The Myb locus encodes the c-Myb transcription factor, which functions as both a transcription activator and repressor. c-Myb is absolutely required for definitive hematopoiesis and has been implicated in a variety of hematopoitic tumors including leukemia and lymphoma as well as solid tumors. In collaboration with Calabretta and colleagues, we recently demonstrated that loss of a single Myb allele severely reduces colony formation in bone marrow progenitors transduced with a p210BCR/ABL producing virus and extended survival in a model of CML blast crisis. This finding has been extended to transformation of B-lineage progenitors in two models of p190BCR/ABL-dependent B-cell leukemia (Waldron et al., manuscript submitted) and in this proposal we provide preliminary evidence that c-Myb is important for the continued survival and proliferation of Abl transformed pre-B cells. Thus, understanding what c-Myb does during normal hematopoiesis and identifying the downstream mediators of c-Myb activity is crucial for understanding c-Myb function during normal hematopoiesis and how c-Myb may function in cancer. However, gaining insight into c-Myb function has been difficult due to the embryonic lethality of null Myb mutations. We have produced mice that carry a loxP targeted Myb locus for conditional deletion by Cre recombinase. We have used these mice to define critical points during B cell development where c-Myb is required. c-Myb is required for the development, proliferation and survival of pro-B cells, transition from the pro-B to pre-B cell compartment as well as maintenance of the pre-B cell compartment. In addition, we reported that c-Myb is crucial for peripheral B cell homeostasis and that c-Myb deficient B cells are hyporesponsive to BAFF, displaying both reduced expression of BAFF-R and increased nuclear distribution of PKC-(. We have used these models to identify tentative targets of c-Myb activity that may mediate downstream c-Myb functions during B cell development. The goal of this proposal is to develop the network of crucial genes that mediate c-Myb activity during different stages of B cell development.

Public Health Relevance

The Myb locus encodes the c-Myb protooncogene, which functions as a transcription regulator. c-Myb is absolutely required for normal hematopoiesis and is associated with a wide variety of human leukemias, lymphomas and other malignancies such as breast and colon cancer. Completion of the proposed work will clarify the role played by c-Myb during normal B cell development and identify direct targets of c-Myb activity that will provide insight into how c-Myb functions in normal hematopoiesis and cancer and identify potential therapeutic targets.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IMM-G (02))
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Marino, Pamela
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University of Virginia
Schools of Medicine
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Fahl, Shawn P; Daamen, Andrea R; Crittenden, Rowena B et al. (2018) c-Myb Coordinates Survival and the Expression of Genes That Are Critical for the Pre-BCR Checkpoint. J Immunol 200:3450-3463
Tang, Fei; Zhang, Peng; Ye, Peiying et al. (2017) A population of innate myelolymphoblastoid effector cell expanded by inactivation of mTOR complex 1 in mice. Elife 6:
Waldron, T; De Dominici, M; Soliera, A R et al. (2012) c-Myb and its target Bmi1 are required for p190BCR/ABL leukemogenesis in mouse and human cells. Leukemia 26:644-53
Tewalt, Eric F; Cohen, Jarish N; Rouhani, Sherin J et al. (2012) Lymphatic endothelial cells induce tolerance via PD-L1 and lack of costimulation leading to high-level PD-1 expression on CD8 T cells. Blood 120:4772-82