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NG2 is a target gene of MLL-AF4 that underlies glucocorticoid resistance in infant MLL-rearranged B-ALL by regulating NR3C1 expression through interaction with FLT3

ABSTRACT: B-cell acute lymphoblastic leukemia (B-ALL) is the most common pediatric cancer, with long-term overall survival rates of 80%. However, B-ALL harboring rearrangements of the MLL gene (also known as KTM2A), hereinafter termed MLLr B-ALL, is frequently seen in infants and is associated with poor 5-year survival (<30%), frequent relapses, and refractoriness to glucocorticoids (GC). GC are an essential part of the treatment backbone for B-ALL and GC resistance is a major clinical predictor of poor outcome. Unraveling the mechanisms of GC resistance in MLLr B-ALL is, therefore, crucial to guide therapeutic strategies that deepen response after induction therapy. Neuron-glial antigen-2 (NG2) expression is a hallmark of MLLr B-ALL and is minimally expressed in healthy hematopoietic cells. We recently reported that NG2 expression is associated with poor prognosis and that anti-NG2 immunotherapy strongly reduces/delays relapse in xenograft models of MLLr B-ALL. However, despite its contribution to MLLr B-ALL pathogenesis and its diagnostic utility, the role of NG2 in MLLr-mediated leukemogenesis/chemoresistance remains elusive. We show here that NG2 is an epigenetically regulated direct target gene of the leukemic MLL-AF4 fusion protein. NG2 negatively regulates the expression of the GC receptor NR3C1, conferring GC chemoresistance to MLLr B-ALL cells in vitro and in vivo. Mechanistically, NG2 interacts with FLT3 to render ligand-independent activation of FLT3 signaling (a hallmark of MLLr B-ALL) and downregulation of NR3C1 via AP-1-mediated transrepression. Collectively, our study elucidates the role of NG2 in GC resistance in MLLr B-ALL through a FLT3/AP-1-mediated downregulation of NR3C1, providing novel therapeutic avenues for MLLr B-ALL.

INSTRUMENT(S): Orbitrap Eclipse

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): B Cell, Cell Culture

DISEASE(S): Lymphoma

SUBMITTER: Narcis Fuentes

LAB HEAD: Prof. Pablo Menendez

PROVIDER: PXD041875 | Pride | 2024-07-12

REPOSITORIES: Pride

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Source:

			Action	DRS
	2022LB006_MEVI_001_01_45pto.msf	Msf
	2022LB006_MEVI_001_01_45pto.raw	Raw
	2022LB006_MEVI_002_01_45pto.msf	Msf
	2022LB006_MEVI_002_01_45pto.raw	Raw
	2022LB006_MEVI_003_01_45pto.msf	Msf

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Project description:MLL-AF4 is a hallmark genomic aberration which arises prenatally in high-risk infant acute lymphoblastic leukemia (ALL). In human embryonic stem cells (hESCs), MLL-AF4 skewed hemato-endothelial specification but was not sufficient for transformation. Additional cooperating genetic insults seem required for MLL-AF4-mediated leukemogenesis. FLT3 is highly expressed in MLL-AF4+ ALL through activating mutations (FLT3-TKD or FLT3-ITD) or increased transcriptional expression, being therefore considered a potential cooperating event in MLL-AF4+ ALL. Here, we explored the developmental impact of FLT3 activation on its own or in cooperation with MLL-AF4 in the hematopoietic fate of hESCs. FLT3 activation did not impact specification of CD45-CD31+ hemogenic precursors but significantly enhanced the formation of CD45+CD34+ and CD45+ blood cells and blood progenitors with clonogenic potential. Importantly, FLT3 activation through FLT3 mutations or FLT3-WT overexpression completely abrogated hematopoietic differentiation from MLL-AF4-expressing hESCs, indicating that FLT3 activation cooperates with MLL-AF4 to inhibit human embryonic hematopoiesis. Cell cycle/apoptosis analyses suggest that FLT3 activation directly impacts hESC specification rather than selective proliferation/survival of hESC-emerging hematopoietic derivatives. Transcriptional profiling supported the limited impact of FLT3 activation on hESC specification towards CD45-hemogenic precursors and the enhanced hematopoiesis upon FLT3 activation, and inhibited hematopoiesis upon MLL-AF4 expression in FLT3-activated hESCs which was associated to large transcriptional changes and regulation of master early hematopoietic genes. Also, although FLT3 activation and MLL-AF4 cooperate to inhibit embryonic hematopoiesis the underlying molecular/genetic mechanisms differ depending on how FLT3 activation is achieved. Finally, FLT3 activation did not cooperate with MLL-AF4 to immortalize/transform hESC-derived hematopoietic cells.

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NG2 is a target gene of MLL-AF4 that underlies glucocorticoid resistance in infant MLL-rearranged B-ALL by regulating NR3C1 expression through interaction with FLT3

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