Zfp521 SUMOylation facilities erythroid hematopoietic reconstitution under stress

Exploring the contribution of Zfp521/ZNF521 on primary hematopoietic stem/progenitor cells and leukemia progression

Hematopoietic stem cells (HSCs) drive cellular turnover in the hematopoietic system by balancing self-renewal and differentiation. In the adult bone marrow (BM), these cells are regulated by a complex cellular microenvironment known as "niche," which involves dynamic interactions between diverse cellular and non-cellular elements. During blood cell maturation, lineage branching is guided by clusters of genes that interact or counteract each other, forming complex networks of lineage-specific transcription factors. Disruptions in these networks can lead to obstacles in differentiation, lineage reprogramming, and ultimately malignant transformation, including acute myeloid leukemia (AML). Zinc Finger Protein 521 (Znf521/Zfp521), a conserved transcription factor enriched in HSCs in both human and murine hematopoiesis, plays a pivotal role in regulating HSC self-renewal and differentiation. Its enforced expression preserves progenitor cell activity, while inhibition promotes differentiation toward the lymphoid and myeloid lineages. Transcriptomic analysis of human AML patient samples has revealed upregulation of ZNF521 in AMLs with the t(9;11) fusion gene MLL-AF9. In vitro studies have shown that ZNF521 collaborates with MLL-AF9 to enhance the growth of transformed leukemic cells, increase colony formation, and activate MLL target genes. Conversely, inhibition of ZNF521 using short-hairpin RNA (shRNA) results in decreased leukemia proliferation, reduced colony formation, and induction of cell cycle arrest in MLL-rearranged AML cell lines. In vivo experiments have demonstrated that mZFP521-deficient mice transduced with MLL-AF9 experience a delay in leukemia development. This review provides an overview of the regulatory network involving ZNF521, which plays a crucial role in controlling both HSC self-renewal and differentiation pathways. Furthermore, we examine the impact of ZNF521 on the leukemic phenotype and consider it a potential marker for MLL-AF9+ AML.

ZNF521 Enhances MLL-AF9-Dependent Hematopoietic Stem Cell Transformation in Acute Myeloid Leukemias by Altering the Gene Expression Landscape

Leukemias derived from the MLL-AF9 rearrangement rely on dysfunctional transcriptional networks. ZNF521, a transcription co-factor implicated in the control of hematopoiesis, has been proposed to sustain leukemic transformation in collaboration with other oncogenes. Here, we demonstrate that ZNF521 mRNA levels correlate with specific genetic aberrations: in particular, the highest expression is observed in AMLs bearing MLL rearrangements, while the lowest is detected in AMLs with FLT3-ITD, NPM1, or CEBPα double mutations. In cord blood-derived CD34⁺ cells, enforced expression of ZNF521 provides a significant proliferative advantage and enhances MLL-AF9 effects on the induction of proliferation and the expansion of leukemic progenitor cells. Transcriptome analysis of primary CD34⁺ cultures displayed subsets of genes up-regulated by MLL-AF9 or ZNF521 single transgene overexpression as well as in MLL-AF9/ZNF521 combinations, at either the early or late time points of an in vitro leukemogenesis model. The silencing of ZNF521 in the MLL-AF9 + THP-1 cell line coherently results in an impairment of growth and clonogenicity, recapitulating the effects observed in primary cells. Taken together, these results underscore a role for ZNF521 in sustaining the self-renewal of the immature AML compartment, most likely through the perturbation of the gene expression landscape, which ultimately favors the expansion of MLL-AF9-transformed leukemic clones.