Grb10 Is a Tumor Suppressor in Human Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a common and potentially fatal hematologic malignancy. Allogeneic stem cell transplantation is the only curative therapy for most subtypes of AML, but carries a significant risk of transplant-related mortality. The development of novel therapies to eradicate AML remains a substantial area of unmet medical need. Growth factor receptor bound protein 10 (Grb10) is a member of the family of imprinted genes. Our laboratory demonstrated that in normal hematopoietic system, deletion of the maternal allele of Grb10 significantly increased hematopoietic stem cell long-term repopulating capacity (Yan et al. Cell Rep 2016). Grb10 has been shown to bind the intracellular domain of various tyrosine kinase receptors, e.g. KIT, FLT3 and RET, as well as low-density lipoprotein receptor-related protein 6, a negative regulator of the Wnt/β-catenin pathway. Analyzing RNAseq data from the Leucegene Project, we found that Grb10 is expressed on the majority of patient AML samples regardless of leukemia mutation profile. Silencing of Grb10 expression via Grb10 shRNA increased the proliferation and colony forming capacity of human AML cell lines, Kasumi-1, THP-1 and OCI-AML3 in vitro (p<0.0001 and p<0.01). Conversely, overexpression of Grb10 suppressed human AML cell growth (p<0.05). In order to determine the role of Grb10 in regulating AML growth in vivo, we transduced bone marrow lineage negative cells from mice with Grb10 maternal allele deletion (Grb10 ^m/+) and wild type (Grb10 ^+/+) mice with HoxA9-Meis1-neo-MSCV (gift from G. Savageau) and transplanted the progeny into congenic mice. Primary and secondary mice transplanted with Grb10^m/+ HoxA9-Meis1 leukemia cells displayed significantly decreased survival compared to mice transplanted with Grb10^+/+ HoxA9-Meis1 cells (p<0.001 and p<0.05). Furthermore, leukemia cells with Grb10 maternal allele deletion displayed an increase cell cycle progression and increased leukemia colony forming capacity. RNAseq analysis of Grb10 ^m/+ leukemia cells from diseased mice revealed significant dysregulation of the canonical Wnt/β catenin signaling pathway compared to Grb10 ^+/+ mice. RT-qPCR analysis confirmed that Wnt/β-catenin target genes, including MYC, CCND1, and SOX2 were significantly up-regulated in Grb10 knockdown human AML cells lines. Taken together, these data suggest that Grb10 is a powerful tumor suppressor in human AML, and represents a novel mechanistic target for the development of new therapies for human AML.