Mir-126 and Mir-195-Mediated Control of B Cell Fate in Leukemic and Normal Cells As a Potential Alternative for Transcriptional Factor

Kotani, Ai; Okuyama, Kazuki; Chanda, Bidisha; Ikawa, Tomokatsu; Kawamoto, Hiroshi; Ando, Kiyoshi; Tojo, Arinobu; Lodish, Harvey F.

doi:10.1182/blood.V120.21.3533.3533

Abstract

Abstract 3533

microRNAs (miRNAs) control many developmental and physiological processes. However, it is assumed to work as a fine tuner in cell fate determination, which has been shown to be regulated by transcription factors.

Here, we challenge this canonical notion.

miR-126 is downregulated in MLL-AF4 ALL, biphenotypic leukemia expressing both B cell and myeloid markers, compared with other types of ALLs. CD19 and CD20, B cell differentiation markers, were upregulated when miR-126 is reexpressed in MLL-AF4 ALLs (Figure 1). Interestingly, we found that miR-126, in leukemic cells, induces B cell differentiation (Figure 2a) without changing the expression of E2A, EBF1, or PAX5, (Figure 2b) which are assumed to be critical regulators of B cell development indicating that miR-126 induced B cell differentiation independently of transcriptional factors, such as PAX5, E2A, and EBF1. To test the hypothesis, we tried to rescue block of B cell differentiation in EBF1 knock-out hematopoietic progenitor cells (EBF1 KO HPCs) by exogenous expression of miR-126. As a result, significant upregulation of B cell markers, such as B220, RAG1/2, and CD79a/b was induced by miR-126 in EBF1 KO HPCs which show complete block at pre-pro B cell stage.(Figure 3a) Moreover, miR-126 increased cell proliferation, indicating EBF1 KO HPCs differentiate into large preB cells. Moreover, miR-195, which is upregulated toward pro B cells then downregulated in B cell differentiation, also can partially rescue block of B cell differentiation in EBF1 KO HPCs. (Figure 3b) The block in B lymphopoiesis imposed by the absence of E2A or Pax5 can be overcome by exogenous expression of EBF1. Conversely E2A or Pax5 failed to compensate the effect of EBF1. Thereafter miR-126 and miR-195 potentiates to play more roles than E2A or Pax5 in this system and act as more than a fine tuner in B cell differentiation. Our results elucidate a novel mechanism for the regulation of cell fate independent of transcriptional factor, establish an important role for miRNAs in mammalian lineage specification, and suggest that miRNA could be a new possible therapeutic target for dedifferentiation induced by deregulation of transcriptional factors in ALL, which calls for further studies.