FHL2 Interacts with Iaspp and Impacts the Biological Functions of Leukemia Cells

Introduction iASPP played an important role in leukemogenesis in our previous study. In order to clarify its mechanism, a yeast two-hybrid screen was performed to find the binding partner of iASPP. In this study, we reported FHL2 as a novel binding partner of iASPP. The biological functions of the communication between FHL2 and iASPP were detected, and its possible mechanisms were investigated in human leukemia cell lines.

Methods A yeast two-hybrid screen was performed to identify FHL2 as a novel binding partner of iASPP. Immunofluorescence, Co-IP and Western blot analysis were used to confirm the communication between FHL2 and iASPP. After FHL2 or iASPP was knocked down in K562 and Kasumi-1 cells by lentiviral, MTT assay and flow cytometry were performed to detect the proliferation, cell cycle distribution and apoptosis rate of leukemic cells, meanwhile Western blot analysis was used to analyze the level of cell cycle- and apoptotic-related proteins. Dual luciferase assay was conducted to investigate the transcriptional activity of p53 on Bax when iASPP and FHL2 were overexpressed or FHL2 was knocked down.

Results FHL2 was highly expressed in K562 and Kasumi-1 cells. FHL2 and iASPP interacted with each other and co-localized in both nucleus and cytoplasm. Either FHL2 or iASPP silenced could reduce cell proliferation, induce cell cycle arrest at G0/G1 phases, and increase cell apoptosis. Western blot analysis showed that the level of p21 increased and anti-apoptotic protein Bcl-2 was reduced. Interestingly, when FHL2 was knocked down, the protein expression level of iASPP also decreased. Similarly, the expression of FHL2 would reduce when iASPP was silenced. Dual luciferase assay suggested that iASPP could reduce the transcriptional activity of p53 on Bax, furthermore, when FHL2 was knocked down at the same time, the transcriptional activity of p53 was rescued.

Conclusions The interaction between FHL2 and iASPP in AML was observed for the first time. Cell proliferation reducing, cell cycle arresting at G0/G1 phases, and cell apoptosis increasing occurred in either FHL2 knockdown or iASPP knockdown. Moreover, iASPP and FHL2 participated in the regulation of the transcriptional activation function of p53. These results indicated that FHL2 might be a novel potential target for AML treatment.