Am J Cancer Res. 2012;2(5):478-91. Epub 2012 Aug 20.
Dysregulation of mechanisms that govern the control of epithelial cell polarity, morphology and plasticity are emerging as key processes in tumor progression. In this study we report amplification and overexpression of PAR6B, an essential component in epithelial cell tight junction (TJ) formation and maintenance of apico-basal polarity, in breast cancer cell lines. Analysis of chromosome 20q13.13 in 11 breast cancer cell lines by fluorescence in situ hybridization (FISH) identified a novel small amplicon centered at PARD6B in 5 cell lines, with copy number ranging from 7 to 27. The presence of the PARD6B amplicon correlated with PARD6B transcript and PAR6B protein abundance. Expression of related isoforms PARD6A and PARD6G were detectable at significantly lower levels. PARD6B overexpression correlated with TJ network formation in cultured cell monolayers. SiRNA-mediated inhibition of PAR6B in MCF7 resulted in loss of TJ assembly and membrane localization of atypical PKCζ (aPKC), but did not affect adherens junction formation. SiRNA-mediated inhibition of CDC42 in MCF7 also resulted in loss of TJ networks, confirming the requirement of a complete PAR6-aPKC-CDC42-PAR3 complex to activate and stabilize TJs. Immunohistochemical analysis of PAR6B expression on breast tumor microarrays indicated exquisite epithelial cell-specificity. Few quantitative differences in staining were observed between normal epithelium and adjacent tumor margins. However staining appeared reduced and cytoplasmic in more poorly differentiated tumors. We propose that quantitative imbalances in the components of pathways governing normal epithelial cell polarity arising from gain or loss of function may radically alter epithelial cell architecture and contribute to tumor progression.
调控上皮细胞极性、形态和可塑性的机制失调，正在成为肿瘤进展的关键过程。在这项研究中，我们报告了 PAR6B 的扩增和过表达，PAR6B 是上皮细胞紧密连接（TJ）形成和顶端-基底极性维持的必需组成部分，在乳腺癌细胞系中。通过荧光原位杂交（FISH）分析 11 个乳腺癌细胞系中的 20q13.13 染色体，在 5 个细胞系中发现了一个位于 PARD6B 中心的新的小扩增子，拷贝数从 7 到 27 不等。PARD6B 扩增子的存在与 PARD6B 转录本和 PAR6B 蛋白丰度相关。相关同工型 PARD6A 和 PARD6G 的表达水平明显较低。PARD6B 的过表达与培养细胞单层中 TJ 网络的形成相关。MCF7 中 PAR6B 的 siRNA 介导抑制导致 TJ 组装丧失和非典型 PKCζ（aPKC）的膜定位丧失，但不影响黏着连接的形成。MCF7 中 CDC42 的 siRNA 介导抑制也导致 TJ 网络的丧失，证实了完整的 PAR6-aPKC-CDC42-PAR3 复合物对于激活和稳定 TJ 的必要性。在乳腺癌肿瘤微阵列上对 PAR6B 表达进行免疫组织化学分析表明，其具有极好的上皮细胞特异性。在正常上皮组织和相邻肿瘤边缘之间观察到染色的定量差异很小。然而，在分化较差的肿瘤中，染色似乎减少且位于细胞质中。我们提出，由于功能获得或丧失，调控正常上皮细胞极性的途径的组分出现定量失衡，可能会从根本上改变上皮细胞的结构，并促进肿瘤的进展。
