

The tumor suppressor prostate apoptosis response-4 (Par-4) has recently turned ‘twenty-five’. Beyond its indisputable role as an apoptosis inducer, an increasing and sometimes bewildering, new roles for Par-4 are being reported. These roles include its ability to regulate autophagy, senescence, and metastasis. This growing range of responses to Par-4 is reflected by our increasing understanding of the various mechanisms through which Par-4 can function. In this review, we summarize the existing knowledge on Par-4 tumor suppressive mechanisms, and discuss how the interaction of Par-4 with different regulators influence cell fate. This review also highlights the new secretory pathway that has emerged and the likely discussion on its clinical implications.

Potential Therapeutic Agents Against Par-4 Target for Cancer Treatment: Where Are We Going?

One of the greatest challenges of cancer therapeutics nowadays is to find selective targets successfully. Prostate apoptosis response-4 (Par-4) is a selective tumor suppressor protein with an interesting therapeutic potential due to its specificity on inducing apoptosis in cancer cells. Par-4 activity and levels can be downregulated in several tumors and cancer cell types, indicating poor prognosis and treatment resistance. Efforts to increase Par-4 expression levels have been studied, including its use as a therapeutic protein by transfection with adenoviral vectors or plasmids. However, gene therapy is very complex and still presents many hurdles to be overcome. We decided to review molecules and drugs with the capacity to upregulate Par-4 and, thereby, be an alternative to reach this druggable target. In addition, Par-4 localization and function are reviewed in some cancers, clarifying how it can be used as a therapeutic target.

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.

Fbxo45 Binds SPRY Motifs in the Extracellular Domain of N-Cadherin and Regulates Neuron Migration during Brain Development

Several events during the normal development of the mammalian neocortex depend on N-cadherin, including the radial migration of immature projection neurons into the cortical plate. Remarkably, radial migration requires the N-cadherin extracellular domain but not N-cadherin-dependent homophilic cell-cell adhesion, suggesting that other N-cadherin-binding proteins may be involved. We used proximity ligation and affinity purification proteomics to identify N-cadherin-binding proteins. Both screens detected MycBP2 and SPRY domain protein Fbxo45, two components of an intracellular E3 ubiquitin ligase. Fbxo45 appears to be secreted by a nonclassical mechanism, not involving a signal peptide and not requiring transport from the endoplasmic reticulum to the Golgi apparatus. Fbxo45 binding requires N-cadherin SPRY motifs that are not involved in cell-cell adhesion. SPRY mutant N-cadherin does not support radial migration in vivo Radial migration was similarly inhibited when Fbxo45 expression was suppressed. The results suggest that projection neuron migration requires both Fbxo45 and the binding of Fbxo45 or another protein to SPRY motifs in the extracellular domain of N-cadherin.

F-box proteins and cancer: an update from functional and regulatory mechanism to therapeutic clinical prospects

E3 ubiquitin ligases play a critical role in cellular mechanisms and cancer progression. F-box protein is the core component of the SKP1-cullin 1-F-box (SCF)-type E3 ubiquitin ligase and directly binds to substrates by various specific domains. According to the specific domains, F-box proteins are further classified into three sub-families: 1) F-box with leucine rich amino acid repeats (FBXL); 2) F-box with WD 40 amino acid repeats (FBXW); 3) F-box only with uncharacterized domains (FBXO). Here, we summarize the substrates of F-box proteins, discuss the important molecular mechanism and emerging role of F-box proteins especially from the perspective of cancer development and progression. These findings will shed new light on malignant tumor progression mechanisms, and suggest the potential role of F-box proteins as cancer biomarkers and therapeutic targets for future cancer treatment.

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.

Regulation of apoptosis by E3 ubiquitin ligases in ubiquitin proteasome system

Apoptosis is an organised ATP-dependent programmed cell death that organisms have evolved to maintain homoeostatic cell numbers and eliminate unnecessary or unhealthy cells from the system. Dysregulation of apoptosis can have serious manifestations culminating into various diseases, especially cancer. Accurate control of apoptosis requires regulation of a wide range of growth enhancing as well as anti-oncogenic factors. Appropriate regulation of magnitude and temporal expression of key proteins is vital to maintain functional apoptotic signalling. Controlled protein turnover is thus critical to the unhindered operation of the apoptotic machinery, disruption of which can have severe consequences, foremost being oncogenic transformation of cells. The ubiquitin proteasome system (UPS) is one such major cellular pathway that maintains homoeostatic protein levels. Recent studies have found interesting links between these two fundamental cellular processes, wherein UPS depending on the cue can either inhibit or promote apoptosis. A diverse range of E3 ligases are involved in regulating the turnover of key proteins of the apoptotic pathway. This review summarises an overview of key E3 ubiquitin ligases involved in the regulation of the fundamental proteins involved in apoptosis, linking UPS to apoptosis and attempts to emphasize the significance of this relationship in context of cancer.

Autophagy is inhibited by ubiquitin ligase activity in the nervous system

Autophagy is an intracellular catabolic process prominent in starvation, aging and disease. Neuronal autophagy is particularly important, as it affects the development and function of the nervous system, and is heavily implicated in neurodegenerative disease. Nonetheless, how autophagy is regulated in neurons remains poorly understood. Using an unbiased proteomics approach, we demonstrate that the primary initiator of autophagy, the UNC-51/ULK kinase, is negatively regulated by the ubiquitin ligase RPM-1. RPM-1 ubiquitin ligase activity restricts UNC-51 and autophagosome formation within specific axonal compartments, and exerts effects broadly across the nervous system. By restraining UNC-51 activity, RPM-1 inhibits autophagosome formation to affect axon termination, synapse maintenance and behavioral habituation. These results demonstrate how UNC-51 and autophagy are regulated subcellularly in axons, and unveils a mechanism for restricting initiation of autophagy across the nervous system. Our findings have important implications beyond nervous system development, given growing links between altered autophagy regulation and neurodegenerative diseases.

Association Study Reveals One Susceptibility Locus with Vitiligo in the Chinese Han Population

Objective: The purpose of this study was to investigate associations between the 14 reported loci (from a meta-analysis of genome-wide association studies [GWAS] in the Caucasian population) and vitiligo in the Chinese Han population. Materials and Methods: In this study 14 single nucleotide polymorphisms (SNPs) at 14 different genetic loci were evaluated for their association with viteligo in a Chinese Han cohort, including 1472 cases and 1472 controls of by using the Sequenom MassArray iPLEX1 system. A Bonferroni adjustment was used for multiple comparisons and p_Bonferroni <0.0056 was considered statistically significant. Results: The T allele of the locus within the FBXO45-NRROS gene (3q29) was significantly associated with vitiligo (odds ratio = 1.22, 95% confidence interval: 1.10-1.36, p = 0.0001). Association at the genotype level was strong (p = 0.0007). The other SNPs were not associated with vitiligo (p_Bonferroni >0.0056). Conclusion: A SNP at the rs6583331 locus 3q29 is associated with the susceptibility of vitiligo in the Chinese Han population, which suggests that there is a common genetic factor predisposing to the development of vitiligo in the Chinese and Caucasian populations.

FBXO45-MYCBP2 regulates mitotic cell fate by targeting FBXW7 for degradation

Cell fate decision upon prolonged mitotic arrest induced by microtubule-targeting agents depends on the activity of the tumor suppressor and F-box protein FBXW7. FBXW7 promotes mitotic cell death and prevents premature escape from mitosis through mitotic slippage. Mitotic slippage is a process that can cause chemoresistance and tumor relapse. Therefore, understanding the mechanisms that regulate the balance between mitotic cell death and mitotic slippage is an important task. Here we report that FBXW7 protein levels markedly decline during extended mitotic arrest. FBXO45 binds to a conserved acidic N-terminal motif of FBXW7 specifically under a prolonged delay in mitosis, leading to ubiquitylation and subsequent proteasomal degradation of FBXW7 by the FBXO45-MYCBP2 E3 ubiquitin ligase. Moreover, we find that FBXO45-MYCBP2 counteracts FBXW7 in that it promotes mitotic slippage and prevents cell death in mitosis. Targeting this interaction represents a promising strategy to prevent chemotherapy resistance.

Silencing of type II phosphatidylinositol 4-kinase β stabilizes prostate apoptosis response-4 and induces apoptosis in cancer cells

Type II phosphatidylinositol 4-kinase β (PtdIns 4-kinase II β) is an enigma among the phosphatidylinositol 4-kinase family. The role of PtdIns 4-kinase II β in MCF-7 cells was addressed with the help of short hairpin RNA (shRNA). PtdIns 4-kinase II β shRNA transfection increased pan-caspase activity and induced apoptosis in cancerous MCF-7 cells. Non-cancerous MCF-10A cells were resistant to PtdIns 4-kinase II β shRNA-induced apoptosis. Caspase 8 and 9 inhibitors rescued MCF-7 cells from apoptosis. Shotgun proteomic studies with Flag-tagged PtdIns 4-kinase II β immunoprecipitates showed tumor suppressor prostate apoptosis response-4 (Par-4) as one of the interacting proteins in HEK293 cells. In reciprocal experiments, Par-4 antibodies co-precipitated PtdIns 4-kinase II β from MCF-7 cells. Deletion of membrane localization motif (ΔCCPCC) or a mutation in ATP-binding region (D304A) of PtdIns 4-kinase II β did not affect its interaction with Par-4. Pull-down assays with GST-PtdIns 4-kinase II β-truncated mutants showed that the region between 101 and 215 amino acid residues is essential for interaction with Par-4. At molecular level, PtdIns 4-kinase II β shRNA transfection increased Par-4 stability, its nuclear localization and inhibition of NF-κB binding to target DNA. Knocking down of Par-4 with siRNA (small interfering RNA) rescued MCF-7 cells from PtdIns 4-kinase II β shRNA-induced apoptosis. These results suggest that PtdIns 4-kinase II β may be a novel regulator of Par-4 through protein–protein interactions. These studies have potential implications in cancer therapy.

pH-Induced Folding of the Caspase-Cleaved Par-4 Tumor Suppressor: Evidence of Structure Outside of the Coiled Coil Domain

Prostate apoptosis response-4 (Par-4) is a 38 kDa largely intrinsically disordered tumor suppressor protein that functions in cancer cell apoptosis. Par-4 down-regulation is often observed in cancer while up-regulation is characteristic of neurodegenerative conditions such as Alzheimer’s disease. Cleavage of Par-4 by caspase-3 activates tumor suppression via formation of an approximately 25 kDa fragment (cl-Par-4) that enters the nucleus and inhibits Bcl-2 and NF-ƙB, which function in pro-survival pathways. Here, we have investigated the structure of cl-Par-4 using biophysical techniques including circular dichroism (CD) spectroscopy, dynamic light scattering (DLS), and intrinsic tyrosine fluorescence. The results demonstrate pH-dependent folding of cl-Par-4, with high disorder and aggregation at neutral pH, but a largely folded, non-aggregated conformation at acidic pH.

PAM forms an atypical SCF ubiquitin ligase complex that ubiquitinates and degrades NMNAT2

PHR (PAM/Highwire/RPM-1) proteins are conserved RING E3 ubiquitin ligases that function in developmental processes, such as axon termination and synapse formation, as well as axon degeneration. At present, our understanding of how PHR proteins form ubiquitin ligase complexes remains incomplete. Although genetic studies indicate NMNAT2 is an important mediator of PHR protein function in axon degeneration, it remains unknown how PHR proteins inhibit NMNAT2. Here, we decipher the biochemical basis for how the human PHR protein PAM, also called MYCBP2, forms a noncanonical Skp/Cullin/F-box (SCF) complex that contains the F-box protein FBXO45 and SKP1 but lacks CUL1. We show FBXO45 does not simply function in substrate recognition but is important for assembly of the PAM/FBXO45/SKP1 complex. Interestingly, we demonstrate a novel role for SKP1 as an auxiliary component of the target recognition module that enhances binding of FBXO45 to NMNAT2. Finally, we provide biochemical evidence that PAM polyubiquitinates NMNAT2 and regulates NMNAT2 protein stability and degradation by the proteasome.

miR-17-3P regulates the proliferation and survival of colon cancer cells by targeting Par4

Colorectal cancer (CRC) is a common malignancy worldwide. However, the pathogenesis by which CRC progression occurs remains to be elucidated. The present study investigated the role of miRNA (miR)‑17‑3P in the regulation of CRC cell survival. Firstly, miR‑17‑3P expression was aberrantly upregulated in human CRC tumor tissues compared with controls. Further results demonstrated that the proliferation capacity of human CRC SW480 and LoVo cells was significantly increased by an miR‑17‑3P specific mimic, and was inhibited by miR‑17‑3P silencing. Conversely, the apoptosis of human CRC cells was remarkably decreased by miR‑17‑3P mimic, and enhanced by miR‑17‑3P suppression compared with control. Additionally, it was observed that there was a potential binding site of miR‑17‑3P on the 3'‑untranslated region of Prostate apoptosis responde‑4 (Par4) and miR‑17‑3P may directly target Par4 mRNA. In human CRC cells, an miR‑17‑3P inhibitor significantly upregulated Par 4 expression, however the miR‑17‑3P mimic reduced Par4expression. Furthermore, Par4 expression exhibited an inhibitory effect on the proliferation of CRC cells transfected with miR‑17‑3P mimic, and exhibited a promoting role in the repressed apoptosis by miR‑17‑3P mimic. Inconclusion, the results of the present study demonstrated that miR‑17‑3P is important in CRC cell survival by targeting Par4, indicating a novel finding regarding human CRC progression.

A Naturally Generated Decoy of the Prostate Apoptosis Response-4 Protein Overcomes Therapy Resistance in Tumors

Primary tumors are often heterogeneous, composed of therapy-sensitive and emerging therapy-resistant cancer cells. Interestingly, treatment of therapy-sensitive tumors in heterogeneous tumor microenvironments results in apoptosis of therapy-resistant tumors. In this study, we identify a prostate apoptosis response-4 (Par-4) amino-terminal fragment (PAF) that is released by diverse therapy-sensitive cancer cells following therapy-induced caspase cleavage of the tumor suppressor Par-4 protein. PAF caused apoptosis in cancer cells resistant to therapy and inhibited tumor growth. A VASA segment of Par-4 mediated its binding and degradation by the ubiquitin ligase Fbxo45, resulting in loss of Par-4 proapoptotic function. Conversely, PAF, which contains this VASA segment, competitively bound to Fbxo45 and rescued Par-4-mediated induction of cancer cell-specific apoptosis. Collectively, our findings identify a molecular decoy naturally generated during apoptosis that inhibits a ubiquitin ligase to overcome therapy resistance in tumors. Cancer Res; 77(15); 4039-50. ©2017 AACR.

miR-107 Promotes Proliferation and Inhibits Apoptosis of Colon Cancer Cells by Targeting Prostate Apoptosis Response-4 (Par4)

Colorectal cancer (CRC) is one of the most common malignancies in the world, with a high incidence and a high mortality. However, the pathogenesis of CRC carcinogenesis is still unexplored. In this study, we investigated the role of miR-107 in the regulation of CRC cell proliferation and apoptosis. First, the expression of miR-107 was observed to be aberrantly increased in human CRC tumor tissues and cell lines when compared to the colonic control tissues and colon epithelial cells. Further study showed that the proliferative and apoptotic capacities of human CRC SW480 and LoVo cells were aberrantly regulated by miR-107. The proliferation of SW480 and LoVo cells was remarkably enhanced by the miR-107 mimic but suppressed by the miR-107 inhibitor when compared to the negative control. On the contrary, the apoptotic rate of both SW480 and LoVo cells was significantly inhibited by miR-107 overexpression but increased by miR-107 inhibition. In addition, we identified prostate apoptosis response-4 (Par4) as a direct target of miR-107 with a potential binding site on the 3'-UTR of mRNA, as evaluated by bioinformatics prediction and luciferase reporter assay. Par4 expression levels were significantly inhibited by the miR-107 mimic but upregulated by the miR-107 inhibitor in both SW480 and LoVo cells. Compared to the control, the increase in Par4 expression significantly inhibited the induction role of miR-107 in the proliferation of SW480 and LoVo cells, and the apoptotic rate of cells repressed by the miR-107 mimic was also reversed by Par4 overexpression. In summary, our results demonstrated that miR-107 exerts a positive role in the survival of CRC cells by directly targeting Par4. This might reveal a novel understanding about human CRC pathogenesis.

TRIM21 is a novel regulator of Par-4 in colon and pancreatic cancer cells

The prostate apoptosis response protein 4 (Par-4) is a tumor-suppressor that has been shown to induce cancer-cell selective apoptosis in a variety of cancers. The regulation of Par-4 expression and activity is a relatively understudied area, and identifying novel regulators of Par-4 may serve as novel therapeutic targets. To identify novel regulators of Par-4, a co-immunoprecipitation was performed in colon cancer cells, and co-precipitated proteins were identified by mass-spectometry. TRIM21 was identified as a novel interacting partner of Par-4, and further shown to interact with Par-4 endogenously and through its PRY-SPRY domain. Additional studies show that TRIM21 downregulates Par-4 levels in response to cisplatin, and that TRIM21 can increase the resistance of colon cancer cells to cisplatin. Furthermore, forced Par-4 expression can sensitize pancreatic cancer cells to cisplatin. Finally, we demonstrate that TRIM21 expression predicts survival in pancreatic cancer patients. Our work highlights a novel mechanism of Par-4 regulation, and identifies a novel prognostic marker and potential therapeutic target for pancreatic cancer.

A journey beyond apoptosis: new enigma of controlling metastasis by pro-apoptotic Par-4

Prostate apoptotic response 4 (Par-4) is coined as a therapeutic protein since owing to its diverse physiologically relevant properties, especially in the cancer perspective. Albeit, Par-4 expression is not restricted to any specific tissue/organ, apart from cell death promotion (due to challenging threats), the other biological role of Par-4 is convincingly emerging. In the recent years, several laboratories have intended to dissect the signaling or mechanisms involved in Par-4 activation to augment apoptosis cascades but new developments in Par-4 research have widened its therapeutic potential. One of these important avenues is the prevention of metastasis by pro-apoptotic Par-4. In this review, we will focus on the therapeutic perspective of Par-4 with a special reference to its (Par-4) virgin prospect of devastating metastasis control.

Post-translational regulation of the cleaved fragment of Par-4 in ovarian and endometrial cancer cells

We recently reported the caspase3-dependent cleavage of Par-4 resulting in the accumulation of a 25kDa cleaved-Par-4 (cl-Par-4) fragment and we investigated in the present study the mechanisms regulating this fragment using cl-Par-4-expressing stable clones derived from ovarian and endometrial cancer cell lines.Cl-Par-4 protein was weakly express in all stable clones despite constitutive expression. However, upon cisplatin treatment, cl-Par-4 levels increased up to 50-fold relative to baseline conditions. Treatment of stable clones with proteasome and translation inhibitors revealed that cisplatin exposure might in fact protect cl-Par-4 from proteasome-dependent degradation. PI3K and MAPK pathways were also implicated as evidenced by an increase of cl-Par-4 in the presence of PI3K inhibitors and a decrease using MAPK inhibitors. Finally using bioinformatics resources, we found diverse datasets showing similar results to those we observed with the proteasome and cl-Par-4 further supporting our data.These new findings add to the complex mechanisms regulating Par-4 expression and activity, and justify further studies addressing the biological significance of this phenomenon in gynaecological cancer cells.

Deregulation of F-box proteins and its consequence on cancer development, progression and metastasis

F-box proteins are substrate receptors of the SCF (SKP1-Cullin 1-F-box protein) E3 ubiquitin ligase that play important roles in a number of physiological processes and activities. Through their ability to assemble distinct E3 ubiquitin ligases and target key regulators of cellular activities for ubiquitylation and degradation, this versatile group of proteins is able to regulate the abundance of cellular proteins whose deregulated expression or activity contributes to disease. In this review, we describe the important roles of select F-box proteins in regulating cellular activities, the perturbation of which contributes to the initiation and progression of a number of human malignancies.

Hey bHLH Proteins Interact with a FBXO45 Containing SCF Ubiquitin Ligase Complex and Induce Its Translocation into the Nucleus

The Hey protein family, comprising Hey1, Hey2 and HeyL in mammals, conveys Notch signals in many cell types. The helix-loop-helix (HLH) domain as well as the Orange domain, mediate homo- and heterodimerization of these transcription factors. Although distinct interaction partners have been identified so far, their physiological relevance for Hey functions is still largely unclear. Using a tandem affinity purification approach and mass spectrometry analysis we identified members of an ubiquitin E3-ligase complex consisting of FBXO45, PAM and SKP1 as novel Hey1 associated proteins. There is a direct interaction between Hey1 and FBXO45, whereas FBXO45 is needed to mediate indirect Hey1 binding to SKP1. Expression of Hey1 induces translocation of FBXO45 and PAM into the nucleus. Hey1 is a short-lived protein that is degraded by the proteasome, but there is no evidence for FBXO45-dependent ubiquitination of Hey1. On the contrary, Hey1 mediated nuclear translocation of FBXO45 and its associated ubiquitin ligase complex may extend its spectrum to additional nuclear targets triggering their ubiquitination. This suggests a novel mechanism of action for Hey bHLH factors.