Elevated Expression of Selenoprotein Synthesis Enzyme SEPHS2 Driven by ATF4 Promotes the Resistance to Ferroptosis in Prostate Cancer.

While it has been reported that antioxidant selenoproteins are crucial for anti-ferroptosis in tumors, it remains unclear whether and how biosynthetic dysregulation of selenoproteins promotes resistance to ferroptosis. By bioinformatics analysis and in vitro confirmatory assays, we screened and identified selenophosphate synthetase 2 (SEPHS2), a key enzyme in a selenoprotein synthesis cascade, as a potential candidate for promoting anti-ferroptosis in tumors. We found that the expression of SEPHS2 was upregulated upon treatment with ferroptosis inducers. Knockdown of SEPHS2 inhibited tumor proliferation, migration and invasion, as well as attenuated selenoprotein biosynthesis to sensitize tumor cells to ferroptosis. Furthermore, our results demonstrated that activating transcription factor 4 (ATF4), a ferroptosis‑related transcription factor, might work as a direct upstream regulator to activate SEPHS2 transcription. Downregulation of ATF4 enhanced sensitivity to ferroptosis, whereas restoration of SEPHS2 expression rescued this effect, suggesting that ferroptosis resistance might be regulated by the ATF4/SEPHS2 axis. Notably, for the in vivo assay, knockdown of either SEPHS2 or ATF4 exhibited the optimal repression of tumor growth when combined with ferroptosis inducers. Thus, our findings highlight that inhibition of ATF4/SEPHS2 signaling might contribute as a novel adjuvant therapeutic strategy to improve the efficacy of ferroptosis-based treatment in tumors.