Figure 6
From: Tumor-derived neomorphic mutations in ASXL1 impairs the BAP1-ASXL1-FOXK1/K2 transcription network
Tumor-derived ASXL1 mutants promote leukemia cell growth through increased cell cycle progression and decreased apoptosis. (A and B) Cell proliferation of ASXL1+/N590 and ASXL1+/− K562 clones, as well as ASXL1+/N646 and ASXL1+/− Kasumi-1 clones under normoxia or hypoxia (1% O2) condition for the indicated time periods. (C) The ratios of G0/G1-phase and G2/M-phase in ASXL1+/N590 and ASXL1+/− clones under hypoxia (1% O2, 24 h). (D) Cell apoptosis and viability in ASXL1+/N590 and ASXL1+/− clones upon serum starvation. The indicated K562 cells were maintained in RPMI-1640 medium without FBS for 48 h. (E) Apoptosis-related markers in ASXL1+/N590 and ASXL1+/− clones upon serum starvation. Cells were cultured as mentioned above in (D). (F) ASXL1+/N590 and ASXL1+/− K562 clones were treated with 2-MeOE2 (HIF-1α inhibitor) for 24 h, and the cytotoxicity was determined by CCK-8 assay as described in the “MATERIALS AND METHODS” section. (G) Working model. C-terminally truncated ASXL1 mutant is expressed at a much higher protein level than wild-type ASXL1, and loses interaction with transcription factors such as FOXK1 and FOXK2, but still interacts with BAP1. Thus, the mutant ASXL1 protein inhibits the interaction between BAP1 and wild-type ASXL1 in a dominant-negative manner, reduces BAP1 enrichment and increases H2AK119 mono-ubiquitination at the promoters of FOXK1/K2 target genes, and impairs the function of BAP1-ASXL1-FOXK1/K2 axis to regulate target genes and leukemia cell growth. Asterisks denote statistical significance with two-tailed Student’s t-test (A, B, C, D, F). *P < 0.05; ***P < 0.001 for the indicated comparison; ns = not significant