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BACKGROUND: Yes Associated Protein (YAP) has been implicated in the control of organ size by regulating cell proliferation and survival. YAP is a transcriptional coactivator that controls cellular responses through interaction with TEAD transcription factors in the nucleus, while its transcriptional functions are inhibited by phosphorylation-dependent translocation to the cytosol. YAP overexpression has been associated with different types of cancer, such as lung, skin, prostate, ovary and liver cancer. Recently, YAP was linked to E-cadherin-dependent regulation of contact inhibition in breast cancer cells. RESULTS: In this study we examined YAP protein expression and cellular localization in 237 cases of human invasive breast cancer by immunohistochemistry and related its expression to clinicopathological features and E-cadherin expression. We observed that invasive lobular carcinoma is characterized by higher expression levels of both nuclear and cytosolic YAP (p < 0.001). Nuclear YAP expression did not associate with other variables such as lymph node involvement, tumor grade, tumor size, mitotic activity or the molecular sub-types of invasive breast cancer. We observed that high nuclear and cytosolic YAP expression are associated with the E-cadherin deficient breast cancer subtype ILC (p < 0.001) and cell lines derived from human breast cancers and conditional mouse models of human lobular breast cancer. CONCLUSIONS: Since our data indicate that nuclear YAP localization is more common in breast cancers lacking functional adherens junctions, it suggests that YAP-mediated transcription may be involved in the development and progression of invasive lobular breast cancer.
Vlug et al. (Wed,) studied this question.