uPAR enhances malignant potential of triple-negative breast cancer by directly interacting with uPA and IGF1R.

BACKGROUND: Due to lack of a targeted therapy for the triple-negative breast cancer (TNBC) patients, it is important to explore this aggressive breast cancer type in more detail and to establish novel therapeutic approaches. TNBC is defined negative for the protein expression of oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). One prominent feature of this cancer type is the frequent overexpression of major components of the urokinase-type plasminogen activator system (uPAS) including uPA, its receptor uPAR and the inhibitor PAI-1, which may be valuable as therapeutic targets. METHODS: Direct interactions of uPAR with interactors were demonstrated by immunoprecipitations and proximity ligation assays. For stable knockdowns of target proteins, lentiviral vectors were used and the effects were analysed by immunoblottings and using in vitro cell viability, migration and invasion assays. Immunohistochemical and statistical analyses of biomarkers and clinical parameters were conducted in a TNBC cohort (n = 174). RESULTS: Direct tumour-promoting interactions of uPAR with uPA and the insulin-like growth factor receptor 1 (IGF1R) were shown in TNBC cells and these interactions were significantly reduced (p = 0.001) when uPAR was downregulated. The combined knockdown of uPAR and uPA or IGF1R additively and significantly reduced cell viability, migration and invasion of the model cell lines. In TNBC tissue, the complexes formed by uPAR with uPA or with IGF1R significantly correlated with the histological grade (p = 0.0019) as well as with cathepsin B and D (p ≤ 0.0001) that are implicated in cell invasion and metastasis. CONCLUSIONS: Our outcomes show that not only overexpressed biomarkers promote tumourigenesis, but rather their interactions further potentiate tumour progression. This study emphasises the potential of combined approaches targeting uPAR and its interactors with regard to an improved therapy of TNBC.

MEK1 Inhibitor Combined with Irradiation Reduces Migration of Breast Cancer Cells Including miR-221 and ZEB1 EMT Marker Expression.

The miR-221 expression is dependent on the oncogenic RAS-RAF-MEK pathway activation and influences epithelial-to-mesenchymal transition (EMT). The Cancer Genome Atlas (TCGA) database analysis showed high gene significance for ZEB1 with EMT module analysis and miR-221 overexpression within the triple-negative breast cancer (TNBC) and HER2+ subgroups when compared to luminal A/B subgroups. EMT marker expression analysis after MEK1 (TAK-733) inhibitor treatment and irradiation was combined with miR-221 and ZEB1 expression analysis. The interaction of miR-221 overexpression with irradiation and its influence on migration, proliferation, colony formation and subsequent EMT target activation were investigated. The results revealed that MEK1 inhibitor treatment combined with irradiation could decrease the migratory potential of breast cancer cells including reduction of miR-221 and corresponding downstream ZEB1 (EMT) marker expression. The clonogenic survival assays revealed that miR-221 overexpressing SKBR3 cells were more radioresistant when compared to the control. Remarkably, the effect of miR-221 overexpression on migration in highly proliferative and highly HER2-positive SKBR3 cells remained constant even upon 8 Gy irradiation. Further, in naturally miR-221-overexpressing MDA-MB-231 cells, the proliferation and migration significantly decrease after miR-221 knockdown. This leads to the assumption that radiation alone is not reducing migration capacity of miR-221-overexpressing cells and that additional factors play an important role in this context. The miR-221/ZEB1 activity is efficiently targeted upon MEK1 inhibitor (TAK-733) treatment and when combined with irradiation treatment, significant reduction in migration of breast cancer cells was shown.

Cyr61 and YB-1 are novel interacting partners of uPAR and elevate the malignancy of triple-negative breast cancer.

The triple-negative breast cancer (TNBC) is a very aggressive tumor type often occurring in young women and is associated with a bad prognosis for the patients. TNBC lacks established targets for breast cancer therapy, such as the estrogen receptor (ER), progesterone receptor (PR) and the human epidermal growth factor receptor 2 (HER2). Therefore, novel therapeutic targets and strategies are needed for an improved treatment of this breast cancer subtype. TNBC and respective cell lines often overexpress proteins of the urokinase plasminogen activator system (uPAS) including uPA, its receptor uPAR and inhibitor PAI-1, which together with co-factors contribute to the malignancy of TNBC. Here, two novel interacting partners of uPAR, the cysteine-rich angiogenic inducer 61 (Cyr61) and the Y-box-binding protein 1 (YB-1) were identified and their differential expression demonstrated in TNBC cells as well as in tumors. In the TNBC cohort, both interactors significantly correlated with expression levels of cathepsin B, c-Met and the tumor grade. In addition, expression levels of Cyr61 significantly correlated with cathepsin D (p=0.03), insulin receptor (p≤0.001), insulin-like growth factor receptor 1 (IGF1R, p=0.015) and also with YB-1 (p=0.0004) levels. The interactions of uPAR with Cyr61 significantly correlated with expression levels of tumor-promoting biomarkers including plasminogen (p=0.0014), cathepsin B (p=0.032), c-Met (p=0.0192) as well as with the tumor grade (p=0.02). In multivariate survival analysis, YB-1 showed independent prognostic value (p=0.01). As the novel interacting partners, also together with uPAR, contribute to tumor progression and metastasis, both may be potential therapeutic targets in breast cancer.

Three-dimensional microtissues essentially contribute to preclinical validations of therapeutic targets in breast cancer.

A 3D microtissues using T47D and JIMT-1 cells were generated to analyze tissue-like response of breast cancer cells after combined human epidermal growth factor receptor 2 (HER2)-targeted treatment and radiation. Following lentiviral knockdown of HER2, we compared growth rate alterations using 2D monolayers, 3D microtissues, and mouse xenografts. Additionally, to model combined therapeutic strategies, we treated HER2-depleted T47D cells and 3D microtissues using trastuzumab (anti-HER2 antibody) in combination with irradiation. Comparison of HER2 knockdown with corresponding controls revealed growth impairment due to HER2 knockdown in T47D 2D monolayers, 3D microtissues, and xenografts (after 2, 12, and ≥40 days, respectively). In contrast, HER2 knockdown was less effective in inhibiting growth of trastuzumab-resistant JIMT-1 cells in vitro and in vivo. Combined administration of trastuzumab and radiation treatment was also analyzed using T47D 3D microtissues. Administration of both, radiation (5 Gy) and trastuzumab, significantly enhanced the growth inhibiting effect in 3D microtissues. To improve the predictive power of potential drugs--as single agents or in combination--here, we show that regarding tumor growth analyses, 3D microtissues are highly comparable to outcomes derived from xenografts. Considering increased limitations for animal experiments on the one hand and strong need of novel drugs on the other hand, it is indispensable to include highly reproducible 3D microtissue platform in preclinical analyses to validate more accurately the capacity of future drug-combined radiotherapy.

Additive impact of HER2-/PTK6-RNAi on interactions with HER3 or IGF-1R leads to reduced breast cancer progression in vivo.

The human epidermal growth factor receptor 2 (HER2) and the protein tyrosine kinase 6 (PTK6) are often co- and over-expressed in invasive breast cancers. At early diagnosis, only distinct groups, such as HER2-or hormone receptor-positive benefit from a targeted therapy. However, a part of these tumours develops resistance within a year of administration of the drug but the majority of the patients depends on general therapies with severe side effects. A PTK6-directed approach does not yet exist. In our present study, we successfully demonstrate, in vitro and in vivo, a significantly additive reduction of tumourigenesis of breast cancer cells simultaneously depleted of both HER2 and PTK6. In comparison with single RNAi approaches, the combined RNAi (co-RNAi) led to a stronger reduced phosphorylation of tumour-promoting proteins. Moreover, the co-RNAi additively decreased cell migration as well as two and three dimensional cell proliferation in vitro. The in vivo experiments showed an additive reduction (p < 0.00001) in the growth of xenografts due to the co-RNAi compared with HER2 or PTK6 RNAi alone. Interestingly, the complexes of HER2 or PTK6 with tumour-relevant interaction partners, such as HER3 or the insulin-like growth factor receptor 1 (IGF-1R), respectively, were also reduced in xenografts although their protein expression levels were not affected following the co-RNAi of HER2 and PTK6. Our present study reveals the potential of using combined HER2- and PTK6- knockdown as a powerful strategy for the treatment of breast cancers. Therefore, the combined inhibition of these proteins may represent an attractive tool for efficient therapy of breast cancers.

Secreted uPAR isoform 2 (uPAR7b) is a novel direct target of miR-221.

miR-221/-222 and components of the urokinase-type plasminogen activator system (uPAS) are associated with metastasis and poor prognosis in breast cancer, including the triple-negative subtype (TNBC). Modification of components of uPAS and involved miRNAs may contribute to targeted therapy for breast cancer patients. miR-221-/-222-overexpressing or miR-221-depleted cells were employed for qRT-PCR and Western blots to show associations of uPAR with miR-221/-222. To substantiate direct targeting of miR-221/-222 within 3' UTR of the uPAR isoform 2, in silico analysesand in vitro assays were conducted. Significant associations between miR-221 and uPAR isoform 2 expressions were observed at the mRNA and protein levels in breast cancer cells representing TNBC. For the first time, the uPAR isoform 2 was demonstrated as direct target for miR-221/-222. Inhibition of miR-221 reduced uPAR protein expression and expression of the tumor cell invasion markers vimentin and RHOC. These results demonstrate a direct and positive regulation of the secreted uPAR isoform 2 by miR-221, increasing its protein expression, a prerequisite for malignancy, while the other uPAR isoforms (1, 3 and 4) are indirectly regulated through miR-10b and miR-221/-222. By targeting uPAR isoforms and/or miRNA-221/-222, the diagnosis and therapy of breast cancer, in particular in TNBC, could be significantly improved.