Browsing Department of Biochemistry and Molecular Biology Theses and Dissertations by Subjects
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Immune regulation of tumor cell plasticity: A promising molecular target in breast cancer metastasisIt is widely accepted that phenotypic plasticity of malignant cells is required during metastatic cascade. However, the specific mechanism of how the tumor microenvironment regulates tumor cell plasticity in metastasis is under intense investigation. We demonstrate here that monocytic and granulocytic subsets of myeloid-derived suppressor cells (MDSC), hereafter called mMDSCs and gMDSCs, infiltrate in the primary tumor and distant organs with different time kinetics and regulate spatiotemporal tumor plasticity. Using co-culture experiments and mouse transcriptome analyses in syngeneic mouse models, we provide evidence that tumor-infiltrating mMDSCs facilitate dissemination from the primary site by inducing the EMT/CSC phenotype. In contrast, pulmonary gMDSC infiltrates support metastatic growth by reverting the EMT/CSC phenotype and promoting tumor cell proliferation. We also observe that lung-derived gMDSCs isolated from tumor-bearing mice enhance metastatic growth of already disseminated tumor cells. Our ongoing studies reveal that calprotectin (S100A8 and S100A9 heterotetramer) is an important regulator of gMDSCs, which play a critical role in promoting breast cancer metastasis by inducing MET-like CSCs as well as suppressing anti-tumor immunity within the pre-metastatic niche. Furthermore, we develop a novel gMDSC-targeting compound that potentially binds to calprotectin and validate its therapeutic utility in a preclinical breast cancer model. Our goal for this study is to elucidate the molecular co-evolution of tumor and immune cells in cancer development and to identify molecular targets to provide alternative therapeutic options for women with metastatic disease.
Molecular Mechanisms Associated with Sustained Urokinase Plasminogen Activator Expression in Metastatic Breast Cancer CellsElevated levels of urokinase plasminogen activator (uPA) are detected in various aggressive cancer types and are closely associated with poor prognosis of cancer. While uPA can be transiently upregulated by diverse extracellular stimuli, only sustained uPA expression contributes to breast cancer invasion/metastasis. However, how sustained uPA expression is regulated and achieved in invasive breast cancer cells is not understood. The overall goal of this study is to elucidate the mechanism responsible for sustained uPA expression. Here, we show that sustained uPA expression is regulated in a mechanism distinct from transiently induced uPA expressions. Interleukin enhancerbinding factor 3 (ILF3) facilitates uPA expression by both activating uPA gene transcription and inhibiting the processing of uPA mRNA-targeting pri-miRNAs. Another part of this study is to investigate the role of the miRNA system in sustained uPA expression and cancer cell invasion. Knockdown of Drosha, DGCR8, or Dicer, key components of miRNA processing machinery led to substantially higher uPA expression and increased in vitro invasion in invasive breast cancer cells, although it was unable to increase the uPA level in non-invasive breast cancer cells. In fact, we identified that uPA mRNA was a direct target of miR-193a/b and miR-181a. Interestingly, we found that the levels of mature miR-193a, miR-193b, and miR-181a, but not their respective primary miRNAs, were lower in high uPA-expressing cells compared to low uPA-expressing cells. Furthermore, the high levels of mature miR-193a, miR-193b, and miR-181a in partly attributed to lower Drosha/DGCR8 expression in high uPA-expressing cells. To identify mechanism pertinent to ILF3 regulation of sustained uPA expression, we found that sustained uPA expression is sensitive to pan-PKC inhibitor and c/nPKC inhibitor, but not cPKC inhibitor, suggesting that ore or more nPKC isotypes are critical for sustained uPA expression. With the aid of siRNAs, we showed that PKCδ and PKCη were involved in sustained uPA expression. To functionally connect PKCδ/η and ILF3, We revealed that the knockdown of PKCδ or PKCη led to ILF3 accumulation in the cytoplasm, the reduction of primary miRNA binding ability, and enhanced production of mature miR-193a/b and miR-181a. These results indicate that ILF3 is a linker between PKCδ/η and uPA expression, and the PKCδ/η-ILF3 signaling axis is important for sustained uPA expression in breast cancer cells.