Musashi-2 attenuates AHR signalling to expand human haematopoietic stem cells

Abstract

Umbilical cord blood (CB)-derived hematopoietic stem cells (HSCs) are essential in many life saving regenerative therapies, but their low number in CB units has significantly restricted their clinical use despite the advantages they provide during transplantation1. Select small molecules that enhance hematopoietic stem and progenitor cell (HSPC) expansion in culture have been identified2,3, however, in many cases their mechanisms of action or the nature of the pathways they impinge on are poorly understood. A greater understanding of the molecular pathways that underpin the unique human HSC self-renewal program will facilitate the development of targeted strategies that expand these critical cell types for regenerative therapies. Whereas transcription factor networks have been shown to influence the self-renewal and lineage decisions of human HSCs4,5, the post-transcriptional mechanisms guiding HSC fate have not been closely investigated. Here we show that overexpression of the RNA-binding protein (RBP) Musashi-2 (MSI2) induces multiple pro-self-renewal phenotypes, including a 17-fold increase in short-term repopulating cells and a net 23-fold ex vivo expansion of long-term repopulating HSCs. By performing a global analysis of MSI2-RNA interactions, we determined that MSI2 directly attenuates aryl hydrocarbon receptor (AHR) signaling through post-transcriptional downregulation of canonical AHR pathway components in CB HSPCs. Our study provides new mechanistic insight into RBP-controlled RNA networks that underlie the self-renewal process and give evidence that manipulating such networks ex vivo can provide a novel means to enhance the regenerative potential of human HSCs.

Induction of expression of aryl hydrocarbon receptor-dependent genes in human HepaRG cell line modified by shRNA and treated with β-naphthoflavone

“…The above-mentioned conclusion is consistent with our earlier findings where expression of some AhR-dependent genes was compared between both, differentiated and undifferentiated, unmodified HepaRG cells [41]. The conclusion is consistent also with the findings of involvement of AhR in development of fetal mouse liver [42] or control of expansion of human hematopoietic stem cells in culture [66]. It was demonstrated that different cell types were involved in AhR-dependent development of mouse liver and in AhR-dependent hepatotoxicity [43].…”

“…Participation of the aryl hydrocarbon receptor in induction of expression of genes connected to regulation of apoptosis or involved in cell proliferation from one side, and in inhibition of genes connected to cell adhesion from the other side could explain some results suggesting involvement of AhR not only in initiation but also in progression of cancer [83]. In agreement with above, novel physiological function for AhR has been proposed recently, as regulator of self-renewal of hematopoietic stem cells [66] or in general, modulator of the balance between differentiation and pluripotentiality in normal and transformed tumor cells [84]. …”

Stem Cells, Cancer, and MUSASHI in Blood and Guts

“…MSI2 overexpression in a conditional murine system results in a transient increase in HSC numbers, and retroviral overexpression results in improved engraftment 16 . Consistent with its role in mouse HSCs, forced expression of MSI2 in human cord blood cells resulted in a 23-fold ex vivo expansion of long-term repopulating activity and a 17-fold increase in short-term repopulating activity 18 . Loss of Msi2 expression in a murine germline gene trap mutant has opposing effects; LSK (Lineage Low , Sca1 + , c-Kit + stem and progenitor) cells are reduced resulting in poor engraftment and a defect in lymphoid primed multipotent progenitor cell (LMPP) activity due to decreased cycling 17 .…”

Mapping Whole-Transcriptome Splicing in Mouse Hematopoietic Stem Cells

“…Msi2 is better known for its role in regulating translation, and our analysis now adds another possible mechanism by which it may influence HSCs. Interestingly, overexpression of human MSI2 was reported to expand HSCs via attenuation of the aryl hydrocarbon receptor pathway as an RNA-binding protein (Rentas et al., 2016). MSI2 also plays a role in malignancy, thus understanding the possible relevance of splicing and RNA regulation in normal stem cells may reveal another layer of regulation (and mis-regulation) in cancer and in cancer stem cells (Barbouti et al., 2003, de Andres-Aguayo et al., 2011, Kharas et al., 2010).…”