Abstract 5103: RNA editing enzyme induces accelerated cell cycle in normal hematopoiesis
Authors: Jiang Qingfei , Zipeto Marianna , Cournt Angela , Leu Heather , Crews Leslie , Morris Sheldon , Jamieson Catriona 
Published: May 2015

We have previously shown that inflammation-responsive RNA editase ADAR1 (ademosine deaminases acting on dsRNA) is a contribution factor in CML (chronic myeloid leukemia) disease progression. Whole transcriptome sequencing (RNA-Seq) data on primary CML chronic phase and CML blast crisis patient demonstrated over-representation of inflammatory IFN-pathways involved in hematological development. The resulting ADAR1 up-regulation plays important roles in both stem cell differentiation and self-renewal, as indicated by in vitro colony-formation assay and in vivo CML xenotransplantation mouse model. Though we have established ADAR1-mediated RNA editing as a novel theraputic target for treating CML, we do not yet understand the underlying mechanism of RNA editase's involvement in normal hematopoietic stem cells self-renewal and differentiation. In our new study, we describe ADAR1's role in cell cycle regulation of normal hematopoietic stem cell and its molecular editing targets.

Normal cord bloods or aged bone marrow samples (CD34+) were lentivirally transduced with either backbone or ADAR1-overexpression vector. The cell cycle status of progenitors was analyzed by FACS and immunofluorescence. The expressions of genes in various cell cycle stages were analyzed by qRT-PCR. CML BC (CD34+) was transduced with lenti-shADAR1 and transplanted into immunodeficient mice. After 20 weeks, hematopoietic organs were harvested and analyzed for cell cycle status by FACS and serial transplantation.

Our results demonstrated that ADAR1 accelerates G0 to G1 phase transition in normal hematopoietic stem cells, coupled with increased cell size and elevated expression of Ki67. The expanded population maintains stemness without any significant increase in differentiation. qRT-PCR microarray of cell cycle genes indicates that p21 expression level is reduced by &gt;70% when ADAR1 is overexpressed. Moreover, shRNA knockdown of ADAR1 in CML BC sample shows a reduction of engraftment in bone marrow and spleen, and an enrichment of G0 population in the remaining cells. A decrease of self-renewal capacity as demonstrated by serial engraftment suggests the residual LSC failed to propagate.

Our finding suggests carefully regulated A-to-I editing by ADAR1 is essential for the maintenance of proper cell grow and proliferation in HSC. It is plausible that the elevated expression level of ADAR1 observed in CML BC LSC contributes to false regulation of cell cycle that leads to the expansion of malignant leukemia stem cells.

Citation Format: Qingfei Jiang, Marianna Zipeto, Angela Cournt, Heather Leu, Leslie Crews, Sheldon Morris, Catriona Jamieson. RNA editing enzyme induces accelerated cell cycle in normal hematopoiesis. [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 5103. doi:10.1158/1538-7445.AM2014-5103