Pu.1 Enrichment To Intronic Enhancers Is Required For Meis1 Gene Expression In Both Hematopoiesis And Leukemogenesis

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PAHematopoiesis is a tightly regulated process with multiple transcription factors (TFs) involved sequentially. Aberrant expression of the lineage specific transcription factors may disturb normal differentiation of hematopoietic cells and result in leukemia. Myeloid Ectropic viral Integration Site 1 (MEIS1), induces and maintains MLL transformation, and plays a rate-limiting regulatory role in MLL leukemogenesis. Meis1 gene is identified as the downstream targets of PU.1, another important hematopoietic transcription factor, which is inversely correlated with worse prognosis. Though multiple regulatory elements have been identified throughout the Meis1 locus, little is known about how PU.1 plays its role on Meis1 gene expression.To gain insight into the transcriptional regulatory role of PU.1 during myeloid differentiation, we isolated the hematopoietic stem/progenitor cells (HSPC, Lin-kit+CD34+ cells) and matured myeloid cells (Lin+Gr1+cells) from bone marrows of C57 mice, performed ChIP sequencing assay, and analyzed PU.1 enrichment and histone modifications. The ChIP seq data was then confirmed with an induced differentiation model of mouse MLL-ENL leukemia cells. In addition to DNaseI hypersensitivity, the PU.1 binding elements were also characterized with H3K4me1 and H3K27ac modification. We studied the transcriptional activation role of one common PU.1 binding elements with luciferase assay. Insertion of PU.1 binding elements before the promoter increased the luciferase reporter activity, suggesting that the PU.1 binding region be the enhancer element of Meis1 gene. The association between PU.1 enrichment and Meis1 gene expression was studied in further with PU.1 knocking down assay in the MLL leukemia cells. Bioinformatics analysis results suggest that there were other transcription factors, including HOXA9 and MEIS1 itself enriched around the PU.1 binding sites. Our results suggest that PU.1 enrichment to the intronic enhancers of Meis1 gene is required for the proper expression during hematopoiesis. PU.1 together with histone modification and many other TFs, including MEIS1 itself, contributed to the hematopoietic expression of Meis1 gene. (The work is supported by National Natural Science Foundation of China (Grant number 81100380) to Y.L.)Citation Format: Yajun Li, Bo Li, Qiang Li, Lixia Zhang, Ping Li. PU.1 enrichment to intronic enhancers is required for meis1 gene expression in both hematopoiesis and leukemogenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2088. doi:10.1158/1538-7445.AM2015-2088