Palmitoylated claudin7 captured in glycolipid-enriched membrane microdomains promotes metastasis via associated transmembrane and cytosolic molecules

Claudin and pancreatic cancer

Due to the lack of timely and accurate screening modalities and treatments, most pancreatic cancer (PCa) patients undergo fatal PCa progression within a short period since diagnosis. The claudin(CLDN) family is expressed specifically as tight junction structure in a variety of tumors, including PCa, and affects tumor progression by changing the cell junctions. Thus far, many of the 27 members of the claudin family, including claudin-18.2 and claudin-4, have significantly aberrantly expression in pancreatic tumors. In addition, some studies have confirmed the role of some claudin proteins in the diagnosis and treatment of pancreatic tumors. By targeting different targets of claudin protein and combining chemotherapy, further enhance tumor cell necrosis and inhibit tumor invasion and metastasis. Claudins can either promote or inhibit the development of pancreatic cancer, which indicates that the diagnosis and treatment of different kinds of claudins require to consider different biological characteristics. This literature summarizes the functional characteristics and clinical applications of various claudin proteins in Pca cells, with a focus on claudin-18.2 and claudin-4.

Protein palmitoylation in cancer: molecular functions and therapeutic potential

Protein S-palmitoylation (hereinafter referred to as protein palmitoylation) is a reversible lipid posttranslational modification catalyzed by the zinc finger DHHC-type containing (ZDHHC) protein family. The reverse reaction, depalmitoylation, is catalyzed by palmitoyl-protein thioesterases (PPTs), including acyl-protein thioesterases (APT1/2), palmitoyl protein thioesterases (PPT1/2), or alpha/beta hydrolase domain-containing protein 17A/B/C (ABHD17A/B/C). Proteins encoded by several oncogenes and tumor suppressors are modified by palmitoylation, which enhances the hydrophobicity of specific protein subdomains, and can confer changes in protein stability, membrane localization, protein-protein interaction, and signal transduction. The importance for protein palmitoylation in tumorigenesis has just started to be elucidated in the past decade; palmitoylation appears to affect key aspects of cancer, including cancer cell proliferation and survival, cell invasion and metastasis, and antitumor immunity. Here we review the current literature on protein palmitoylation in the various cancer types, and discuss the potential of targeting of palmitoylation enzymes or palmitoylated proteins for tumor treatment.

Claudins as biomarkers of differential diagnosis and prognosis of tumors

Claudins are a superfamily of transmembrane proteins, the optimal expression and localization of which are important for the normal physiological function of the epithelium and any imbalance may have pathological consequences. Not only insufficient but also excessive production of claudins in cancer cells, as well as their aberrant localization, equally manifest the formation of a malignant phenotype. Many works are distinguished by contradictory data, which demonstrate the action of the same claudins both in the role of tumor-growth suppressors and promoters in the same cancers. The most important possible causes of significant discrepancies in the results of the works are a considerable variability of sampling and the absence of a consistent approach both to the assessment of the immune reactivity of claudins and to the differential analysis of their subcellular localization. Combined, these drawbacks hinder the histological assessment of the link between claudins and tumor progression. In particular, ambiguous expression of claudins in breast cancer subtypes, revealed by various authors in immunohistochemical analysis, not only fails to facilitate the identification of the claudin-low molecular subtype but rather complicates these efforts. Research into the role of claudins in carcinogenesis has undoubtedly confirmed the potential value of this class of proteins as significant biomarkers in some cancer types; however, the immunohistochemical approach to the assessment of claudins still has limitations, needs standardization, and, to date, has not reached a diagnostic or a prognostic value.

uPAR-expressing melanoma exosomes promote angiogenesis by VE-Cadherin, EGFR and uPAR overexpression and rise of ERK1,2 signaling in endothelial cells

Exosomes (Exos) have been reported to promote pre-metastatic niche formation, proliferation, angiogenesis and metastasis. We have investigated the role of uPAR in melanoma cell lines-derived Exos and their pro-angiogenic effects on human microvascular endothelial cells (HMVECs) and endothelial colony-forming cells (ECFCs). Melanoma Exos were isolated from conditioned media of A375 and M6 cells by differential centrifugation and filtration. Tunable Resistive Pulse Sensing (TRPS) and Nanoparticle tracking analysis were performed to analyze dimension and concentration of Exos. The CRISPR–Cas 9 technology was exploited to obtain a robust uPAR knockout. uPAR is expressed in melanoma Exos that are internalized by HMVECs and ECFCs, enhancing VE-Cadherin, EGFR and uPAR expression in endothelial cells that undergo a complete angiogenic program, including proliferation, migration and tube formation. uPAR loss reduced the pro-angiogenic effects of melanoma Exos in vitro and in vivo by inhibition of VE-Cadherin, EGFR and uPAR expression and of ERK1,2 signaling in endothelial cells. A similar effect was obtained with a peptide that inhibits uPAR–EGFR interaction and with the EGFR inhibitor Gefitinib, which also inhibited melanoma Exos-dependent EGFR phosphorylation. This study suggests that uPAR is required for the pro-angiogenic activity of melanoma Exos. We propose the identification of uPAR-expressing Exos as a potentially useful biomarker for assessing pro-angiogenic propensity and eventually monitoring the response to treatment in metastatic melanoma patients.

Role of tight junctions in the epithelial-to-mesenchymal transition of cancer cells

The epithelial-mesenchymal transition (EMT) is an essential step in cancer progression. Epithelial cells possess several types of cell-cell junctions, and tight junctions are known to play important roles in maintaining the epithelial program. EMT is characterized by a loss of epithelial markers, including E-cadherin and tight junction proteins. Somewhat surprisingly, the evidence is accumulating that upregulated expression of tight junction proteins plays an important role in the EMT of cancer cells. Tight junctions have distinct tissue-specific and cancer-specific regulatory mechanisms, enabling them to play different roles in EMT. Tight junctions and related signaling pathways are attractive targets for cancer treatments; signal transduction inhibitors and monoclonal antibodies for tight junction proteins may be used to suppress EMT, invasion, and metastasis. Here we review the role of bicellular and tricellular tight junction proteins during EMT. Further investigation of regulatory mechanisms of tight junctions during EMT in cancer cells will inform the development of biomarkers for predicting prognosis as well as novel therapies.

ZDHHC12-mediated claudin-3 S-palmitoylation determines ovarian cancer progression

The membrane protein claudin-3 (CLDN3) is critical for the formation and maintenance of tight junction and its high expression has been implicated in dictating malignant progression in various cancers. However, the post-translational modification of CLDN3 and its biological function remains poorly understood. Here, we report that CLDN3 is positively correlated with ovarian cancer progression both in vitro and in vivo. Of interest, CLDN3 undergoes S-palmitoylation on three juxtamembrane cysteine residues, which contribute to the accurate plasma membrane localization and protein stability of CLDN3. Moreover, the deprivation of S-palmitoylation in CLDN3 significantly abolishes its tumorigenic promotion effect in ovarian cancer cells. By utilizing the co-immunoprecipitation assay, we further identify ZDHHC12 as a CLDN3-targating palmitoyltransferase from 23 ZDHHC family proteins. Furthermore, the knockdown of ZDHHC12 also significantly inhibits CLDN3 accurate membrane localization, protein stability and ovarian cancer cells tumorigenesis. Thus, our work reveals S-palmitoylation as a novel regulatory mechanism that modulates CLDN3 function, which implies that targeting ZDHHC12-mediated CLDN3 S-palmitoylation might be a potential strategy for ovarian cancer therapy.

A Novel Model of Cancer Drug Resistance: Oncosomal Release of Cytotoxic and Antibody-Based Drugs

Extracellular vesicles (EVs), such as exosomes or oncosomes, often carry oncogenic molecules derived from tumor cells. In addition, accumulating evidence indicates that tumor cells can eject anti-cancer drugs such as chemotherapeutics and targeted drugs within EVs, a novel mechanism of drug resistance. The EV-releasing drug resistance phenotype is often coupled with cellular dedifferentiation and transformation in cells undergoing epithelial-mesenchymal transition (EMT), and the adoption of a cancer stem cell phenotype. The release of EVs is also involved in immunosuppression. Herein, we address different aspects by which EVs modulate the tumor microenvironment to become resistant to anticancer and antibody-based drugs, as well as the concept of the resistance-associated secretory phenotype (RASP).

Distinct Origin of Claudin7 in Early Tumor Endosomes Affects Exosome Assembly

Microvesicles are the body's most powerful intercellular communication system and cancer-initiating cell microvesicles (CIC-TEX) reprogram Non-CIC towards fortified malignancy. Claudin7, a CIC-biomarker in gastrointestinal tumors, is recovered in TEX. Recent evidence suggesting individual cells delivering distinct microvesicles became of particular interest for claudin7, which is part of tight junctions (TJ) and glycolipid-enriched membrane domains (GEM), GEM-located claudin7 is palmitoylated. This offered the unique possibility of exploring the contribution of a CIC marker and its origin from distinct membrane domains on CIC-TEX biogenesis and activities. Proteome and miRNA analysis of wild-type, claudin7-knockdown and a rescue with claudin7 harboring a mutated palmitoylation site (mP) of a rat pancreatic and a human colon cancer line uncovered significant, only partly overlapping contributions of palmitoylated and non-palmitoylated claudin7 to TEX composition. Palmitoylated claudin7 facilitates GEM-integrated plasma membrane and associated signaling molecule recruitment; non-palmitoylated claudin7 supports recruitment of trafficking components, proteins engaged in fatty acid metabolism and TJ proteins into TEX. Claudin7mP also assists TEX recovery of selected miRNA. Thus, distinctly located claudin7 affects CIC-TEX composition and TJ-derived cld7 might play a unique role in equipping CIC-TEX with transporters and lipid metabolism-regulating molecules, awareness of distinct TEX populations being crucial facing therapeutic translation.

Exosomes, metastases, and the miracle of cancer stem cell markers

Cancer-initiating cells (CIC) are the driving force in tumor progression. There is strong evidence that CIC fulfill this task via exosomes (TEX), which modulate and reprogram stroma, nontransformed cells, and non-CIC. Characterization of CIC, besides others, builds on expression of CIC markers, many of which are known as metastasis-associated molecules. We here discuss that the linkage between CIC/CIC-TEX and metastasis-associated molecules is not fortuitously, but relies on the contribution of these markers to TEX biogenesis including loading and TEX target interactions. In addition, CIC markers contribute to TEX binding- and uptake-promoted activation of signaling cascades, transcription initiation, and translational control. Our point of view will be outlined for pancreas and colon CIC highly expressing CD44v6, Tspan8, EPCAM, claudin7, and LGR5, which distinctly but coordinately contribute to tumor progression. Despite overwhelming progress in unraveling the metastatic cascade and the multiple tasks taken over by CIC-TEX, there remains a considerable gap in linking CIC biomarkers, TEX, and TEX-initiated target modulation with metastasis. We will try to outline possible bridges, which could allow depicting pathways for new and expectedly powerful therapeutic interference with tumor progression.

Claudin7-dependent exosome-promoted reprogramming of nonmetastasizing tumor cells

Claudin7 (cld7) is a cancer-initiating cell (CIC) marker in gastrointestinal tumors, a cld7-knockdown (kd) being accompanied by loss of tumor progression. Tumor exosomes (TEX) restoring CIC activities, we explored the contribution of cld7. This became particularly interesting, as tight junction (TJ)- and glycolipid-enriched membrane domain (GEM)-derived cld7 is recruited into distinct TEX. TEXs were derived from CIC or cld7kd cells of a rat pancreatic and a human colon cancer line. TEX derived from pancreatic cancer cld7kd cells rescued with palmitoylation site-deficient cld7 (cld7mP) allowed selectively evaluating the contribution of GEM-derived TEX, only palmitoylated cld7 being integrated into GEM. Cld7 CIC-TEX promoted tumor cell dissemination and metastatic growth without a major impact on proliferation, apoptosis resistance and epithelial-mesenchymal transition. Instead, migration, invasion and (lymph)angiogenesis were strongly supported, only migration being selectively fostered by GEM-derived cld7 TEX. CIC-TEX coculture of cld7kd cells uncovered significant changes in the cld7kd cell protein and miRNA profiles. However, changes did not correspond to the CIC-TEX profile, CIC-TEX rather initiating integrin, protease and RTK, particularly lymphangiogenic receptor activation. CIC-TEX preferentially rescuing cld7kd-associated defects in signal transduction was backed up by an RTK inhibitor neutralizing the impact of CIC-TEX on tumor progression. In conclusion, cld7 contributes to selective steps of the metastatic cascade. Defects of cld7kd and cld7mP cells in migration, invasion and (lymph)angiogenesis are effaced by CIC-TEX that act by signaling cascade activation. Accordingly, RTK inhibitors are an efficient therapeutic defeating CIC-TEX.

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.

Claudin-7 downregulation induces metastasis and invasion in colorectal cancer via the promotion of epithelial-mesenchymal transition. Biochem Biophys Res Commun. 2019;508:797-804. [PMID: 30528239 DOI: 10.1016/j.bbrc.2018.10.049]

The dysregulation of the tight junctions (TJs) protein claudin-7 is closely related to the development and metastasis of colorectal cancer (CRC). The aim of this study was to investigate the expression of claudin-7 and characterize the relationship between claudin-7 expression and epithelial-mesenchymal transition (EMT) in CRC. In this study, the expression of claudin-7, E-cadherin, vimentin and snail-1 was detected by immunohistochemistry (IHC) in a set of 80 CRC specimens comprising 20 specimens each of well-differentiated, moderately differentiated, poorly differentiated and liver metastases tissues. The correlation between claudin-7 and EMT-related proteins in the stably transfected claudin-7 knockdown HCT116 cell line was analyzed by IHC, immunofluorescence (IF), Western blotting (WB) and nude mouse xenograft models. The results revealed that the expression of claudin-7 was downregulated as CRC tissue differentiation grade decreased, and that low claudin-7 expression corresponded to the downregulation of E-cadherin (r = 0.725, p < 0.001) and upregulation of vimentin (r = -0.376, p = 0.001) and snail-1 (r = -0.599, p < 0.001). Additionally, in the claudin-7 knockdown HCT116 cell line, the staining intensity and expression of E-cadherin was decreased, while the immunoreactivity and expression of vimentin and snail-1 was increased. Futhermore, the result of tumor formation experiment was consistent with CRC tissues. In conclusion, the expression of claudin-7 in CRC is downregulated as differentiation grade decreases. Claudin-7 downregulation may promote the invasion and metastasis of CRC by regulating EMT. Our results provide new perspectives for a potential therapeutic target for CRC.

Therapeutic Targeting Cancer-Initiating Cell Markers by Exosome miRNA: Efficacy and Functional Consequences Exemplified for claudin7 and EpCAM

AIM: Transfer of exosomes (Exo) miRNA was described interfering with tumor progression. We here explored for claudin7 (cld7) and EpCAM (EpC), cancer-initiating-cell markers in colorectal and pancreatic cancer, the efficacy of Exo loading with miRNA and miRNA transfer. METHODS: Exo were collected from nontransformed mouse (NIH3T3) and rat lung fibroblasts (rFb), which were transfected with Tspan8 cDNA (NIH3T3-Tspan8, rFb-Tspan8). Exo were loaded by electroporation with miRNA. The transfer of Exo-miRNA was evaluated in vitro and in vivo in a rat pancreatic (ASML) and a human colon (SW948) cancer line. RESULTS: NIH3T3-Tspan8- or rFb-Tspan8-Exo were efficiently loaded with cld7- or EpC-miRNA. Exo targeting in vivo was strongly improved by tailoring with Tspan8. Exo-miRNA transfer into tumor targets promoted cld7, respectively, EpC downregulation by 33%-60%. Cld7 silencing was accompanied by reduced expression of additional cancer-initiating cell markers and NOTCH. EpC silencing reduced vimentin, N-cadherin, and Nanog expression. The Exo-miRNA transfer affected anchorage-independent growth, motility, and invasion. CONCLUSIONS: Exo are efficiently loaded with miRNA, miRNA-delivery being supported by Exo tailoring. Partial cld7 and EpC silencing by Exo miRNA affects metastasis-promoting tumor cell activities. The findings suggest miRNA loading of tailored Exo as an easy approachable and efficient adjuvant therapy.

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.

Palmitoylation is a post-translational modification of Alix regulating the membrane organization of exosome-like small extracellular vesicles

BACKGROUND

Virtually all cell types have the capacity to secrete nanometer-sized extracellular vesicles, which have emerged in recent years as potent signal transducers and cell-cell communicators. The multifunctional protein Alix is a bona fide exosomal regulator and skeletal muscle cells can release Alix-positive nano-sized extracellular vesicles, offering a new paradigm for understanding how myofibers communicate within skeletal muscle and with other organs. S-palmitoylation is a reversible lipid post-translational modification, involved in different biological processes, such as the trafficking of membrane proteins, achievement of stable protein conformations, and stabilization of protein interactions.

METHODS

Here, we have used an integrated biochemical-biophysical approach to determine whether S-palmitoylation contributes to the regulation of extracellular vesicle production in skeletal muscle cells.

RESULTS

We ascertained that Alix is S-palmitoylated and that this post-translational modification influences its protein-protein interaction with CD9, a member of the tetraspanin protein family. Furthermore, we showed that the structural organization of the lipid bilayer of the small (nano-sized) extracellular vesicle membrane with altered palmitoylation is qualitatively different compared to mock control vesicles.

CONCLUSIONS

We propose that S-palmitoylation regulates the function of Alix in facilitating the interactions among extracellular vesicle-specific regulators and maintains the proper structural organization of exosome-like extracellular vesicle membranes.

GENERAL SIGNIFICANCE

Beyond its biological relevance, our study also provides the means for a comprehensive structural characterization of EVs.

CD44/CD44v6 a Reliable Companion in Cancer-Initiating Cell Maintenance and Tumor Progression

Metastasis is the leading cause of cancer death, tumor progression proceeding through emigration from the primary tumor, gaining access to the circulation, leaving the circulation, settling in distant organs and growing in the foreign environment. The capacity of a tumor to metastasize relies on a small subpopulation of cells in the primary tumor, so called cancer-initiating cells (CIC). CIC are characterized by sets of markers, mostly membrane anchored adhesion molecules, CD44v6 being the most frequently recovered marker. Knockdown and knockout models accompanied by loss of tumor progression despite unaltered primary tumor growth unraveled that these markers are indispensable for CIC. The unexpected contribution of marker molecules to CIC-related activities prompted research on underlying molecular mechanisms. This review outlines the contribution of CD44, particularly CD44v6 to CIC activities. A first focus is given to the impact of CD44/CD44v6 to inherent CIC features, including the crosstalk with the niche, apoptosis-resistance, and epithelial mesenchymal transition. Following the steps of the metastatic cascade, we report on supporting activities of CD44/CD44v6 in migration and invasion. These CD44/CD44v6 activities rely on the association with membrane-integrated and cytosolic signaling molecules and proteases and transcriptional regulation. They are not restricted to, but most pronounced in CIC and are tightly regulated by feedback loops. Finally, we discuss on the engagement of CD44/CD44v6 in exosome biogenesis, loading and delivery. exosomes being the main acteurs in the long-distance crosstalk of CIC with the host. In brief, by supporting the communication with the niche and promoting apoptosis resistance CD44/CD44v6 plays an important role in CIC maintenance. The multifaceted interplay between CD44/CD44v6, signal transducing molecules and proteases facilitates the metastasizing tumor cell journey through the body. By its engagement in exosome biogenesis CD44/CD44v6 contributes to disseminated tumor cell settlement and growth in distant organs. Thus, CD44/CD44v6 likely is the most central CIC biomarker.

Identification and dynamics of the human ZDHHC16-ZDHHC6 palmitoylation cascade

S-Palmitoylation is the only reversible post-translational lipid modification. Knowledge about the DHHC palmitoyltransferase family is still limited. Here we show that human ZDHHC6, which modifies key proteins of the endoplasmic reticulum, is controlled by an upstream palmitoyltransferase, ZDHHC16, revealing the first palmitoylation cascade. The combination of site specific mutagenesis of the three ZDHHC6 palmitoylation sites, experimental determination of kinetic parameters and data-driven mathematical modelling allowed us to obtain detailed information on the eight differentially palmitoylated ZDHHC6 species. We found that species rapidly interconvert through the action of ZDHHC16 and the Acyl Protein Thioesterase APT2, that each species varies in terms of turnover rate and activity, altogether allowing the cell to robustly tune its ZDHHC6 activity.

Developmental Expression of Claudins in the Mammary Gland

Claudins are a large family of membrane proteins whose classic function is to regulate the permeability of tight junctions in epithelia. They are tetraspanins, with four alpha-helices crossing the membrane, two extracellular loops, a short cytoplasmic N-terminus and a longer and more variable C-terminus. The extracellular ends of the helices are known to undergo side-to-side (cis) interactions that allow the formation of claudin polymers in the plane of the membrane. The extracellular loops also engage in head-to-head (trans) interactions thought to mediate the formation of tight junctions. However, claudins are also present in intracellular structures, thought to be vesicles, with less well-characterized functions. Here, we briefly review our current understanding of claudin structure and function followed by an examination of changes in claudin mRNA and protein expression and localization through mammary gland development. Claudins-1, 3, 4, 7, and 8 are the five most prominent members of the claudin family in the mouse mammary gland, with varied abundance and intracellular localization during the different stages of post-pubertal development. Claudin-1 is clearly localized to tight junctions in mammary ducts in non-pregnant non-lactating animals. Cytoplasmic puncta that stain for claudin-7 are present throughout development. During pregnancy claudin-3 is localized both to the tight junction and basolaterally while claudin-4 is found only in sparse puncta. In the lactating mouse both claudin-3 and claudin-8 are localized at the tight junction where they may be important in forming the paracellular barrier. At involution and under challenge by lipopolysaccharide claudins -1, -3, and -4 are significantly upregulated. Claudin-3 is still colocalized with tight junction molecules but is also distributed through the cytoplasm as is claudin-4. These largely descriptive data provide the essential framework for future mechanistic studies of the function and regulation of mammary epithelial cell claudins.

Tracing Cellular Origin of Human Exosomes Using Multiplex Proximity Extension Assays

Extracellular vesicles (EVs) are membrane-coated objects such as exosomes and microvesicles, released by many cell-types. Their presence in body fluids and the variable surface composition and content render them attractive potential biomarkers. The ability to determine their cellular origin could greatly move the field forward. We used multiplex proximity extension assays (PEA) to identify with high specificity and sensitivity the protein profiles of exosomes of different origins, including seven cell lines and two different body fluids. By comparing cells and exosomes, we successfully identified the cells originating the exosomes. Furthermore, by principal component analysis of protein patterns human milk EVs and prostasomes released from prostate acinar cells clustered with cell lines from breast and prostate tissues, respectively. Milk exosomes uniquely expressed CXCL5, MIA, and KLK6, whereas prostasomes carried NKX31, GSTP1, and SRC, highlighting that EVs originating from different origins express distinct proteins. In conclusion, PEA provides a powerful protein screening tool in exosome research, for purposes of identifying the cell source of exosomes, or new biomarkers in diseases such as cancer and inflammation.

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

Claudins (CLDNs), the major integral membrane proteins at tight junction, play critical roles in apical cell-to-cell adhesion, maintenance of epithelial polarity, and formation of impermeable barriers between epithelial cells.We investigated in this study the expression of CLDNs- Claudin1 (CLDN1) and Claudin7 (CLDN7), and their relation to tumor progression in nasopharyngeal cancer (NPC). CLDN7, rather than CLDN1, showed higher expression in both undifferentiated tumor tissue and the poorly differentiated CNE2 cells, compared with differentiated tissue and the highly differentiated CNE1 cells. Furthermore, knockdown of CLDN7 dramatically inhibited the metastasis and invasion of CNE2 cells suggesting that CLDN7 could act as a biomarker for NPC metastasis.Cycling hypoxia could induce significant changes in CLDN1 and CLDN7 expression in NPC cells. Genetics analysis demonstrated that CLDN1/CLDN7 were not only regulated directly by HIF1a but also affected each other through a feedback mechanism. CLDN7 acted as a bridge to promote HIF1a-induced P18 expression and cell differentiation. Taken together, our results provide evidence that adjusting the oxygenation time and cycles in NPC might be an effective method to prevent / delay the metastasis of poorly differentiated NPC cells.