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HOXB4 target genes in adult hematopoietic stem and progenitor cells (HSC/HPCs)

ABSTRACT: HOXB4 mediates expansion of adult and embryo-derived hematopoietic stem cells (HSCs) when expressed ectopically. To define the underlying molecular mechanisms, we performed gene expression profiling in combination with subsequent functional analysis using enriched adult HSCs expressing inducible HOXB4. A substantial number of the identified HOXB4 target genes are involved in signaling pathways important for controlling self-renewal, maintenance and differentiation of stem cells. Functional assays performed on selected pathways confirmed the biological coherence of the array results. HOXB4 activity protected adult HSCs from the detrimental effects mediated by the proinflammatory cytokine TNF-alpha. Furthermore, we demonstrate that HOXB4 activity and FGF-signaling are intertwined. HOXB4-mediated expansion of adult HSCs was enhanced by specific and complete inhibition of FGF-receptors. Based on our results we propose that HOXB4 governs pivotal cell-intrinsic pathways involved in the regulation of cell cycle, differentiation and apoptosis. Our results strongly suggest that HOXB4 modulates the response of HSCs to multiple extrinsic signals in a concerted manner, thereby shifting the balance towards stem cell self-renewal. Keywords: plus/minus induction of HOXB4 activity by treatment with 4-hydroxytamoxifen (TMX)

ORGANISM(S): Mus musculus

PROVIDER: GSE9010 | GEO | 2007/09/11

SECONDARY ACCESSION(S): PRJNA102495

REPOSITORIES: GEO

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Project description:HOXB4 mediates expansion of adult and embryo-derived hematopoietic stem cells (HSCs) when expressed ectopically. To define the underlying molecular mechanisms, we performed gene expression profiling in combination with subsequent functional analysis using enriched adult HSCs expressing inducible HOXB4. A substantial number of the identified HOXB4 target genes are involved in signaling pathways important for controlling self-renewal, maintenance and differentiation of stem cells. Functional assays performed on selected pathways confirmed the biological coherence of the array results. HOXB4 activity protected adult HSCs from the detrimental effects mediated by the proinflammatory cytokine TNF-alpha. Furthermore, we demonstrate that HOXB4 activity and FGF-signaling are intertwined. HOXB4-mediated expansion of adult HSCs was enhanced by specific and complete inhibition of FGF-receptors. Based on our results we propose that HOXB4 governs pivotal cell-intrinsic pathways involved in the regulation of cell cycle, differentiation and apoptosis. Our results strongly suggest that HOXB4 modulates the response of HSCs to multiple extrinsic signals in a concerted manner, thereby shifting the balance towards stem cell self-renewal. Experiment Overall Design: To understand the mechanisms of HOXB4 activity, we wished to identify target genes of HOXB4 in adult hematopoietic stem and progenitor cells (HSC/HPCs). We thus transduced murine HSC/HPCs with a retroviral vector that co-expresses EGFP and a tamoxifen-inducible form of HOXB4 (HOXB4-ER). Upon addition of 4-hydroxytamoxifen (TMX), the HOXB4-ER fusion protein translocates from the cytoplasm to the nucleus, consequently being capable of modulating gene expression. Transduced cell populations were expanded for 14 days in the presence of TMX. Thereafter, HOXB4-ER+LSK (GFP+ , lineage negative, Sca1+, ckit+) cells were flow cytometrically isolated and cultivated either with or without TMX for 1 or 4 hours. Inactivation of HOXB4 activity by TMX withdrawal was intended to mimic the naturally occurring down-regulation of HOXB4 in differentiating stem cells. RNA was prepared after the aforementioned times and the transcriptional profiles of HOXB4-ER+LSK +/- TMX analyzed using the Affymetrixâ¢ platform. As a control, profiling was also performed with LSK cells expressing unmodified constitutively active HOXB4 (HOXB4const) Â± TMX, to exclude changes in gene expression due to unknown effects of tamoxifen itself. RNAs from adult LSK cells were processed for use on Affymetrix GeneChips Mouse Genome 430 2.0. All quality parameters for the arrays were confirmed to be in the recommended range.