Role of SUMO activating enzyme in cancer stem cell maintenance and self-renewal

CD34+KLF4+ Stromal Stem Cells Contribute to Endometrial Regeneration and Repair

The regenerative capacity of the human endometrium requires a population of local stem cells. However, the phenotypes, locations, and origin of these cells are still unknown. In a mouse menstruation model, uterine stromal SM22α⁺-derived CD34⁺KLF4⁺ stem cells are activated and integrate into the regeneration area, where they differentiate and incorporate into the endometrial epithelium; this process is correlated with enhanced protein SUMOylation in CD34⁺KLF4⁺ cells. Mice with a stromal SM22α-specific SENP1 deletion (SENP1smKO) exhibit accelerated endometrial repair in the regeneration model and develop spontaneous uterine hyperplasia. Mechanistic studies suggest that SENP1 deletion induces SUMOylation of ERα, which augments ERα transcriptional activity and proliferative signaling in SM22α⁺CD34⁺KLF4⁺ cells. These cells then transdifferentiate to the endometrial epithelium. Our study reveals that CD34⁺KLF4⁺ stromal-resident stem cells directly contribute to endometrial regeneration, which is regulated through SENP1-mediated ERα suppression.

The regenerative capacity of the human endometrium requires a population of local stem cells. Here, Yin et al. show that uterine stromal SM22α⁺CD34⁺KLF4⁺ stem cells are activated by ERα SUMOylation and integrate into the regeneration area, where they differentiate and incorporate into the endometrial epithelium.

CSN6-TRIM21 axis instigates cancer stemness during tumorigenesis

Background

Cancer stem cells (CSCs) are responsible for tumour initiation, metastasis and recurrence. However, the mechanism of CSC formation, maintenance and expansion in colorectal cancer (CRC) remains poorly characterised.

Methods

The role of COP9 signalosome subunit 6 (CSN6) in regulating cancer stemness was evaluated by organoid formation and limited dilution analysis. The role of CSN6–TRIM21–OCT1–ALDH1A1 axis in CSC formation was evaluated in vitro and in vivo. The association of CSN6, TRIM21 and ALDH1A1 expression was validated by a tissue microarray with 267 CRC patients.

Results

The results showed that CSN6 is critical for sphere formation and maintaining the growth of patient-derived organoids (PDOs). We characterised the role of CSN6 in regulating cancer stemness, which involves the TRIM21 E3 ubiquitin ligase, transcription factor POU class 2 homeobox 1 (OCT1) and cancer stem cell marker aldehyde dehydrogenase 1 A1 (ALDH1A1). Our data showed that CSN6 facilitates ubiquitin-mediated degradation of TRIM21, which in turn decreases TRIM21-mediated OCT1 ubiquitination and subsequently stabilises OCT1. Consequently, OCT1 stabilisation leads to ALDH1A1expression and promotes cancer stemness. We further showed that the protein expression levels of CSN6, TRIM21 and ALDH1A1 can serve as prognostic markers for human CRC.

Conclusions

In conclusion, we validate a pathway for cancer stemness regulation involving ALDH1A1 levels through the CSN6–TRIM21 axis, which may be utilised as CRC molecular markers and be targeted for therapeutic intervention in cancers.

Patient-derived scaffolds uncover breast cancer promoting properties of the microenvironment

Tumor cells interact with the microenvironment that specifically supports and promotes tumor development. Key components in the tumor environment have been linked to various aggressive cancer features and can further influence the presence of subpopulations of cancer cells with specific functions, including cancer stem cells and migratory cells. To model and further understand the influence of specific microenvironments we have developed an experimental platform using cell-free patient-derived scaffolds (PDSs) from primary breast cancers infiltrated with standardized breast cancer cell lines. This PDS culture system induced a series of orchestrated changes in differentiation, epithelial-mesenchymal transition, stemness and proliferation of the cancer cell population, where an increased cancer stem cell pool was confirmed using functional assays. Furthermore, global gene expression profiling showed that PDS cultures were similar to xenograft cultures. Mass spectrometry analyses of cell-free PDSs identified subgroups based on their protein composition that were linked to clinical properties, including tumor grade. Finally, we observed that an induction of epithelial-mesenchymal transition-related genes in cancer cells growing on the PDSs were significantly associated with clinical disease recurrences in breast cancer patients. Patient-derived scaffolds thus mimics in vivo-like growth conditions and uncovers unique information about the malignancy-inducing properties of tumor microenvironment.

m6A modification-mediated CBX8 induction regulates stemness and chemosensitivity of colon cancer via upregulation of LGR5

BACKGROUND

Colon cancer (CC) cells can exhibit stemness and expansion capabilities, which contribute to resistance to conventional chemotherapies. Aberrant expression of CBX8 has been identified in many types of cancer, but the cause of this aberrant CBX8 expression and whether CBX8 is associated with stemness properties in CC remain unknown.

METHODS

qRT-PCR and IHC were applied to examine CBX8 levels in normal and chemoresistant CC tissues. Cancer cell stemness and chemosensitivity were evaluated by spheroid formation, colony formation, Western blot and flow cytometry assays. RNA-seq combined with ChIP-seq was used to identify target genes, and ChIP, IP and dual luciferase reporter assays were applied to explore the underlying mechanisms.

RESULTS

CBX8 was significantly overexpressed in chemoresistant CC tissues. In addition, CBX8 could promote stemness and suppress chemosensitivity through LGR5. Mechanistic studies revealed that CBX8 activate the transcription of LGR5 in a noncanonical manner with assistance of Pol II. CBX8 recruited KMT2b to the LGR5 promoter, which maintained H3K4me3 status to promote LGR5 expression. Moreover, m6A methylation participated in the upregulation of CBX8 by maintaining CBX8 mRNA stability.

CONCLUSIONS

Upon m6A methylation-induced upregulation, CBX8 interacts with KMT2b and Pol II to promote LGR5 expression in a noncanonical manner, which contributes to increased cancer stemness and decreased chemosensitivity in CC. This study provides potential new therapeutic targets and valuable prognostic markers for CC.

The role of TRIM family proteins in the regulation of cancer stem cell self-renewal

The tripartite-motif (TRIM) family of proteins represents one of the largest classes of putative single protein RING-finger E3 ubiquitin ligases. The members of this family are characterized by an N-terminal TRIM motif containing one RING-finger domain, one or two zinc-finger domains called B boxes (B1 box and B2 box), and a coiled-coil region. The TRIM motif can be found in isolation or in combination with a variety of C-terminal domains, and based on C-terminus, TRIM proteins are classified into 11 distinct groups. Because of the complex nature of TRIM proteins, they are implicated in a variety of cellular functions and biological processes, including regulation of cell proliferation, cell division and developmental processes, cancer transformation, regulation of cell metabolism, autophagocytosis, modification of chromatin status, regulation of gene transcription, post-translational modifications, and interactions with pathogens. Here, we demonstrate the specific activities of TRIM family proteins that contribute to the cancer stem cell phenotype. A growing body of evidence demonstrates that several TRIM members guarantee the acquisition of stem cell properties and the ability to sustain stem-like phenotype by cancer cells using distinct mechanisms. For other members, further work is needed to understand their full contribution to stem cell self-renewal. Identification of TRIM proteins that possess the potential to serve as therapeutic targets may result in the development of new therapeutic strategies. Finally, these strategies may result in the disruption of the machinery of stemness acquisition, which may prevent tumor growth, progression, and overcome the resistance to anticancer therapies.

The JAK2/STAT3/CCND2 Axis promotes colorectal Cancer stem cell persistence and radioresistance

Background

Radiotherapy (RT) is a highly effective multimodal nonsurgical treatment that is essential for patients with advanced colorectal cancer (CRC). Nevertheless, cell subpopulations displaying intrinsic radioresistance survive after RT. The reactivation of their proliferation and successful colonization at local or distant sites may increase the risk of poor clinical outcomes. Recently, radioresistant cancer cells surviving RT were reported to exhibit a more aggressive phenotype than parental cells, although the underlying mechanisms remain unclear.

Methods

By investigating public databases containing CRC patient data, we explored potential radioresistance-associated signaling pathways. Then, their mechanistic roles in radioresistance were investigated through multiple validation steps using patient-derived primary CRC cells, human CRC cell lines, and CRC xenografts.

Results

Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling was activated in radioresistant CRC tissues in correlation with local and distant metastases. JAK2 was preferentially overexpressed in the CRC stem cell subpopulation, which was accompanied by the phosphorylation of STAT proteins, especially STAT3. JAK2/STAT3 signaling played an essential role in promoting tumor initiation and radioresistance by limiting apoptosis and enhancing clonogenic potential. Mechanistically, the direct binding of STAT3 to the cyclin D2 (CCND2) promoter increased CCND2 transcription. CCND2 expression was required for persistent cancer stem cell (CSC) growth via the maintenance of an intact cell cycle and proliferation with low levels of DNA damage accumulation.

Conclusion

Herein, we first identified JAK2/STAT3/CCND2 signaling as a resistance mechanism for the persistent growth of CSCs after RT, suggesting potential biomarkers and regimens for improving outcomes among CRC patients.

Current and Future Horizons of Patient-Derived Xenograft Models in Colorectal Cancer Translational Research

Our poor understanding of the intricate biology of cancer and the limited availability of preclinical models that faithfully recapitulate the complexity of tumors are primary contributors to the high failure rate of novel therapeutics in oncology clinical studies. To address this need, patient-derived xenograft (PDX) platforms have been widely deployed and have reached a point of development where we can critically review their utility to model and interrogate relevant clinical scenarios, including tumor heterogeneity and clonal evolution, contributions of the tumor microenvironment, identification of novel drugs and biomarkers, and mechanisms of drug resistance. Colorectal cancer (CRC) constitutes a unique case to illustrate clinical perspectives revealed by PDX studies, as they overcome limitations intrinsic to conventional ex vivo models. Furthermore, the success of molecularly annotated "Avatar" models for co-clinical trials in other diseases suggests that this approach may provide an additional opportunity to improve clinical decisions, including opportunities for precision targeted therapeutics, for patients with CRC in real time. Although critical weaknesses have been identified with regard to the ability of PDX models to predict clinical outcomes, for now, they are certainly the model of choice for preclinical studies in CRC. Ongoing multi-institutional efforts to develop and share large-scale, well-annotated PDX resources aim to maximize their translational potential. This review comprehensively surveys the current status of PDX models in translational CRC research and discusses the opportunities and considerations for future PDX development.

Regulation of miR-34b/c-targeted gene expression program by SUMOylation

The miR-34 family of microRNAs suppresses the expression of proteins involved in pluripotency and oncogenesis. miR-34 expression is frequently reduced in cancers; however, the regulation of their expression is not well understood. We used genome-wide miRNA profiling and mechanistic analysis to show that SUMOylation regulates miR-34b/c expression, which impacts the expression of c-Myc and other tested miR-34 targets. We used site-directed mutagenesis and other methods to show that protein kinase B (also known as Akt) phosphorylation of FOXO3a plays an important role in SUMOylation-dependent expression of miR-34b/c. This study reveals how the miR-34-targeted gene expression program is regulated by SUMOylation and shows that SUMOylation need not regulate target proteins through direct modification, but instead can act through the expression of their targeting miRNAs.

TSPAN8 promotes cancer cell stemness via activation of sonic Hedgehog signaling

Cancer stem cells (CSCs) represent a major source of treatment resistance and tumor progression. However, regulation of CSCs stemness is not entirely understood. Here, we report that TSPAN8 expression is upregulated in breast CSCs, promotes the expression of the stemness gene NANOG, OCT4, and ALDHA1, and correlates with therapeutic resistance. Mechanistically, TSPAN8 interacts with PTCH1 and inhibits the degradation of the SHH/PTCH1 complex through recruitment of deubiquitinating enzyme ATXN3. This results in the translocation of SMO to cilia, downstream gene expression, resistance of CSCs to chemotherapeutic agents, and enhances tumor formation in mice. Accordingly, expression levels of TSPAN8, PTCH1, SHH, and ATXN3 are positively correlated in human breast cancer specimens, and high TSPAN8 and ATXN3 expression levels correlate with poor prognosis. These findings reveal a molecular basis of TSPAN8-enhanced Sonic Hedgehog signaling and highlight a role for TSPAN8 in promoting cancer stemness.

Tetraspanin 8 (TSPAN8) has been implicated in a number of different tumours, but the underlying mechanisms remain unclear. Here, in breast cancer the authors highlight a role for TSPAN8 in promoting tumorigenesis through the activation of Hedgehog signalling.

The Expression of Yes-Associated Protein (YAP) Maintains Putative Cancer Stemness and Is Associated with Poor Prognosis in Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is resistant to most chemotherapeutic agents. Yes-associated protein (YAP) is related to tumor progression; however, its role in ICC remains unknown. We investigated the mechanism underlying YAP-mediated cancer progression by focusing on the property of cancer stem cells (CSCs) in ICC. Immunohistochemistry results revealed the positive YAP expression in 37 of 52 resected ICC cases. Those with positive YAP expression showed poor prognosis in Kaplan-Meier analysis (P = 0.023). YAP expression was associated with vimentin and the putative CSC marker, hepatic oval cell marker 6 (OV-6). The knockdown of YAP expression using specific siRNAs in ICC cells decreased octamer-binding transcription factor 4 (OCT4) expression in Western blot analyses and OV-6 and CD133 expression in flow cytometry analysis. Verteporfin, a YAP inhibitor, decreased N-cadherin and OCT4 expression in Western blot analyses. In vitro sphere formation and anoikis resistance assays revealed the impairment in CSC property and anoikis resistance in response to the decrease in YAP expression. Verteporfin treatment activated the protein kinase B/mechanistic target of rapamycin signaling pathway and dramatically impaired IL-6-stimulated STAT3 phosphorylation in ICC cells. The combination of verteporfin and rapamycin, an inhibitor of mechanistic target of rapamycin phosphorylation, inhibited cell proliferation and tumor growth. In conclusion, verteporfin regulates multiple signaling pathways and, in combination with rapamycin, might be a promising therapeutic strategy for ICC treatment.

Oct1/Pou2f1 is selectively required for colon regeneration and regulates colon malignancy

The transcription factor Oct1/Pou2f1 promotes poised gene expression states, mitotic stability, glycolytic metabolism and other characteristics of stem cell potency. To determine the effect of Oct1 loss on stem cell maintenance and malignancy, we deleted Oct1 in two different mouse gut stem cell compartments. Oct1 deletion preserved homeostasis in vivo and the ability to establish organoids in vitro, but blocked the ability to recover from treatment with dextran sodium sulfate, and the ability to maintain organoids after passage. In a chemical model of colon cancer, loss of Oct1 in the colon severely restricted tumorigenicity. In contrast, loss of one or both Oct1 alleles progressively increased tumor burden in a colon cancer model driven by loss-of-heterozygosity of the tumor suppressor gene Apc. The different outcomes are consistent with prior findings that Oct1 promotes mitotic stability, and consistent with differentially expressed genes between the two models. Oct1 ChIPseq using HCT116 colon carcinoma cells identifies target genes associated with mitotic stability, metabolism, stress response and malignancy. This set of gene targets overlaps significantly with genes differentially expressed in the two tumor models. These results reveal that Oct1 is selectively required for recovery after colon damage, and that Oct1 has potent effects in colon malignancy, with outcome (pro-oncogenic or tumor suppressive) dictated by tumor etiology.

Colorectal cancer is the second leading cause of cancer death in the United States. Approximately 35% of diagnosed patients eventually succumb to disease. The high incidence and mortality due to colon cancer demand a better understanding of factors controlling the physiology and pathophysiology of the gastrointestinal tract. Previously, we and others showed that the widely expressed transcription factor Oct1 is expressed at higher protein levels in stem cells, including intestinal stem cells. Here we use deletion of a conditional mouse Oct1 (Pou2f1) allele in two different intestinal stem cell compartments to study gut homeostasis. We then proceed to investigate the effect of Oct1 loss in colon regeneration and malignancy. The results indicate that Oct1 loss is dispensable for maintenance of the mouse gut, but required for recovery after damage to the colon epithelium. We also find that Oct1 loss has opposing effects in two different mouse colon cancer models, and further that the two models are associated with different gene expression signatures. The differentially expressed genes are enriched for Oct1 targets, suggesting that differential gene control by Oct1 is one mechanism underlying the different outcomes.

Allosteric Inhibition of Ubiquitin-like Modifications by a Class of Inhibitor of SUMO-Activating Enzyme

Ubiquitin-like (Ubl) post-translational modifications are potential targets for therapeutics. However, the only known mechanism for inhibiting a Ubl-activating enzyme is through targeting its ATP-binding site. Here we identify an allosteric inhibitory site in the small ubiquitin-like modifier (SUMO)-activating enzyme (E1). This site was unexpected because both it and analogous sites are deeply buried in all previously solved structures of E1s of ubiquitin-like modifiers (Ubl). The inhibitor not only suppresses SUMO E1 activity, but also enhances its degradation in vivo, presumably due to a conformational change induced by the compound. In addition, the lead compound increased the expression of miR-34b and reduced c-Myc levels in lymphoma and colorectal cancer cell lines and a colorectal cancer xenograft mouse model. Identification of this first-in-class inhibitor of SUMO E1 is a major advance in modulating Ubl modifications for therapeutic aims.

CKIP-1 limits foam cell formation and inhibits atherosclerosis by promoting degradation of Oct-1 by REGγ

Atherosclerosis-related cardiovascular diseases are the leading cause of mortality worldwide. Macrophages uptake modified lipoproteins and transform into foam cells, triggering an inflammatory response and thereby promoting plaque formation. Here we show that casein kinase 2-interacting protein-1 (CKIP-1) is a suppressor of foam cell formation and atherosclerosis. Ckip-1 deficiency in mice leads to increased lipoprotein uptake and foam cell formation, indicating a protective role of CKIP-1 in this process. Ablation of Ckip-1 specifically upregulates the transcription of scavenger receptor LOX-1, but not that of CD36 and SR-A. Mechanistically, CKIP-1 interacts with the proteasome activator REGγ and targets the transcriptional factor Oct-1 for degradation, thereby suppressing the transcription of LOX-1 by Oct-1. Moreover, Ckip-1-deficient mice undergo accelerated atherosclerosis, and bone marrow transplantation reveals that Ckip-1 deficiency in hematopoietic cells is sufficient to increase atherosclerotic plaque formation. Therefore, CKIP-1 plays an essential anti-atherosclerotic role through regulation of foam cell formation and cholesterol metabolism.

In atherosclerotic plaques, transformation of macrophages into foam cells is a key step in initiating the inflammatory response. Here Fan et al. show that casein kinase 2-interacting protein-1 (CKIP-1) limits foam cell formation and atherosclerosis by preventing expression of the scavenger receptor LOX-1 through REGγ-mediated degradation of Oct-1.

BPTF promotes hepatocellular carcinoma growth by modulating hTERT signaling and cancer stem cell traits

Bromodomain PHD finger transcription factor (BPTF), a core subunit of nucleosome-remodeling factor (NURF) complex, plays an important role in chromatin remodeling. However, its precise function and molecular mechanism involved in hepatocellular carcinoma (HCC) growth are still poorly defined. Here, we demonstrated the tumor-promoting role of BPTF in HCC progression. BPTF was highly expressed in HCC cells and tumor tissues of HCC patients compared with normal liver cells and tissues. Knockdown of BPTF inhibited cell proliferation, colony formation and stem cell-like traits in HCC cells. In addition, BPTF knockdown effectively sensitized the anti-tumor effect of chemotherapeutic drugs and induced more apoptosis in HCC cells. Consistently, knockdown of BPTF in a xenograft mouse model also suppressed tumor growth and metastasis accompanied by the suppression of cancer stem cells (CSC)-related protein markers. Moreover, the mechanism study showed that the tumor-promoting role of BPTF in HCC was realized by transcriptionally regulating the expression of human telomerase reverse transcriptase (hTERT). Furthermore, we found that HCC patients with high BPTF expression displayed high hTERT expression, and high BPTF or hTERT expression level was positively correlated with advanced malignancy and poor prognosis in HCC patients. Collectively, our results demonstrate that BPTF promotes HCC growth by targeting hTERT and suggest that the BPTF-hTERT axis maybe a novel and potential therapeutic target in HCC.

MicroRNA-302a/d inhibits the self-renewal capability and cell cycle entry of liver cancer stem cells by targeting the E2F7/AKT axis

BACKGROUND

There is increasing evidence that liver cancer stem cells (LCSCs) contribute to hepatocellular carcinoma (HCC) initiation and progression. MicroRNA (miRNA) plays a significant functional role by directly regulating respective targets in LCSCs-triggered HCC, however, little is known about the function of the miRNA-302 family in LCSCs.

METHODS

MiRNAs microarray was used to detect the miRNAs involved in LCSCs maintenance and differentiation. Biological roles and the molecular mechanism of miRNA-302a/d and its target gene E2F7 were detected in HCC in vitro. The expression and correlation of miRNA-302a/d and E2F7 in HCC patients was evaluated by quantitative PCR and Kaplan-Meier survival analysis.

RESULTS

We found that the miRNA-302 family was downregulated during the spheroid formation of HCC cells and patients with lower miRNA-302a/d expression had shorter overall survival (OS) and progression-free survival (PFS). Moreover, E2F7 was confirmed to be directly targeted and inhibited by miRNA-302a/d. Furthermore, concomitant low expression of miRNA-302a/d and high expression of E2F7 correlated with a shorter median OS and PFS in HCC patients. Cellular functional analysis demonstrated that miRNA-302a/d negatively regulates self-renewal capability and cell cycle entry of liver cancer stem cells via suppression of its target gene E2F7 and its downstream AKT/β-catenin/CCND1 signaling pathway.

CONCLUSIONS

Our data provide the first evidence that E2F7 is a direct target of miRNA-302a/d and miRNA-302a/d inhibits the stemness of LCSCs and proliferation of HCC cells by targeting the E2F7/AKT/β-catenin/CCND1 signaling pathway.

Decreased expression of TRIM21 indicates unfavorable outcome and promotes cell growth in breast cancer

Background

Tripartite motif-containing protein 21 (TRIM21), an E3 ubiquitin ligase, has been implicated in autoimmune diseases. Dysregulation of TRIM21 contributes to the progression of human malignancies, but its role and clinical significance in breast cancer remain unclear.

Methods

The expression of TRIM21 was examined by quantitative real-time PCR, Western blot, and immunohistochemistry. The role of TRIM21 in the progression of breast cancer was determined using in vitro and in vivo models. The upstream regulation of TRIM21 was investigated by luciferase reporter assay.

Results

Here, we showed that TRIM21 expression in breast cancer tissues was decreased at both the mRNA and protein levels in comparison to that in nontumorous tissues. TRIM21 expression was closely associated with tumor size, estrogen receptor, human epidermal growth factor receptor 2, and clinical stage. Low TRIM21 expression was correlated with poor overall and disease-free survival in two independent cohorts containing 1,219 patients with breast cancer. A multivariate Cox regression model suggested TRIM21 as an independent factor for overall survival. In vitro data revealed that TRIM21 expression was suppressed by miR-494-3p directly targeting the 3′ untranslated region of TRIM21. Overexpression of TRIM21 impeded cell proliferation and tumor growth in breast cancer, whereas TRIM21 depletion enhanced these capacities.

Conclusion

Collectively, our findings indicate that TRIM21 serves as a potential prognostic biomarker and functions as a tumor suppressor in breast cancer.

Protein SUMOylation modification and its associations with disease

SUMOylation, as a post-translational modification, plays essential roles in various biological functions including cell growth, migration, cellular responses to stress and tumorigenesis. The imbalance of SUMOylation and deSUMOylation has been associated with the occurrence and progression of various diseases. Herein, we summarize and discuss the signal crosstalk between SUMOylation and ubiquitination of proteins, protein SUMOylation relations with several diseases, and the identification approaches for SUMOylation site. With the continuous development of bioinformatics and mass spectrometry, several accurate and high-throughput methods have been implemented to explore small ubiquitin-like modifier-modified substrates and sites, which is helpful for deciphering protein SUMOylation-mediated molecular mechanisms of disease.

The role of HGF-MET pathway and CCDC66 cirRNA expression in EGFR resistance and epithelial-to-mesenchymal transition of lung adenocarcinoma cells

Background

Epithelial-to-mesenchymal transition (EMT) has, in recent years, emerged as an important tumor cell behavior associated with high metastatic potential and drug resistance. Interestingly, protein SUMOylation and hepatocyte growth factor could respectively reduce the effect of small molecule inhibitors on tyrosine kinase activity of mutated epidermal growth factor receptor of lung adenocarcinomas (LADC). The actual mechanism is yet to be resolved.

Methods

Immunohistochemistry was used to stain proteins in LADC specimens. Protein expression was confirmed by Western blotting. In vitro, expression of proteins was determined by Western blotting and immunocytochemistry. Levels of circular RNA were determined by reverse transcription-polymerase chain reaction.

Results

SAE2 and cirRNA CCDC66 were highly expressed in LADC. Expression of SAE2 was mainly regulated by EGFR; however, expression of cirRNA CCDC66 was positively regulated by FAK and c-Met but negatively modulated by nAchR7α. EGFR-resistant H1975 also highly expressed cirRNA CCDC66. Immediate response of hypoxia increased phosphorylated c-Met, SAE2, and epithelial-to-mesenchymal transition. Either activation of FAK or silencing of nAchR7α increased cirRNA CCDC66.

Conclusions

HGF/c-Met regulates expression of SAE2 and cirRNA CCDC66 to increase EMT and drug resistance of LADC cells. Multimodality drugs concurrently aiming at these targets would probably provide more benefits for cancer patients.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0557-9) contains supplementary material, which is available to authorized users.

Streptonigrin Inhibits SENP1 and Reduces the Protein Level of Hypoxia-Inducible Factor 1α (HIF1α) in Cells

Streptonigrin (CAS no. 3930-19-6) is a natural product shown to have antitumor activities in clinical trials conducted in the 1960s-1970s. However, its use in clinical studies eventually faded, and the molecular mechanisms of streptonigrin antitumor effects remain poorly defined. Despite its lack of current clinical use, efforts on its total synthesis have continued. Here, we show that streptonigrin binds and inhibits the SUMO-specific protease SENP1. NMR studies identified that streptonigrin binds to SENP1 on the surface where SUMO binds and disrupts SENP1-SUMO1 interaction. Site-directed mutations in combination with NMR chemical shift perturbation suggest key roles of aromatic π stacking interactions in binding streptonigrin. Treatment of cells with streptonigrin resulted in increased global SUMOylation levels and reduced level of hypoxia inducible factor alpha (HIF1α). These findings inform both the design of SENP1 targeting strategy and the modification of streptonigrin to improve its efficacy for possible future clinical use.

XIAP Limits Autophagic Degradation of Sox2 and Is A Therapeutic Target in Nasopharyngeal Carcinoma Stem Cells

Rationale: Nasopharyngeal carcinoma (NPC) is the most frequent head and neck tumor in South China. The presence of cancer stem cells (CSCs) in NPC contributes to tumor maintenance and therapeutic resistance, while the ability of CSCs to escape from the apoptosis pathway may render them the resistant property to the therapies. Inhibitor of apoptosis proteins family proteins (IAPs), which are overexpressed in nasopharyngeal carcinoma stem cells, may play an important role in maintaining nasopharyngeal cancer stem cell properties. Here, we develop a novel CSC-targeting strategy to treat NPC through inhibiting IAPs.

Methods: Human NPC S-18 and S-26 cell lines were used as the model system in vitro and in vivo. Fluorescence activated cell sorting (FACS) assay was used to detect nasopharyngeal SP cells and CD44+ cells. The characteristics of CSCs were defined by sphere suspension culture, colony formation assay and cell migration. The role of XIAP on the regulation of Sox2 protein stability and ERK1-mediated phosphorylation of Sox2 signaling pathway were analyzed using immunoblotting, immunoprecipitation, immunofluorescence, phosphorylation mass spectrometry, siRNA silencing and plasmid overexpression. The correlation between XIAP and Sox2 in NPC biopsies and their role in prognosis was performed by immunohistochemistry. APG-1387 or chemotherapies-induced cell death and apoptosis in S-18 and S-26 were determined by WST, immunoblotting and flow cytometry assay.

Results: IAPs, especially X chromosome-linked IAP (XIAP), were elevated in CSCs of NPC, and these proteins were critically involved in the maintenance of CSCs properties by enhancing the stability of Sox2. Mechanistically, ERK1 kinase promoted autophagic degradation of Sox2 via phosphorylation of Sox2 at Ser251 and further SUMOylation of Sox2 at Lys245 in non-CSCs. However, XIAP blocked autophagic degradation of Sox2 by inhibiting ERK1 activation in CSCs. Additionally, XIAP was positively correlated with Sox2 expression in NPC tissues, which were associated with NPC progression. Finally, we discovered that a novel antagonist of IAPs, APG-1387, exerted antitumor effect on CSCs. Also, the combination of APG-1387 with CDDP /5-FU has a synergistic effect on NPC.

Conclusion: Our study highlights the importance of IAPs in the maintenance of CSCs in NPC. Thus, XIAP is a promising therapeutic target in CSCs and suggests that NPC patients may benefit from a combination treatment of APG-1387 with conventional chemotherapy.

BRCA1 through Its E3 Ligase Activity Regulates the Transcription Factor Oct1 and Carbohydrate Metabolism

The tumor suppressor BRCA1 regulates the DNA damage response (DDR) and other processes that remain incompletely defined. Among these, BRCA1 heterodimerizes with BARD1 to ubiquitylate targets via its N-terminal E3 ligase activity. Here, it is demonstrated that BRCA1 promotes oxidative metabolism by degrading Oct1 (POU2F1), a transcription factor with proglycolytic and tumorigenic effects. BRCA1 E3 ubiquitin ligase mutation skews cells toward a glycolytic metabolic profile while elevating Oct1 protein. CRISPR-mediated Oct1 deletion reverts the glycolytic phenotype. RNA sequencing (RNAseq) confirms deregulation of metabolic genes downstream of Oct1. BRCA1 mediates Oct1 ubiquitylation and degradation, and mutation of two ubiquitylated Oct1 lysines insulates the protein against BRCA1-mediated destabilization. Oct1 deletion in MCF-7 breast cancer cells does not perturb growth in standard culture, but inhibits growth in soft agar and xenograft assays. In primary breast cancer clinical specimens, Oct1 protein levels correlate positively with tumor aggressiveness and inversely with BRCA1. These results identify BRCA1 as an Oct1 ubiquitin ligase that catalyzes Oct1 degradation to promote oxidative metabolism and restrict tumorigenicity. Mol Cancer Res; 16(3); 439-52. ©2018 AACR.

SUMOylation in brain ischemia: Patterns, targets, and translational implications

Post-translational protein modification by small ubiquitin-like modifier (SUMO) regulates a myriad of homeostatic and stress responses. The SUMOylation pathway has been extensively studied in brain ischemia. Convincing evidence is now at hand to support the notion that a major increase in levels of SUMOylated proteins is capable of inducing tolerance to ischemic stress. Therefore, the SUMOylation pathway has emerged as a promising therapeutic target for neuroprotection in the face of brain ischemia. Despite this, it is prudent to acknowledge that there are many key questions still to be addressed in brain ischemia related to SUMOylation. Accordingly, herein, we provide a critical review of literature within the field to summarize current knowledge and in so doing highlight pertinent translational implications of the SUMOylation pathway in brain ischemia.

Bridging the divide: preclinical research discrepancies between triple-negative breast cancer cell lines and patient tumors

Triple-negative breast cancer (TNBC) is the most refractory subtype of breast cancer and disproportionately accounts for the majority of breast cancer related deaths. Effective treatment of this disease remains an unmet medical need. Over the past several decades, TNBC cell lines have been used as the foundation for drug development and disease modeling. However, ever-mounting research demonstrates striking differences between cell lines and clinical TNBC tumors, disconnecting bench research and actual clinical responses. In this review, we discuss the limitations of cell lines and the importance of using patients' tumors for translational research, and highlight the usage of patient-derived xenograft (PDXs) models that have emerged as a clinically relevant platform for preclinical studies. PDX tumors possess tumor heterogeneity with similar cellular, molecular, genetic and epigenetic properties akin to those found within patients' tumors. Moreover, PDX and clinical tumors possess abnormal vasculature with higher blood vessel permeability, a feature that is not always demonstrated in in vivo cell line xenografts. Development of clinically relevant, novel drug-nanoparticles capable of accumulating in PDX tumors through the enhanced permeability and retention effect in tumor vasculature may lead to new and effective TNBC treatments.

SENP1 promotes hypoxia-induced cancer stemness by HIF-1α deSUMOylation and SENP1/HIF-1α positive feedback loop

OBJECTIVE

We investigated the effect and mechanism of hypoxic microenvironment and hypoxia-inducible factors (HIFs) on hepatocellular carcinoma (HCC) cancer stemness.

DESIGN

HCC cancer stemness was analysed by self-renewal ability, chemoresistance, expression of stemness-related genes and cancer stem cell (CSC) marker-positive cell population. Specific small ubiquitin-like modifier (SUMO) proteases 1 (SENP1) mRNA level was examined with quantitative PCR in human paired HCCs. Immunoprecipitation was used to examine the binding of proteins and chromatin immunoprecipitation assay to detect the binding of HIFs with hypoxia response element sequence. In vivo characterisation was performed in immunocompromised mice and stem cell frequency was analysed.

RESULTS

We showed that hypoxia enhanced the stemness of HCC cells and hepatocarcinogenesis through enhancing HIF-1α deSUMOylation by SENP1 and increasing stabilisation and transcriptional activity of HIF-1α. Furthermore, we demonstrated that SENP1 is a direct target of HIF-1/2α and a previously unrecognised positive feedback loop exists between SENP1 and HIF-1α.

CONCLUSIONS

Taken together, our findings suggest the significance of this positive feedback loop between HIF-1α and SENP1 in contributing to the increased cancer stemness in HCC and hepatocarcinogenesis under hypoxia. Drugs that specifically target SENP1 may offer a potential novel therapeutic approach for HCC.

Cancer Stem Cell Hypothesis for Therapeutic Innovation in Clinical Oncology? Taking the Root Out, Not Chopping the Leaf

Clinical oncology is in need of therapeutic innovation. New hypotheses and concepts for translation of basic research to novel diagnostics and therapeutics are called for. In this context, the cancer stem cell (CSC) hypothesis rests on the premise that tumors comprise tumor cells and a subset of tumor-initiating cells, CSCs, in a quiescent state characterized by slow cell cycling and expression of specific stem cell surface markers with the capability to maintain a tumor in vivo. The CSCs have unlimited self-renewal abilities and propagate tumors through division into asymmetric daughter cells. This differentiation is induced by both genetic and environmental factors. Another characteristic of CSCs is their therapeutic resistance, which is due to their quiescent state and slow dividing. Notably, the CSC phenotype differs greatly between patients and different cancer types. The CSCs may differ genetically and phenotypically and may include primary CSCs and metastatic stem cells circulating within the blood system. Targeting CSCs will require the knowledge of distinct stem cells within the tumor. CSCs can differentiate into nontumorigenic cells and this has been touted as the source of heterogeneity observed in many solid tumors. The latter cannot be fully explained by epigenetic regulation or by the clonal evolution theory. This heterogeneity markedly influences how tumors respond to therapy and prognosis. The present expert review offers an analysis and synthesis of the latest research and concepts on CSCs, with a view to truly disruptive innovation for future diagnostics and therapeutics in clinical oncology.

SUMO conjugation - a mechanistic view

The regulation of protein fate by modification with the small ubiquitin-related modifier (SUMO) plays an essential and crucial role in most cellular pathways. Sumoylation is highly dynamic due to the opposing activities of SUMO conjugation and SUMO deconjugation. SUMO conjugation is performed by the hierarchical action of E1, E2 and E3 enzymes, while its deconjugation involves SUMO-specific proteases. In this review, we summarize and compare the mechanistic principles of how SUMO gets conjugated to its substrate. We focus on the interplay of the E1, E2 and E3 enzymes and discuss how specificity could be achieved given the limited number of conjugating enzymes and the thousands of substrates.