Growth factor erv1-like (Gfer)/augmenter of liver regeneration (ALR) sustains redox homeostasis and apoptosis resistance in oral squamous cell carcinoma (OSCC) stroma and oxidizes STAT3 through its sulfhydryl oxidase activity

Background Oral squamous cell carcinoma (OSCC) progression is strongly influenced by the tumor microenvironment, particularly cancer-associated fibroblasts (CAFs). The Augmenter of Liver Regeneration (ALR), also known as growth factor erv1-like (Gfer), may contribute to stromal homeostasis through its redox-regulatory and anti-apoptotic functions. However, its role in OSCC-associated fibroblasts and its potential interaction with Signal Transducer and Activator of Transcription 3 (STAT3) remain insufficiently characterized. Methods Gfer was silenced in OSCC-derived fibroblasts to investigate its effects on reactive oxygen species (ROS) levels and apoptosis-related markers, including Bcl-2, Bax, caspase-9, and caspase-3. Recombinant Gfer (rGfer) was assessed for flavin adenine dinucleotide (FAD) content and sulfhydryl oxidase activity toward STAT3 thiol groups. The exosomal markers CD63, Alix, and HSP70 were also evaluated in OSCC-derived extracellular vesicles. Results Gfer knockdown significantly increased ROS levels and promoted a pro-apoptotic shift, characterized by reduced Bcl-2 expression, increased Bax levels, and activation of caspase-9 and caspase-3, consistent with the intrinsic apoptotic pathway. Recombinant Gfer contained FAD and catalyzed rapid oxidation of STAT3 thiol groups with high efficiency, supporting its sulfhydryl oxidase activity and identifying STAT3 as a candidate physiological substrate. CD63, Alix, and HSP70 were confirmed as exosomal markers, supporting their potential utility in characterizing OSCC-associated extracellular vesicles. Conclusion Gfer may contribute to maintaining redox homeostasis and mitochondrial integrity in OSCC-associated fibroblasts, potentially supporting a tumor-promoting stromal environment. Its activity toward STAT3 suggests a possible link between redox regulation and oncogenic signaling. These findings highlight Gfer as a potential target for future therapeutic research and support further investigation of extracellular vesicle markers for OSCC diagnosis.