Cycling hypoxia affects cell invasion and proliferation through direct regulation of claudin1 / claudin7 expression, and indirect regulation of P18 through claudin7

Antibody-mediated targeting of Claudins in cancer

Tight junctions (TJs) are large intercellular adhesion complexes that maintain cell polarity in normal epithelia and endothelia. Claudins are critical components of TJs, forming homo- and heteromeric interaction between adjacent cells, which have emerged as key functional modulators of carcinogenesis and metastasis. Numerous epithelial-derived cancers display altered claudin expression patterns, and these aberrantly expressed claudins have been shown to regulate cancer cell proliferation/growth, metabolism, metastasis and cell stemness. Certain claudins can now be used as biomarkers to predict patient prognosis in a variety of solid cancers. Our understanding of the distinct roles played by claudins during the cancer progression has progressed significantly over the last decade and claudins are now being investigated as possible diagnostic markers and therapeutic targets. In this review, we will summarize recent progress in the use of antibody-based or related strategies for targeting claudins in cancer treatment. We first describe pre-clinical studies that have facilitated the development of neutralizing antibodies and antibody-drug-conjugates targeting Claudins (Claudins-1, -3, -4, -6 and 18.2). Next, we summarize clinical trials assessing the efficacy of antibodies targeting Claudin-6 or Claudin-18.2. Finally, emerging strategies for targeting Claudins, including Chimeric Antigen Receptor (CAR)-T cell therapy and Bi-specific T cell engagers (BiTEs), are also discussed.

Hypoxia disrupt tight junctions and promote metastasis of oral squamous cell carcinoma via loss of par3

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a highly malignant tumor that is frequently associated with lymph node metastasis, resulting in poor prognosis and survival in patients. In the tumor microenvironment, hypoxia plays an important role in regulating cellular responses such as progressive and rapid growth and metastasis. In these processes, tumor cells autonomously undergo diverse transitions and acquire functions. However, hypoxia-induced transition of OSCC and the involvement of hypoxia in OSCC metastasis remain unclear. Therefore, in this study, we aimed to elucidate the mechanism of hypoxia-induced OSCC metastasis and particularly, its impact on tight junctions (TJs).

METHODS

The expression of hypoxia-inducible factor 1-alpha (HIF-1α) was detected in tumor tissues and adjacent normal tissues from 29 patients with OSCC using reverse transcription quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and immunohistochemistry (IHC). The migration and invasion abilities of OSCC cell lines treated with small interfering (si)RNA targeting HIF-1α or cultured in hypoxic conditions were analyzed using Transwell assays. The effect of HIF-1α expression on in vivo tumor metastasis of OSCC cells was evaluated using lung metastasis model.

RESULTS

HIF-1α was overexpressed in patients with OSCC. OSCC metastasis was correlated with HIF-1α expression in OSCC tissues. Hypoxia increased the migration and invasion abilities of OSCC cell lines by regulating the expression and localization of partitioning-defective protein 3 (Par3) and TJs. Furthermore, HIF-1α silencing effectively decreased the invasion and migration abilities of OSCC cell lines and restored TJ expression and localization via Par3. The expression of HIF-1α was positively regulated the OSCC metastasis in vivo.

CONCLUSIONS

Hypoxia promotes OSCC metastasis by regulating the expression and localization of Par3 and TJ proteins. HIF-1α positively correlates to OSCC metastasis. Lastly, HIF-1α expression could regulate the expression of Par3 and TJs in OSCC. This finding may aid in elucidating the molecular mechanisms of OSCC metastasis and progression and developing new diagnostic and therapeutic approaches for OSCC metastasis.

Evaluation of the Prognostic Relevance of Differential Claudin Gene Expression Highlights Claudin-4 as Being Suppressed by TGFβ1 Inhibitor in Colorectal Cancer

Background: Claudins (CLDNs) are a family of closely related transmembrane proteins that have been linked to oncogenic transformation and metastasis across a range of cancers, suggesting that they may be valuable diagnostic and/or prognostic biomarkers that can be used to evaluate patient outcomes. However, CLDN expression patterns associated with colorectal cancer (CRC) remain to be defined.

Methods: The mRNA levels of 21 different CLDN family genes were assessed across 20 tumor types using the Oncomine database. Correlations between these genes and patient clinical outcomes, immune cell infiltration, clinicopathological staging, lymph node metastasis, and mutational status were analyzed using the GEPIA, UALCAN, Human Protein Atlas, Tumor Immune Estimation Resource, STRING, Genenetwork, cBioportal, and DAVID databases in an effort to clarify the potential functional roles of different CLDN protein in CRC. Molecular docking analyses were used to probe potential interactions between CLDN4 and TGFβ1. Levels of CLDN4 and CLDN11 mRNA expression in clinical CRC patient samples and in the HT29 and HCT116 cell lines were assessed via qPCR. CLDN4 expression levels in these 2 cell lines were additionally assessed following TGFβ1 inhibitor treatment.

Results: These analyses revealed that COAD and READ tissues exhibited the upregulation of CLDN1, CLDN2, CLDN3, CLDN4, CLDN7, and CLDN12 as well as the downregulation of CLDN5 and CLDN11 relative to control tissues. Higher CLDN11 and CLDN14 expression as well as lower CLDN23 mRNA levels were associated with poorer overall survival (OS) outcomes. Moreover, CLDN2 and CLDN3 or CLDN11 mRNA levels were significantly associated with lymph node metastatic progression in COAD or READ lower in COAD and READ tissues. A positive correlation between the expression of CLDN11 and predicted macrophage, dendritic cell, and CD4+ T cell infiltration was identified in CRC, with CLDN12 expression further being positively correlated with CD4+ T cell infiltration whereas a negative correlation was observed between such infiltration and the expression of CLDN3 and CLDN15. A positive correlation between CLDN1, CLDN16, and neutrophil infiltration was additionally detected, whereas neutrophil levels were negatively correlated with the expression of CLDN3 and CLDN15. Molecular docking suggested that CLDN4 was able to directly bind via hydrogen bond with TGFβ1. Relative to paracancerous tissues, clinical CRC tumor tissue samples exhibited CLDN4 and CLDN11 upregulation and downregulation, respectively. LY364947 was able to suppress the expression of CLDN4 in both the HT29 and HCT116 cell lines.

Conclusion: Together, these results suggest that the expression of different CLDN family genes is closely associated with CRC tumor clinicopathological staging and immune cell infiltration. Moreover, CLDN4 expression is closely associated with TGFβ1 in CRC, suggesting that it and other CLDN family members may represent viable targets for antitumor therapeutic intervention.

CLAUDIN7 modulates trophectoderm barrier function to maintain blastocyst development in pigs

Trophectoderm (TE) barrier function is an essential prerequisite for blastocyst development. CLAUDIN7 (CLDN7), a member of CLAUDINS family, is involved in regulating intercellular exchange and cell polarity in epithelium cells. However, the role of CLDN7 in porcine early embryo development is yet to be explored. Here, we found that CLDN7 was highly conserved in different species and was widely expressed in different tissues. Remarkably, CLDN7 expression maintained a low level from GV oocyte to 4-cell stage whereas its expression exhibited a higher level from 8-cell stage onwards. Microinjection of siRNA into cytoplasm effectively knocked down expression of CLDN7 mRNA and protein in porcine embryos. CLDN7 knockdown not only significantly reduced blastocyst rates of embryos derived from parthenogenetic activation and in vitro fertilization, but also reduced number of total cells and TE cells in the resulting blastocysts. Furthermore, CLDN7 knockdown led to a significant reduction in expression of multiple genes associated with tight junction assembly and fluid accumulation. A permeability assay revealed that CLDN7 knockdown disrupted tight junction assembly and paracellular sealing in the TE epithelium. Taken together, these results demonstrate that CLDN7 regulates porcine blastocyst development via modulating trophectoderm barrier function.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

miR-21-5p promotes cell proliferation and G1/S transition in melanoma by targeting CDKN2C

Human melanoma is a highly malignant tumor originating from cutaneous melanocytes. The noncoding RNA microRNA (miR)‐21‐5p has been reported to be expressed at high levels in malignant melanocytic skin tissues, but its potential functional role in melanoma remains poorly understood. Here, we explored the cellular effects of miR‐21‐5p on melanoma in vitro and the underlying mechanisms. Quantitative real‐time PCR was used to show that miR‐21‐5p is significantly up‐regulated in clinical samples from patients with melanoma as compared with adjacent noncancerous tissues. Overexpression of miR‐21‐5p significantly enhanced, whereas knockdown attenuated, cell proliferation and G1/S transition in melanoma cell lines (A375 and M14). Luciferase reporter assays were used to show that the cyclin‐dependent kinase inhibitor 2C (CDKN2C) is a downstream target of miR‐21‐5p. Furthermore, miR‐21‐5p mimics resulted in a decrease in CDKN2C expression, and CDKN2C expression was observed to be inversely correlated with miR‐21‐5p expression in melanoma tissues. Rescue experiments were performed to show that overexpression of CDKN2C partially reversed the effects of miR‐21‐5p up‐regulation on A375 cells. Consistently, knockdown of CDKN2C abolished the effects of miR‐21‐5p down‐regulation on A375 cells. Overall, our studies demonstrate that miR‐21‐5p can promote the growth of melanoma cells by targeting CDKN2C, which may induce G0/G1 phase arrest of melanoma cells.

Flow-Encoded Oxygen Control to Track the Time-Dependence of Molecular Changes Induced by Static or Cycling Hypoxia

Detecting the effects of low oxygen on cell function is often dependent on monitoring the expression of a number of hypoxia markers. The time dependence of the appearance and stability of these markers varies between cell lines. Assessing cellular marker dynamics is also critical to determining how quickly cells respond to transient changes in oxygen levels that occurs with cycling hypoxia. We fabricated a manifold designed to use flow-encoding to produce sequential changes in gas mixtures delivered to a permeable-bottom 96-well plate. We show how this manifold and plate design can be used to expose cells to either static or cycling hypoxic conditions for eight different time periods thereby facilitating the study of the time-response of cells to altered oxygen environments. Using this device, we monitored the time-dependence of molecular changes in human PANC-1 pancreatic carcinoma and Caco-2 colon adenocarcinoma cells exposed to increasing periods of static or cycling hypoxia. Using immunohistochemistry, both cell lines show detectable levels of the marker protein hypoxia-inducible factor-1α (HIF-1α) after 3 h of exposure to static hypoxia. Cycling hypoxia increased the expression level of HIF-1α compared to static hypoxia. Both static and cycling hypoxia also increased glucose uptake and aldehyde dehydrogenase activity. This new device offers a facile screening approach to determine the kinetics of cellular alterations under varying oxygen conditions.

Acute vs. Chronic vs. Cyclic Hypoxia: Their Differential Dynamics, Molecular Mechanisms, and Effects on Tumor Progression

Hypoxia has been shown to increase the aggressiveness and severity of tumor progression. Along with chronic and acute hypoxic regions, solid tumors contain regions of cycling hypoxia (also called intermittent hypoxia or IH). Cyclic hypoxia is mimicked in vitro and in vivo by periodic exposure to cycles of hypoxia and reoxygenation (H-R cycles). Compared to chronic hypoxia, cyclic hypoxia has been shown to augment various hallmarks of cancer to a greater extent: angiogenesis, immune evasion, metastasis, survival etc. Cycling hypoxia has also been shown to be the major contributing factor in increasing the risk of cancer in obstructive sleep apnea (OSA) patients. Here, we first compare and contrast the effects of acute, chronic and intermittent hypoxia in terms of molecular pathways activated and the cellular processes affected. We highlight the underlying complexity of these differential effects and emphasize the need to investigate various combinations of factors impacting cellular adaptation to hypoxia: total duration of hypoxia, concentration of oxygen (O2), and the presence of and frequency of H-R cycles. Finally, we summarize the effects of cycling hypoxia on various hallmarks of cancer highlighting their dependence on the abovementioned factors. We conclude with a call for an integrative and rigorous analysis of the effects of varying extents and durations of hypoxia on cells, including tools such as mechanism-based mathematical modelling and microfluidic setups.

Ping-Pong-Tumor and Host in Pancreatic Cancer Progression

Metastasis is the main cause of high pancreatic cancer (PaCa) mortality and trials dampening PaCa mortality rates are not satisfying. Tumor progression is driven by the crosstalk between tumor cells, predominantly cancer-initiating cells (CIC), and surrounding cells and tissues as well as distant organs, where tumor-derived extracellular vesicles (TEX) are of major importance. A strong stroma reaction, recruitment of immunosuppressive leukocytes, perineural invasion, and early spread toward the peritoneal cavity, liver, and lung are shared with several epithelial cell-derived cancer, but are most prominent in PaCa. Here, we report on the state of knowledge on the PaCIC markers Tspan8, alpha6beta4, CD44v6, CXCR4, LRP5/6, LRG5, claudin7, EpCAM, and CD133, which all, but at different steps, are engaged in the metastatic cascade, frequently via PaCIC-TEX. This includes the contribution of PaCIC markers to TEX biogenesis, targeting, and uptake. We then discuss PaCa-selective features, where feedback loops between stromal elements and tumor cells, including distorted transcription, signal transduction, and metabolic shifts, establish vicious circles. For the latter particularly pancreatic stellate cells (PSC) are responsible, furnishing PaCa to cope with poor angiogenesis-promoted hypoxia by metabolic shifts and direct nutrient transfer via vesicles. Furthermore, nerves including Schwann cells deliver a large range of tumor cell attracting factors and Schwann cells additionally support PaCa cell survival by signaling receptor binding. PSC, tumor-associated macrophages, and components of the dysplastic stroma contribute to perineural invasion with signaling pathway activation including the cholinergic system. Last, PaCa aggressiveness is strongly assisted by the immune system. Although rich in immune cells, only immunosuppressive cells and factors are recovered in proximity to tumor cells and hamper effector immune cells entering the tumor stroma. Besides a paucity of immunostimulatory factors and receptors, immunosuppressive cytokines, myeloid-derived suppressor cells, regulatory T-cells, and M2 macrophages as well as PSC actively inhibit effector cell activation. This accounts for NK cells of the non-adaptive and cytotoxic T-cells of the adaptive immune system. We anticipate further deciphering the molecular background of these recently unraveled intermingled phenomena may turn most lethal PaCa into a curatively treatable disease.

Emerging clinical significance of claudin-7 in colorectal cancer: a review

Tight junctions (TJs) play an important role in maintaining cell polarity and regulating cell permeability. In recent years, many studies have shown that TJ proteins, especially claudin-7, are closely related to inflammation and the development of various malignant tumors. Claudin-7 plays a significant role in maintaining the physiological functions and pathological conditions of the TJ barrier. The dysregulation of claudin-7 plays a tumor suppressor role or conversely has carcinogenic effects in different target tissues or cells, but the exact underlying mechanism is still unclear. In this review, we will summarize the expression pattern of claudin-7 in tumors, focusing on the expression and regulation of claudin-7 in colorectal cancer and discussing the correlation between claudin-7 and invasion, metastasis and epithelial–mesenchymal transition (EMT) in colorectal cancer. The construction of Cldn7^−/− mice and conventional claudin-7 knockout mouse models has helped determine the mechanisms by which claudin-7 promotes tumorigenesis. Elucidation of the expression and subcellular localization of claudin-7 under pathological conditions will help develop claudin-7 as a useful biomarker for detecting and diagnosing cancer, and thus may help combat the occurrence, development, and invasion of cancers.