RAB3D/MDM2/β-catenin/c-MYC axis exacerbates the malignant behaviors of acute myeloid leukemia cells in vitro and in vivo.

RAB3D, a small Ras-like GTPase involved in regulating secretory pathway, plays a cancer-promoting role in several solid tumors. However, its role in leukemogenesis remains unknown yet. Acute myeloid leukemia (AML) is a common acute leukemia with a high mortality. Here, we found the higher expression of RAB3D in bone marrow mononuclear cells derived from AML patients (n = 54) versus healthy participants (n = 20). The following loss- and gain-of-function experiments demonstrated that RAB3D promoted growth, enhanced colony formation and accelerated G1/S transition of U937, THP-1 and KG-1 AML cells. RAB3D silencing inhibited tumorigenesis of AML cells in vivo and delayed AML cells-induced death of mice. Interestingly, the expression of RAB3D is positively correlated with that of an oncogene mouse double minute 2 (MDM2) in bone marrow mononuclear cells of AML patients (r = 0.923, p < 0.001). Intracellular MDM2 was conjugated with more ubiquitins and degraded faster when RAB3D was silenced. A commonly therapeutic target of AML, β-catenin signaling, was activated by RAB3D overexpression, but deactivated after MDM2 was silenced. The RAB3D-induced proliferation acceleration and β-catenin activation were abolished by MDM2 knockdown, implying that RAB3D function by stabilizing MDM2. In addition, c-MYC, a β-catenin downstream effector, was recruited directly to the RAB3D gene promoter (-360/-349 and -136/-125 sites) and induced its transcription. Collectively, this study demonstrates that RAB3D may exacerbate the malignant behaviors of AML cells through forming a positive feedback loop with MDM2/β-catenin/c-MYC signaling. RAB3D might be a novel target of clinical AML treatment.