A Dominant-Negative Isoform of IKAROS Expands Primitive Normal Human Hematopoietic Cells

• Published in: Stem cell reports 2014-11, Vol.3 (5), p.841-857
• Main Authors: Beer, Philip A., Knapp, David J.H.F., Kannan, Nagarajan, Miller, Paul H., Babovic, Sonja, Bulaeva, Elizabeth, Aghaeepour, Nima, Rabu, Gabrielle, Rostamirad, Shabnam, Shih, Kingsley, Wei, Lisa, Eaves, Connie J.
• Format: Article
• Language: English
• Subjects: Animals; B-Lymphocytes - cytology; B-Lymphocytes - metabolism; Blotting, Western; Cell Differentiation; Cell Proliferation; Cells, Cultured; Fetal Blood - cytology; Gene Expression Profiling; Granulocytes - cytology; Granulocytes - metabolism; HeLa Cells; Hematopoietic Stem Cell Transplantation - methods; Hematopoietic Stem Cells - cytology; Hematopoietic Stem Cells - metabolism; Humans; Ikaros Transcription Factor - genetics; Ikaros Transcription Factor - metabolism; Interleukin Receptor Common gamma Subunit - deficiency; Interleukin Receptor Common gamma Subunit - genetics; Mice, Inbred C57BL; Mice, Inbred NOD; Mice, Knockout; Mice, SCID; Microscopy, Confocal; Protein Isoforms - genetics; Protein Isoforms - metabolism; Transplantation, Heterologous
• ISSN: 2213-6711; 2213-6711
• DOI: 10.1016/j.stemcr.2014.09.006

Disrupted IKAROS activity is a recurrent feature of some human leukemias, but effects on normal human hematopoietic cells are largely unknown. Here, we used lentivirally mediated expression of a dominant-negative isoform of IKAROS (IK6) to block normal IKAROS activity in primitive human cord blood cells and their progeny. This produced a marked (10-fold) increase in serially transplantable multipotent IK6+ cells as well as increased outputs of normally differentiating B cells and granulocytes in transplanted immunodeficient mice, without producing leukemia. Accompanying T/natural killer (NK) cell outputs were unaltered, and erythroid and platelet production was reduced. Mechanistically, IK6 specifically increased human granulopoietic progenitor sensitivity to two growth factors and activated CREB and its targets (c-FOS and Cyclin B1). In more primitive human cells, IK6 prematurely initiated a B cell transcriptional program without affecting the hematopoietic stem cell-associated gene expression profile. Some of these effects were species specific, thus identifying novel roles of IKAROS in regulating normal human hematopoietic cells. [Display omitted] •IKAROS protein is abundantly expressed in primitive human hematopoietic cells•IK6 enhances human blood stem cell expansion in vivo without causing leukemia•IK6 has a unique profile of lineage-specific effects on human hematopoietic cells•IK6 activates B-lineage transcripts prematurely in human blood stem cells This study reveals a role for IKAROS in the regulation of normal human hematopoietic stem cells (HSCs). In this report, Eaves and colleagues demonstrate that disruption of IKAROS activity expands human HSCs and enhances their outputs of normally differentiating granulocytic and B-lineage cells, without inducing leukemic transformation.