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Support of carcinoma metastasis by integrin a6-CD151-PKC complexes

Martin E Hemler

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National Institutes of Health (NIH)
Tumor metastasis is the leading cause of death in breast cancer and many other types of carcinoma. As normal polarized epithelia transitions to aggressive metastatic carcinoma, the α6ß4 integrin plays a central role. When hemidesmosomes disassemble, α6ß4 reformats to an actin associated complex, not seen in normal polarized epithelia. We aim to understand specific 'pro-invasion/metastasis' properties of the reformatted α6ß4 complex, and demonstrate how it may be therapeutically exploited for novel metastasis treatment. Integrin α6ß4 nearly always associates closely with tetraspanin protein CD151, which recruits PKCα, leading to PKC-dependent integrin phosphorylation, which controls reversible integrin-actin association, needed for cell migration/invasion. Hence, α6ß4 and CD151 work together within a novel Metastatic-Carcinoma-Integrin-CD151-PKC (MCICP) complex selectively operative during invasion and metastasis. We hypothesize that i) MCICP is essential for invasion/metastasis, and ii) key molecular interactions (e.g. PKCα-CD151; CD151-α6ß4) within MCICP are suitable for cancer-specific therapeutic targeting (since they are absent or dispensable in normal polarized epithelia). To test these hypotheses, we will first, assess MCICP contributions to carcinoma metastasis in vivo. Human breast cancer patient samples will be tested for the MCICP complex, and results will be correlated with patient disease outcomes. Also, we will utilize modified/mutated breast carcinoma cells, and mouse models, to assess in vivo MCICP contributions to breast cancer progression and metastasis. We predict that elevated MCICP will correlate significantly with increased metastasis and/or with poor clinical outcome, and that disruption of MCICP will markedly impair invasion/metastasis in vivo. Second, to determine consequences of targeting specific molecular interactions within the MCICP complex, we will i) precisely map the CD151-PKCα association site, and ii) show effects of disrupting CD151-PKCα and α6ß4-CD151 associations on key α6ß4 serine phosphorylations. Also, we will show effects of MCICP disruption on iii) integrin-dependent adhesion strengthening (using magnetic microbeads), iv) reversible PKC-dependent integrin-actin connections (using single particle tracking), and v) other integrin functions. Finally, we will use tandem affinity purificaton, quantitative iTRAQ mass spectrometry and phosphopeptide analysis to obtain unbiased evidence regarding MCICP components. Our essential new information regarding critical MCICP interaction sites (e.g. PKCα-CD151; CD151-α6) should enable development of pioneering anti-carcinoma metastasis therapies.

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