All Publications

  • Differentiation and loss of malignant character of spontaneous pulmonary metastases in patient-derived breast cancer models Cancer Research Bockhorn, J., Prat, A., Chang, Y., Liu, X., Huang, S., Shang, M., Nwachukwu, C., Gomez-Vega, M., Harrell, J., Olopade, O., Perou, C., Liu, H. 2014
  • MicroRNA-30c targets cytoskeleton genes involved in breast cancer cell invasion BREAST CANCER RESEARCH AND TREATMENT Bockhorn, J., Yee, K., Chang, Y., Prat, A., Huo, D., Nwachukwu, C., Dalton, R., Huang, S., Swanson, K. E., Perou, C. M., Olopade, O. I., Clarke, M. F., Greene, G. L., Liu, H. 2013; 137 (2): 373-382


    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.

    View details for DOI 10.1007/s10549-012-2346-4

    View details for Web of Science ID 000313201100005

    View details for PubMedID 23224145

  • MicroRNA-30c inhibits human breast tumour chemotherapy resistance by regulating TWF1 and IL-11 NATURE COMMUNICATIONS Bockhorn, J., Dalton, R., Nwachukwu, C., Huang, S., Prat, A., Yee, K., Chang, Y., Huo, D., Wen, Y., Swanson, K. E., Qiu, T., Lu, J., Park, S. Y., Dolan, M. E., Perou, C. M., Olopade, O. I., Clarke, M. F., Greene, G. L., Liu, H. 2013; 4


    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.

    View details for DOI 10.1038/ncomms2393

    View details for Web of Science ID 000316614600063

    View details for PubMedID 23340433

  • Removal of lactate dehydrogenase-elevating virus from human-in-mouse breast tumor xenografts by cell-sorting JOURNAL OF VIROLOGICAL METHODS Liu, H., Bockhorn, J., Dalton, R., Chang, Y., Qian, D., Zitzow, L. A., Clarke, M. F., Greene, G. L. 2011; 173 (2): 266-270


    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.

    View details for DOI 10.1016/j.jviromet.2011.02.015

    View details for Web of Science ID 000290836400014

    View details for PubMedID 21354210

  • Novel Semisynthetic Method for Generating Full Length beta-Amyloid Peptides BIOPOLYMERS Bockhorn, J. J., Lazar, K. L., Gasser, A. J., Luther, L. M., Qahwash, I. M., Chopra, N., Meredith, S. C. 2010; 94 (4): 511-520


    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 Alzheimer's 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.

    View details for DOI 10.1002/bip.21391

    View details for Web of Science ID 000279447700018

    View details for PubMedID 20593467

  • Genome-wide screen of Saccharomyces cerevisiae null allele strains identifies genes involved in selenomethionine resistance PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Bockhorn, J., Balar, B., He, D., Seitomer, E., Copeland, P. R., Kinzy, T. G. 2008; 105 (46): 17682-17687


    Selenomethionine (SeMet) is a potentially toxic amino acid, and yet it is a valuable tool in the preparation of labeled proteins for multiwavelength anomalous dispersion or single-wavelength anomalous dispersion phasing in X-ray crystallography. The mechanism by which high levels of SeMet exhibits its toxic effects in eukaryotic cells is not fully understood. Attempts to use Saccharomyces cerevisiae for the preparation of fully substituted SeMet proteins for X-ray crystallography have been limited. A screen of the viable S. cerevisiae haploid null allele strain collection for resistance to SeMet was performed. Deletion of the CYS3 gene encoding cystathionine gamma-lyase resulted in the highest resistance to SeMet. In addition, deletion of SSN2 resulted in both increased resistance to SeMet as well as reduced levels of Cys3p. A methionine auxotrophic strain lacking CYS3 was able to grow in media with SeMet as the only source of Met, achieving essentially 100% occupancy in total proteins. The CYS3 deletion strain provides advantages for an easy and cost-effective method to prepare SeMet-substituted protein in yeast and perhaps other eukaryotic systems.

    View details for DOI 10.1073/pnas.0805642105

    View details for Web of Science ID 000261225600023

    View details for PubMedID 19004804

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