Fbxw11 Variants Promotes Proliferation of Leukemia Cells By Activating the NF-κB Signaling Pathway

Fbxw11, as a member of F-box proteins family, is a constituent of the SCF (Skp1-Cul1-F box) ubiquitin ligase complex. This ligase ubiquitinates specifically phosphorylated substrates and controls the degradation and half-life of key cellular regulators. So, Fbxw11 play a pivotal role in many aspects of hematopoiesis and tumorigenesis through regulating various signal transduction pathways. We found two transcript variants (Fbxw11c and Fbxw11d) in mouse bone marrow. However the role of Fbxw11 variants in the development of leukemia and the underlying mechanisms remain largely unknown. In this study, we cloned three transcript variants (Fbxw11a, Fbxw11c and Fbxw11d) to study the biological function of Fbxw11 in leukemia.

In order to investigate the role of Fbxw11 variants in leukemia, we established L1210 cell lines with over-expression of Fbxw11a, Fbxw11c and Fbxw11d respectively using the lentivirus system. The effect of Fbxw11 variants on proliferation of leukemia cells in vitro was first detected. Growth curve of leukemia cells with Fbxw11a, Fbxw11c or Fbxw11d over-expression was established by cell counting. The results suggested that over-expression of Fbxw11 variants stimulated the growth of leukemia cells. Then MTT experiment was carried out to study the effect of Fbxw11 variants on leukemia cell proliferation and the results showed that Fbxw11 variants increased the proliferation of L1210 cells in vitro.

To further confirm the effects of Fbxw11 variants on proliferation of leukemia cells in vivo, tumor xenografts model with over-expression of Fbxw11a, Fbxw11c and Fbxw11d in DBA/2 mice was established. Leukemia cells L1210 with over-expression of Fbxw11a, Fbxw11c and Fbxw11d respectively were transplanted into DBA/2 mice by hypodermic injection. The tumor growth curves showed that tumor growth was increased in Fbxw11 variants over-expression group compared to the control group. Mice were sacrificed on day 28 after transplantation, greater volume of the xenograft tumors were obtained from Fbxw11 variants over-expression group than control group. Therefore, Over-expression of Fbxw11 variants could increase growth of tumor in vivo.

To further investigate the molecular mechanism under the effect of Fbxw11 variants on proliferation of leukemia cells, we tested the apoptosis and cell cycle of leukemia cells with Fbxw11 variants over-expression. Over-expression of Fbxw11 variants did not affect the cell apoptosis but accelerated the process of cell cycle. These results revealed that the increased cell proliferation was not due to decrease in cell apoptosis but due to increase in cell cycle. In addition, we tested the effect of Fbxw11 variants on the signal transduction by dual-luciferase reporter gene system. The results showed that over-expression of Fbxw11 variants caused the activation of NF-κB signaling pathway.

In conclusion, our findings suggest that Fbxw11 variants have promoting effect on cell proliferation of leukemia cells. The effect of Fbxw11 variants on cell proliferation are due to accelerated the process of cell cycle but not decreasing in cell apoptosis. Further study demonstrated that Fbxw11 variants promote cell proliferation through activating the NF-κB signaling pathway. The important role of Fbxw11 in regulating the development of leukemia suggests that a potent rationale for developing Fbxw11 as a potential therapeutic target against leukemia.