Bio

Academic Appointments


Professional Education


  • Ph.D., Penn State University (2007)
  • M.D, Beijing Medical University (1998)

Research & Scholarship

Current Research and Scholarly Interests


My interest is three-fold:
1. Investigation of how oncogene expression maintains tumor neoplastic state (mentored by Dr. Dean Felsher, Professor of Medicine-Oncology).
2. Computational screening of differentiation therapy for leukemia and solid tumors (mentored by Dr. David Dill, Professor of Computer Science).
3. Early tumorigenesis and early cancer detection, in particular pancreatic cancer.

Publications

Journal Articles


  • Oncogene addiction: resetting the safety switch? Oncotarget Li, Y., Choi, P. S., Felsher, D. W. 2014; 5 (18): 7986-7987

    Abstract

    Commentary on: Li Y, Choi PS, Casey SC, Dill DL, Felsher DW. MYC through miR-17-92 Suppresses Specific Target Genes to Maintain Survival, Autonomous Proliferation, and a Neoplastic State. Cancer Cell. 2014 ;26:262-72.

    View details for PubMedID 25275297

  • Activation of Cre Recombinase Alone Can Induce Complete Tumor Regression PLOS ONE Li, Y., Choi, S., Casey, S. C., Felsher, D. W. 2014; 9 (9)
  • Addiction to multiple oncogenes can be exploited to prevent the emergence of therapeutic resistance. Proceedings of the National Academy of Sciences of the United States of America Choi, P. S., Li, Y., Felsher, D. W. 2014; 111 (32): E3316-24

    Abstract

    Many cancers exhibit sensitivity to the inhibition of a single genetic lesion, a property that has been successfully exploited with oncogene-targeted therapeutics. However, inhibition of single oncogenes often fails to result in sustained tumor regression due to the emergence of therapy-resistant cells. Here, we report that MYC-driven lymphomas frequently acquire activating mutations in β-catenin, including a previously unreported mutation in a splice acceptor site. Tumors with these genetic lesions are highly dependent on β-catenin for their survival and the suppression of β-catenin resulted in marked apoptosis causally related to a decrease in Bcl-xL expression. Using a novel inducible inhibitor of β-catenin, we illustrate that, although MYC withdrawal or β-catenin inhibition alone results in initial tumor regression, most tumors ultimately recurred, mimicking the clinical response to single-agent targeted therapy. Importantly, the simultaneous combined inhibition of both MYC and β-catenin promoted more rapid tumor regression and successfully prevented tumor recurrence. Hence, we demonstrated that MYC-induced tumors are addicted to mutant β-catenin, and the combined inactivation of MYC and β-catenin induces sustained tumor regression. Our results provide a proof of principle that targeting multiple oncogene addicted pathways can prevent therapeutic resistance.

    View details for DOI 10.1073/pnas.1406123111

    View details for PubMedID 25071175

  • MYC through miR-17-92 Suppresses Specific Target Genes to Maintain Survival, Autonomous Proliferation, and a Neoplastic State. Cancer cell Li, Y., Choi, P. S., Casey, S. C., Dill, D. L., Felsher, D. W. 2014; 26 (2): 262-272

    Abstract

    The MYC oncogene regulates gene expression through multiple mechanisms, and its overexpression culminates in tumorigenesis. MYC inactivation reverses turmorigenesis through the loss of distinguishing features of cancer, including autonomous proliferation and survival. Here we report that MYC via miR-17-92 maintains a neoplastic state through the suppression of chromatin regulatory genes Sin3b, Hbp1, Suv420h1, and Btg1, as well as the apoptosis regulator Bim. The enforced expression of miR-17-92 prevents MYC suppression from inducing proliferative arrest, senescence, and apoptosis and abrogates sustained tumor regression. Knockdown of the five miR-17-92 target genes blocks senescence and apoptosis while it modestly delays proliferative arrest, thus partially recapitulating miR-17-92 function. We conclude that MYC, via miR-17-92, maintains a neoplastic state by suppressing specific target genes.

    View details for DOI 10.1016/j.ccr.2014.06.014

    View details for PubMedID 25117713

  • Inactivation of MYC reverses tumorigenesis JOURNAL OF INTERNAL MEDICINE Li, Y., Casey, S. C., Felsher, D. W. 2014; 276 (1): 52-60

    Abstract

    The MYC proto-oncogene is an essential regulator of many normal biological programmes. MYC, when activated as an oncogene, has been implicated in the pathogenesis of most types of human cancers. MYC overexpression in normal cells is restrained from causing cancer through multiple genetically and epigenetically controlled checkpoint mechanisms, including proliferative arrest, apoptosis and cellular senescence. When pathologically activated in the correct epigenetic and genetic contexts, MYC bypasses these mechanisms and drives many of the 'hallmark' features of cancer, including uncontrolled tumour growth associated with DNA replication and transcription, cellular proliferation and growth, protein synthesis and altered cellular metabolism. MYC also dictates tumour cell fate by enforcing self-renewal and by abrogating cellular senescence and differentiation programmes. Moreover, MYC influences the tumour microenvironment, including activating angiogenesis and suppressing the host immune response. Provocatively, brief or even partial suppression of MYC back to its physiological levels of activation can lead to the restoration of intrinsic checkpoint mechanisms, resulting in acute and sustained tumour regression associated with tumour cells undergoing proliferative arrest, differentiation, senescence and apoptosis, as well as remodelling of the tumour microenvironment, recruitment of an immune response and shutdown of angiogenesis. Hence, tumours appear to be addicted to the MYC oncogene because of both tumour cell intrinsic and host-dependent mechanisms. MYC is important for the regulation of both the initiation and maintenance of tumorigenesis. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1111/joim.12237

    View details for Web of Science ID 000337787500006

  • MYC Activation Is a Hallmark of Cancer Initiation and Maintenance COLD SPRING HARBOR PERSPECTIVES IN MEDICINE Gabay, M., Li, Y., Felsher, D. W. 2014; 4 (6)
  • An essential role for the immune system in the mechanism of tumor regression following targeted oncogene inactivation IMMUNOLOGIC RESEARCH Casey, S. C., Li, Y., Felsher, D. W. 2014; 58 (2-3): 282-291

    Abstract

    Tumors are genetically complex and can have a multitude of mutations. Consequently, it is surprising that the suppression of a single oncogene can result in rapid and sustained tumor regression, illustrating the concept that cancers are often "oncogene addicted." The mechanism of oncogene addiction has been presumed to be largely cell autonomous as a consequence of the restoration of normal physiological programs that induce proliferative arrest, apoptosis, differentiation, and/or cellular senescence. Interestingly, it has recently become apparent that upon oncogene inactivation, the immune response is critical in mediating the phenotypic consequences of oncogene addiction. In particular, CD4(+) T cells have been suggested to be essential to the remodeling of the tumor microenvironment, including the shutdown of host angiogenesis and the induction of cellular senescence in the tumor. However, adaptive and innate immune cells are likely involved. Thus, the effectors of the immune system are involved not only in tumor initiation, tumor progression, and immunosurveillance, but also in the mechanism of tumor regression upon targeted oncogene inactivation. Hence, oncogene inactivation may be an effective therapeutic approach because it both reverses the neoplastic state within a cancer cell and reactivates the host immune response that remodels the tumor microenvironment.

    View details for DOI 10.1007/s12026-014-8503-6

    View details for Web of Science ID 000336333700015

    View details for PubMedID 24791942

  • Activation of cre recombinase alone can induce complete tumor regression. PloS one Li, Y., Choi, P. S., Casey, S. C., Felsher, D. W. 2014; 9 (9): e107589

    Abstract

    The Cre/loxP system is a powerful tool for generating conditional genomic recombination and is often used to examine the mechanistic role of specific genes in tumorigenesis. However, Cre toxicity due to its non-specific endonuclease activity has been a concern. Here, we report that tamoxifen-mediated Cre activation in vivo induced the regression of primary lymphomas in p53-/- mice. Our findings illustrate that Cre activation alone can induce the regression of established tumors.

    View details for DOI 10.1371/journal.pone.0107589

    View details for PubMedID 25208064

  • Oncogene withdrawal engages the immune system to induce sustained cancer regression. Journal for immunotherapy of cancer Casey, S. C., Li, Y., Fan, A. C., Felsher, D. W. 2014; 2: 24-?

    Abstract

    The targeted inactivation of a single oncogene can induce dramatic tumor regression, suggesting that cancers are "oncogene addicted." Tumor regression following oncogene inactivation has been thought to be a consequence of restoration of normal physiological programs that induce proliferative arrest, apoptosis, differentiation, and cellular senescence. However, recent observations illustrate that oncogene addiction is highly dependent upon the host immune cells. In particular, CD4(+) helper T cells were shown to be essential to the mechanism by which MYC or BCR-ABL inactivation elicits "oncogene withdrawal." Hence, immune mediators contribute in multiple ways to the pathogenesis, prevention, and treatment of cancer, including mechanisms of tumor initiation, progression, and surveillance, but also oncogene inactivation-mediated tumor regression. Data from both the bench and the bedside illustrates that the inactivation of a driver oncogene can induce activation of the immune system that appears to be essential for sustained tumor regression.

    View details for DOI 10.1186/2051-1426-2-24

    View details for PubMedID 25089198

  • PERK eIF2 alpha kinase is required to regulate the viability of the exocrine pancreas in mice BMC CELL BIOLOGY Iida, K., Li, Y., McGrath, B. C., Frank, A., Cavener, D. R. 2007; 8

    Abstract

    Deficiency of the PERK eIF2 alpha kinase in humans and mice results in postnatal exocrine pancreatic atrophy as well as severe growth and metabolic anomalies in other organs and tissues. To determine if the exocrine pancreatic atrophy is due to a cell-autonomous defect, the Perk gene was specifically ablated in acinar cells of the exocrine pancreas in mice.We show that expression of PERK in the acinar cells is required to maintain their viability but is not required for normal protein synthesis and secretion. Exocrine pancreatic atrophy in PERK-deficient mice was previously attributed to uncontrolled ER-stress followed by apoptotic cell death based on studies in cultured fibroblasts. However, we have found no evidence for perturbations in the endoplasmic reticulum or ER-stress and show that acinar cells succumb to a non-apoptotic form of cell death, oncosis, which is associated with a pronounced inflammatory response and induction of the pancreatitis stress response genes. We also show that mice carrying a knockout mutation of PERK's downstream target, ATF4, exhibit pancreatic deficiency caused by developmental defects and that mice ablated for ATF4's transcriptional target CHOP have a normal exocrine pancreas.We conclude that PERK modulates secretory capacity of the exocrine pancreas by regulating cell viability of acinar cells.

    View details for DOI 10.1186/1471-2121-8-38

    View details for Web of Science ID 000250924800001

    View details for PubMedID 17727724

  • PERK EIF2AK3 control of pancreatic beta cell differentiation and proliferation is required for postnatal glucose homeostasis CELL METABOLISM Zhang, W., Feng, D., Li, Y., Iida, K., McGrath, B., Cavener, D. R. 2006; 4 (6): 491-497

    Abstract

    Mutations in PERK (EIF2AK3) result in permanent neonatal diabetes as well as several other anomalies that underlie the human Wolcott-Rallison syndrome, and these anomalies are mirrored in Perk knockout mice. To identify the cause of diabetes in PERK-deficient mice, we generated a series of tissue- and cell-specific knockouts of the Perk gene and performed a developmental analysis of the progression to overt diabetes. We discovered that PERK is specifically required in the insulin-secreting beta cells during the fetal and early neonatal period as a prerequisite for postnatal glucose homeostasis. However, PERK expression in beta cells is not required at the adult stage to maintain beta cell functions and glucose homeostasis. We show that PERK-deficient mice exhibit severe defects in fetal/neonatal beta cell proliferation and differentiation, resulting in low beta cell mass, defects in proinsulin trafficking, and abrogation of insulin secretion that culminate in permanent neonatal diabetes.

    View details for DOI 10.1016/j.cmet.2006.11.002

    View details for Web of Science ID 000242751500012

    View details for PubMedID 17141632

  • Proinsulin disulfide maturation and misfolding in the endoplasmic reticulum JOURNAL OF BIOLOGICAL CHEMISTRY Liu, M., Li, Y. L., Cavener, D., Arvan, P. 2005; 280 (14): 13209-13212

    Abstract

    Upon nonreducing Tris-Tricine-urea-SDS-PAGE, newly synthesized proinsulin from pancreatic islets of normal rodents forms a band fast mobility representing the native disulfide isomer, which is efficiently secreted. In addition at least two slower migrating "isomer 1 and 2" bands are recovered, not discernible under reducing conditions, which represent minor species that exhibit less efficient secretion. Although rats and mice have two proinsulin genes, three distinct migrating species are also produced upon proinsulin expression from a single wild-type human proinsulin cDNA. The "Akita-type" proinsulin mutation, which causes dominant-negative diabetes mellitus due to point mutation C(A7)Y that leaves B7-cysteine without its disulfide pairing partner, is recovered as a form that near quantitatively co-migrates with the aberrant isomer 1 band of proinsulin. Anomalous migration is also demonstrated for several other mutants lacking a single cysteine. In islets from PERK-/- mice, which exhibit premature loss of pancreatic beta cells, hypersynthesis of proinsulin increases the amount of nonnative proinsulin isomers. Such findings appear consistent with an hypothesis that supranormal production of nonnative proinsulin may predispose to pancreatic beta cell toxicity.

    View details for DOI 10.1074/jbc.C400475200

    View details for Web of Science ID 000228095500003

    View details for PubMedID 15705595

  • PERK eIF2 alpha kinase regulates neonatal growth by controlling the expression of circulating insulin-like growth factor-I derived from the liver ENDOCRINOLOGY Li, Y. L., Iida, K., O'Neil, J., Zhang, P. C., Li, S. A., Frank, A., Gabai, A., Zambito, F., Liang, S. H., Rosen, C. J., Cavener, D. R. 2003; 144 (8): 3505-3513

    Abstract

    Humans afflicted with the Wolcott-Rallison syndrome and mice deficient for PERK (pancreatic endoplasmic reticulum eIF2alpha kinase) show severe postnatal growth retardation. In mice, growth retardation in Perk-/- mutants is manifested within the first few days of neonatal development. Growth parameters of Perk-/- mice, including comparison of body weight to length and organ weights, are consistent with proportional dwarfism. Tibia growth plates exhibited a reduction in proliferative and hypertrophic chondrocytes underlying the longitudinal growth retardation. Neonatal Perk-/- deficient mice show a 75% reduction in liver IGF-I mRNA and serum IGF-I within the first week, whereas the expression of IGF-I mRNA in most other tissues is normal. Injections of IGF-I partially reversed the growth retardation of the Perk-/- mice, whereas GH had no effect. Transgenic rescue of PERK activity in the insulin- secreting beta-cells of the Perk-/- mice reversed the juvenile but not the neonatal growth retardation. We provide evidence that circulating IGF-I is derived from neonatal liver but is independent of GH at this stage. We propose that PERK is required to regulate the expression of IGF-I in the liver during the neonatal period, when IGF-I expression is GH-independent, and that the lack of this regulation results in severe neonatal growth retardation.

    View details for DOI 10.1210/en.2003-0236

    View details for Web of Science ID 000184258700032

    View details for PubMedID 12865332

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