Hyperbaric oxygen targets RCN1 to modulate ER-mitochondria crosstalk and ameliorate sorafenib resistance in...

The emergence of resistance to tyrosine kinase inhibitors (TKIs) compromises their clinical benefits in patients with hepatocellular carcinoma (HCC), in part due to adaptive responses triggered by tumor hypoxia. In this study, we leverage hyperbaric oxygen (HBO) therapy as a sensitizing strategy in sorafenib-resistant HCC. We demonstrate that HBO significantly enhances the anti-tumor effect of sorafenib by stimulating calcium transfer from the endoplasmic reticulum (ER) to mitochondria, resulting in ER stress and mitochondrial dysfunction. Mechanistically, we show that hypoxia upregulates HNF4A, a transcriptional suppressor of RCN1, and HBO therapy effectively inhibits this hypoxia-driven HNF4A/RCN1 axis. Downregulation of RCN1, a calcium-binding protein overexpressed in sorafenib-resistant HCC, strengthens ER-mitochondria coupling. Subsequently, RCN1 suppression attenuates its interaction with IP3R1 through the EFh1/2 domain, facilitating IP3R1-GRP75 dissociation and the activation of mitochondrial calcium-uptake machinery. Using its EF-hand domains, RCN1 senses fluctuations in ER calcium concentration and accordingly employs a feedback mechanism to fine-tune its binding to IP3R1. In xenograft and spontaneous models, combined HBO-TKIs treatment delays tumor progression and modulates the HNF4A/RCN1 axis. Taken together, our findings elucidate a hitherto uncharacterized role of HBO in regulating ER-mitochondria calcium homeostasis and support its clinical application as an adjunctive therapy in TKI-resistant HCC.