Mesenchymal stem cells (MSCs) are multipotent progenitors present in the bone marrow stroma and in subcutaneous abdominal fat, an abundant and easily accessible source of MSCs with the ability to differentiate along multiple lineage pathways. The stem cell-associated transcription co-factor Zinc Finger Protein 521 (ZNF521/zfp521) has been implicated in the control of the homeostasis of hematopoietic, neural and osteo-adipogenic progenitors. Here we document through the analysis of a panel of human adipose-derived stem cells (hADSCs), that ZNF521 strongly inhibits the generation of mature adipocytes. Enforced overexpression of ZNF521 in these cells resulted in a significant delay and reduction in adipocyte differentiation upon exposure to inducers of adipogenesis. Of particular relevance, ZNF521 was able to inhibit the expression of ZNF423, recently identified as an essential commitment factor necessary for the generation of pre-adipocytes. Conversely, silencing of ZNF521 was found to significantly enhance the adipogenic differentiation of hADSCs. Inhibition of adipogenesis by ZNF521 was at least in part due to inhibition of EBF1. Taken together, these results confirm a role for ZNF521 as a key negative regulator of adipocyte differentiation of hADSCs.

Preventive therapy can target hormone-responsive breast cancer (BC) by treatment with selective estrogen receptor modulators (SERMs) and reduce the incidence of BC. Genome-wide association studies have identified single nucleotide polymorphisms (SNPs) with relevant predictive values, SNPs in the ZNF423 gene were associated with decreased risk of BC during SERM therapy, and SNPs in the Cathepsin O gene with an increased risk. ZNF423, which was not previously associated with BC is a multifunctional transcription factor known to have a role in development, neurogenesis, and adipogenesis and is implicated in other types of cancer. ZNF423 is transcriptionally controlled by the homolog ZNF521, early B cell factor transcription factor, epigenetic silencing of the promoter by CpG island hyper-methylation, and also by ZNF423 itself in an auto-regulatory loop. In BC cells, ZNF423 expression is found to be induced by estrogen, dependent on the binding of the estrogen receptor and calmodulin-like 3 to SNPs in ZNP423 intronic sites in proximity to consensus estrogen response elements. ZNF423 has also been shown to play a mechanistic role by trans-activating the tumor suppressor BRCA1 and thus modulating the DNA damage response. Even though recent extensive trial studies did not classify these SNPs with the highest predictive values, for inclusion in polygenic SNP analysis, the mechanism unveiled in these studies has introduced ZNF423 as a factor important in the control of the estrogen response. Here, we aim at providing an overview of ZNF423 expression and functional role in human malignancies, with a specific focus on its implication in hormone-responsive BC.

Human adipose-derived stem cells (hADSCs) are multipotent mesenchymal cells that can differentiate into adipocytes, chondrocytes, and osteocytes. During osteoblastogenesis, the osteoprogenitor cells differentiate into mature osteoblasts and synthesize bone matrix components. Zinc finger protein 521 (ZNF521/Zfp521) is a transcription co-factor implicated in the regulation of hematopoietic, neural, and mesenchymal stem cells, where it has been shown to inhibit adipogenic differentiation. The present study is aimed at determining the effects of ZNF521 on the osteoblastic differentiation of hADSCs to clarify whether it can influence their osteogenic commitment. The enforced expression or silencing of ZNF521 in hADSCs was achieved by lentiviral vector transduction. Cells were cultured in a commercial osteogenic medium for up to 20 days. The ZNF521 enforced expression significantly reduced osteoblast development as assessed by the morphological and molecular criteria, resulting in reduced levels of collagen I, alkaline phosphatase, osterix, osteopontin, and calcium deposits. Conversely, ZNF521 silencing, in response to osteoblastic stimuli, induced a significant increase in early molecular markers of osteogenesis and, at later stages, a remarkable enhancement of matrix mineralization. Together with our previous findings, these results show that ZNF521 inhibits both adipocytic and osteoblastic maturation in hADSCs and suggest that its expression may contribute to maintaining the immature properties of hADSCs.

ZNF521 is a transcription co-factor with recognized regulatory functions in haematopoietic, osteo-adipogenic and neural progenitor cells. Among its diverse activities, ZNF521 has been implicated in the regulation of medulloblastoma (MB) cells, where the Hedgehog (HH) pathway, has a key role in the development of normal cerebellum and of a substantial fraction of MBs. Here a functional cross-talk is shown for ZNF521 with the HH pathway, where it interacts with GLI1 and GLI2, the major HH transcriptional effectors and enhances the activity of HH signalling. In particular, ZNF521 cooperates with GLI1 and GLI2 in the transcriptional activation of GLI (glioma-associated transcription factor)-responsive promoters. This synergism is dependent on the presence of the N-terminal, NuRD-binding motif in ZNF521, and is sensitive to HDAC (histone deacetylase) and GLI inhibitors. Taken together, these results highlight the role of ZNF521, and its interaction with the NuRD complex, in determining the HH response at the level of transcription. This may be of particular relevance in HH-driven diseases, especially regarding the MBs belonging to the SHH (sonic HH) subgroup where a high expression of ZNF521 is correlated with that of HH pathway components.

Acute myeloid leukemia (AML), the most common acute leukemia in the adult, is believed to arise as a consequence of multiple molecular events that confer on primitive hematopoietic progenitors unlimited self-renewal potential and cause defective differentiation. A number of genetic aberrations, among which a variety of gene fusions, have been implicated in the development of a transformed phenotype through the generation of dysfunctional molecules that disrupt key regulatory mechanisms controlling survival, proliferation, and differentiation in normal stem and progenitor cells. Such genetic aberrations can be recreated experimentally to a large extent, to render normal hematopoietic stem cells “bad”, analogous to the leukemic stem cells. Here, we wish to provide a brief outline of the complementary experimental approaches, largely based on gene delivery and more recently on gene editing, employed over the last two decades to gain insights into the molecular mechanisms underlying AML development and progression and on the prospects that their applications offer for the discovery and validation of innovative therapies.