A role for the TGF -Par6 polarity pathway in breast cancer progression

Center for Systems Biology, Samuel Lunenfeld Research Institute, Room 1078 Mount Sinai Hospital, 600 University Avenue, Toronto, ON, Canada M5G 1X5.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 09/2009; 106(33):14028-33. DOI: 10.1073/pnas.0906796106
Source: PubMed


The role of polarity signaling in cancer metastasis is ill defined. Using two three-dimensional culture models of mammary epithelial cells and an orthotopic mouse model of breast cancer, we reveal that Par6 signaling, which is regulated directly by TGFbeta, plays a role in breast cancer metastasis. Interference with Par6 signaling blocked TGFbeta-dependent loss of polarity in acini-like structures formed by non-transformed mammary cells grown in three-dimensional structures and suppressed the protrusive morphology of mesenchymal-like invasive mammary tumor cells without rescuing E-cadherin expression. Moreover, blockade of Par6 signaling in an in vivo orthotopic model of metastatic breast cancer induced the formation of ZO-1-positive epithelium-like structures in the primary tumor and suppressed metastasis to the lungs. Analysis of the pathway in tissue microarrays of human breast tumors further revealed that Par6 activation correlated with markers of the basal carcinoma subtype in BRCA1-associated tumors. These studies thus reveal a key role for polarity signaling and the control of morphologic transformation in breast cancer metastasis.

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Available from: Alicia Viloria-Petit, Oct 01, 2015
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    • "Moreover, TGFb-induced p-Par6Ser 345 has been implicated in cell polarity regulation. Interference with Par6 signalling blocks TGFb-induced loss of acini-like structure and protrusive invasion in mammary tumour cells, which has a crucial role in regulating EMT and metastasis in breast cancer progression (Viloria-Petit et al, 2009). "
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    ABSTRACT: The Par complex - comprising partition-defective 6 (Par6), Par3, and atypical protein kinase C (aPKC) - is crucial for cell polarisation, the loss of which contributes to cancer progression. Transforming growth factor β (TGFβ)-induced phosphorylation of Par6 on the conserved serine 345 is implicated in epithelial-to-mesenchymal transition (EMT) in breast cancer. Here we investigated the importance of phosphorylated Par6 in prostate cancer. We generated a p-Par6(345)-specific antibody and verified its specificity in vitro. Endogenous p-Par6(345) was analysed by immunoblotting in normal human prostate RWPE1 and prostate cancer (PC-3U) cells. Subcellular localisation of p-Par6(345) in migrating TGFβ-treated PC-3U cells was analysed by confocal imaging. Invasion assays of TGFβ-treated PC-3U cells were performed. p-Par6 expression was immunohistochemically analysed in prostate cancer tissues. TGFβ induced Par6 phosphorylation on Ser345 and its recruitment to the leading edge of the membrane ruffle in migrating PC-3U cells, where it colocalised with aPKCζ. The p-Par6-aPKCζ complex is important for cell migration and invasion, as interference with this complex prevented prostate cancer cell invasion. High levels of activated Par6 correlated with aggressive prostate cancer. Increased p-Par6Ser(345) levels in aggressive prostate cancer tissues and cells suggest that it could be a useful novel biomarker for predicting prostate cancer progression.British Journal of Cancer advance online publication, 10 March 2015; doi:10.1038/bjc.2015.71
    British Journal of Cancer 03/2015; 112(7). DOI:10.1038/bjc.2015.71 · 4.84 Impact Factor
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    • "We have previously shown that blocking Par6 activation suppresses loss of polarity and reduces apoptosis in response to TGFβ in 3D acini-like structures of NMuMG cells [18]. To confirm this, and to determine whether this phenomenon is restricted to cells growing as 3D structures, we evaluated apoptotic response to TGFβ1 in monolayers of NMuMG cells. "
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    ABSTRACT: We previously observed that the TGFbeta-Par6 pathway mediates loss of polarity and apoptosis in NMuMG cells. Here we investigate the contribution of Par6 versus TGFbeta receptor I activation to TGFbeta-induced apoptosis in association with changes in apico-basal polarity. We focus on the effect of Par6 activation on alpha6beta4 integrin expression and localization, and Nuclear Factor-kappaB (p65/RelA) activation, previously shown to mediate polarity-dependent cell survival. Using immunoblotting and/or immunofluorescence we investigated the effect of TGFbeta1 on apoptosis, alpha6, beta4 and beta1 integrin expression/localization, and p65/RelA phosphorylation/localization in monolayer and three-dimensional (3D) cultures of NMuMG cells with an overactive or inactive Par6 pathway. Results were quantified by band densitometry or as percent of 3D structures displaying a phenotype. Differences among means were compared by two-way ANOVA. Blocking Par6 activation inhibits TGFbeta-induced apoptosis. Par6 overactivation enhances TGFbeta-induced apoptosis, notably after 6-day exposure to TGFbeta (p < 0.001), a time when parental NMuMG cells no longer respond to TGFbeta apoptotic stimuli. 48-hour TGFbeta treatment reduced beta4 integrin levels in NMuMG monolayers and significantly reduced the basal localization of alpha6 (p < 0.001) and beta4 (p < 0.001) integrin in NMuMG 3D structures, which was dependent on both Par6 and TGFbeta receptor I activation and paralleled apoptotic response. After 6-day exposure to TGFbeta, Par6-dependent changes to beta4 integrin were no longer apparent, but there was reduced phosphorylation of p65/RelA (p < 0.001) only in Par6 overexpressing cells. Differences in p65/RelA localization were not observed among the different cell lines after 48-hour TGFbeta exposure. Par6 and TGFbeta receptor I activation are both necessary for TGFbeta-induced apoptosis in NMuMG cells. Importantly, Par6 overexpression enhances the sensitivity of NMuMG to TGFbeta-induced apoptosis, notably upon prolonged exposure to this growth factor, when NMuMG parental cells are usually apoptosis-resistant. Thus, endogenous Par6 level might be important in determining whether TGFbeta will function as either a pro-apoptotic or pro-survival factor in breast cancer, and potentially aid in predicting patient's prognosis and therapy response.
    Cancer Cell International 03/2014; 14(1):19. DOI:10.1186/1475-2867-14-19 · 2.77 Impact Factor
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    • "Since many polarity proteins act as scaffolding or adaptor proteins without any enzymatic activity, it may be possible to target specific protein–protein interaction domains using available high-through put screening methods for small molecule inhibitors of phosphorylation-dependent protein–protein interactions.110 For example, this may have utility in Par6 over-expressing breast tumors to uncouple Par6 from TGF-β receptor in the treatment of metastatic breast cancer.106 A more feasible approach may be to inhibit the polarity kinases. "
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    ABSTRACT: Breast cancer is a heterogeneous group of diseases that frequently exhibits loss of growth control, and disrupted tissue organization and differentiation. Several recent studies indicate that apical-basal polarity provides a tumor-suppressive function, and that disrupting polarity proteins affects many stages of breast cancer progression from initiation through metastasis. In this review we highlight some of the recent advances in our understanding of the molecular mechanisms by which loss of apical-basal polarity deregulates apoptosis, proliferation, and promotes invasion and metastasis in breast cancer.
    Breast Cancer: Targets and Therapy 01/2014; 6:15-27. DOI:10.2147/BCTT.S43764
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