Expression of occludin in human rectal carcinoid tumours as a possible marker for glandular differentiation

Polarity proteins as regulators of cell junction complexes: implications for breast cancer

The epithelium of multicellular organisms possesses a well-defined architecture, referred to as polarity that coordinates the regulation of essential cell features. Polarity proteins are intimately linked to the protein complexes that make the tight, adherens and gap junctions; they contribute to the proper localization and assembly of these cell-cell junctions within cells and consequently to functional tissue organization. The establishment of cell-cell junctions and polarity are both implicated in the regulation of epithelial modifications in normal and cancer situations. Uncovering the mechanisms through which cell-cell junctions and epithelial polarization are established and how their interaction with the microenvironment directs cell and tissue organization has opened new venues for the development of cancer therapies. In this review, we focus on the breast epithelium to highlight how polarity and cell-cell junction proteins interact together in normal and cancerous contexts to regulate major cellular mechanisms such as migration. The impact of these proteins on epigenetic mechanisms responsible for resetting cells toward oncogenesis is discussed in light of increasing evidence that tissue polarity modulates chromatin function. Finally, we give an overview of recent breast cancer therapies that target proteins involved in cell-cell junctions.

Tight junctions: a barrier to the initiation and progression of breast cancer?

Breast cancer is a complex and heterogeneous disease that arises from epithelial cells lining the breast ducts and lobules. Correct adhesion between adjacent epithelial cells is important in determining the normal structure and function of epithelial tissues, and there is accumulating evidence that dysregulated cell-cell adhesion is associated with many cancers. This review will focus on one cell-cell adhesion complex, the tight junction (TJ), and summarize recent evidence that TJs may participate in breast cancer development or progression. We will first outline the protein composition of TJs and discuss the functions of the TJ complex. Secondly we will examine how alterations in these functions might facilitate breast cancer initiation or progression; by focussing on the regulatory influence of TJs on cell polarity, cell fate and cell migration. Finally we will outline how pharmacological targeting of TJ proteins may be useful in limiting breast cancer progression. Overall we hope to illustrate that the relationship between TJ alterations and breast cancer is a complex one; but that this area offers promise in uncovering fundamental mechanisms linked to breast cancer progression.

Downregulated P1 promoter-driven hepatocyte nuclear factor-4alpha expression in human colorectal carcinoma is a new prognostic factor against liver metastasis

Liver metastases are the most critical prognostic factors for patients with colorectal carcinomas (CRC). It has been reported that the dysregulation of hepatocyte nuclear factor-4alpha (HNF4alpha) expression is linked to the development of CRC, gastric cancer and hepatocellular carcinoma. The purpose of the present paper was to examine the P1 and P2 promoter-driven HNF4alpha (P1 and P2) expression in surgically resected CRC. Immunohistochemically, P1, P2, MUC1 and CD10 expression were evaluated in 63 cases of primary CRC. Positive staining with P1, P2, MUC1 and CD10 antibodies were observed in 37 (59%), 63 (100%), 42 (67%) and 27 (43%) cases, respectively. Loss or decreased P1 expression was observed with respect to the depth of the tumor invasion. The frequency of P1-positive expression in Dukes' C and D tumors was significantly lower than that in Dukes' A and B tumors. There was a relationship between the loss of P1 expression and metachronous liver metastases, and the survival rate of the P1-negative patients without liver metastasis at the time of the primary CRC resection tended to be worse than that of the P1-positive patients. These findings suggest that downregulation of P1 expression is involved in tumor metastasis and a worse prognosis.

Sodium/potasium ATPase (Na+, K+-ATPase) and ouabain/related cardiac glycosides: a new paradigm for development of anti- breast cancer drugs?

Prolonged exposure to 17beta-estradiol (E2) is a key etiological factor for human breast cancer. The biological effects and carcinogenic effects of E2 are mediated via estrogen receptors (ERs), ERalpha and ERbeta. Anti-estrogens, e.g. tamoxifen, and aromatase inhibitors have been used to treat ER-positive breast cancer. While anti-estrogen therapy is initially successful, a major problem is that most tumors develop resistance and the disease ultimately progresses, pointing to the need of developing alternative drugs targeting to other critical targets in breast cancer cells. We have identified that Na+, K+-ATPase, a plasma membrane ion pump, has unique/valuable properties that could be used as a potentially important target for breast cancer treatment: (a) it is a key player of cell adhesion and is involved in cancer progression; (b) it serves as a versatile signal transducer and is a target for a number of hormones including estrogens and (d) its aberrant expression and activity are implicated in the development and progression of breast cancer. There are several lines of evidence indicating that ouabain and related digitalis (the potent inhibitors of Na+, K+-ATPase) possess potent anti-breast cancer activity. While it is not clear how the suggested anti-cancer activity of these drugs work, several observations point to ouabain and digitalis as being potential ER antagonists. We critically reviewed many lines of evidence and postulated a novel concept that Na+, K+-ATPase in combination with ERs could be important targets of anti-breast cancer drugs. Modulators, e.g. ouabain and related digitalis could be useful to develop valuable anti-breast cancer drugs as both Na+, K+-ATPase inhibitors and ER antagonists.

Changes of occludin expression in intestinal mucosa after burn in rats

In severely burned rats, hyperemia, edema and other pathological injuries occur in the intestinal mucosa. Ultramicroscopically, the microvilli, tight junction and organelles are disrupted. Occludin is a functional component of tight junctions. The purpose of the present study is to investigate changes of occludin expression, and to further elucidate the relationship between occludin expression and ultrastructure damage. The fluorescence intensity of occludin was detected in intestinal wall by the method of immunofluorescence histochemistry and confocal laser scanning microscopy (CLSM). Expression of occludin and its mRNA were determined by western blotting and RT-PCR, respectively. Changes of intestinal mucosa ultrastructure were observed by TEM. The results showed that fluorescence intensity of occludin at 3PBH was enhanced, higher than that of the control group, being 80.77+/-8.38 and 72.86+/-4.74, respectively, and reached a peak at 12PBH (116.14+/-6.89). The expression levels of occludin at 3PBH and 6PBH were 1.21+/-0.02 and 1.53+/-0.14 times that of the control group, respectively, and there were significant differences (P<0.01) between 3PBH group and 6PBH group and control group. The levels of occludin mRNA were also enhanced. At 12PBH, the level reached a peak (P<0.01), being 2.00+/-0.24 times that of the control group. Coincidently, the structure of the tight junction between epithelial cells was disrupted on a large scale under TEM. We speculate that up-regulation of epithelial occludin may play a role in enhancing paracellular permeability and be related to the damage to the tight junction.

Expression of occludin, a tight-junction-associated protein, in human lung carcinomas

Occludin is a tight-junction-associated transmembrane protein, and previous observations suggested that occludin might play a crucial role in the formation and maintenance of organized tubular structures. Based on these observations, we explored the possible role of occludin immunostaining in the diagnosis of lung carcinomas. A total of 68 lung carcinomas and surrounding normal lung tissues were studied. A formalin-fixed, paraffin-embedded section from each tumor was stained with a new anti-occludin monoclonal antibody raised in our laboratory. In normal lung tissues, the anti-occludin antibody strongly stained the apicoluminal borders of the bronchial/bronchiolar epithelia and bronchial glands as a dot or short line. The antibody also stained the intercellular borders of alveolar epithelia. In cancer cells that faced lumina of all adenocarcinomas, regardless of grade, including bronchioloalveolar carcinomas, occludin showed an expression pattern identical to that of the normal bronchial and alveolar epithelia. Occludin reactivity was not noted in any cases of squamous cell carcinoma, large cell carcinoma, small cell carcinoma, or large cell neuroendocrine carcinoma. The results of the present study suggest that occludin can serve as an immunohistochemical indicator of the "true" glandular differentiation that forms tubulo-papillary structures in human lung carcinoma tissues.