The role of Par6 in apoptosis is suggested to be due to the activation of aPKC by Par6 [114]. 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. == 1. Introduction == Breast cancer is the most common form of cancer among women in North Oxybutynin America and the majority of European nations. Each year, it is diagnosed in an estimated 1 million women worldwide, and is the cause of death of over 400 000 [1]. The incidence of breast cancer increases with age and doubles every 10 years until the menopause, supporting a link with hormonal status [2]. Specific life events associated with an enhanced breast cancer risk include reproductive factors, nulliparity, radiation exposure, hormonal status, obesity, family history, and many others [3,4]. Breast cancer is a heterogeneous disease in which genetic and environmental factors interact to initiate carcinogenesis. However, 10% of all breast cancer cases have a strong hereditary component in which half carry a deleterious mutation in the high penetrance genes BRCA1 or BRCA2. These account for over 50% of familial breast cancer cases and confer a lifetime risk of 6080% [5]. In its simplest forms, breast cancer can be subclassified into preinvasive and invasive disease categories. Neoplastic conversion to invasive cancer likely occurs sometime during the preinvasive histological phases of usual hyperplasia, atypical hyperplasia, and ductal carcinoma in situ (DCIS) [611]. One hypothesis suggests the existence of genetically distinct subgroups of DCIS, only some of which subsequently progress to invasive ductal carcinoma (IDC) [1214]. An alternate theory proposes that DCIS progresses from low to high grades and then to invasive cancer with progressive accumulation of genomic changes. However, the large extent to which the genome is altered in DCIS indicates that genomic Oxybutynin instability most likely precedes phenotypic evidence of invasion, and highlights Oxybutynin the importance of environmental components on the development of invasive cancer [6]. Recent data have shown significant reductions in the mortality rates of breast cancer, which have been mainly attributed to improved screening techniques, improved surgical and radiotherapy interventions and also the utilization of traditional chemotherapies in a more efficacious manner. Large-scale translational research studies have also identified many important new biomarkers predictive of poor prognosis in breast cancer patients [1517]. However, much remains to be understood about the development and progression of breast cancer. Our review will address the contribution of altered epithelial cell-cell adhesion to the development and progression of breast cancer, with particular emphasis on the role of the tight junction (TJ) adhesion complex in these processes. == 2. TJs and KIAA1557 Physiological Cell-Cell Adhesion == Cell-cell adhesion is necessary for the assembly of coherent sheets of barrier-forming epithelial cells that line the breast ducts and lobules. However cell-cell contacts are far from being static structures which maintain barriers by simply holding cells together. In fact cell-cell contacts undergo constant remodelling to allow the extrusion of apoptotic cells as well as the incorporation of newly differentiated epithelial cells, derived from progenitor cells, without loss of barrier function [18]. Cell-cell contacts must also be remodelled depending on the developmental stage of the breast, whether in response to increased proliferative demands of puberty and pregnancy, increased differentiation during lactation, or increased apoptosis in conjunction with gland remodelling during involution [19]. Finally, during wound healing, epithelial cells can undergo coordinated movement and proliferation to bridge the wound, and establish new cell-cell contacts with epithelial cells from the opposing side of the wound [20]. Epithelial cell-cell contacts consist of three main adhesive structures: tight junctions (TJs), adherens junctions and desmosomes, as well as gap junctions for cell-cell communication (Figure 1). In polarized epithelial cells the tight junction and adherens junction are asymmetrically.
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