Purpose Dysregulation of miRNA profile has been associated with a broad spectrum of cellular processes underlying progression of various human malignancies. Increasing evidence suggests that specific microRNA clusters might be of clinical utility, especially in triple-negative breast carcinoma (TNBC), devoid of both predictive markers and potential therapeutic targets. Here we provide a comprehensive review of the existing data on microRNAs in TNBC, their molecular targets, a putative role in invasive progression with a particular emphasis on the epithelial-to-mesenchymal transition (EMT) and acquisition of stem-cell properties (CSC), regarded both as prerequisites for metastasis, and significance for therapy. Methods PubMed and Medline databases were systematically searched for the relevant literature. 121 articles have been selected and thoroughly analysed. Results Several miRNAs associated with EMT/CSC and invasion were identified as significantly (1) upregulated: miR-10b, miR-21, miR-29, miR-9, miR-221/222, miR-373 or (2) downregulated: miR-145, miR-199a-5p, miR-200 family, miR-203, miR-205 in TNBC. Dysregulation of miR-10b, miR-21, miR-29, miR-145, miR-200 family, miR-203, miR-221/222 was reported of prognostic value in TNBC patients. Conclusion Available data suggest that specific microRNA clusters might play an important role in biology of TNBC, understanding of which should assist disease prognostication and therapy.

Ecto-5′-nucleotidase is a GPI-anchored enzyme localized in cell membrane lipid rafts. Although it is highly expressed in many tumour cells, its specific function during tumorigenesis is unclear. We have found that, among different melanoma cells, upregulated expression of ecto-5′-nucleotidase is associated with a highly invasive phenotype. Analysis of other cell membrane proteins involved in melanoma adhesion and metastasis demonstrated that expression of α₅, β₁, β₃-integrin subunits and CD44 was elevated gradually in accordance with increasing metastatic potential. Expression of α_v-integrin and caveolin-1 was seen mostly in cells derived from metastatic melanomas. Furthermore, in contrast to N-cadherin, which was unaltered in all lines, we could not detect E-cadherin in any cell type. Functional assays demonstrated that highly expressed ecto-5′-nucleotidase is a catalytically competent protein that is very sensitive to inhibition by concanavalin A. The interaction with concanavalin A also caused increased association of ecto-5′-nucleotidase-rich lipid rafts with much heavier cytoskeletal complexes as determined by density gradient centrifugation. A similar shift towards heavier cytoskeletal fractions also took place with other proteins coexpressed with ecto-5′-nucleotidase, such as α_v, α₅, β₁ and β₃-integrins, caveolin-1 and CD44. As ConA-induced clustering may reflect the interactions of membrane proteins with extracellular matrix, we also analysed the effect of several extracellular matrix proteins on the in-situ activity of ecto-5′-nucleotidase in WM9 cells and found that tenascin C strongly inhibited ecto-5′-nucleotidase activity and adenosine generation from AMP. We also developed WM9 cells with reduced ecto-5′-nucleotidase expression and tested differences in cell adhesion on various extracellular matrix proteins. WM9^(eN−) cells attached significantly weaker to tenascin C layer. These observations indicate that expression of ecto-5′-nucleotidase correlates with a number of metastasis-related markers and thus may have a function in this process. Furthermore, our data suggest that, in addition to generating adenosine, ecto-5′-nucleotidase may have independent roles in adhesion and interaction with extracellular matrix components in melanoma.

Integrin receptors for cell adhesion to extracellular matrix have important roles in promoting tumor growth and progression. Integrin α3β1 is highly expressed in breast cancer cells in which it is thought to promote invasion and metastasis; however, its roles in regulating malignant tumor cell behavior remain unclear. In the current study, we used short-hairpin RNA (shRNA) to show that suppression of α3β1 in a human breast cancer cell line, MDA-MB-231, leads to decreased tumorigenicity, reduced invasiveness, and decreased production of factors that stimulate endothelial cell migration. Real-time PCR revealed that suppression of α3β1 caused a dramatic reduction in expression of the cyclooxygenase-2 (COX-2) gene, which is frequently overexpressed in breast cancers and has been exploited as a therapeutic target. Decreased COX-2 was accompanied by reduced prostaglandin E2 (PGE₂), a major prostanoid produced downstream of COX-2 and an important effector of COX-2 signaling. shRNA-mediated suppression of COX-2 showed that it has a role in tumor cell invasion and cross-talk to endothelial cells. Furthermore, treatment with PGE₂ restored these functions in α3β1-deficient MDA-MB-231 cells. These findings identify a role for α3β1 in regulating two properties of tumor cells that facilitate cancer progression: invasiveness and ability to stimulate endothelial cells. They also reveal a novel role for COX-2 as a downstream effector of α3β1 in tumor cells, thereby identifying α3β1 as a potential therapeutic target to inhibit breast cancer. Cancer Res; 70(15); 6359–67. ©2010 AACR.

The tetraspanin CD151 forms stoichiometric complexes with laminin-binding integrins (e.g., α3β1, α6β1, and α6β4) and regulates their ligand-binding and signaling functions. We have found that high expression of CD151 in breast cancers is associated with decreased overall survival (3.44-fold higher risk of death). Five-year estimated survival rates were 45.8% (95% confidence interval, 16.4-71.4%) for CD151-positive patients and 79.9% (95% confidence interval, 62.2-90.0%) for CD151-negative patients. Furthermore, CD151 was positively associated with axillary lymph node involvement. To study the biological significance of this observation, we investigated the contribution of CD151 in breast cancer tumorigenesis using MDA-MB-231 cells as a model system. Stable down-regulation of this tetraspanin by short-hairpin RNA decreased the tumorigenicity of these cells in mice. Detailed immunohistologic analysis of CD151(+) and CD151(−) xenografts showed differences in tumor vascular pattern. Vascularization observed at the subcutaneous border of the CD151(+) tumors was less pronounced or absent in the CD151(−) xenografts. In vitro experiments have established that depletion of CD151 did not affect the inherent proliferative capacity of breast cancer cells in three-dimensional extracellular matrices, but modified their responses to endothelial cells in coculture experiments. The modulatory activity of CD151 was dependent on its association with both α3β1 and α6β4 integrins. These data point to a new role of CD151 in tumorigenesis, whereby it functions as an important regulator of communication between tumor cells and endothelial cells. These results also identify CD151 as a potentially novel prognostic marker and target for therapy in breast cancer. (Mol Cancer Res 2009;7(6):787–98)

Ecto-5'-nucleotidase (eN, CD73) mediates extracellular adenosine production from 5'-AMP. Non-enzymatic functions of eN have also been reported. The aim of the study was to investigate the role of ecto-5'-nucleotidase in aggressive melanoma behaviour. Analysis of the involvement of eN in adhesion, migration and invasion revealed eN functions unknown to date. We found that following eN blockade by concanavalin A, the strength of adhesion to different ECM proteins was not altered, but at the same time the invasion ability of the cells was decreased. On the other hand, knocking down eN in melanoma cells did not influence cell invasion but abolished their migration on tenascin C (TnC). Ecto-5'-nucleotidase seems to fulfil a more distinct role as a receptor than as an enzyme in the cell interaction and mobility on TnC. Ecto-5'-nucleotidase activates also focal adhesion kinase and enhances the formation of complexes upon cell adhesion to TnC. All these observations prove that an eN-TnC complex is involved in cell migration and invasion and thus in the regulation of melanoma progression.