FoxO3a-Mediated Modulation of PD-L1 Expression and Inhibition by Dihydroartemisinin in Triple-Negative Breast Cancer

Tumour immunotherapy targeting PD-1/PD-L1 shows promise, but the regulatory mechanisms of PD-L1 and its small-molecule modulators remain unclear. This study investigated FoxO3a-mediated PD-L1 regulation and the PD-L1-inhibitory role of dihydroartemisinin (DA) in triple-negative breast cancer (TNBC). FoxO3a overexpression significantly increased PD-L1 expression and impaired T cell-mediated cytotoxicity, while knockdown exerted opposite effects in TNBC cells. Promoter motif analysis and dual-luciferase assays revealed FoxO3a binding to the s155 site on the PD-L1 promoter in MDA-MB-231 cells; mutation of s155 abolished this interaction. ChIP-PCR confirmed FoxO3a binding to the PD-L1 promoter at s155. Furthermore, DA, a clinical antimalarial, reduced PD-L1 and FoxO3a levels, sensitising TNBC cells to T cell killing in TNBC cells. Mechanistically, DA enhanced IRE1/IKK phosphorylation, promoting FoxO3a Ser644 phosphorylation and ubiquitination. Crucially, s155 was required for DA-induced PD-L1 suppression in MDA-MB-231 cells. These findings demonstrate PD-L1 as a direct transcriptional target of FoxO3a and identify DA as a potential TNBC therapeutic targeting the IRE1/IKK/FoxO3a/PD-L1 axis.