BackgroundDefects in tight junctions, gate-keepers of the integrity of the epidermal barrier function, are known to contribute to cancer development. As such, enhancing our understanding of how the expression of proteins involved in these junctions is regulated in cancer, remains a priority. Although the expression of one of these proteins, claudin 1, is down regulated in most invasive human breast cancers (HBC), we have recently shown that high levels of claudin 1, characterized tumors belonging to the very aggressive basal-like breast cancer (BLBC) subtype. In these tumors, the claudin 1 protein, usually localized in the cell membrane, is often mislocalized to the cytoplasm.MethodsTo examine the clinical relevance of this observation, we have generated and analyzed an invasive HBC tissue microarray consisting of 151 breast tumor samples; 79 of which presented a basal-like phenotype (i.e. ER-ve, PR-ve HER2-ve, CK5/6 or EGFR+ve). We also interrogated the outcome of claudin 1 knockdown in a human BLBC cell line, BT-20.ResultsImmunohistochemical analysis of this patient cohort revealed a significant association between high claudin 1 expression and BLBCs in women 55 years of age and older. Interestingly, no significant association was found between claudin 1 and nodal involvement, tumor grade or tumor size. Regression analysis however, showed a significant positive association between claudin 1 and claudin 4, even though claudin 4 did not significantly correlate with patient age. Claudin 1 knockdown in BT-20 cells resulted in decreased cell migration. It also significantly altered the expression of several genes involved in epithelial-mesenchymal-transition (EMT); in particular, SERPINE 1 (PAI1) and SSP1 (osteopontin), known to inhibit EMT and cancer cell migration. Conversely, genes known to maintain EMT through their interaction, SNAIL2, TCF4 and FOXC2 were significantly down regulated.ConclusionsThe association of high claudin 1 protein levels observed in tumors derived from older women with BLBC, suggests that claudin 1 has the potential to serve as a marker which can identify a specific subgroup of patients within the BLBC subtype and thus, further contribute to the characterization of these ill-defined breast cancers. More importantly, our studies strongly suggest that claudin 1 directly participates in promoting breast cancer progression, possibly through the alteration of expression of EMT genes.

Poxviridae is a diverse family of large dsDNA viruses (130 to 300 kb) which replicate exclusively in the cytoplasm of infected cells and exhibit a varied host range (1). Some members are specific to a single host, such as variola virus, the causative agent of smallpox, while others, such as vaccinia virus, display a broad host range. Poxviruses encode a number of immunomodulatory proteins, e.g., host range proteins (2). Orthopoxviruses encode a number of host range genes, such as SPI-1, K1L, C7L, p28/N1R, B5R, K3L, and E3L, the alteration or deletion of which restricts the virus replication in specific cell lines (3). These host range genes display varied restrictions and biological functions. For example, SPI-1 is required for vaccinia virus replication in PK15 and A549 cells and in mice (4, 5). K1L, an ankyrin repeat-containing protein which inhibits IkB-␣ degradation and interferon (IFN)-stimulated effectors, is required for replication in RK13 cells (6). A double deletion of C7L and K1L leads to restriction of the virus replication in PK1, RK13, and multiple human cell lines, while C7L deletion alone suppresses apoptosis and limits replication in hamster Dede cells (7). P28/N1R, an E3-RING finger ubiquitin ligase involved in protein degradation and apoptosis suppression, is required for replication in mouse macrophage (8, 9), while B5R, a membrane glycoprotein, activates Src, allowing growth in VERO, CEF, PK15, and quail (QT-6) cells (10).The most studied vaccinia host range gene is E3L. E3 protein is expressed early in the virus replication cycle and is known to suppress multiple innate immune pathways (3,11,12). E3 protein possesses biochemical capacities to bind Z-form DNA via the Z-DNA binding domain (ZBD) toward the N terminus and to bind to dsRNA through the C-terminal dsRNA binding domain (DRBD) (13,14). Since the best characterized biological functions of vaccinia virus E3 protein, such as host range function and inhibition of innate immune responses (e.g., cytokine expression, apoptosis and interferon-induced antiviral activity), all are mediated primarily via the DRBD region of E3 protein (15-17), generally it has been believed that E3 protein functions through seques-