Homoharringtonine promotes non-small-cell lung cancer cell death via modulating HIF-1α/ERβ/E2F1 feedforward loop

Objectives: Hypoxia conditions promote the adaptation and progression of non-small-cell lung cancer (NSCLC) via hypoxia-inducible factors (HIF). HIF-1α may regulate estrogen receptor β (ERβ) and promote the progression of NSCLC. The phytochemical homoharringtonine (HHT) exerts strong inhibitory potency on NSCLC, with molecular mechanism under hypoxia being elusive. Methods: The effects of HHT on NSCLC growth were determined by cell viability assay, colony formation, flow cytometry, and H460 xenograft models. Western blotting, molecular docking program, site-directed mutagenesis assay, immunohistochemical assay, and immunofluorescence assay were performed to explore the underlying mechanisms of HHT-induced growth inhibition in NSCLC. Key findings: HIF-1α/ERβ signaling-related E2F1 is highly expressed and contributes to unfavorable survival and tumor growth. The findings in hypoxic cells, HIF-1α overexpressing cells, as well as ERβ- or E2F1-overexpressed and knockdown cells suggest that the HIF-1α/ERβ/E2F1 feedforward loop promotes NSCLC cell growth. HHT suppresses HIF-1α/ERβ/E2F1 signaling via the ubiquitin-proteasome pathway, which is dependent on the inhibition of the protein expression of HIF-1α and ERβ. Molecular docking and site-directed mutagenesis revealed that HHT binds to the GLU305 site of ERβ. HHT inhibits cell proliferation and colony formation and promotes apoptosis in both NSCLC cells and xenograft models. Conclusion: The formation of the HIF-1α/ERβ/E2F1 feedforward loop promotes NSCLC growth and reveals a novel molecular mechanism by which HHT induces cell death in NSCLC.