FOXO1-mediated nuclear sequestration of STAT3 and AKT1 triggers FOXO3-dependent autophagic death in hypoxic granulosa cells

FOXO proteins, especially FOXO1 and FOXO3, are recognized for their roles in controlling apoptosis and autophagy. Both apoptosis and autophagy have been induced in granulosa cells (GCs) by hypoxic conditions in ovarian follicles; however, the exact contribution of FOXO proteins and autophagy to the regulation of GCs apoptosis under hypoxia remains unclear. In this investigation of porcine GCs, we reveal that FOXO1 promotes apoptosis in response to hypoxia through FOXO3-dependent autophagy. We describe how mechanistically, FOXO1 forms a complex with the transcription factor STAT3 during hypoxia. Guided by FOXO1, this complex undergoes nuclear translocation and effectively attaches to the STAT3-responsive element (SRE) located in the FOXO3 promoter region, thereby enhancing the transcriptional expression of FOXO3. Simultaneously, FOXO1 associates with AKT1, thus facilitating its nuclear entry and subsequently reducing the Ser253 phosphorylation of FOXO3, leading to FOXO3 detachment from 14-3-3 and promoting FOXO3 translocation into the nucleus. FOXO3 subsequently stimulates the upregulation of ATG3, ultimately initiating autophagy and autophagy-dependent apoptosis. Our results suggest that hypoxia acts through FOXO1 to induce autophagic death in porcine GCs by promoting the expression and nuclear import of FOXO3.