Continued use of trastuzumab in PTEN-deficient HER2+ breast cancer induces the epithelial-to-mesenchymal transition (EMT), transforms HER2+ to triple negative breast cancer, and expands breast cancer stem cells (BCSCs). Using cancer cell lines with two distinct states, epithelial and mesenchymal, we identified novel targets during EMT in PTEN-deficient trastuzumab-resistant breast cancer. Differential gene expression and distinct responses to a small molecule in BT474 (HER2+ trastuzumab-sensitive) and the PTEN-deficient trastuzumab-resistant derivative (BT474-PTEN-LTT) provided the selection tools to identify targets during EMT. siRNA knockdown and small molecule inhibition confirmed MEOX1 as one of the critical molecular targets to regulate both BCSCs and mesenchymal-like cell proliferation. MEOX1 was associated with poor survival, lymph node metastasis, and stage of breast cancer patients. These findings suggest that MEOX1 is a clinically relevant novel target in BCSCs and mesenchymal-like cancer cells in PTEN-deficient trastuzumab resistant breast cancer and may serve as target for future drug development.

Triple-negative breast cancer (TNBC) is the most difficult subtype of breast cancer to treat due to a paucity of effective targeted therapies. Many studies have reported that breast cancer stem cells (BCSCs) are enriched in TNBC and are responsible for chemoresistance and metastasis. In this study, we identify LRP8 as a novel positive regulator of BCSCs in TNBC. LRP8 is highly expressed in TNBC compared to other breast cancer subtypes and its genomic locus is amplified in 24% of TNBC tumors. Knockdown of LRP8 in TNBC cell lines inhibits Wnt/β-catenin signaling, decreases BCSCs, and suppresses tumorigenic potential in xenograft models. LRP8 knockdown also induces a more differentiated, luminal-epithelial phenotype and thus sensitizes the TNBC cells to chemotherapy. Together, our study highlights LRP8 as a novel therapeutic target for TNBC as inhibition of LRP8 can attenuate Wnt/β-catenin signaling to suppress BCSCs.

Background: MEOX1 is a homeobox transcriptional factor, and plays essential roles in regulating somite development. Our previous study indicated that MEOX1 is a critical molecular target in mesenchymal-like cancer cells in PTEN-deficient Trastuzumab resistant breast cancer. Despite the potential implication of MEOX1 for the cancer progression, no previous studies examined its level and clinical significance in lung cancer tissues. In this study, we aimed to detect the MEOX1 expression and correlate its level with clinical outcome in non-small-cell lung cancer patients (NSCLC).Methods: MEOX1 gene expression in lung cancer was examined by using the Oncomine database. MEOX1 protein levels were evaluated by IHC using the corresponding primary antibody on two different commercial lung cancer tissue arrays. siRNA knockdown was used to elucidate the function of MEOX1.Results: Analysis of the Oncomine datasets identified that an elevation of MEOX1 in gene amplification in lung cancer tissues in comparison to normal lung tissues. Immunohistochemistical analysis demonstrated that MEOX1 was localized predominantly in the nucleus, and positive rate was 67.3% (111/165) in NSCLC samples. Statistical analysis revealed high levels of MEOX1 significantly correlated with Lymph Node Metastasis and Stage. Kaplan-Meier survival analysis showed that high levels of MEOX1 were significantly associated with unfavorable survival in NSCLC patients, and MEOX1 nucleus staining had worse survival, than did patients with overall expression in lung squamous cell carcinoma patients. Multivariate Cox's regression analysis found that MEOX1 was an independent poor prognostic predictor for patients with NSCLC. Silencing of MEOX1 by specific SiRNA significantly inhibited H460 and H1299 cell proliferation and sphere formation in serum-free medium.Conclusions: Our results firstly indentified that high levels of MEOX1 especially nuclear staining was an independent prognostic factor for NSCLC, and it served a essential roles in the regulation of cell proliferation and colony formation in vitro. It may represent a potential target for the NSCLC treatment.

Triple-negative breast cancer (TNBC) is an aggressive cancer subtype for which effective therapies are unavailable. TNBC has a high frequency of tumor protein P53 (P53) and phosphatase and tensin homolog (PTEN) deficiencies, and combined P53/PTEN deficiency is associated with poor prognosis and poor response to anticancer therapies. In this study, we discovered that combined P53/PTEN deficiency in TNBC activates expression of the transcription factor mesenchyme homeobox 1 (MEOX1). We found that MEOX1 is expressed only in TNBC deficient in P53 or PTEN and that its expression is undetectable in luminal A, luminal B, and HER2+ subtypes as well as in normal breast cells with wild type P53/PTEN. Notably, siRNA knockdown of both P53 and PTEN activated MEOX1 expression in breast cancer cells, whereas individual knockdowns of either P53 or PTEN had only minimal effects on MEOX1 expression. MEOX1 knockdown abolished cell proliferation of P53/PTEN-deficient TNBC in vitro and inhibited tumor growth in vivo, but had no effect on the proliferation of luminal and HER2+ cancer cells and of normal breast cells. RNA-Seq and immunoblotting analyses showed that the MEOX1 knockdown decreases expression of tyrosine kinase 2 (TYK2), signal transducer and activator of transcription 5B (STAT5B), and STAT6 in P53- and PTEN-deficient TNBC cells. These results reveal the effects of combined P53/PTEN deficiency on MEOX1 expression and TNBC cell proliferation, suggesting that MEOX1 may serve as a potential therapeutic target for managing P53- and PTEN-deficient TNBC.

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