M2 macrophage-secreted KYNU promotes stemness remodeling and malignant behavior in endometrial cancer via the SOD2-mtROS-ERO1α-UPRER axis.

Background: M2 macrophages are known to be involved in tumorigenesis. However, the mechanism by which they promote tumor progression in endometrial cancer (EC) remains largely unknown. Kynureninase (KYNU) has been found to be associated with the progression of various tumors, but research on endometrium is limited to embryo transfer. Therefore, a better understanding of KYNU as a potential therapeutic target in EC treatment is needed. This study aimed to elucidate the mechanism by which M2 macrophage-secreted KYNU influences the malignant biological and stemness remodeling of EC via the SOD2-mtROS-ERO1α and endoplasmic reticulum unfolded protein response (UPR^ER) pathway.

Methods: We used flow cytometry for cell sorting. Fluorescence experiments were conducted to reveal spatial position of protein, and. Western blot and qRT‒PCR were used to detect the protein and mRNA levels, respectively. The interaction between KYNU and superoxide dismutase 2 (SOD2) was demonstrated using coimmunoprecipitation experiments. Furthermore, the mechanism between activating transcription factor 4 (ATF4) and the KYNU was assessed using chromatin immunoprecipitation and dual luciferase assays. Cell Counting Kit-8, flow cytometry, and transwell assays were used to detect tumor cell proliferation, apoptosis, and invasion capacities. Student's t test and one-way analysis of variance (ANOVA) were used to compare groups.

Results: M2 macrophage-secreted KYNU induced malignant behavior and stemness via the SOD2-mtROS-ERO1α-UPR^ER pathway, contributing to a positive feedback loop for tumor cell self-protection. Mechanistically, KYNU and its metabolite 3-hydroxyanthranillic acid (3-HAA) upregulated the expression of SOD2, thereby decreasing mitochondrial reactive oxygen species (mtROS). KYNU inhibitors affected the spatial overflow of mtROS from mitochondria to the endoplasmic reticulum (ER). Endoplasmic reticulum oxidoreductin 1α (ERO1α) was sensitively affected by KYNU-induced changes in the redox environment, stimulating the PERK-eIF2α-ATF4 pathway of the UPR^ER. This in turn promoted oxidative folding, reduced the level of misfolded protein (MFP), and maintained tumor survival and progression. Additionally, ATF4 acted as a transcription factor in the KYNU promoter region, amplifying KYNU tumorigenesis in a positive feedback manner.

Conclusion: M2-secreted KYNU promotes the malignant behavior and stemness remodeling of EC via the SOD2-mtROS-ERO1α-UPR^ER axis and establishes a positive feedback loop. Thus, KYNU is a potential therapeutic target for EC treatment.