Reexpression of the TJ protein CLDN1 induces apoptosis in breast tumor spheroids

Abstract

Solid tumor development is complex and encompasses alterations in a variety of physiologic processes such as enhanced proliferative capacity, resistance toward apoptosis, metastatic potential and escape from immunologic detection. However, beside these diverse and multiple changes occurring in tumors, cellular accessibility of nutrients and growth factors must be present continuously. To ensure early neoplastic survival, the onset of neovascularization is one of the most significant hallmarks during tumor progression. 1,2 One rate-limiting step of growing tumors may be the diffusion of molecules into the paracellular space. Therefore, it has been hypothesized that the presence of intact functional tight junctions (TJs) in tumors of epithelial origin might limit the optimal supply of biomolecules necessary for cell growth and survival. 3,4 In fact, several reports provide evidence for the relevance of functional loss of TJs in developing human tumors in vivo. Diminished TJ formation has been reported for hepatocellular carcinoma, 5 thyroid tumors 6 and colon carcinoma. 7 In experimental animal models, alterations of TJs have been observed in canine bladder carcinoma 8 and murine mammary carcinoma. 9 Furthermore, the loss of TJ-associated molecules such as ZO-1 has been correlated with tumor progression. 10,11 Finally, the relevance of TJ complexes in tumorigenesis is highlighted by the fact that loss of TJ-associated tumor suppressor genes also results in tumor formation in imaginal disks of Drosophila. 12,13 TJs constitute the barrier of paracellular flux in epithelia and control the permeation of molecules between the apical lumen and basolateral face. Identification of the multiple proteins that constitute the epithelia-or tissue-specific TJs have only recently been elucidated. 14 -19 One of the first molecules associated with the TJ, occludin, was identified as a requisite integral protein. 20 However, in the murine occludin knockout TJ-like structures were still present. The 4-transmembrane proteins claudin-1 and -2 were then shown to reconstitute the TJ. 21 It has been suggested that claudin-1 and -2 might recruit occludin to TJs, 22 and both claudins have been shown to interact with intracellular TJ-associated proteins from the membrane-associated guanylate kinase (MAGUK) family. Sequence and similarity analysis have revealed the existence of a claudin family with up to more than 20 proteins, 15,17,23 but for only a few members of the claudin family has a specialized function been identified. 24 -30 In parallel with the identification of the murine claudin-1 and -2, we identified the human counterpart of the murine claudin-1, previously called SEMP1, in a differential display approach comparing isogenic exponentially growing, nontumorigenic and senescent human epithelial breast cells. 26 The human claudin-1 (CLDN1), which shares a 98% amino acid homology to the murine claudin-1, is expressed in many human tissues containing epithelium, such as mammary gland. Of particular interest in this regard is that...

Claudin-1 and claudin-5 expression patterns differentiate lung squamous cell carcinomas from adenocarcinomas

“…27 Here we showed that CLDN-1 expression is high in lung squamous cell carcinomas (both by protein detection and transcript quantification), but reduced or undetected in adenocarcinomas. Interestingly, an increase in CLDN-1 expression was observed in keratinized regions of squamous cell carcinoma of the epidermis, 14 and in colon cancers, 28 whereas a decrease or loss of expression was reported in breast cancer cell lines 29,30 and tumors. 31 These findings suggest that a squamous cell tumor phenotype is more likely to be correlated with high Tight junction proteins in human lung carcinomas S Paschoud et al CLDN-1 expression, whereas tumors with glandular components are more likely to lose CLDN-1 expression.…”

Claudin-1 Has Tumor Suppressive Activity and Is a Direct Target of RUNX3 in Gastric Epithelial Cells

“…Reports on the expression of claudin family in other types of cancer are also controversial. In breast cancer, decreased expression of claudin-1 and -7 was reported 41 , but increased claudin-1 and -4 expression in the basal-like subtype 42 and increased claudin-4 expressin in poor prognosis and high tumor grade 43 were also published. In colon cancer, while decreased expression of claudin-1 was reported to be associated with higher tumor grade 44 , an opposite conclusion has also been reported 45 In the present study, we found that claudin-1 is a direct target of RUNX3.…”

Discovery, design, and synthesis of anti-metastatic lead phenylmethylene hydantoins inspired by marine natural products

“…Spheroid disaggregation assay was selected to asses this activity. 29,[32][33][34] Since tumor cells are generally released in clumps, attach to the preferred extracellular matrix (ECM), and then radially migrate in all directions, spheroid disaggregation assay was considered a better in vitro model of tumor metastasis compared to the linear invasion assays. 29,[32][33][34] To avoid repeated addition of exogenous CT during long incubation period of 48 h, PC-3M-CT+ cells were used because they secrete large amounts of CT and have CTR.…”

“…29,30,33,34 In brief, 5 Â 10 4 /mL cells in RPMI 1640 serum-free medium were placed on 96-well low-attachment tissue culture plates. The plates were rocked on a gyrorotatory shaker in a CO 2 incubator at 37°C for 2 days, at the end of which the spheroids measuring 150-300 lm in diameter ($4 Â 10 4 cells/spheroid) were formed.…”