Our Science – Keller Website

Jonathan R. Keller, Ph.D.

Laboratory of Cancer Prevention Head, Hematopoiesis and Stem Cell Biology Section Senior Investigator (Contr) National Cancer Institute at Frederick Building 560, Room 12-03 P.O. Box B Frederick, MD 27102-1201 Phone:   301-846-1461 Fax:   301-846-6646 E-Mail:   kellerj@ncifcrf.gov

Biography

Dr. Jonathan Keller obtained his Ph.D. under the direction of James Ihle at George Washington University, where he characterized and purified interleukin 3. He has a longstanding interest in the molecular and cellular regulation of hematopoietic cell growth and differentiation.

Research

Molecular and Cellular Characterization of Hematopoietic Cell Growth/Differentiation

Hematopoiesis is a multi-stage developmental process that is maintained throughout life by a limited number of hematopoietic stem cells (HSC), which proliferate, self renew, and differentiate into mature blood cells of all lineages. Central questions about the molecular events that regulate HSC quiescence, survival, self-renewal, and lineage commitment remain to be answered. In this regard, transcription factors are essential for stem cell and lineage development by regulating the expression of hematopoietic growth factors (HGF), HGF receptors, other transcription factors, and lineage specific genes. Our current efforts are aimed at defining the function of specific transcription factors and transcriptional regulators as mediators of these processes using stem cell line models; knock-out mice and normal hematopoietic cells. A basic understanding of the molecular and cellular regulation of HSC is important for cancer research and will contribute to 1) an improved understanding of the leukemogenic process, 2) developing biopharmaceuticals to treat leukemia and lymphoma, 3) developing more efficient and safe methods to transfer therapeutic genes to HSC and 4) improving bone marrow transplantation and methods for regenerative medicine.

Molecular Regulation of Hematopoietic Stem Cell Growth and Differentiation

The molecular events that regulate lineage commitment and terminal differentiation of HSC are largely unknown. To define the molecular regulation of myeloid cell development we used two cell line models including primitive erythroid myeloid lymphoid (EML) cells and more committed myeloid progenitor (MPRO) cells that are blocked at distinct stages of hematopoietic development. Using these cell line models, differential display PCR, subtractive cloning and micro array analysis, we have identified several genes regulated during hematopoietic cell differentiation. One of these genes is IFI-205, a previously described gene of unknown function. IFI-205 is a member of the interferon-inducible p200 gene family (IFI-200), which is induced in normal HSC under conditions that promote myelomonocytic cell differentiation (stem cell factor, SCF, plus interleukin 3, IL-3). IFI-205 encodes a nuclear protein that inhibits IL-3-dependent progenitor cell proliferation and serum-induced NIH-3T3 cell proliferation. This is the first reported function for the IFI-205 protein. Current studies are directed at better understanding the potential tumor suppressive activities of this family of proteins in hematopoietic cells and their role in regulating differentiation and apoptosis. Specifically, we plan to evaluate the function IFI-205 and a closely related family member, IFI-204, in HSC (and EML cells) during the early stages of myeloid development in vitro and in vivo using retroviral vectors and siRNA. We have also proposed to study the pathways that regulate IFI-205 expression, including the IL-3 and Notch ligand signal transduction pathways.

Function of Id Family of Transcription Factors in Myeloid Development

In our search for transcription factors involved in regulating myeloid development, we found that the inhibitor of DNA binding proteins (Id) were also differentially expressed in EML and MPRO cell lines. Id proteins are members of the helix loop helix (HLH) family of proteins that function as dominant negative regulators of other basic HLH proteins, which are involved in regulating cell proliferation and differentiation. We found little or no Id1 and Id2 transcripts in purified HSC or EML cells, while they were expressed in more differentiated common myeloid progenitors (CMP) and further increased in granulocyte macrophage progenitors (GMP) or differentiating EML cells, suggesting that Id1 and Id2 expression increases during myeloid progenitor cell maturation. Id1 expression can be induced in EML cells, and HSC by IL-3. We discovered that common lymphoid progenitors (CLP) and purified B and T cells express little or no Id1 protein. Finally, over expression of Id1 impairs erythroid and lymphoid maturation. Therefore, we hypothesize that induction of Id1 expression by IL-3 may instruct HSC toward a myeloid cell fate, versus B-lymphoid or erythroid cell fates. We plan to evaluate the role of Id1 in cell fate decisions in normal HSC and their progenitors during the development of murine and human leukemias.

Role of CCAAT-enhancer binding proteins (C/EBP) in Cell Fate Decisions During Myeloid Development

We currently engaged in studies to investigate the function of the bZip transcription factor, C/EBPalpha, in growth arrest and differentiation of hematopoietic progenitor cells (HPC) cells using C/EBPalpha null mice. We found that HPC that lack C/EBPalpha were hyper proliferative, failed to differentiate, and showed increased self-renewal potential in vitro, and gave rise to a myelodysplastic syndrome (MDS) when transplanted in vivo. This finding is consistent with the discovery that a subset of human acute myeloid leukemia (AML) patients has mutations in the C/EBPalpha gene. We also uncovered a novel macrophage defect in C/EBPalpha knock-out mice and found that that there was an increase in erythroid progenitors in the fetal liver of these mice. We hypothesized that C/EBPalpha is required for CMP to differentiate into bi-potential GMP and their progeny. Furthermore, that elevated levels of C/EBPalpha in the CMP may suppress the development of the megakaryocyte/erythroid progenitor (MEP) and promote myeloid development. Our current studies are focused on defining the functional role of C/EBPalpha in myeloid versus erythroid cell fate decisions. In addition, we have proposed studies to use C/EBPalpha knock-out cells to develop animal models of acute myelogenous leukemia.

This page was last updated on 6/11/2008.