Jessica Bockhorn

MicroRNA-30c inhibits human breast tumour chemotherapy resistance by regulating TWF1 and IL-11.

Chemotherapy resistance frequently drives tumour progression. However, the underlying molecular mechanisms are poorly characterized. Epithelial-to-mesenchymal transition has been shown to correlate with therapy resistance, but the functional link and signalling pathways remain to be elucidated. Here we report that microRNA-30c, a human breast tumour prognostic marker, has a pivotal role in chemoresistance by a direct targeting of the actin-binding protein twinfilin 1, which promotes epithelial-to-mesenchymal transition. An interleukin-6 family member, interleukin-11 is identified as a secondary target of twinfilin 1 in the microRNA-30c signalling pathway. Expression of microRNA-30c inversely correlates with interleukin-11 expression in primary breast tumours and low interleukin-11 correlates with relapse-free survival in breast cancer patients. Our study demonstrates that microRNA-30c is transcriptionally regulated by GATA3 in breast tumours. Identification of a novel microRNA-mediated pathway that regulates chemoresistance in breast cancer will facilitate the development of novel therapeutic strategies.

MicroRNA-30c Targets Cytoskeleton Genes Involved in Breast Cancer Cell Invasion

Metastasis remains a significant challenge in treating cancer. A better understanding of the molecular mechanisms underlying metastasis is needed to develop more effective treatments. Here, we show that human breast tumor biomarker miR-30c regulates invasion by targeting the cytoskeleton network genes encoding twinfilin 1 (TWF1) and vimentin (VIM). Both VIM and TWF1 have been shown to regulate epithelial-to-mesenchymal transition. Similar to TWF1, VIM also regulates F-actin formation, a key component of cellular transition to a more invasive mesenchymal phenotype. To further characterize the role of the TWF1 pathway in breast cancer, we found that IL-11 is an important target of TWF1 that regulates breast cancer cell invasion and STAT3 phosphorylation. The miR-30c-VIM/TWF1 signaling cascade is also associated with clinical outcome in breast cancer patients.

Differentiation and Loss of Malignant Character of Spontaneous Pulmonary Metastases in Patient-Derived Breast Cancer Models

Patient-derived human-in-mouse xenograft models of breast cancer (PDX models) that exhibit spontaneous lung metastases offer a potentially powerful model of cancer metastasis. In this study, we evaluated the malignant character of lung micrometastases that emerge in such models after orthotopic implantation of human breast tumor cells into the mouse mammary fat pad. Interestingly, relative to the parental primary breast tumors, the lung metastasis (met)-derived mammary tumors exhibited a slower growth rate and a reduced metastatic potential with a more differentiated epithelial status. Epigenetic correlates were determined by gene array analyses. Lung met-derived tumors displayed differential expression of negative regulators of cell proliferation and metabolism and positive regulators of mammary epithelial differentiation. Clinically, this signature correlated with breast tumor subtypes. We identified hsa-miR-138 (miR-138) as a novel regulator of invasion and epithelial-mesenchymal transition in breast cancer cells, acting by directly targeting the polycomb epigenetic regulator EZH2. Mechanistic investigations showed that GATA3 transcriptionally controlled miR-138 levels in lung metastases. Notably, the miR-138 activity signature served as a novel independent prognostic marker for patient survival beyond traditional pathologic variables, intrinsic subtypes, or a proliferation gene signature. Our results highlight the loss of malignant character in some lung micrometastatic lesions and the epigenetic regulation of this phenotype.

miR-206 Inhibits Stemness and Metastasis of Breast Cancer by Targeting MKL1/IL11 Pathway

Purpose: Effective targeting of cancer stem cells is necessary and important for eradicating cancer and reducing metastasis-related mortality. Understanding of cancer stemness-related signaling pathways at the molecular level will help control cancer and stop metastasis in the clinic. Experimental Design: By analyzing miRNA profiles and functions in cancer development, we aimed to identify regulators of breast tumor stemness and metastasis in human xenograft models in vivo and examined their effects on self-renewal and invasion of breast cancer cells in vitro. To discover the direct targets and essential signaling pathways responsible for miRNA functions in breast cancer progression, we performed microarray analysis and target gene prediction in combination with functional studies on candidate genes (overexpression rescues and pheno-copying knockdowns). Results: In this study, we report that hsa-miR-206 suppresses breast tumor stemness and metastasis by inhibiting both self-renewal and invasion. We identified that among the candidate targets, twinfilin (TWF1) rescues the miR-206 phenotype in invasion by enhancing the actin cytoskeleton dynamics and the activity of the mesenchymal lineage transcription factors, megakaryoblastic leukemia (translocation) 1 (MKL1), and serum response factor (SRF). MKL1 and SRF were further demonstrated to promote the expression of IL11, which is essential for miR-206s function in inhibiting both invasion and stemness of breast cancer. Conclusions: The identification of the miR-206/TWF1/MKL1-SRF/IL11 signaling pathway sheds lights on the understanding of breast cancer initiation and progression, unveils new therapeutic targets, and facilitates innovative drug development to control cancer and block metastasis. Clin Cancer Res; 23(4); 1091–103. ©2016 AACR.

Novel semisynthetic method for generating full length β-amyloid peptides

Bacterial expression of full length beta-amyloid (Abeta) is problematic because of toxicity and poor solubility of the expressed protein, and a strong tendency of Met35 to become oxidized in inclusion bodies. We have developed a semisynthetic method in which Abeta1-29 is expressed in bacteria as part of a fusion protein with a C-terminal intein and Chitin-Binding Domain (CBD). There is also a single residue, N-terminal Met extension. The protein, Met-Abeta1-29-Intein-CBD, is well expressed and highly water-soluble. After binding of the expressed protein to Chitin beads, treatment with sodium 2-mercapto-ethane sulfonate (MESNA) yields Met-Abeta1-29-MESNA, with a C-terminal thioester suitable for native chemical ligation. Met-Abeta1-29-MESNA is first subjected to CNBr cleavage, which removes the N-terminal Met residue, but leaves the thioester intact. We synthesized NH2-A30C-Abeta30-40, which has an N-terminal Cys residue and is the partner for native chemical ligation with Met-Abeta1-29-MESNA. Native chemical ligation proceeds rapidly and efficiently (>90% yield) to give A30C-Abeta1-40. The final step is selective desulfurization using Raney-Ni, which also proceeds rapidly and efficiently (>90% yield) to give native sequence Abeta1-40. Overall, this system is highly efficient, and can yield approximately 8-10 mg of pure Abeta1-40 from one liter of bacterial culture medium. This procedure is adaptable for producing other Abeta peptides. We have also expressed an Abeta construct bearing a point mutation associated with one type of familial Alzheimers Disease, the Iowa mutation, i.e., Met-D23N-Abeta1-29-Intein-CBD. Since expression of the intein-containing fusion protein is robust in minimal media as well as standard enriched media, this procedure also can be readily modified for incorporating 15N or 13C labels for NMR. Future work will also include extending this system to longer Abeta peptides, such as Abeta1-42.

Removal of lactate dehydrogenase-elevating virus from human-in-mouse breast tumor xenografts by cell-sorting

Lactate dehydrogenase-elevating virus (LDV) can infect transplantable mouse tumors or xenograft tumors in mice through LDV-contaminated mouse biological materials, such as Matrigel, or through mice infected with LDV. LDV infects specifically mouse macrophages and alters immune system and tumor phenotype. The traditional approaches to remove LDV from tumor cells, by transplanting tumors into rats or culturing tumor cells in vitro, are inefficient, labor-intensive and time-consuming. Furthermore, these approaches are not feasible for primary tumor cells that cannot survive tissue culture conditions or that may change phenotype in rats. This study reports that fluorescence-activated cell sorting (FACS) is a simple and efficient approach for purifying living primary human breast tumor cells from LDV(+) mouse stromal cells, which can be completed in a few hours. When purified from Matrigel contaminated LDV(+) tumors, sorted human breast tumor cells, as well as tumors grown from sorted cells, were shown to be LDV-free, as tested by PCR. The results demonstrate that cell sorting is effective, much faster and less likely to alter tumor cell phenotype than traditional methods for removing LDV from xenograft models. This approach may also be used to remove other rodent-specific viruses from models derived from distinct tissues or species with sortable markers, where virus does not replicate in the cells to be purified.

Niclosamide inhibits epithelial-mesenchymal transition and tumor growth in lapatinib-resistant human epidermal growth factor receptor 2-positive breast cancer

Acquired resistance to lapatinib, a human epidermal growth factor receptor 2 kinase inhibitor, remains a clinical problem for women with human epidermal growth factor receptor 2-positive advanced breast cancer, as metastasis is commonly observed in these patients. Niclosamide, an anti-helminthic agent, has recently been shown to exhibit cytotoxicity to tumor cells with stem-like characteristics. This study was designed to identify the mechanisms underlying lapatinib resistance and to determine whether niclosamide inhibits lapatinib resistance by reversing epithelial-mesenchymal transition. Here, two human epidermal growth factor receptor 2-positive breast cancer cell lines, SKBR3 and BT474, were exposed to increasing concentrations of lapatinib to establish lapatinib-resistant cultures. Lapatinib-resistant SKBR3 and BT474 cells exhibited up-regulation of the phenotypic epithelial-mesenchymal transition markers Snail, vimentin and α-smooth muscle actin, accompanied by activation of nuclear factor-кB and Src and a concomitant increase in stem cell marker expression (CD44(high)/CD24(low)), compared to naive lapatinib-sensitive SKBR3 and BT474 cells, respectively. Interestingly, niclosamide reversed epithelial-mesenchymal transition, induced apoptosis and inhibited cell growth by perturbing aberrant signaling pathway activation in lapatinib-resistant human epidermal growth factor receptor 2-positive cells. The ability of niclosamide to alleviate stem-like phenotype development and invasion was confirmed. Collectively, our results demonstrate that lapatinib resistance correlates with epithelial-mesenchymal transition and that niclosamide inhibits lapatinib-resistant cell viability and epithelial-mesenchymal transition. These findings suggest a role of niclosamide or derivatives optimized for more favorable bioavailability not only in reversing lapatinib resistance but also in reducing metastatic potential during the treatment of human epidermal growth factor receptor 2-positive breast cancer.

Electrophoretic cytopathology resolves ERBB2 forms with single-cell resolution

AbstractIn addition to canonical oncoproteins, truncated isoforms and proteolysis products are implicated in both drug resistance and disease progression. In HER2-positive breast tumors, expression of truncated HER2 isoforms resulting from alternative translation and/or carboxy-terminal fragments (CTFs) resulting from proteolysis (collectively, t-erbB2) have been associated with shortened progression-free survival of patients. Thus, to advance clinical pathology and inform treatment decisions, we developed a high-selectivity cytopathology assay capable of distinguishing t-erbB2 from full-length HER2 expression without the need for isoform-specific antibodies. Our microfluidic, single-cell western blot, employs electrophoretic separations to resolve full-length HER2 from the smaller t-erbB2 in each ~28 pL single-cell lysate. Subsequently, a pan-HER2 antibody detects all resolved HER2 protein forms via immunoprobing. In analysis of eight breast tumor biopsies, we identified two tumors comprised of 15% and 40% t-erbB2-expressing cells. By single-cell western blotting of the t-erbB2-expressing cells, we observed statistically different ratios of t-erbB2 proteins to full-length HER2 expression. Further, target multiplexing and clustering analyses scrutinized signaling, including ribosomal S6, within the t-erbB2-expressing cell subpopulation. Taken together, cytometric assays that report both protein isoform profiles and signaling state offer cancer classification taxonomies with unique relevance to precisely describing drug resistance mechanisms in which oncoprotein isoforms/fragments are implicated.Breast cancer: A precision test for truncated oncoproteins in single cellsA single-cell western blot provides a simple way of studying whether a cancer-related protein found in breast tumors has transcriptionally or post-translationally modified to a truncated form, which is implicated in resistance to targeted therapies. The microfluidic assay, developed by Amy E. Herr from the University of California, Berkeley,
USA, and colleagues at Stanford University, involves first dissociating a breast tumor, then isolating each tumor cell in cell-sized well on a microscope slide. Isolated in the well, each cell is broken up and HER2 proteins are size-separated via single-cell electrophoresis, before being immobilized and finally detected with a fluorescent probe that binds to both the full-length and truncated HER2 proteins. Herr’s team assayed eight patient samples and identified two tumor samples with mixed populations of full-length and truncated HER2 proteins, a finding with therapeutic and prognostic relevance for patients.

Abstract 352: HER2 protein isoform heterogeneity investigated by single-cell western blotting

Accounting for ∼20% of breast cancers, half of metastatic HER2-positive breast cancer patients treated with trastuzumab plus chemotherapy will experience progression of disease within one year. Trastuzumab treatment, though associated with improvement in median overall survival, still sees drug resistance as an unmet challenge. Differential response to therapy may arise from tumor heterogeneity. Further complicating the situation is the fact that HER2/erbB2 biology is complex. HER2 is not simply one full-length protein (p185) overexpressed on tumor cell surfaces, but also includes truncated isoforms, t-erbB2 (e.g., 95 and 110 kDa isoforms) lacking the extracellular domain targeted by trastuzumab (and pertuzumab and T-DM1). The t-erbB2 isoforms are implicated in tumorigenesis, metastasis, and therapeutic response. Given existing pathology and life sciences tools, the high heterogeneity and need for single cell resolution presents a tremendous challenge. We introduce here a novel microfluidic device to quantitatively assess HER2 protein isoforms in heterogeneous tumor biopsies with single-cell resolution. The single-cell western blot (scWB) provides both the sensitivity and specificity needed to detect t-erbB2 isoforms owing to use of a single-cell electrophoretic protein separation followed by immunoprobing. The assay further provides enough sensitivity to obviate the need for cell pooling, which obscures cell-to-cell heterogeneity. We assay ∼10009s of single cells on one microscope slide in a 4-6 hr workflow. First, we validated that the scWB can separate full length (p185) from truncated (p95) HER2 in single p185- and p95-genetically engineered CHO cells. The p95 was resolved from p185 protein in a short ∼1 mm separation lane (resolution = 0.97±0.03, n>500 cells). Next, we assessed a HER2-positive breast cancer cell line (BT474) and found This first-in-kind study demonstrates a powerful single-cell resolution multiplexing capability including for phospho-proteins. We are now applying the novel scWB to measure t-erbB2 in HER2-positive and triple positive (ER/PR/HER2) breast tumor biopsies and will report our results at AACR. Taken together, the microfluidic single-cell resolution western provides a sensitive, quantitative, and multiplexed tool to assay clinically-relevant oncoprotein isoforms that are currently difficult or impossible to assay. Correlating isoform expression ratios with clinical outcomes may confer a more comprehensive understanding of drug resistance responses derived from oncoprotein isoform profiles within heterogeneous cancer cell populations. Citation Format: Ginny (Chi-Chih) Kang, Toby M. Ward, Jessica Bockhorn, Mark D. Pegram, Amy E. Herr. HER2 protein isoform heterogeneity investigated by single-cell western blotting. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 352.

Abstract 2018: Investigation of ITAF's role in the pathophysiology of breast cancer

A subset of cellular mRNAs can initiate cap-independent translation via internal ribosome entry sites (IRES) structures, thus maintaining translation when cap-dependent translation is compromised. Many of these IRES harboring mRNAs encode canonical oncoproteins such as c-MYC, VEGF and EGFR. Cells use IRES-mediated translation under conditions that are common to the tumor microenvironment, including nutrient deprivation, hypoxia, inflammation, and DNA damage, leading to the hypothesis that cancer cells use cap-independent translation to survive pro-apoptotic pressure. To investigate this possibility, we profiled IRES trans-activating factors (ITAFs), which are accessory proteins that regulate IRES activity in the cells. ITAFs are members of the heterogeneous nuclear ribonucleoprotein (hnRNP) family that participate in diverse nuclear functions, including RNA splicing, DNA repair, and transcription. During cap-independent translation, ITAFs egress into the endoplasmic reticulum (ER) to form a complex with the 40S ribosome and other accessory proteins to regulate translation of client IRES harboring mRNAs. We hypothesize that ITAFs could influence the pathophysiology of breast cancer by controlling the translation of onco-and antiapoptotic proteins. In this study, we profiled the expression of two ITAFs, interleukin enhancer binding protein 2 (ILF2) and splicing factor proline/glutamine-rich (SFPQ) in normal and breast cancer specimens, and investigated the biological effects of these ITAFs in both cancer cell lines and preclinical in vivo models using knockout studies. Additionally, we investigated the impact of their subcellular localization in cancer cells and the translation of their client mRNAs under ER stress using immunoblots as well as polysome and immunofluorescence analysis. Finally, we investigated the impact of inhibiting nuclear pore translocation on the function of ITAFs in breast cancer cells, using a selective inhibitor of nuclear export (SINE) compound. Analysis of microarray datasets from cancer and normal tissue specimens (The Cancer Genome Atlas, METABRIC, and University of North Carolina datasets) revealed that expression of several ITAFs is upregulated in malignant tissues compared to normal controls (p Citation Format: Jessica Bockhorn, Toby M. Ward, J. Chuck Harrell, Xiaofei Liu, Gaby Fuchs, Mark D. Pegram. Investigation of ITAF9s role in the pathophysiology of breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2018.