Regeneration-associated WNT Signaling Is Activated in Long-term Reconstituting AC133bright Acute Myeloid Leukemia Cells

Abstract

Acute myeloid leukemia (AML) is a genetically heterogeneous clonal disorder characterized by two molecularly distinct self-renewing leukemic stem cell (LSC) populations most closely related to normal progenitors and organized as a hierarchy. A requirement for WNT/β-catenin signaling in the pathogenesis of AML has recently been suggested by a mouse model. However, its relationship to a specific molecular function promoting retention of self-renewing leukemia-initiating cells (LICs) in human remains elusive. To identify transcriptional programs involved in the maintenance of a self-renewing state in LICs, we performed the expression profiling in normal (n = 10) and leukemic (n = 33) human long-term reconstituting AC133(+) cells, which represent an expanded cell population in most AML patients. This study reveals the ligand-dependent WNT pathway activation in AC133(bright) AML cells and shows a diffuse expression and release of WNT10B, a hematopoietic stem cell regenerative-associated molecule. The establishment of a primary AC133(+) AML cell culture (A46) demonstrated that leukemia cells synthesize and secrete WNT ligands, increasing the levels of dephosphorylated β-catenin in vivo. We tested the LSC functional activity in AC133(+) cells and found significant levels of engraftment upon transplantation of A46 cells into irradiated Rag2(-/-)γc(-/-) mice. Owing to the link between hematopoietic regeneration and developmental signaling, we transplanted A46 cells into developing zebrafish. This system revealed the formation of ectopic structures by activating dorsal organizer markers that act downstream of the WNT pathway. In conclusion, our findings suggest that AC133(bright) LSCs are promoted by misappropriating homeostatic WNT programs that control hematopoietic regeneration.

Intronless WNT10B-short variant underlies new recurrent allele-specific rearrangement in acute myeloid leukaemia

“…We recently reported evidence supporting the influence of the haematopoietic regeneration-associated WNT10B on AC133 bright cells in human AML via an autocrine/paracrine loop20.…”

Control of AC133/CD133 and impact on human hematopoietic progenitor cells through nucleolin

“…By contrast, mutant derivatives (CD133mutAB-pGL3, CD133mutBC-pGL3 and CD133mutAC-pGL3), lacking sequence motifs required for binding of nucleolin, were not activated and largely devoid of promoter activity (Figure 4a, lanes 3-8). Activity of CD133WT-pGL3 reporter construct was dependent on nucleolin concentration, paralleling the amounts of nucleolin expression vector employed (Figure 4a, lanes [11][12][13][14][15][16][17]. By contrast, nucleolin devoid of 288 N-terminal aa, which only marginally influenced cell surface AC133 and CD133 transcript levels (Figures 1a and 2a), could not activate CD133WT-pGL3 reporter construct (Figure 4b).…”

“…58 Aberrant WNT signaling is causatively involved in development of certain types of leukemia. 26,59 WNT/β-catenin is associated with LSC from mixed-lineage leukemia, from chronic myeloid leukemia and acute myelogenous leukemia, 15 providing opportunities for therapeutic intervention. 26,59 Moreover, Bcl-2 is upregulated in functionally defined human LSCs, offering a potential therapeutic target for their selective eradication.…”

“…3,12 Thus, implication of AC133 for prospective isolation of tumor-initiating cells in childhood acute lymphoblastic leukemia, mantle cell lymphoma and in acute myelogenous leukemia was reported. [13][14][15] Furthermore, CD133 is required for growth of AC133+ acute lymphoblastic leukemia cells. 16 Human AC133 expression is controlled at multiple levels, partly in a tissue-specific fashion.…”

“…(a) EMSA with labeled oligonucleotides CD133A (lanes 1-5), CD133B (lanes 6-10), CD133C (lanes[11][12][13][14][15] or AP2 (lanes[16][17]. Lanes 1, 3-6, 8-11 and 13-16-EMSA with nucleolin-GST protein.…”