Gene expression profiling of HOXB4-transduced murine hematopoietic stem cells

Overexpression of HOXB4 in hematopoietic stem cells (HSCs) leads to increased self-renewal without causing hematopoietic malignancies in transplanted mice. The molecular basis of HOXB4-mediated benign HSC expansion in vivo is not well understood. To gain further insight into the molecular events underlying HOXB4-mediated HSC expansion, we analyzed gene expression changes at multiple time points in Lin-Sca1+c-kit+ (LSK) cells from mice transplanted with bone marrow (BM) cells transduced with a MSCV-HOXB4-ires-YFP vector. A distinct HOXB4 transcriptional program was reproducibly induced and stabilized by 12 weeks after transplant. Dynamic expression changes were observed in genes critical for HSC self-renewal as well as genes involved in myeloid and B cell differentiation. Prdm16, a transcription factor associated with human acute myeloid leukemia (AML), was markedly repressed by HOXB4 but upregulated by HOXA9 and HOXA10, suggesting that Prdm16 downregulation was involved in preventing leukemia in HOXB4 transplanted mice. Functional evidence to support this mechanism was obtained by enforcing co-expression of sPrdm16 and HOXB4, which led to enhanced self-renewal, myeloid expansion, and leukemia. Altogether, these studies define the transcriptional pathways involved in HOXB4 HSC expansion in vivo and identify repression of Prdm16 transcription as a mechanism by which expanding HSCs avoid leukemic transformation. 5-FU treated bone marrow cells from female C57Bl/6L mice were transduced with concentrated supernatant from GPE+86-derived producer cells containing MSCV-HOXB4-ires-YFP or MSCV-ires-GFP retroviral vectors. Transduced cells were transplanted into lethally irradiated C57Bl/6L mice. HOXB4-YFP or GFP expressing LSK cells were sorted from transplanted mice at 6, 12 and 24 weeks post transplantation, of which RNA was extracted for microarray.