A recent study led by Dr. WANG Lan’s group from Shanghai Institute of Nutrition and Health (SINH) of the Chinese Academy of Sciences (CAS) revealed the cell non-autonomous role of the inhibitor of DNA binding 1 (ID1) in acute myeloid leukemia (AML), demonstrating the mechanism of the inhibitor of ID1 in the initiation and development of AML cell-non-autonomously. This study, published online in Blood, provided a novel therapeutic strategy for the clinical treatment of AML. 

AML is a type of malignant tumor originating from hematopoietic stem/progenitor cells (HSPCs), and is characterized by enhanced clonal expansion and differentiation block of immature myeloid cells in the bone marrow. It is the most common form of adult leukemia, and its high heterogeneity limits prognosis and outcomes. While clinical governance of AML has improved significantly, challenges remain in the overall survival time, the recurrence, etc. Therefore, there is an urgent need to explore the mechanisms by which AML occurs and to develop new therapeutic strategies. 

The initiation and development of AML is often accompanied by abnormal gene expression. Dr. WANG’s lab has uncovered that ID1 is a target gene for AML1-ETO, a leukemogenic fusion protein, and that ID1 interacts directly with AKT1 to promote AKT1 phosphorylation, thereby accelerating the initiation and progression of leukemia. The lab has also uncovered the differential action of Id1 in MLL-AF9-driven leukemia based on cell of origin. Id1 ablation in fetal liver HSPCs significantly weakens the development of leukemia, whereas Id1 loss in bone marrow HSPCs accelerates leukemogenesis. 

In this study, the researchers found that ID1 is highly expressed in mesenchymal stem cells (MSCs) derived from AML patients, especially in AML subtypes M2 and M5.  

The researchers performed ChIP-seq analysis to investigate the potential mechanism of ID1 upregulation in MSCs derived from AML patients. They found that AML1-ETO and MLL-AF9 directly bind to the promoter region of BMP6. Using shRNA to knock down BMP6 in Kasumi-1 and THP-1 cells, they observed significant downregulation of ID1 protein levels in HS-5 cells co-cultured with these cells, suggesting that AML cells promote the ID1 expression in stromal cells through BMP6 secretion.  

The researchers then carried out the follow-up experiments in AML mouse models. ID1 deletion in host bone marrow microenvironment (BMM) delayed the onset and progression of AML1-ETO9a or MLL-AF9-driven AML and significantly inhibited the self-renewal of leukemia stem cells (LSCs). Knocking out of ID1 in mesenchymal cells significantly suppresses the proliferation of co-cultured AML cells. 

By analyzing bone marrow supernatant fluid (BMSF) of Id1^+/+ and Id1^-/- recipients with AML, the researchers found a significant downregulation of Angptl7, a member of the secreted glycoprotein family that supports HSPCs expansion, in the BMSF of Id1^-/- recipients with AML. To examine that ANGPTL7 is regulated by ID1 in the BMM, they performed in vitro co-culture assays. They supplemented recombinant ANGPTL7 in ID1^-/- HS-5 cells, which significantly rescued proliferation suppression and cell cycle arrest in co-cultured AML cells. To assess the function of Angptl7 in the progression of AML in vivo, they attempted an intra-BM transfusion of Angptl7 to the recipient, and found that intra-BM transfusion of Angptl7 significantly accelerated AML progression in Id1^-/- recipients. 

To understand the cellular non-autonomous role of ID1 in leukemogenesis, the researchers revealed that ID1 interacts with RNF4, a ubiquitin E3 ligase of SP1 through mass spectrometry analysis and GST-Pull down assays. Co-IP analysis showed that the interaction between the C terminal of ID1 and the SIM region of RNF4 weakens the ubiquitination of SP1, followed by an upregulation of ANGPTL7. ID1 interacts with RNF4 to inhibit SP1 degradation, which contributes to AML progression non-cell-autonomously. 

This study revealed that ID1 regulated ANGPTL7 expression is required for the occurrence and development of AML cell-non-autonomously by maintaining self-renewal of LSCs, and that AML cells promote ID1 expression in the BMM by secreting BMP6. It also revealed that ID1 controls the initiation and progression of leukemia in a cell-autonomous role, and that the regulatory loop of ID1 between MSCs and LSCs has already demonstrated the importance of ID1 as a therapeutic target for AML.