ErbB2+ human breast cancer is a major clinical problem. Prior results have suggested that tetraspanin CD151 might contribute to ErbB2-driven breast cancer growth, survival, and metastasis. In other cancer types, CD151 sometimes supports tumor growth and metastasis. However, a definitive test of CD151 effects on de novo breast cancer initiation, growth, and metastasis has not previously been done. We used CD151 gene-deleted mice expressing the MMTV-ErbB2 transgene to show that CD151 strongly supports ErbB2+ mammary tumor initiation and metastasis. Delayed tumor onset (by 70-100 days) in the absence of CD151 was accompanied by reduced survival of mammary epithelial cells and impaired activation of FAK- and MAPK-dependent pathways. Both primary tumors and metastatic nodules showed smooth, regular borders, consistent with a less invasive phenotype. Furthermore, consistent with impaired oncogenesis and decreased metastasis, CD151-targeted MCF-10A/ErbB2 cells showed substantial decreases in three-dimensional colony formation, EGF-stimulated tumor cell motility, invasion, and transendothelial migration. These CD151-dependent functions were largely mediated through α6β4 integrin. Moreover, CD151 ablation substantially prevented PKC- and EGFR/ERK-dependent α6β4 integrin phosphorylation, consistent with retention of epithelial cell polarity and intermediate filament cytoskeletal connections, which helps to explain diminished metastasis. Finally, clinical data analyses revealed a strong correlation between CD151 and ErbB2 expression and metastasis-free survival of breast cancer patients. In conclusion, we provide strong evidence that CD151 collaborates with LB integrins (particularly α6β4 and ErbB2 (and EGFR) receptors to regulate multiple signaling pathways, thereby driving mammary tumor onset, survival, and metastasis. Consequently, CD151 is a useful therapeutic target in malignant ErbB2+ breast cancer.

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Human ovarian cancer is diagnosed in the late, metastatic stages but the underlying mechanisms remain poorly understood. We report a surprising functional link between CD151-α3β1 integrin complexes and the malignancy of serous-type ovarian cancer. Analyses of clinical specimens indicate that CD151 expression is significantly reduced or diminished in 90% of metastatic lesions, while it remains detectable in 58% of primary tumors. These observations suggest a putative tumor-suppressing role of CD151 in ovarian cancer. Indeed, our analyses show that knocking down CD151 or α3 integrin enhances tumor cell proliferation, growth and ascites production in nude mice. These changes are accompanied by impaired cell-cell contacts and aberrant expression of E-cadherin, Mucin 5AC and fibronectin, largely reminiscent of an epithelial to mesenchymal transition (EMT)-like change. Importantly, Slug, a master regulator of EMT, is markedly elevated. Knocking down Slug partially restores CD151-α3β1 integrin complex-dependent suppression of cell proliferation. Moreover, disruption of these adhesion protein complexes is accompanied by a concomitant activation of canonical Wnt signaling, including elevated levels of β-catenin and Axin-2 as well as resistance to the inhibition in β-catenin-dependent transcriptional complexes. Together, our study demonstrates that CD151-α3β1 integrin complexes regulate ovarian tumor growth by repressing Slug-mediated EMT and Wnt signaling.

Transvaginal ultrasonography (TVS) is an integral part of all major ovarian cancer screening trials. TVS is accurate in detecting abnormalities in ovarian volume and morphology, but is less reliable in differentiating benign from malignant ovarian tumors. When used as the only screening test, TVS is sensitive, but has a low positive predictive value. Therefore, serum biomarkers and tumor morphology indexing are used together with TVS to identify ovarian tumors at high risk for malignancy. This allows preoperative triage of high-risk cases to major cancer centers for therapy while decreasing unnecessary surgery for benign disease. Ovarian cancer screening has been associated with a decrease in stage at detection in most trials, thereby allowing treatment to be initiated when the disease is most curable.

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