Person:

Goessling, Wolfram

Leukemia stem cells (LSCs) are capable of limitless self-renewal and are responsible for the maintenance of leukemia. Because selective eradication of LSCs could offer substantial therapeutic benefit, there is interest in identifying the signaling pathways that control their development. We studied LSCs in mouse models of acute myelogenous leukemia (AML) induced either by coexpression of the Hoxa9 and Meis1a oncogenes or by the fusion oncoprotein MLL-AF9. We show that the Wnt/β-catenin signaling pathway is required for self-renewal of LSCs that are derived from either hematopoietic stem cells (HSC) or more differentiated granulocyte-macrophage progenitors (GMP). Because the Wnt/β-catenin pathway is normally active in HSCs but not in GMP, these results suggest that reactivation of β-catenin signaling is required for the transformation of progenitor cells by certain oncogenes. β-catenin is not absolutely required for self-renewal of adult HSCs; thus, targeting the Wnt/β-catenin pathway may represent a new therapeutic opportunity in AML.

Cell-based therapies hold the potential to alleviate the growing burden of liver diseases. Such therapies require human hepatocytes, which, within the stromal context of the liver, are capable of many rounds of replication. However, this ability is lost ex vivo and human hepatocyte sourcing has been limiting many fields of research for decades. Here, we developed a high-throughput screening platform for primary human hepatocytes to identify small molecules in two different classes that can be used to generate renewable sources of functional human hepatocytes. One class induced functional proliferation of primary human hepatocytes in vitro. The second class enhanced hepatocyte functions and promoted differentiation of iPS-derived hepatocytes, toward a phenotype more mature than what was previously obtainable. The identification of these small molecules can help to address a major challenge impacting many facets of liver research and may lead to the development of novel therapeutics for liver diseases.

The incidence of human papillary thyroid cancer (PTC) is increasing and an aggressive subtype of this disease is resistant to treatment with vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor. VEGFR2 promotes angiogenesis by triggering endothelial cell proliferation and migration. However, the molecular mechanisms governing VEGFR2 stability in vivo remain unknown. Additionally, whether VEGFR2 influences PTC cell migration is not clear. We show that the ubiquitin E3 ligase SCF(^{β-TRCP}) promotes ubiquitination and destruction of VEGFR2 in a casein kinase I (CKI)–dependent manner. β-TRCP knockdown or CKI inhibition causes accumulation of VEGFR2, resulting in increased activity of signaling pathways downstream of VEGFR2. β-TRCP–depleted endothelial cells exhibit enhanced migration and angiogenesis in vitro. Furthermore, β-TRCP knockdown increased angiogenesis and vessel branching in zebrafish. Importantly, we found an inverse correlation between β-TRCP protein levels and angiogenesis in PTC. We also show that β-TRCP inhibits cell migration and decreases sensitivity to the VEGFR2 inhibitor sorafenib in poorly differentiated PTC cells. These results provide a new biomarker that may aid a rational use of tyrosine kinase inhibitors to treat refractory PTC.

Hematopoietic stem cells (HSCs) are used in transplantation therapy to reconstitute the hematopoietic system. Human cord blood (hCB) transplantation has emerged as an attractive alternative treatment option when traditional HSC sources are unavailable, however, the absolute number of hCB HSCs transplanted is significantly lower than bone marrow or mobilized peripheral blood stem cells (MPBSCs). We previously demonstrated that dimethyl-prostaglandin E2 (dmPGE2) increased HSCs in vertebrate models. Here, we describe preclinical analyses of the therapeutic potential of dmPGE2-treatment using human and non-human primate HSCs. dmPGE2 significantly increased total human hematopoietic colony formation in vitro and enhanced engraftment of unfractionated and CD34+ hCB following xenotransplantation. In non-human primate autologous transplantation, dmPGE2-treated CD34+ MPBSCs showed stable multilineage engraftment over one year post-infusion. Together, our analyses indicated that dmPGE2 mediates conserved responses in HSCs from human and non-human primates, and provided sufficient preclinical information to support proceeding to an FDA-approved phase 1 clinical trial.

SUMMARY Vitamin D insufficiency is a worldwide epidemic affecting billions of individuals, including pregnant women and children. Despite its high incidence, the impact of active vitamin D3 (1,25(OH)D3) on embryonic development beyond osteo-regulation remains largely undefined. Here, we demonstrate that 1,25(OH)D3 availability modulates zebrafish hematopoietic stem and progenitor cell (HSPC) production. Loss of Cyp27b1-mediated biosynthesis or vitamin D receptor (VDR) function by gene knockdown resulted in significantly reduced runx1 expression and Flk1+cMyb+ HSPC numbers. Selective modulation in vivo and in vitro in zebrafish indicated that vitamin D3 acts directly on HSPCs, independent of calcium regulation, to increase proliferation. Notably, ex vivo treatment of human HSPCs with 1,25(OH)D3 also enhanced hematopoietic colony numbers, illustrating conservation across species. Finally, gene expression and epistasis analysis indicated that CXCL8 (IL-8) was a functional target of vitamin D3-mediated HSPC regulation. Together, these findings highlight the relevance of developmental 1,25(OH)D3 availability for definitive hematopoiesis and suggest potential therapeutic utility in HSPC expansion.