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Haematologica 2019 Volume 104(7):1388-1395
Acute Lymphoblastic Leukemia
The side population enriches for leukemia-propagating cell activity
and Wnt pathway expression in zebrafish acute lymphoblastic leukemia
Jeremy T. Baeten,1 Michael R. Waarts,1 Margaret M. Pruitt,1 Wen-Ching Chan,2 Jorge Andrade2 and Jill L.O. de Jong1*
1University of Chicago, Biological Sciences Division, Department of Pediatrics, Chicago and 2University of Chicago, Center for Research Informatics, Chicago, IL, USA
ABSTRACT
Cancer stem cells have been strongly linked to resistance and relapse in many malignancies. However, purifying them from within the bulk tumor has been challenging, so their precise genetic and functional characteristics are not well defined. The side pop- ulation assay exploits the ability of some cells to efflux Hoechst dye via ATP-binding cassette transporters. Stem cells have increased expression of these transporters and this assay has been shown to enrich for stem cells in various tissues and cancers. This study identifies the side popula- tion within a zebrafish model of acute lymphoblastic leukemia and cor- relates the frequency of side population cells with the frequency of leukemia stem cells (more precisely referred to as leukemia-propagating cells within our transplantation model). In addition, the side population within the leukemia evolves with serial transplantation, increasing in tandem with leukemia-propagating cell frequency over subsequent gen- erations. Sorted side population cells from these tumors are enriched for leukemia-propagating cells and have enhanced engraftment compared to sorted non-side population cells when transplanted into syngeneic recip- ients. RNA-sequencing analysis of sorted side population cells compared to non-side population cells identified a shared expression profile within the side population and pathway analysis yielded Wnt-signaling as the most overrepresented. Gene set enrichment analysis showed that stem cell differentiation and canonical Wnt-signaling were significantly upreg- ulated in the side population. Overall, these results demonstrate that the side population in zebrafish acute lymphoblastic leukemia significantly enriches for leukemia-propagating cells and identifies the Wnt pathway as a likely genetic driver of leukemia stem cell fate.
Introduction
Although arising from a single cell initially, over time cancer cells acquire a series of genetic and epigenetic changes. At the time of diagnosis, the cancer consists of a heterogeneous collection of cells with differences in gene expression, proliferative capacity, morphology, and metastatic potential. Defined by their capacity to repop- ulate a tumor from a single cell, cancer stem cells (CSC) also evolve over time, lead- ing to therapy resistance and relapse.1 Increased tumor heterogeneity and CSC have been associated with resistance and relapse for many tumor types, including acute myelogenous leukemia and acute lymphoblastic leukemia (ALL).2-5
ALL is the most common pediatric cancer with approximately 3,000 new cases each year.6 It can be derived from either T cells or B cells, with B-cell ALL (B-ALL) typically having much more positive treatment outcomes. T-cell ALL (T-ALL) is a more aggressive malignancy, resulting from the transformation of immature T cells.7,8 While the cure rate for pediatric patients has improved with more intensive treatment regimens, prognosis is bleak for the 20% of children and 60% of adult patients with refractory and relapsed T-ALL.9 Relapses and refractory disease are
Correspondence:
JILL L.O. DE JONG
jdejong@peds.bsd.uchicago.edu
Received: September 7, 2018. Accepted: January 9, 2019. Pre-published: January 10, 2019.
doi:10.3324/haematol.2018.206417
Check the online version for the most updated information on this article, online supplements, and information on authorship & disclosures: www.haematologica.org/content/104/7/1388
©2019 Ferrata Storti Foundation
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