Somatic and germline mutations in GATA2 were recently identified in patients diagnosed with MonoMAC, the hallmarks of which include mono cytopenia, B-cell and NK-cell lymphopenia, susceptibility to opportunistic infections (e.g. MAC), and a strong propensity to develop hypocellular MDS/AML or CMML. GATA2 mutations were also recently identified in other related disorders: Emberger syndrome (primary lymphedema with myelodysplasia), Familial MDS/AML, and DCML (Dendritic Cell, Monocytes, Lymphoid Deficiency). Family members with GATA2 mutations show variable penetrance and expressivity indicating that other factors may be required for development of disease and phenotype. GATA2 mutations are thought to result in loss of function or haploinsufficiency, but the precise mechanism for the development of cytopenias, immunodeficiency, and susceptibility to MDS remains to be elucidated. MicroRNA (miR) represents a unique mechanism of post-transcriptional gene regulation. In this study we generated microRNA profiles of patient derived MonoMAC cell lines followed by functional studies to identify aberrant miRs and their targets, which could potentially cooperate with GATA2 deficiency in generating hematologic disease. Inducible deletion of Myeloid Leukemia Cell 1 (Mcl1), a member of the Bcl2 family, in mice results in the loss of hematopoietic stem cells (HSCs) and progenitors, and in development of cytopenias.
RNA was isolated from EBV-immortalized B cells of 10 healthy controls and 13 MonoMAC patients with MDS and defined mutations in GATA2. microRNA expression profiles were generated using the Agilent high density human microRNA array. Array data were normalized to the data point of 75th percentile signal strength and to a set of spike-in and control probes. The differences between the means of experimental groups were analyzed by Mann-Whitney rank sum test. The miRs with significant p values (p≤ 0.05) and fold change (≥ 2-fold) in both normalization methods were selected for further analysis. TargetScan was utilized to predict the mRNA targets of aberrantly expressed miRs. miR targets were validated by functional studies in the Ly8 cell line.
Eight miRs were significantly differentially expressed (≥ 2-fold; p ≤ 0.05) as determined by microRNA microarray profiles. Six miRs showed increased expression in monoMAC cell lines compared to controls (miR-9, −181a-2–3p, −181c, −181c-3p, −486–3p, −582–5p) while two miRs showed significantly decreased expression (miR-223, −424–3p). Among the differentially expressed miRs that were validated by quantitative RT-PCR was miR-181c, which demonstrated a 2.2 fold increase in expression in MonoMAC cell lines (p = 0.013). Among the target transcripts potentially regulated by miR-181c, MCL1 expression was significantly decreased (2 fold; p = 0.018) in monoMAC cell lines in comparison to control cell lines. Transient transfection of miR-181c in Ly8 cells resulted in 40% decrease of MCL1 mRNA level, suggesting that miR-181c negatively regulates MCL1 in MonoMAC.
These findings indicate that MonoMAC/GATA2 deficiency is associated with significantly decreased expression of MCL1 possibly through negative regulation involving miR-181c. Deletion of Mcl1 is known to cause apoptosis, loss of HSCs, and cytopenias in murine studies. Thus, down-regulation of MCL1 seen in MonoMAC/GATA2 deficiency may similarly favor unregulated apoptosis and the depletion of hematopoietic progenitors resulting in cytopenias, immunodeficiency, and risk of MDS/AML.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.