A SUMOylation-dependent HIF-1α/CLDN6 negative feedback mitigates hypoxia-induced breast cancer metastasis

CLDN6 inhibits breast cancer growth and metastasis through SREBP1-mediated RAS palmitoylation

BACKGROUND

Breast cancer (BC) ranks as the third most fatal malignant tumor worldwide, with a strong reliance on fatty acid metabolism. CLDN6, a candidate BC suppressor gene, was previously identified as a regulator of fatty acid biosynthesis; however, the underlying mechanism remains elusive. In this research, we aim to clarify the specific mechanism through which CLDN6 modulates fatty acid anabolism and its impact on BC growth and metastasis.

METHODS

Cell function assays, tumor xenograft mouse models, and lung metastasis mouse models were conducted to evaluate BC growth and metastasis. Human palmitic acid assay, triglyceride assay, Nile red staining, and oil red O staining were employed to investigate fatty acid anabolism. Reverse transcription polymerase chain reaction (RT-PCR), western blot, immunohistochemistry (IHC) assay, nuclear fractionation, immunofluorescence (IF), immunoprecipitation and acyl-biotin exchange (IP-ABE), chromatin immunoprecipitation (ChIP), dual luciferase reporter assay, and co-immunoprecipitation (Co-IP) were applied to elucidate the underlying molecular mechanism. Moreover, tissue microarrays of BC were analyzed to explore the clinical implications.

RESULTS

We identified that CLDN6 inhibited BC growth and metastasis by impeding RAS palmitoylation both in vitro and in vivo. We proposed a unique theory suggesting that CLDN6 suppressed RAS palmitoylation through SREBP1-modulated de novo palmitic acid synthesis. Mechanistically, CLDN6 interacted with MAGI2 to prevent KLF5 from entering the nucleus, thereby restraining SREBF1 transcription. The downregulation of SREBP1 reduced de novo palmitic acid synthesis, hindering RAS palmitoylation and subsequent endosomal sorting complex required for transport (ESCRT)-mediated plasma membrane localization required for RAS oncogenic activation. Besides, targeting inhibition of RAS palmitoylation synergized with CLDN6 to repress BC progression.

CONCLUSIONS

Our findings provide compelling evidence that CLDN6 suppresses the palmitic acid-induced RAS palmitoylation through the MAGI2/KLF5/SREBP1 axis, thereby impeding BC malignant progression. These results propose a new insight that monitoring CLDN6 expression alongside targeting inhibition of palmitic acid-mediated palmitoylation could be a viable strategy for treating oncogenic RAS-driven BC.

SENP1 reduces oxidative stress and apoptosis in renal ischaemia-reperfusion injury by deSUMOylation of HIF-1α

Renal ischaemia-reperfusion injury (RIRI) is a primary cause of acute kidney damage, occurring frequently in situations like renal transplantation, yet the underlying mechanisms were not fully understood. Sentrin-specific protease 1 (SENP1) is an important member of the SENP family, which is widely involved in various diseases. However, the role of SENP1 in RIRI has been unclear. In our study, we discovered that SENP1 was involved in RIRI and reduced renal cell apoptosis and oxidative stress at elevated levels. Further mechanistic studies showed that hypoxia-inducible factor-1α (HIF-1α) was identified as a substrate of SENP1. Furthermore, SENP1 deSUMOylated HIF-1α, which reduced the degradation of HIF-1α, and exerted a renoprotective function. In addition, the protective function was lost after application of the HIF-1α specific inhibitor KC7F2. Briefly, our results fully demonstrated that SENP1 reduced the degradation of HIF-1α and attenuated oxidative stress and apoptosis in RIRI by regulating the deSUMOylation of HIF-1α, suggesting that SENP1 may serve as a potential therapeutic target for the treatment of RIRI.

Suppressing SENP1 inhibits esophageal squamous carcinoma cell growth via SIRT6 SUMOylation

PURPOSE

Esophageal squamous cell carcinoma (ESCC) is a prevalent tumor in the gastrointestinal tract, but our understanding of the molecular mechanisms underlying ESCC remains incomplete. Existing studies indicate that SUMO specific peptidase 1 (SENP1) plays a crucial role in the development and progression of various malignant tumors through diverse molecular mechanisms. However, the functional mechanism and clinical implications of SENP1 in the progression of ESCC remain unclear.

METHODS

Bulk RNA-Sequencing (RNA-seq) was used to compare potential genes in the esophageal tissues of mice with ESCC to the control group. The up-regulated SENP1 was selected. The protein level of SENP1 in ESCC patient samples was analyzed by immunohistochemistry and western blot. The potential prognostic value of SENP1 on overall survival of ESCC patients was examined using tissue microarray analysis and the Kaplan-Meier method. The biological function was confirmed through in vitro and in vivo knockdown approaches of SENP1. The role of SENP1 in cell cycle progression and apoptosis of ESCC cells was analyzed by flow cytometry and western blot. The downstream signaling pathways regulated by SENP1 were investigated via using RNA-Seq. SENP1-associated proteins were identified through immunoprecipitation. Overexpression of Sirtuin 6 (SIRT6) wildtype and mutant was performed to investigate the regulatory role of SENP1 in ESCC progression in vitro.

RESULTS

Our study discovered that SENP1 was upregulated in ESCC tissues and served as a novel prognostic factor. Moreover, SENP1 enhanced cell proliferation and migration of ESCC cell lines in vitro, as well as promoted tumor growth in vivo. Thymidine kinase 1 (TK1), Geminin (GMNN), cyclin dependent kinase 1(CDK1), and cyclin A2 (CCNA2) were identified as downstream genes of SENP1. Mechanistically, SENP1 deSUMOylated SIRT6 and subsequently inhibited SIRT6-mediated histone 3 lysine 56 (H3K56) deacetylation on those downstream genes. SIRT6 SUMOylation mutant (4KR) rescued the growth inhibition upon SENP1 depletion.

CONCLUSIONS

SENP1 promotes the malignant progression of ESCC by inhibiting the deacetylase activity of SIRT6 pathway through deSUMOylation. Our findings suggest that SENP1 may serve as a valuable biomarker for prognosis and a target for therapeutic intervention in ESCC.

The Janus face of HIF-1α in ischemic stroke and the possible associated pathways

Stroke is the most devastating disease, causing paralysis and eventually death. Many clinical and experimental trials have been done in search of a new safe and efficient medicine; nevertheless, scientists have yet to discover successful remedies that are also free of adverse effects. This is owing to the variability in intensity, localization, medication routes, and each patient's immune system reaction. HIF-1α represents the modern tool employed to treat stroke diseases due to its functions: downstream genes such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. Its role can be achieved via two downstream EPO and VEGF strongly related to apoptosis and antioxidant processes. Recently, scientists paid more attention to drugs dealing with the HIF-1 pathway. This review focuses on medicines used for ischemia treatment and their potential HIF-1α pathways. Furthermore, we discussed the interaction between HIF-1α and other biological pathways such as oxidative stress; however, a spotlight has been focused on certain potential signalling contributed to the HIF-1α pathway. HIF-1α is an essential regulator of oxygen balance within cells which affects and controls the expression of thousands of genes related to sustaining homeostasis as oxygen levels fluctuate. HIF-1α's role in ischemic stroke strongly depends on the duration and severity of brain damage after onset. HIF-1α remains difficult to investigate, particularly in ischemic stroke, due to alterations in the acute and chronic phases of the disease, as well as discrepancies between the penumbra and ischemic core. This review emphasizes these contrasts and analyzes the future of this intriguing and demanding field.

Distinctive tumorigenic significance and innovative oncology targets of SUMOylation

Protein SUMOylation, a post-translational modification, intricately regulates diverse biological processes including gene expression, cell cycle progression, signaling pathway transduction, DNA damage response, and RNA metabolism. This modification contributes to the acquisition of tumorigenicity and the maintenance of cancer hallmarks. In malignancies, protein SUMOylation is triggered by various cellular stresses, promoting tumor initiation and progression. This augmentation is orchestrated through its specific regulatory mechanisms and characteristic biological functions. This review focuses on elucidating the fundamental regulatory mechanisms and pathological functions of the SUMO pathway in tumor pathogenesis and malignant evolution, with particular emphasis on the tumorigenic potential of SUMOylation. Furthermore, we underscore the potential therapeutic benefits of targeting the SUMO pathway, paving the way for innovative anti-tumor strategies by perturbing this dynamic and reversible modifying process.

Emerging role of SENP1 in tumorigenesis and cancer therapy

Acting as a cysteine protease, small ubiquitin-like modifier (SUMO)/sentrin-specific protease1 (SENP1) involved in multiple physiological and pathological processes through processing the precursor SUMO protein into mature form and deSUMOylating target protein. It has been reported that SENP1 is highly expressed and plays a carcinogenic role in various cancers. In this paper, we mainly explore the function and mechanism of SENP1 in tumor cell proliferation, apoptosis, invasion, metastasis, stemness, angiogenesis, metabolism and drug resistance. Furthermore, the research progress of SENP1 inhibitors for cancer treatment is introduced. This study aims to provide theoretical references for cancer therapy by targeting SENP1.

SENP1-mediated SUMOylation of SIRT1 affects glioma development through the NF-κB pathway

Gliomas are the most common primary brain tumors in adults. Although they exist in different malignant stages, most gliomas are clinically challenging because of their infiltrative growth patterns and inherent relapse tendency with increased malignancy. Epigenetic alterations have been suggested to be an important factor for glioma genesis. Using mRNA probe hybridization, we identified SUMO-specific protease 1 (SENP1) as the most significantly upregulated SUMOylation regulator in glioma. Moreover, SENP1 was overexpressed in gliomas and predicted poor prognoses. Depletion of SENP1 reduced glioma cell activity, cycle arrest, and increased apoptotic activity. Mechanistically, SENP1 inhibited the protein expression of sirtuin 1 (SIRT1) through de-SUMOylation, and SIRT1 inhibited the activity of nuclear factor kappaB (NF-κB) by deacetylation. Rescue experiments revealed that downregulation of SIRT1 reversed the inhibitory effect of sh-SENP1 on glioma cell malignant phenotype, while downregulation of NF-κB reversed the activating effect of sh-SIRT1 on glioma cell malignant phenotype. Thus, SENP1-mediated de-SUMOylation of SIRT1 might be therapeutically important in gliomas.

CLDN6 inhibits colorectal cancer proliferation dependent on restraining p53 ubiquitination via ZO-1/PTEN axis

Colorectal cancer (CRC) is one of the most common cancers in the world. Abnormal proliferation is a chief characteristic of cancer and is the initiation of CRC progression. As an important component of tight junctions, CLDN6 regulates the proliferation of multiple tumors. Our previous study showed that CLDN6 was low expressed in CRC, and CLDN6 overexpression inhibited CRC proliferation. However, the specific mechanism of how CLDN6 works remains unclear. This research aimed to reveal the relationship between CLDN6 and clinical features, as well as the molecular mechanism by which CLDN6 inhibited CRC proliferation. We found that low expression of CLDN6 was associated with pathological grade and prognosis of CRC patients, and confirmed that CLDN6 inhibited CRC proliferation dependent on p53. Mechanically, we elucidated that CLDN6 regulated ubiquitination to enhance p53 stability and nuclear import by PTEN/AKT/MDM2 pathway. Through the PDZ-binding motif (PBM), CLDN6 bound to ZO-1 to interact with PTEN, and regulate AKT/MDM2 pathway. Collectively, our data enriched the theoretical basis for CLDN6 as a potential biomarker for diagnosis, therapy and prognosis of CRC.

Anti-apoptotic capacity of MALAT1 on hippocampal neurons correlates with CASP3 DNA methylation in a mouse model of autism

Prior evidence has suggested the alleviatory effect of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) on neuroinflammation in neurodegenerative diseases. This study primarily investigates the underlying mechanism of how the long non-coding RNA MALAT1 affects neuronal apoptosis in the hippocampus of mice with autism spectrum disorder (ASD). The findings demonstrate that CASP3 is highly expressed while MALAT1 is downregulated in the hippocampal neurons of autistic mice. MALAT1 mainly localizes within the cell nucleus and recruits DNA methyltransferases (including DNMT1, DNMT3a, and DNMT3b) to the promoter region of CASP3, promoting its methylation and further inhibiting its expression. In vitro experiments reveal that reducing MALAT1 expression promotes the expression of CASP3 and Bax while suppressing Bcl-2 expression, thereby enhancing cellular apoptosis. Conversely, increasing MALAT1 expression yields the opposite effect. Consequently, these results further confirm the role of MALAT1 in suppressing neuronal apoptosis in the hippocampus of mice with ASD through the regulation of CASP3 promoter methylation. Thus, this research unveils the significant roles of MALAT1 and CASP3 in the pathogenesis of ASD, offering new possibilities for future therapeutic interventions.

Binding of YY1/CREB to an Enhancer Region Triggers Claudin 6 Expression in H. pylori LPS-Stimulated AGS Cells

Aberrant expression of the tight junction protein claudin 6 (CLDN6) is a hallmark of gastric cancer progression. Its expression is regulated by the cAMP response element-binding protein (CREB). In gastric cancer induced by Helicobacter pylori (H. pylori) there is no information regarding what transcription factors induce/upregulate the expression of CLDN6. We aimed to identify whether CREB and Yin Yang1 (YY1) regulate the expression of CLDN6 and the site where they bind to the promoter sequence. Bioinformatics analysis, H. pylori lipopolysaccharide (LPS), YY1 and CREB silencing, Western blot, luciferase assays, and chromatin immunoprecipitation experiments were performed using the stomach gastric adenocarcinoma cell line AGS. A gen reporter assay suggested that the initial 2000 bp contains the regulatory sequence associated with CLDN6 transcription; the luciferase assay demonstrated three different regions with transcriptional activity, but the -901 to -1421 bp region displayed the maximal transcriptional activity in response to LPS. Fragment 1279-1421 showed CREB and, surprisingly, YY1 occupancy. Sequential Chromatin Immunoprecipitation (ChIP) experiments confirmed that YY1 and CREB interact in the 1279-1421 region. Our results suggest that CLDN6 expression is regulated by the binding of YY1 and CREB in the 901-1421 enhancer, in which a non-described interaction of YY1 with CREB was established in the 1279-1421 region.

Hypoxia inducible factor-1α (HIF-1α) in breast cancer: The crosstalk with oncogenic and onco-suppressor factors in regulation of cancer hallmarks

Low oxygen level at tumor microenvironment leads to a condition, known as hypoxia that is implicated in cancer progression. Upon hypoxia, HIF-1α undergoes activation and due to its oncogenic function and interaction with other molecular pathways, promotes tumor progression. The HIF-1α role in regulating breast cancer progression is described, Overall, HIF-1α has upregulation in breast tumor and due to its tumor-promoting function, its upregulation is in favor of breast tumor progression. HIF-1α overexpression prevents apoptosis in breast tumor and it promotes cell cycle progression. Silencing HIF-1α triggers cycle arrest and decreases growth. Migration of breast tumor enhances by HIF-1α signaling and it mainly induces EMT in providing metastasis. HIF-1α upregulation stimulates drug resistance and radio-resistance in breast tumor. Furthermore, HIF-1α signaling induces immune evasion of breast cancer. Berberine and pharmacological intervention suppress HIF-1α signaling in breast tumor and regulation of HIF-1α by non-coding RNAs occurs. Furthermore, HIF-1α is a biomarker in clinic.

The emerging roles of SUMOylation in the tumor microenvironment and therapeutic implications

Tumor initiation, progression, and response to therapies depend to a great extent on interactions between malignant cells and the tumor microenvironment (TME), which denotes the cancerous/non-cancerous cells, cytokines, chemokines, and various other factors around tumors. Cancer cells as well as stroma cells can not only obtain adaption to the TME but also sculpt their microenvironment through a series of signaling pathways. The post-translational modification (PTM) of eukaryotic cells by small ubiquitin-related modifier (SUMO) proteins is now recognized as a key flexible pathway. Proteins involved in tumorigenesis guiding several biological processes including chromatin organization, DNA repair, transcription, protein trafficking, and signal conduction rely on SUMOylation. The purpose of this review is to explore the role that SUMOylation plays in the TME formation and reprogramming, emphasize the importance of targeting SUMOylation to intervene in the TME and discuss the potential of SUMOylation inhibitors (SUMOi) in ameliorating tumor prognosis.

CLDN6 inhibits breast cancer metastasis through WIP-dependent actin cytoskeleton-mediated autophagy

BACKGROUND

As a breast cancer suppressor gene, CLDN6 overexpression was found to inhibit breast cancer metastasis in our previous studies, but the specific mechanism remains unclear. This study aimed to clarify the role and mechanism of CLDN6 in inhibiting breast cancer metastasis.

METHODS

Western blot, immunofluorescence and transmission electron microscopy were performed to detect autophagy. Wound healing, transwell assays and lung metastasis mouse models were used to examine breast cancer metastasis. Phalloidin staining and immunofluorescent staining were used to observe actin cytoskeleton. mRNA seq, RT-PCR, western blot, chromatin immunoprecipitation, dual luciferase reporter assay, co-immunoprecipitation and immunofluorescence were performed to define the molecular mechanism. The expression levels and clinical implication of CLDN6, WIP and LC3 in breast cancer tissues were evaluated using immunohistochemistry.

RESULTS

We demonstrated that CLDN6 inhibited breast cancer metastasis through autophagy in vitro and vivo. We unraveled a novel mechanism that CLDN6 regulated autophagy via WIP-dependent actin cytoskeleton assembly. Through its PDZ-binding motif, overexpressed CLDN6 interacted with JNK and upregulated JNK/c-Jun pathway. C-Jun promoted WIP expression at the transcriptional level. Notably, we observed c-Jun transcriptionally upregulated CLDN6 expression, and there was a positive feedback loop between CLDN6 and JNK/c-Jun. Finally, we found that CLDN6, WIP and LC3 expression correlated with each other, and WIP expression was significantly associated with lymph node metastasis of breast cancer patients.

CONCLUSIONS

The data provide a new insight into the inhibitory effects of CLDN6-mediated autophagy on breast cancer metastasis, and revealed the new mechanism of CLDN6 regulating autophagy through WIP-dependent actin cytoskeleton. Our findings enrich the theoretical basis for CLDN6 as a potential biomarker for breast cancer diagnosis and therapy.

HIF-1α contributes to metastasis in choriocarcinoma by regulating DEC1 expression

PURPOSE

To elucidate the underlying mechanism of HIF-1α in migration and invasion of choriocarcinoma.

METHODS

Cell proliferation was determined by CCK-8 assay when cell invasion was detected by transwell assay. The protein expression was detected by western blotting, immunohistochemistry, and qPCR assay.

RESULT

HIF-1α was shown to be strongly expressed in both clinical tumour tissues and cell lines in choriocarcinoma. When HIF-1α was efficiently knocked down in JEG3 cells, the proliferation rate was reduced by approximately 50% and the number of cells that migrated through the transwell insert was greatly decreased. The cell invasion rate was also significantly reduced. Moreover, typical markers of epithelial-mesenchymal transition such as E-cadherin, were increased, while vimentin and α-SMA were decreased after HIF-1α knockdown. In contrast, overexpression of DEC1 reversed the effects of HIF-1α knockdown. Cell proliferation, migration, and invasion were partially recovered. The level of E-cadherin was decreased, while the level of vimentin and α-SMA was increased. In addition, the level of β-catenin and LEF1 was downregulated after HIF-1α knockdown. The expression of MMP2 and MMP9 also declined. However, overexpression of DEC1 after HIF-1α knockdown partially reversed the expression pattern of these molecules.

CONCLUSION

HIF-1α contributed to EMT and metastasis through activation of canonical β-catenin signalling in choriocarcinoma and this process was dependent on DEC1. This study provides a new mechanism of HIF-1α in choriocarcinoma and suggests that intervention with DEC1 might be a promising therapeutic choice for choriocarcinoma.

The role and mechanism of claudins in cancer

Claudins are a tetraspan membrane protein multigene family that plays a structural and functional role in constructing tight junctions. Claudins perform crucial roles in maintaining cell polarity in epithelial and endothelial cell sheets and controlling paracellular permeability. In the last two decades, increasing evidence indicates that claudin proteins play a major role in controlling paracellular permeability and signaling inside cells. Several types of claudins are dysregulated in various cancers. Depending on where the tumor originated, claudin overexpression or underexpression has been shown to regulate cell proliferation, cell growth, metabolism, metastasis and cell stemness. Epithelial-to-mesenchymal transition is one of the most important functions of claudin proteins in disease progression. However, the exact molecular mechanisms and signaling pathways that explain why claudin proteins are so important to tumorigenesis and progression have not been determined. In addition, claudins are currently being investigated as possible diagnostic and treatment targets. Here, we discuss how claudin-related signaling pathways affect tumorigenesis, tumor progression, and treatment sensitivity.

Conducive target range of breast cancer: Hypoxic tumor microenvironment

Breast cancer is a kind of malignant tumor disease that poses a serious threat to human health. Its biological characteristics of rapid proliferation and delayed angiogenesis, lead to intratumoral hypoxia as a common finding in breast cancer. HIF as a transcription factor, mediate a series of reactions in the hypoxic microenvironment, including metabolic reprogramming, tumor angiogenesis, tumor cell proliferation and metastasis and other important physiological and pathological processes, as well as gene instability under hypoxia. In addition, in the immune microenvironment of hypoxia, both innate and acquired immunity of tumor cells undergo subtle changes to support tumor and inhibit immune activity. Thus, the elucidation of tumor microenvironment hypoxia provides a promising target for the resistance and limited efficacy of current breast cancer therapies. We also summarize the hypoxic mechanisms of breast cancer treatment related drug resistance, as well as the current status and prospects of latest related drugs targeted HIF inhibitors.

Hypoxia signaling in human health and diseases: implications and prospects for therapeutics

Molecular oxygen (O₂) is essential for most biological reactions in mammalian cells. When the intracellular oxygen content decreases, it is called hypoxia. The process of hypoxia is linked to several biological processes, including pathogenic microbe infection, metabolic adaptation, cancer, acute and chronic diseases, and other stress responses. The mechanism underlying cells respond to oxygen changes to mediate subsequent signal response is the central question during hypoxia. Hypoxia-inducible factors (HIFs) sense hypoxia to regulate the expressions of a series of downstream genes expression, which participate in multiple processes including cell metabolism, cell growth/death, cell proliferation, glycolysis, immune response, microbe infection, tumorigenesis, and metastasis. Importantly, hypoxia signaling also interacts with other cellular pathways, such as phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-B (NF-κB) pathway, extracellular signal-regulated kinases (ERK) signaling, and endoplasmic reticulum (ER) stress. This paper systematically reviews the mechanisms of hypoxia signaling activation, the control of HIF signaling, and the function of HIF signaling in human health and diseases. In addition, the therapeutic targets involved in HIF signaling to balance health and diseases are summarized and highlighted, which would provide novel strategies for the design and development of therapeutic drugs.

Iron increases lipid deposition via oxidative stress-mediated mitochondrial dysfunction and the HIF1α-PPARγ pathway

Iron is an essential micro-element, involved in multiple biological activities in vertebrates. Excess iron accumulation has been identified as an important mediator of lipid deposition. However, the underlying mechanisms remain unknown. In the present study, we found that a high-iron diet significantly increased intestinal iron content and upregulated the mRNA expression of two iron transporters (zip14 and fpn1). Intestinal iron overload increased lipogenesis, reduced lipolysis and promoted oxidative stress and mitochondrial dysfunction. Iron-induced lipid accumulation was mediated by hypoxia-inducible factor-1 α (HIF1α), which was induced in response to mitochondrial oxidative stress following inhibition of prolyl hydroxylase 2 (PHD2). Mechanistically, iron promoted lipid deposition by enhancing the DNA binding capacity of HIF1α to the pparγ and fas promoters. Our results provide experimental evidence that oxidative stress, mitochondrial dysfunction and the HIF1α-PPARγ pathway are critical mediators of iron-induced lipid deposition.

Estrogen Receptor and Claudin-6 Might Play Vital Roles for Long-Term Prognosis in Patients With Luminal A Breast Cancer Who Underwent Neoadjuvant Chemotherapy

Purpose

It is well-known that the pathological complete response (pCR) rate in patients with luminal A cancer (LAC) is lower than those of other subtypes of breast cancer. The phenotype of cancer often alters after neoadjuvant chemotherapy (NAC) which may be related to hypoxia, and the latter might induce the drift of the estrogen receptor (ER). The phenotype drift in local advanced LAC after NAC might influence the long-term prognosis.

Methods

The oxygen concentration of cancer tissues during NAC was recorded and analyzed (n = 43). The expression of ER and claudin-6 was detected in pre- and post-NAC specimens.

Results

NAC might induce the cycling intracanceral hypoxia, and the pattern was related to NAC response. The median follow-up time was 61 months. Most of the patients (67%) with stable or increased ER and claudin-6 expression exhibited perfect prognosis (DFS = 100%, 61 months). About 20% of patients with decreased claudin-6 would undergo the poor prognosis (DFS = 22.2%, 61 months). The contrasting prognosis (100% vs. 22.2%) had nothing to do with the response of NAC in the above patients. Only 13% patients had stable claudin-6 and decreased ER, whose prognosis might relate to the response of NAC.

Conclusion

NAC might induce cycling intracanceral hypoxia to promote the phenotype drift in local advanced LAC, and the changes in ER and claudin-6 after NAC would determine the long-term prognosis.

CLDN6 inhibits breast cancer cell malignant behavior by suppressing ERK signaling

Claudin 6 (CLDN6) is an important component of tight junctions. Through the PDZ binding motif, CLDN6 binds to a variety of signaling proteins that contain the PDZ domain to regulate different signaling pathways, and plays an important role in the occurrence and development of tumors. Our previous work showed that CLDN6 was expressed at low levels in breast cancer cells, and overexpression of CLDN6 inhibited breast cancer cell proliferation, migration and invasion. However, the mechanism of how CLDN6 works remains unclear. In this study, we aimed to explore the mechanism by which CLDN6 inhibits breast cancer cell malignant behavior. As a result, overexpression of CLDN6 inhibited the proliferation of breast cancer cells along with the downregulation of cyclin D1, which plays an important role in regulating cell proliferation. After overexpression of Sp1 in CLDN6-overexpressing cells, the expression of cyclin D1 was upregulated. On the other hand, CLDN6 inhibited breast cancer cell migration and invasion along with the downregulation of IL-8, CXCR2 and FAK. When treated with IL-8, the migration and invasion ability were promoted along with the upregulation of CXCR2 and p-FAK, and the cytoskeleton was rearranged in CLDN6-overexpressing cells. Furthermore, when treated with the ERK signaling activator PMA, the proliferation, migration and invasion abilities were promoted along with the upregulation of Sp1, cyclin D1 and IL-8 in CLDN6-overexpressin cells. In conclusion, CLDN6 suppressed ERK/Sp1/cyclin D1 and ERK/IL-8 signaling to inhibit proliferation, migration and invasion in breast cancer cells. The mechanism may provide experimental evidence for the treatment of breast cancer targeting CLDN6.

SUMOylation and NEDDylation in Primary and Metastatic Cancers to Bone

Post-translational modifications comprise series of enzymatically-driven chemical modifications, virtually involving the entire cell proteome, that affect the fate of a target protein and, in turn, cell activity. Different classes of modifications can be established ranging from phosphorylation, glycosylation, ubiquitination, acetylation, methylation, lipidation and their inverse reactions. Among these, SUMOylation and NEDDylation are ubiquitin-like multi-enzymatic processes that determine the bound of SUMOs and NEDD8 labels, respectively, on defined amino acidic residues of a specific protein and regulate protein function. As fate-determinants of several effectors and mediators, SUMOylation and NEDDylation play relevant roles in many aspects of tumor cell biology. Bone represents a preferential site of metastasis for solid tumors (e.g., breast and prostate cancers) and the primary site of primitive tumors (e.g., osteosarcoma, chondrosarcoma). Deregulation of SUMOylation and NEDDylation affects different aspects of neoplastic transformation and evolution such as epithelial-mesenchymal transition, adaptation to hypoxia, expression and action of tumor suppressors and oncogenic mediators, and drug resistance. Thereby, they represent potential therapeutic targets. This narrative review aims at describing the involvement and regulation of SUMOylation and NEDDylation in tumor biology, with a specific focus on primary and secondary bone tumors, and to summarize and highlight their potentiality in diagnostics and therapeutic strategies.

YTHDF1 upregulation mediates hypoxia-dependent breast cancer growth and metastasis through regulating PKM2 to affect glycolysis

N6-methyladenosine modification is the most common RNA modification mechanism in mammals. YTHDF1, a m⁶A reader, can recognize the m⁶A of mRNAs to facilitate the interaction with the mRNA ribosome assembly and recruitment of translation initiators to promote translation. From a clinical perspective, YTHDF1 upregulation is frequently observed in breast cancer, but its involvement in those cancer-related events is still unclear. Here we report that YTHDF1 is a cancer driver capable of facilitating the proliferation and invasion of breast cancer cells as well as enhancing tumorigenicity and metastasis through promoting glycolysis. We found that tumor hypoxia can transcriptionally induce HIF1α and post-transcriptionally inhibit the expression of miR-16-5p to promote YTHDF1 expression, which could sequentially enhance tumor glycolysis by upregulating PKM2 and eventually increase the tumorigenesis and metastasis potential of breast cancer cells. Inhibiting YTHDF1 via gene knockdown or miR-16-5p would significantly abolish YTHDF1-dependent tumor growth and metastasis. In summary, we identified the role of the YTHDF1-PKM2 signal axis in the occurrence and development of breast cancer, which can be used as a potential target for breast cancer treatment.

KHDRBS3 promotes paclitaxel resistance and induces glycolysis through modulated MIR17HG/CLDN6 signaling in epithelial ovarian cancer

Paclitaxel (PTX) resistance contributes to mortality in epithelial ovarian cancer (EOC). Aerobic glycolysis is elevated in the tumor environment and may influence resistance to PTX in EOC. KH domain-containing, RNA-binding signal transduction-associated protein 3 (KHDRBS3) is an RNA binding protein that is up-regulated in EOC, but its underlying mechanism in EOC is unclear. Here, we investigate the role of KHDRBS3 in glycolysis and increased resistance to PTX. Expression of KHDRBS3 and Claudin (CLDN6) were measured in EOC tissue and cells by quantitative real-time PCR, western blotting and immunohistochemistry. The biological functions of KHDRBS3, MIR17HG and CLDN6 were examined using MTT, colony formation, apoptosis and seahorse assays in vitro. For in vivo experiments, a xenograft model was used to investigate the effects of KHDRBS3 and MIR17HG in EOC. Here, we investigate the role of KHDRBS3 in glycolysis and increased resistance to PTX. The expression of KHDRBS3 was up-regulated in PTX-resistant cells. KHDRBS3 knockdown restrained the IC₅₀ of PTX, cell proliferation, colony formation and glycolysis in SKOV3-R and A2780-R cells in vitro and enhanced PTX sensitivity in a xenograft mouse model in vivo. KHDRBS3 interacts with lncRNA MIR17HG, which is down-regulated in EOC tissue and cells. The effect of KHDRBS3 overexpression on PTX resistance and glycolysis was rescued by MIR17HG overexpression. Additionally, MIR17HG interacts with the 3'UTR of CLDN6 and negatively regulates CLDN6 expression. MIR17HG overexpression suppressed the IC₅₀ of PTX and glycolysis by targeting CLDN6. Our results reveal a KHDRBS3-MIR17HG-CLDN6 regulatory axis that contributes to enhanced glycolysis in EOC and represents a potential target for therapy.

CLDN6 Suppresses c-MYC-Mediated Aerobic Glycolysis to Inhibit Proliferation by TAZ in Breast Cancer

Claudin 6 (CLDN6) was found to be a breast cancer suppressor gene, which is lowly expressed in breast cancer and inhibits breast cancer cell proliferation upon overexpression. However, the mechanism by which CLDN6 inhibits breast cancer proliferation is unclear. Here, we investigated this issue and elucidated the molecular mechanisms by which CLDN6 inhibits breast cancer proliferation. First, we verified that CLDN6 was lowly expressed in breast cancer tissues and that patients with lower CLDN6 expression had a worse prognosis. Next, we confirmed that CLDN6 inhibited breast cancer proliferation through in vitro and in vivo experiments. As for the mechanism, we found that CLDN6 inhibited c-MYC-mediated aerobic glycolysis based on a metabolomic analysis of CLDN6 affecting cellular lactate levels. CLDN6 interacted with a transcriptional co-activator with PDZ-binding motif (TAZ) and reduced the level of TAZ, thereby suppressing c-MYC transcription, which led to a reduction in glucose uptake and lactate production. Considered together, our results suggested that CLDN6 suppressed c-MYC-mediated aerobic glycolysis to inhibit the proliferation of breast cancer by TAZ, which indicated that CLDN6 acted as a novel regulator of aerobic glycolysis and provided a theoretical basis for CLDN6 as a biomarker of progression in breast cancer.

CLDN6: From Traditional Barrier Function to Emerging Roles in Cancers

Claudins (CLDNs) are the most important tight junction proteins, which are mainly expressed in endothelial cells or epithelial cells in a tissue-specific manner. As a member of the CLDNs family, CLDN6 is highly expressed in fetal tissues such as the stomach, pancreas, lung, and kidney, but is not expressed in corresponding adult tissues. The expression of CLDN6 is regulated by a variety of factors, including but not limited to stimuli and transcription factors, DNA methylation, and post-translational modifications. CLDN6 has been found to have a key role in the formation of barriers, especially the lung epithelial barrier and the epidermal permeability barrier (EPB). Importantly, the roles of CLDN6 in cancers have gained focus and are being investigated in recent years. Strong evidence indicates that the altered expression of CLDN6 is linked to the development of various cancers. Malignant phenotypes of tumors affected by CLDN6 include proliferation and apoptosis, migration and invasion, and drug resistance, which are regulated by CLDN6-mediated key signaling pathways. Given the important role in tumors and its low or no expression in normal tissues, CLDN6 is an ideal target for tumor therapy. This review aims to provide an overview of the structure and regulation of CLDN6, and its traditional barrier function, with a special emphasis on its emerging roles in cancers, including its impact on the malignant phenotypes, signal-modulating effects, the prognosis of tumor patients, and clinical applications in cancers.

Claudin 6: Therapeutic prospects for tumours, and mechanisms of expression and regulation (Review)

Tight junctions (TJs) are an important component of cell connectivity; they maintain cell polarity, permeability and adhesion, and participate in the regulation of cell proliferation and differentiation. The claudin (CLDN) family is integral to TJs, and CLDN6 is an important member of this family. Abnormal expression of CLDN6 can destroy the integrity of TJs through various mechanisms and can serve multiple roles in the occurrence and development of tumours. CLDN6 is widely expressed in various tumours but rarely expressed in healthy adult tissues. The aim of this review is to critically examine the recent literature on CLDN6, including its structure, expression in different tumours, regulatory mechanisms and therapeutic prospects. Although some conclusions are controversial, in certain tumours, such as liver, ovarian, endometrial and oesophageal cancer, and atypical teratoid/rhabdoid tumours, research consistently shows that CLDN6 is expressed in tumour tissues but is not expressed or is expressed at low levels in surrounding tissues. In these tumours, CLDN6 has potential as a carcinoembryonic antigen and a therapeutic target.

SUMOylation Wrestles With the Occurrence and Development of Breast Cancer

Breast cancer has the highest incidence among cancers and is the most frequent cause of death in women worldwide. The detailed mechanism of the pathogenesis of breast cancer has not been fully elucidated, and there remains a lack of effective treatment methods for the disease. SUMOylation covalently conjugates a large amount of cellular proteins, and affects their cellular localization and biological activity to participate in numerous cellular processes. SUMOylation is an important process and imbalance of SUMOylation results in the progression of human diseases. Increasing evidence shows that numerous SUMOylated proteins are involved in the occurrence and development of breast cancer. This review summarizes a series of studies on protein SUMOylation in breast cancer in recent years. The study of SUMOylated proteins provides a comprehensive understanding of the pathophysiology of breast cancer and provides evolving therapeutic strategies for the treatment of breast cancer.