Alan D. Friedman
One focus of our research is on the transcriptional regulation of early myeloid (granulocyte and monocyte) differentiation. Myeloid cells derive from pluripotent hematopioetic stem cells, which also give rise to the Lymphoid and Erythroid lineages. Our investigations will provide insight into commitment decisions being made in these early stem cells. Our second focus is on the mechanisms of action of acute myeloid leukemia (AML) oncoproteins. Many subsets of AML are associated with chromosomal translocations which encode abberant trascription factors. These oncoproteins likely disrupt the normal pathway of myeloid differentiation.
Within the early myeloid genes myeloperoxidase (MPO) and neutrophil elastase (NE) we have identified both promoter proximal and more distal myeloid enhancers. We have identified four proteins which regulate these enhancers thus far, PEBP2/CBF, C/EBP, c-Myb, and PU.1. Present investigations aim to identify mechanisms of cooperativity between these factors, to identify additional factors which regulate the MPO and NE enhancers, to identify biochemical pathways which link myeloid cell surface receptors, such as the G-CSF Receptor, to these factors, and to assess the ability of these enhancers to direct early myeloid-specific expression in transgenic mice.
The genes encoding the two subunits of PEBP2/CBF are located at the breakpoints of two chromosomal abnormalities associated with acute myeloid leukemia, t(8;21) and inv(16). We are developing cell culture models for leukemias to uncover the mechanisms of action of these oncoporteins, including the identification of their proximate genetic targets by differential screening methods. These target genes are likely regulated by PEBP2/CBF during normal myelopoiesis as well. We are also developing transgenic murine models for these leukemias.
We showed that within hematopoiesis, C/EBP family members are expressed specifically in myeloid cells. Expression of a dominant-negative C/EBF family member, GADD153 or CHOP, in myeloid cells induced their apoptosis. Thus, C/EBPs, like the PEBP2/CBFs, likely regulate both differentiation markers and cell cycle control genes in immature myeloid cells. We intend to identify additional C/EBP target genes as well. In addition, as GADD153 is inducible by DNA-damage, we are determining whether the GADD153 gene is mutated in human AMLs.