Activated-ATF6a is an ER stress-inducing oncoprotein metabolically restricting immunosurveillance [bulk RNA-seq of Atf6 KO DEN/HFD]

Hepatocellular carcinoma (HCC) is the fastest growing cause of cancer-related mortality with limited therapies. While endoplasmic reticulum (ER)-stress and the unfolded protein response (UPR) are implicated in HCC, the involvement of the UPR-transducer activating transcription factor 6 alpha (ATF6a) remains unclear. In contrast to the well-characterized role of ATF6a-activation as an adaptive response to ER-stress, we here demonstrate its hitherto unknown function as an ER stress-inducing oncoprotein and metabolic master-regulator restricting cancer-immunosurveillance. In human HCC, ATF6a-activation significantly correlated with reduced patient-survival, tumor-progression, local immunosuppression, and higher recurrence rates of liver-cancer upon hepatectomy. Hepatocyte-specific ATF6a-activation in mice induced progressive hepatitis with ER-stress, immunosuppression, and hepatocyte-proliferation. Concomitantly, activated-ATF6a increased glycolysis and repressed gluconeogenic enzyme fructose-1,6-bisphosphatase 1 (FBP1). Restoring FBP1 expression prevented ATF6a-activation-related pathologies. Prolonged ATF6a-activation in hepatocytes triggered hepatocarcinogenesis, intratumoral T-cell infiltration, and nutrient-deprived immune-exhaustion. Immune-checkpoint blockade (ICB) efficiently restored immunosurveillance and dramatically reduced HCC. In line, HCC patients with a significantly higher ATF6a-activation signature presented complete response to ICB monotherapy. Targeting Atf6 via germline, hepatocyte-specific ablation, or therapeutic delivery of antisense-oligonucleotides dampened HCC in preclinical liver-cancer models. Thus, prolonged ATF6a-activation drives ER-stress, leading to aberrant glucose metabolism-dependent immunosuppression in liver cancer. Our findings propose persistently activated ATF6a as an oncoprotein, stratification-marker for liver-cancer ICB, and targetable therapeutic strategy against HCC. Overall design: Gene expression analysis of Atf6 KO DEN/HFD mice using RNA-seq