Our laboratory is interested in mechanisms of dysregulated signaling in hematologic malignancies. Myeloproliferative neoplasms (MPNs) are clonal disorders driven by pathogenetic mutations in regulatory members of the JAK-STAT pathway. While highly specific inhibitors of JAK2 have shown promise in early clinical trials, a deeper understanding of MPN pathogenesis is necessary to determine the rational use of these targeted therapies. Ongoing research is focused in three main areas:
Identification and functional characterization of LNK mutations in MPNs and related disorders
We recently identified novel mutations in the adaptor protein LNK, a negative regulator of JAK-STAT signaling (Figure 1) (Oh et al., Blood 2010 Aug 12;116(6):988-92), in patients with MPNs and related disorders. In our initial study, we identified two MPN patients with novel LNK mutations affecting the pleckstrin homology (PH) and/or SH2 domains. Cell lines and primary patient samples expressing these mutant LNK forms exhibited aberrant cytokine-dependent JAK-STAT signaling and proliferation. In follow-up studies, we have identified several additional patients with LNK mutations. These mutations are predominantly heterozygous and affect highly conserved residues in the PH domain, suggesting that LNK mutations contribute to MPN pathogenesis via haploinsufficiency and/or dominant negative effects. We are thus using a combination of cell lines, mouse models, and human primary patient samples to evaluate the effects of LNK mutations on JAK-STAT signaling, proliferation, and MPN pathogenesis in vivo. As the majority of these LNK mutations spare the N-terminal dimerization domain, one possibility is that mutant LNK binds and sequesters wild-type LNK, thereby resulting in a dominant negative effect.
Figure 1. Mechanisms of dysregulated JAK-STAT signaling in myeloproliferative neoplasms (MPNs)
(A) Activating mutations in tyrosine kinases (e.g. MPL, JAK2) lead to cytokine-independent JAK-STAT activation.
(B) The adaptor protein LNK negatively regulates JAK-STAT signaling by binding to MPL and JAK2, thereby inhibiting downstream STAT activation. LNK loss-of-function mutations would potentially result in aberrant JAK-STAT activation, but may still require cytokine stimulation.
Application of phospho-specific flow cytometry and next-generation mass cytometry approaches to the interrogation of perturbed signaling networks in MPNs
The single cell resolution of flow cytometry permits the examination of multiple interacting cell subsets within a specific blood or bone marrow patient sample. We are therefore utilizing phospho-specific flow cytometry (phospho-flow) to evaluate aberrant signaling networks in MPN patients. This approach focuses on the evaluation of primary patient samples, rather than cell line models, which can yield artifactual results. In addition, we examine cells in both basal and potentiated states (e.g. following cytokine stimulation and/or exposure to targeted inhibitors), thereby providing deeper insights about the response of specific cell populations to a dynamic environment. To facilitate large-scale phospho-proteomic studies, we are applying next-generation elemental mass cytometry approaches to the evaluation of aberrant signaling in MPNs. Given the inherent spectral limitations with fluorescence-based cytometry, the simultaneous measurement of >10 parameters becomes increasingly problematic (Figure 2). By instead utilizing elemental mass (i.e. heavy metal) tags, the evaluation of >30 (and likely up to 100) parameters with an elemental mass cytometer (CyTOF) becomes possible. These approaches will enable us to delineate signaling networks across the full hematopoietic continuum.
Figure 2. Inherent spectral limitations of fluorescence cytometry can be overcome with elemental mass cytometry
Conjugating antibodies to heavy metal tags enables the simultaneous measurement of 30+ parameters using a mass cytometer (CyTOF).
Integration of phospho-proteomic and genomic approaches to connect phenotype with underlying genotype
In addition to JAK2, MPL, and LNK, the recent identification of mutations in several other genes (Figure 3) has illustrated the genetic complexity of MPNs. The aggregate contribution of these mutations to MPN pathogenesis, however, is not fully understood. In addition, there remain many MPN cases for which no pathogenetic molecular alteration has been described. Thus, we are pursuing large-scale genomic profiling studies (e.g. whole genome sequencing) in MPNs. An integrated genomic and proteomic approach will provide a fuller understanding of MPN pathogenesis and may lead to the identification of novel targets for therapeutic intervention.
Figure 3. Clonal evolution and genetic complexity in myeloproliferative neoplasms (MPNs)
MPNs are derived from hematopoietic stem/progenitor cells and may acquire one or more pathogenetic mutations at various disease stages. The interplay between these and other yet to be discovered mutations in MPN pathogenesis is not well understood.
|1992-1996||A.B. in Biochemical Sciences, cum laude, Harvard University, Cambridge, MA
(Advisor: Joseph G. Sodroski, M.D.)
|1996-2004||M.D., Ph.D. in Cancer Biology, Medical Scientist Training Program, Northwestern University Feinberg School of Medicine, Chicago, IL
(Advisor: Laimonis A. Laimins, Ph.D.)
|2004-2006||Internal Medicine Residency, Stanford University School of Medicine, Stanford, CA|
|2006-2010||Hematology/Oncology Fellowship, Stanford University School of Medicine, Stanford, CA|
|2008-2010||Postdoctoral Fellowship, Stanford University School of Medicine, Stanford, CA
(Advisors: Garry P. Nolan, Ph.D., Jason Gotlib, M.D., M.S.)
|2010-present||Assistant Professor, Division of Hematology, Department of Medicine, Washington University School of Medicine, St. Louis, MO|
|1998||Student Fellowship, 18th International Papillomavirus Conference, Barcelona, Spain|
|2001||Gramm Travel Fellowship Award, Robert H. Lurie Comprehensive Cancer Center of Northwestern University, Chicago, IL|
|2001||Student Fellowship, 19th International Papillomavirus Conference, Florianopolis, Brazil|
|2008||Best Poster Award, Stanford Hematology and Oncology Divisions Annual Research Retreat, Pacific Grove, CA|
|2009-2010||Co-investigator, Stanford Cancer Center Developmental Cancer Research Award (PI: Gotlib)|
|2009-2011||NIH Loan Repayment Program Award|
|2010||American Association for Cancer Research GlaxoSmithKline Outstanding Clinical Scholar Award, AACR Annual Meeting, Washington, DC|
|2010||American Association for Cancer Research Aflac, Inc. Scholar-in-Training Award, AACR Translational Cancer Medicine Meeting, San Francisco, CA|
|2010||American Society of Hematology Travel Award, ASH Annual Meeting, Orlando, FL|
|2011||American Cancer Society Institutional Research Grant, Siteman Cancer Center|
|2011-2012||American Society of Clinical Oncology Young Investigator Award|
|2011-2012||Leukemia Research Foundation New Investigator Award|
|2011-2013||Sidney Kimmel Scholar Award|
|2011-2013||NHLBI Heme Scholar Award|
|2000-2002||Medical Scientist Training Program Admissions Committee, Northwestern University Feinberg School of Medicine, Chicago, IL|
|2006-present||American Society of Hematology|
|2008-present||Associate Faculty Member, Faculty of 1000 Medicine, Myeloproliferative Disorders|
|2009-present||American Association for Cancer Research|
|2010-present||American Society of Clinical Oncology|
|2010-present||Editorial Board, Therapeutic Advances in Hematology|