Atypical E-cadherin expression in cell clusters overlying focally disrupted mammary myoepithelial cell layers: implications for tumor cell motility and invasion

Mechanostimulation of breast myoepithelial cells induces functional changes associated with DCIS progression to invasion

Women with ductal carcinoma in situ (DCIS) have an increased risk of progression to invasive breast cancer. Although not all women with DCIS will progress to invasion, all are treated as such, emphasising the need to identify prognostic biomarkers. We have previously shown that altered myoepithelial cells in DCIS predict disease progression and recurrence. By analysing DCIS duct size in sections of human breast tumour samples, we identified an associated upregulation of integrin β6 and an increase in periductal fibronectin deposition with increased DCIS duct size that associated with the progression of DCIS to invasion. Our modelling of the mechanical stretching myoepithelial cells undergo during DCIS progression confirmed the upregulation of integrin β6 and fibronectin expression in isolated primary and cell line models of normal myoepithelial cells. Our studies reveal that this mechanostimulated DCIS myoepithelial cell phenotype enhances invasion in a TGFβ-mediated upregulation of MMP13. Immunohistochemical analysis identified that MMP13 was specifically upregulated in DCIS, and it was associated with progression to invasion. These findings implicate tissue mechanics in altering the myoepithelial cell phenotype in DCIS, and that these alterations may be used to stratify DCIS patients into low and high risk for invasive progression.

Myoepithelial cell differentiation markers in ductal carcinoma in situ progression

We describe a preclinical model that investigates progression of early-stage ductal carcinoma in situ (DCIS) and report that compromised myoepithelial cell differentiation occurs before transition to invasive disease. Human breast cancer MCF10DCIS.com cells were delivered into the mouse mammary teat by intraductal injection in the absence of surgical manipulations and accompanying wound-healing confounders. DCIS-like lesions developed throughout the mammary ducts with full representation of human DCIS histologic patterns. Tumor cells were incorporated into the normal mammary epithelium, developed ductal intraepithelial neoplasia and DCIS, and progressed to invasive carcinoma, suggesting the model provides a rigorous approach to study early stages of breast cancer progression. Mammary glands were evaluated for myoepithelium integrity with immunohistochemical assays. Progressive loss of the myoepithelial cell differentiation markers p63, calponin, and α-smooth muscle actin was observed in the mouse myoepithelium surrounding DCIS-involved ducts. p63 loss was an early indicator, calponin loss intermediate, and α-smooth muscle actin a later indicator of compromised myoepithelium. Loss of myoepithelial calponin was specifically associated with gain of the basal marker p63 in adjacent tumor cells. In single time point biopsies obtained from 16 women diagnosed with pure DCIS, a similar loss in myoepithelial cell markers was observed. These results suggest that further research is warranted into the role of myoepithelial cell p63 and calponin expression on DCIS progression to invasive disease.

Glucocorticoids and histone deacetylase inhibitors cooperate to block the invasiveness of basal-like breast cancer cells through novel mechanisms

Aggressive cancers often express E-cadherin in cytoplasmic vesicles rather than on the plasma membrane and this may contribute to the invasive phenotype of these tumors. Therapeutic strategies are not currently available that restore the anti-invasive function of E-cadherin in cancers. MDA-MB-231 cells are a frequently used model of invasive triple-negative breast cancer, and these cells express low levels of E-cadherin that is mislocalized to cytoplasmic vesicles. MDA-MB-231 cell lines stably expressing wild-type E-cadherin or E-cadherin fused to glutathione S-transferase or green fluorescent protein were used as experimental systems to probe the mechanisms responsible for cytoplasmic E-cadherin localization in invasive cancers. Although E-cadherin expression partly reduced cell invasion in vitro, E-cadherin was largely localized to the cytoplasm and did not block the invasiveness of the corresponding orthotopic xenograft tumors. Further studies indicated that the glucocorticoid dexamethasone and the highly potent class I histone deacetylase (HDAC) inhibitor largazole cooperated to induce E-cadherin localization to the plasma membrane in triple-negative breast cancers, and to suppress cellular invasion in vitro. Dexamethasone blocked the production of the cleaved form of the CDCP1 (that is, CUB domain-containing protein 1) protein (cCDCP1) previously implicated in the pro-invasive activities of CDCP1 by upregulating the serine protease inhibitor plasminogen activator inhibitor-1. E-cadherin preferentially associated with cCDCP1 compared with the full-length form. In contrast, largazole did not influence CDCP1 cleavage, but increased the association of E-cadherin with γ-catenin. This effect on E-cadherin/γ-catenin complexes was shared with the nonisoform selective HDAC inhibitors trichostatin A (TSA) and vorinostat (suberoylanilide hydroxamic acid, SAHA), although largazole upregulated endogenous E-cadherin levels more strongly than TSA. These results demonstrate that glucocorticoids and HDAC inhibitors, both of which are currently in clinical use, cooperate to suppress the invasiveness of breast cancer cells through novel, complementary mechanisms that converge on E-cadherin.

Non-receptor tyrosine kinase 2 reaches its lowest expression levels in human breast cancer during regional nodal metastasis

Almost half of breast Ductal Carcinoma in situ are likely to remain non threatening in situ lesions with no invasion to the surrounding stroma and no metastases. The majority of focal disruptions in myoepithelial (ME) cell layers indicative of invasion onset were found to be overlying epithelial cell clusters with no or substantially reduced estrogen receptor α (ERα) expression. Here we report the down-regulation of tyrosine kinase-2 (TYK2) and up-regulation of strumpellin expression, among other proteins in ERα(-) cells located at disrupted ME layers compared to adjacent ERα(+) cells overlying an intact myoepithelial layer. ERα(+) and ERα(-) cells were microdissected from the same in vivo human breast cancer tissues, proteins were extracted and separated utilizing Differential in-Gel Electrophoresis followed by trypsin digestion, MALDI-TOF analysis, and protein identification. Proteins expressed by ERα(-) cell clusters were found to express higher levels of strumpellin that binds to valosin-containing protein (VCP) to slow-down wound closure and promote growth; and lower levels of TYK2, a jak protein necessary for lineage specific differentiation. TYK2 levels were further analyzed by immunohistochemistry in a cohort composed of 70 patients with broad clinical characteristics. TYK2 levels were minimal in TxN1M0 breast cancers which is the stage where the initial regional lymph node metastasis is observed. Our data highlight the role of TYK2 downregulation in breast cancer cell de-differentitation and initiation of regional metastasis. In addition, the aggressiveness of the ERα(-) cell clusters compared to ERα(+) ones present in the same duct of the same patient was confirmed.

Self-organization is a dynamic and lineage-intrinsic property of mammary epithelial cells

Loss of organization is a principle feature of cancers; therefore it is important to understand how normal adult multilineage tissues, such as bilayered secretory epithelia, establish and maintain their architectures. The self-organization process that drives heterogeneous mixtures of cells to form organized tissues is well studied in embryology and with mammalian cell lines that were abnormal or engineered. Here we used a micropatterning approach that confined cells to a cylindrical geometry combined with an algorithm to quantify changes of cellular distribution over time to measure the ability of different cell types to self-organize relative to each other. Using normal human mammary epithelial cells enriched into pools of the two principal lineages, luminal and myoepithelial cells, we demonstrated that bilayered organization in mammary epithelium was driven mainly by lineage-specific differential E-cadherin expression, but that P-cadherin contributed specifically to organization of the myoepithelial layer. Disruption of the actomyosin network or of adherens junction proteins resulted in either prevention of bilayer formation or loss of preformed bilayers, consistent with continual sampling of the local microenvironment by cadherins. Together these data show that self-organization is an innate and reversible property of communities of normal adult human mammary epithelial cells.

Tumor cell budding from focally disrupted tumor capsules: a common pathway for all breast cancer subtype derived invasion?

Human breast cancer represents a group of highly heterogeneous lesions consisting of about 20 morphologically and immnohistochemically distinct subtypes with substantially different prognoses. Our recent studies have suggested that all breast cancer subtypes, however, may share a common pathway, tumor cell budding from focally disrupted tumor capsules, for their invasion. The potential mechanisms and clinical implications of our observations are discussed.

Aberrant c-erbB2 expression in cell clusters overlying focally disrupted breast myoepithelial cell layers: a trigger or sign for emergence of more aggressive cell clones?

Our recent studies revealed that cell clusters overlying focal myoepithelial cell layer disruption (FMCLD) had a significantly higher frequency of genetic instabilities and expression of invasion-related genes than their adjacent counterparts within the same duct. Our current study attempted to assess whether these cell clusters would also have elevated c-erbB2 expression. Human breast tumors (n=50) with a high frequency of FMCLD were analyzed with double immunohistochemistry, real-time RT-PCR, and chromogenic in situ hybridization for c-erbB2 protein and gene expression. Of 448 FMCLD detected, 404 (90.2%) were associated with cell clusters that had intense c-erbB2 immunoreactivities primarily in their cytoplasm, in contrast to their adjacent counterparts within the same duct, which had no or barely detectable c-erbB2 expression. These c-erbB2 positive cells were arranged as tongue-like projections, "puncturing" into the stroma, and about 20% of them were in direct continuity with tube-like structures that resembled blood vessels. Aberrant c-erbB2 expression was also seen in clusters of architecturally normal-appearing ducts that had distinct cytological abnormalities in both ME and epithelial cells, whereas not in their clear-cut normal counterparts. Molecular assays detected markedly higher c-erbB2 mRNA and gene amplification in cell clusters associated with FMCLD than in those associated with non-disrupted ME cell layers. Our findings suggest that cell clusters overlying FMCLD may represent the precursors of pending invasive lesions, and that aberrant c-erbB2 expression may trigger or signify the emergence of biologically more aggressive cell clones.