liu lab


Lab Members: (pictured from right to left)
Dr. Kebin Liu
John Klement, MD/PhD Student
Priscilla Redd, Graduate Student
Dafeng Yang, Laboratory Manager
Chunwan Lu, Assistant Research Scientist
Mohammed Ibrahim, Graduate Student
Wei Xiao, Postdoctoral Fellow

Research Projects
Genetic and epigenetic regulation of PD-1 and PD-L1 in immune and cancer cells 
      Significant advances have been made in checkpoint blockade cancer immunotherapy for many types of human cancers over the past few years, but pancreatic and colorectal cancers stand out as two of the few human cancers where anti-PD-L1/PD-1 immunotherapy has been unsuccessful. Pancreatic cancer shows no response to anti-PD-L1/PD-1 immunotherapy, whereas, only the MSI-H subset of colorectal cancer which accounts for only 4% of all human colorectal cancer cases responds to anti-PD-L/PD-L1 immunotherapy. What distinguishes pancreatic and colorectal cancers from other human cancers immunologically is currently unknown. It was observed in some human cancers that the expression level of PD-L1 is a response predictor to anti-PD-1/PD-L1 immunotherapy. However, new clinical data has now challenged this notion. Using a recently developed highly specific and FDA-approved anti-PD-L1 mAb, we have demonstrated that PD-L1 is abundantly expressed in both tumor cells and myeloid-derived suppressor cells (MDSCs) in human pancreatic and colon carcinoma tissues. We also demonstrated for the first time that PD-L1 transcription is regulated by an epigenetic mechanism in the tumor cells. Furthermore, we have shown that anti-PD-1/PD-L1 mAb can effectively activate cytotoxic T lymphocytes (CTLs) in the tumor microenvironment. In addition, we have shown that FasL of CTLs is essential for tumor growth control in orthotopic pancreatic and colon cancer mouse models. Because CTLs suppress tumor growth through inducing tumor cell death, our observations thus strongly suggest that tumor cell resistance to cell death induction, in addition to PD-L1 expression level, might be an underlying mechanism of pancreatic and colon cancer non-responsiveness to anti-PD-1/PD-L1 immunotherapy. Therefore, our research focus are two folds:1) the molecular mechanism underlying PD-L1 expression in tumor cells and tumor-induced MDSCs; and 2) the molecular mechanism underlying dysregulation of pancreatic and colon cancer cell death pathways, particularly the Fas-mediated cell death pathways. Our objective is to develop molecular target-based therapy to sensitize pancreatic and colon cancer to anti-PD-1/PD-L1 immunotherapy.
Related publications:
1.  Chunwan Lu, Amy V. Paschall, Huidong Shi, Natasha Savage, Jennifer L. Waller, Maria E. Sabbatini, Nicholas H. Oberlies, Cedric Pearce, Kebin Liu. 2017. The MLL1-H3K4me3 Axis-Mediated Up-Regulation of PD-L1 Contributes to Pancreatic Cancer Immune Evasion. JNCI. 109:djw 283.
2.  Chunwan Lu, Priscilla S. Redd, Jeffrey R. Lee, Natasha Savage, and Kebin Liu. 2016. The expression profiles and regulation of PD-L1 in tumor-induced myeloid-derived suppressor cells. OncoImmunology. 5:e1247135.
3.  Chunwan Lu, Asif Talukder, Natasha Savage, Nagendra Singh and Kebin Liu. 2017. Jak-STAT-mediated chronic inflammation impairs cytotoxic T lymphocyte activation to decrease anti-PD-1 immunotherapy efficacy in pancreatic cancer. OncoImmunology. In Press.

 Expression regulation and function of IRF8 in immune and cancer cells
      IRF8 is a transcription factor of the interferon regulatory factor family, which also includes IRF1, IRF2, IRF3, IRF4, IRF5, IRF6, IRF7, and IRF9. Unlike other members of the family, IRF8 has for decades been thought to be restricted to cells of the myeloid and lymphoid lineages (i.e., hematopoietic lineages). We discovered for the first time that IRF8 is constitutively expressed in certain human colon epithelial and cancer cells. Furthermore, IRF8 is also inducible by IFNg in colon cancer and other types of cancer cells. We determined that IRF8 is a key apoptosis regulator. Furthermore, we also determined for the first time that the IRF8 promoter DNA is often hypermethylated in human and mouse colon carcinoma cells. Our findings that IRF8 functions as an apoptosis regulator and IRF8 expression is silenced by DNA methylation in colon carcinoma cells has since been validated and extended to other types of human cancers and normal epithelial cells by other investigators. Our current interests are two folds: 1) IRF8 expression regulation and function in T cells and MDSCs; and 2) IRF8 function in colon epithelial inflammation and suppression of epithelial cell transformation.
Related publications:
1. Priscilla S. Redd, Mohammed L. Ibrahim, John D. Klement, Sarah K. Sharman, Amy V. Paschall, Dafeng Yang, Asha Nayak-Kapoor, and Kebin Liu. 2017.  SETD1B activates iNOS expression in myeloid-derived suppressor cells. Cancer Res. In Press.
2.  Amy V. Paschall, Ruihua Zhang, Chen-Feng Qi, Kankana Bardhan, Liang Peng, Geming Lu, Jianjun Yang, Miriam Merad, Tracy McGaha, Gang Zhou, Andrew Mellor, Scott I. Abrams, Herbert C. Morse III, Keiko Ozato, Huabao Xiong, and Kebin Liu. 2015. IFN Regulatory Factor 8 Represses GM-CSF Expression in T cells to Affect Myeloid Cell Lineage Differentiation. J. Immunol. 194:2369-79.
3.  Jeremy D. Waight, Colleen Netherby, Mary L. Hensen, Austin Miller, Qiang Hu, Song Liu, Paul N. Bogner, Matthew R. Farren, Kelvin P. Lee, Kebin Liu, and Scott I. Abrams. 2013. Myeloid-derived suppressor cell development is regulated by a STAT/IRF8 axis. J.  Clin Investigation. 123:4464-4478.
4.  Xiaolin Hu, Kankana Bardhan, Amy V. Paschall, Dafeng Yang, Jennifer L. Waller, Mary Anne Park. Asha Nayak-Kapoor, Thomas A. Samuel, Scott I. Abrams, and Kebin Liu. 2013. Deregulation of Apoptotic Factors Bcl-xL and Bax Confers Apoptotic Resistance to Myeloid-derived Suppressor Cells and Contributes to Their Persistence in Tumors.  J. Bio. Chem. 288:19103-19115.
5.  Jine Yang, Xiaolin Hu, Mary Zimmerman, Christina M. Torres, Dafeng Yang, Sylvia B. Smith, and Kebin Liu. 2011. IRF8 Regulates Bax Transcription in vivo in Primary Myeloid Cells.  J. Immunol. 187:4426-30.
6.  Xiaolin Hu, Dafeng Yang, Mary Zimmerman, Feiyan Liu, Jine Yang, Swati Kannan, Andreas Burchert, Zdzislaw Szulc, Alicja Bielawska, Keiko Ozato, Kapil Bhalla, and Kebin Liu. 2011. IRF8 Regulates Acid Ceramidase Expression to Mediate Apoptosis and Suppresses Myelogeneous Leukemia. Cancer Res. 71:2882-91.
7.  Dafeng Yang, Muthusmy Thangaraju, Kristy Greeneltch, Darren Browning, Patricia Schoenlein, Tomohiko Tamura, Keiko Ozato, Vadivel Ganapathy, Scott I. Abrams, and Kebin Liu. 2007. Repression of IRF8 by DNA Methylation is a Molecular Determinant of Apoptotic Resistant and Metastatic Phenotype in Metastatic Tumor Cells. Cancer Res. 67:3301-3309.

Epigenetic and immune regulation of colon cancer stem cell homeostasis and cancer chemoresistance and immune evasion
      Cancer stem cells/initiating cells, including colon cancer stem cells, were initially considered to be a subset of undifferentiated tumor cells with well-defined phenotypic and molecular markers. However, emerging evidence indicates instead that colon cancer stem cells are heterogeneous subsets of tumor cells that are continuously reshaped by the dynamic interactions between genetic, epigenetic, and immune factors in the tumor microenvironment. Thus, the colon cancer stem cell phenotypes and responsiveness to chemotherapy may not only be a tumor cell-intrinsic feature, but also depend on tumor-extrinsic microenvironmental factors. Furthermore, emerging evidence also implicates colon cancer stem cells in potential immune evasion. Our objective is to understand how colon cancer stem cell-intrinsic mechanisms cooperate with the extrinsic microenvironmental factors to dynamically shape colon cancer stem cell resistance to chemotherapy and immunotherapy. 
Related publications:
1.  Amy V. Paschall, Dafeng Yang, Chunwan Lu, Priscilla S. Redd, Jeong-Hyeon Choi, Christopher M. Heaton, Jeffrey R. Lee, Asha Nayak-Kapoor, Kebin Liu. 2016. CD133+CD24lo defines a 5-Fluorouracil-resistant colon cancer stem cell-like phenotype. Oncotarget. doi: 10.18632/oncotarget.12168.
2.  Amy V. Paschall and Kebin Liu, 2015. Epigenetic and Immune Regulation of Colorectal Cancer Stem Cells. Curr Colorectal Cancer Rep. 11:414-421.
3.  Amy V. Paschall, Dafeng Yang, Chunwan Lu, Jeong-Hyeon Choi, Xia Li, Feiyan Liu, Mario Figueroa, Nicholas H. Oberlies, Cedric Pearce, Wendy B. Bollag, Asha Nayak-Kapoor, Kebin Liu. 2015. H3K9 Trimethylation Silences Fas Expression to Confer Colon Carcinoma Immune Escape and 5-Fluorouracil Chemoresistance. J. Immunol. 195:1868-82.

 Functions of NF-κB as a molecular link between immune cells and cancer cells in the tumor microenvironment
      Low level of NF-kB activity is constitutively present in many types of human cancer cells and NF-kB activation often promotes tumor growth and progression, providing a strong rationale for anticancer strategies that inhibit NF-kB signaling. However, compelling experimental data, including our data, have also shown that NF-kB also acts to promote apoptosis in multiple types of cells. The proapoptotic function of NF-kB in the death receptor-mediated apoptosis pathway has been well demonstrated in tumor cells. The molecular mechanisms underlying these contrasting functions of NF-kB in cell death and proliferation is currently unknown. Our interest is to test the hypothesis that subunit composition of the NF-kB protein complexes determines NF-kB functions in cancer cell apoptosis and survival, and also in T cell activation and effector function.
Related publications:
1.  Priscilla S. Simon, Kankana Bardhan, May R. Chen, Amy V. Paschall, Chunwan Lu, Roni J. Bollag, Feng-Chong Kong, JianYue Jin, Feng-Ming Kong, Jennifer L. Waller, Raphael E. Pollock, and Kebin Liu. 2016. NF-kB Functions as a Molecular Link between Tumor Cells and Th1/Tc1 T Cells in the Tumor Microenvironment to Exert Radiation-mediated Tumor Suppression. Oncotarget. 7:23395-415. doi: 10.18632/oncotarget.8246.
2.  Priscilla S. Simon, Sarah K. Sharman, Chunwan Lu, Dafeng Yang, Amy V. Paschall, Sidhartha S. Tulachan and Kebin Liu. 2015. The NF-kB p65 and p50 homodimer cooperate with IRF8 to activate iNOS transcription. BMC Cancer. 15:770.
3.  Feiyan Liu, Kankana Bardhan, Dafeng Yang, Muthusamy Thangaraju, Vadivel Ganapathy, Jennifer L. Waller, Georgia Liles, Jeffrey R. Lee, and Kebin Liu. 2012. NF-қB Directly Regulates Fas Transcription to Modulate Fas-mediated Apoptosis and Tumor Suppression. J. Biol. Chem. 287:25530-40.
4.  Xiaolin Hu, Mary Zimmerman, Kankana Bardhan, Dafeng Yang, Jennifer L. Waller, Georgia B. Liles, Jeffrey R. Lee, Raphael Pollock, Dina Lev, Carl F. Ware, Ellen Garber, Veronique Bailly, Jeffrey L. Browning, and Kebin Liu. 2013. Lymphotoxin β receptor mediates caspase-dependent tumor cell apoptosis in vitro and tumor suppression in vivo despite induction of NF-kB activation. Carcinogenesis. 34:1105-1114.

 Development of ceramide mechanism-based cancer immunotherapy
      Compelling experimental data from mouse models and human patients have shown that sphingolipid deregulation, namely the balance between ceramide and S1P, is a key factor in tumor pathogenesis, progression and cancer cell resistance to chemotherapeutic agents and radiation. The crucial roles of ceramide in tumor development and cancer cell responses to therapy have led to extensive efforts to target the ceramide metabolism pathways for anticancer therapy. We have been performing studies to elucidate the molecular mechanism underlying regulation of ceramidase expression in cancer cells. We have also been collaborating with chemist and structure biologist to design molecular target-selective ceramide analogs as enhancers of CTL-based cancer immunotherapy. It is well-known that ceramide regulates Fas receptor clustering and Fas-mediated apoptosis. Therefore, our objective is to develop ceramidase-specific inhibitors and/or ceramide analogs that specifically regulate Fas function in cancer cells to enhance the efficacy of FasL+ CTL-based cancer immunotherapy.
 Related publications:
1.  Feiyan Liu, Xia Li, Chunwan Lu, Aiping Bai, Jacek Bielawski, Alicja Bielawska, Brendan Marshall, Patricia V. Schoenlein, Iryna O. Lebedyeva and Kebin Liu. Ceramide activates lysosomal cathepsin B and cathepsin D to attenuate autophagy and induces ER stress to suppress myeloid-derived suppressor cells. Oncotarget. DOI: 10.18632/oncotarget.13438.
2.  Genevieve L. Coe, Priscilla S. Redd, Amy V. Paschall, Chunwan Lu, Lilly Gu, Thomas Albers, Iryna O. Lebedyeva, and Kebin Liu. 2016. Ceramide mediates FasL-induced caspase 8 activation in colon carcinoma cells to enhance FasL-induced cytotoxicity by tumor-specific cytotoxic T lymphocytes Sci. Rep. 6:30816 doi:10.1038/srep30816.
3.  Amy V Paschall, Mary A Zimmerman, Christina M Torres, Dafeng Yang, May R Chen, Xia Li, Erhard Bieberich, Aiping Bai, Jacek Bielawski, Alicja Bielawska and Kebin Liu. 2014. Ceramide targets xIAP and cIAP1 to sensitize metastatic colon and breast cancer cells to apoptosis induction to suppress tumor progression. BMC Cancer. 14:24.
4.  Xiaolin Hu, Dafeng Yang, Mary Zimmerman, Feiyan Liu, Jine Yang, Swati Kannan, Andreas Burchert, Zdzislaw Szulc, Alicja Bielawska, Keiko Ozato, Kapil Bhalla, and Kebin Liu. 2011. IRF8 Regulates Acid Ceramidase Expression to Mediate Apoptosis and Suppresses Myelogeneous Leukemia. Cancer Res. 71:2882-91.

 List of publications: