ASPM mediates nuclear entrapment of FOXM1 via liquid-liquid phase separation to promote progression of hepatocarcinoma

Abstract

Fork-head box protein M1 (FOXM1) plays critical roles in development and progression of multiple cancers, including hepatocellular carcinoma (HCC). However, the exact regulatory hierarchy of FOXM1 remains unclear. Here, a genome-wide screen is performed to identify intranuclear proteins that promote FOXM1 transcription activity via liquid–liquid phase separation (LLPS). Abnormal spindle-like microcephaly associated (ASPM) is identified to interact with FOXM1 protein via LLPS and enhance its stability by preventing proteasome-mediated degradation. ChIP-sequencing data show ASPM and FOXM1 co-occupy the promoters of multiple genes to promote their transcription, enhancing FOXM1-driven oncogenic progression. In functional experiments, inhibition of ASPM suppresses tumor growth of HCC cells in vivo and in vitro, while overexpression of ASPM has opposite effects. Importantly, reconstitution of FOXM1 partially compensates for the weakened proliferative capacity of HCC cells caused by ASPM silencing. Intriguingly, FOXM1 binds to the promoter region of ASPM and transcriptionally activates ASPM expression in HCC cells. Furthermore, we find that a higher co-expression of ASPM and FOXM1 significantly correlates with poor prognosis in HCC patients. It indicates a double positive feedback loop between ASPM and FOXM1 which coordinately promotes the aggressive progression of HCC. Collectively, we demonstrate that LLPS and transcriptional regulation form an oncogenic double positive feedback loop between ASPM and FOXM1. This provides a rationale strategy to treat HCC by targeting this mechanism.