The Role Of Microrna-15a/16 In Early B1 Cell Development In A Mouse Model Of Chronic Lymphocytic Leukemia

New Zealand Black (NZB) mouse is a de-novo model of chronic lymphocytic leukemia (CLL) that has been studied as a model of B-cell lymphoproliferative disorder. In most human CLL and NZB there is decreased expression of the microRNA miR15a/16. In NZB (and some CLL patients) this is due a point mutation six bases downstream from pre-miR-16 region. In both NZB mouse model and human CLL, the disease is characterized by the presence of a malignant clone of B-1 cells expressing dull levels of CD5 (T cell marker), CD11b (myeloid marker) and B220 (B cell marker). In this report we investigated the molecular pathways that result in increased B-1 lineage development in the mouse model of CLL. Initially we observed that in NZB, the B-1 lineage cells had reduced expression of Pu.1 when compared to NZB B-2 cells. PU.1 is a transcription factor required for B lineage differentiation and PU.1 knockout mice were previously found by others to have only B-1 lineage cell differentiation. To study early B1/B2 divergent cell development pathways in the context of CLL and shed light on the potential malignant cell origin of this disease, we generated induced pluripotent stem cells (iPS) from NZB spleen stromal fibroblasts. Our in vivo and in vitro studies on NZB iPS and hematopoietic progenitors (LSK) differentiation towards B-cell lineage cells followed by multicolor flow based cell sorting revealed a substantial block in the maturation of NZB iPS cells compared to wild type counterparts. Preliminary data using congenic NZB mice with corrected mir-15a/16-1 locus demonstrated that normal levels of miR-15a/16 regulate B-cell differentiation towards a higher expression of PU.1 and B220 (CD45R) and lower levels of CD11b suggestive of an enhanced B2 cell maturation pathway. Our results support the hypothesis that decreased miR-15a plays a role in B1 lymphocyte development bias in the course of B cell maturation by regulating the expression of a number of genes such as B220, PU.1 and CD11b. This work will help further uncover early molecular events which determine the increased B1 versus B2 lineage commitment associated with low levels of miR-15a/16 as an initial lesion in the development of CLL. Citation Format: Chingiz Underbayev, Siddha Kasar, Heba Degheidy, Gerald Marti, Marilyn Lightfoote, Elizabeth Raveche. The role of microRNA-15a/16 in early B1 cell development in a mouse model of chronic lymphocytic leukemia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4791. doi:10.1158/1538-7445.AM2014-4791