Neutrophil elastase-mediated proteolysis of the tumor suppressor p200 CUX1 promotes cell proliferation and inhibits cell differentiation in APL

Aims: Neutrophil elastase (NE) is a critical proteolytic enzyme that is involved in cancer. We previously reported high NE expression in peripheral blood neutrophils from acute promyelocytic leukemia (APL) patients. The present study aimed to elucidate the specific role and mechanisms of NE in APL development. Materials and methods: NE expression was detected in APL bone marrow samples and analyzed in the BloodSpot database. CCK-8 assay and flow cytometry were used to assess cell proliferation and cell cycle distribution, respectively. The expression levels of proliferation and differentiation markers were measured by Western blotting and quantitative real-time PCR. The co-expression and interaction of NE and p200 cut-like homeobox 1 (CUX1) were evaluated by indirect immunofluorescence, co-immunoprecipitation, and in situ proximity ligation assay. Key findings: NE was highly expressed in APL bone marrow and blood neutrophils. NE overexpression promoted the proliferation and inhibited the differentiation of NB4 cells, whereas NE downregulation achieved the opposite results in U937 cells. Mechanistically, NE interacted with and effectively hydrolyzed the tumor suppressor p200 CUX1. Rescue experiments revealed that p200 CUX1 upregulation reversed the functional influence of NE on APL cells. Significance: NE-mediated proteolysis of the tumor suppressor p200 CUX1 promotes APL progression. NE/p200 CUX1 axis is a novel and promising therapeutic target for APL treatment.