The overexpression and altered localization of the atypical protein kinase C λ/ι in breast cancer correlates with the pathologic type of these tumors

SummaryBreast cancer is one of the common malignant diseases among women in Japan as well as in western countries, and its incidence continues to increase. Normal mammary duct epithelial cells exhibit a well-organized apicobasal polarity, which forms the basis for their specific structure and function. Although the loss of epithelial cell polarity is one of the major changes that occur during the progression of tumor cells, including breast cancer, the underlying molecular mechanisms for this, as well as their relationship to other changes such as increased proliferation and metastasis, remain to be elucidated. The atypical protein kinase C λ/ι (aPKCλ/ι) is involved in several signal transduction pathways, including the establishment of epithelial cell polarity. In this study we evaluated the expression and localization of aPKCλ/ι in breast cancer by immunohistochemistry and compared our findings with the clinicopathologic factors associated with the tumor specimens. We detected aPKCλ/ι protein overexpression in 88 of the 110 breast cancer cases (80.0%) under study, expect for decreased expression in a few cases. The immunoreactivity of aPKCλ/ι was generally weak in ductal carcinoma in situ, but strong in invasive ductal carcinoma (IDC; P = .022). The correlation between apical or cytoplasmic aPKCλ/ι localization and tumor pathologic type (ie, atypical ductal hyperplasia, ductal carcinoma in situ. or IDC) was also demonstrated (P < .001). These results thus indicate that the normal apicobasal polarity is lost upon the progression of a breast lesion to IDC. This is also the first evidence to show aPKCλ/ι overexpression in breast cancer and demonstrates that its localization is associated with the trend of pathologic type of the tumor.