The epithelial-mesenchymal transition (EMT), one of the main mechanisms underlying development of cancer metastasis, induces stem-like properties in epithelial cells. Bmi1 is a polycomb-group protein that maintains self-renewal, and is frequently overexpressed in human cancers. Here, we show the direct regulation of BMI1 by the EMT regulator, Twist1. Furthermore, Twist1 and Bmi1 were mutually essential to promote EMT and tumour-initiating capability. Twist1 and Bmi1 act cooperatively to repress expression of both E-cadherin and p16INK4a. In patients with head and neck cancers, increased levels of both Twist1 and Bmi1 correlated with downregulation of E-cadherin and p16INK4a, and was associated with the worst prognosis. These results suggest that Twist1-induced EMT and tumour-initiating capability in cancer cells occurs through chromatin remodelling, which leads to unfavourable clinical outcomes.

Metformin has been reported to possess antitumor activity and maintain high cytotoxic T lymphocyte (CTL) immune surveillance. However, the functions and detailed mechanisms of metformin's role in cancer immunity are not fully understood. Here, we show that metformin increases CTL activity by reducing the stability and membrane localization of programmed death ligand-1 (PD-L1). Furthermore, we discover that AMP-activated protein kinase (AMPK) activated by metformin directly phosphorylates S195 of PD-L1. S195 phosphorylation induces abnormal PD-L1 glycosylation, resulting in its ER accumulation and ER-associated protein degradation (ERAD). Consistently, tumor tissues from metformin-treated breast cancer patients exhibit reduced PD-L1 levels with AMPK activation. Blocking the inhibitory signal of PD-L1 by metformin enhances CTL activity against cancer cells. Our findings identify a new regulatory mechanism of PD-L1 expression through the ERAD pathway and suggest that the metformin-CTLA4 blockade combination has the potential to increase the efficacy of immunotherapy.

Recently, the PD-1 antibody nivolumab, which was approved for advanced HCC refractory to sorafenib, demonstrated a 20% objective response rate in advanced HCC (13). While this is an encouraging step in HCC therapy, it also provides great opportunity to improve therapeutic efficacy. Because mechanism-driven Glycosylation of immune receptors and ligands, such as T cell receptor and coinhibitory molecules, regulates immune signaling activation and immune surveillance. However, how oncogenic signaling initiates glycosylation of coinhibitory molecules to induce immunosuppression remains unclear. Here we show that IL-6-activated JAK1 phosphorylates programmed death-ligand 1 (PD-L1) Tyr112, which recruits the endoplasmic reticulum-associated N-glycosyltransferase STT3A to catalyze PD-L1 glycosylation and maintain PD-L1 stability. Targeting of IL-6 by IL-6 antibody induced synergistic T cell killing effects when combined with anti-T cell immunoglobulin mucin-3 (anti-Tim-3) therapy in animal models. A positive correlation between IL-6 and PD-L1 expression was also observed in hepatocellular carcinoma patient tumor tissues. These results identify a mechanism regulating PD-L1 glycosylation initiation and suggest the combination of anti-IL-6 and anti-Tim-3 as an effective marker-guided therapeutic strategy.

Epithelial-mesenchymal transition (EMT), which is characterized by the suppression of the adhesion protein E-cadherin, is a crucial process that promotes metastasis and stem-like properties of cancer cells. However, the dissociation of cellular aggregates is not sufficient to explain why cancer cells move, and the motile nature of cancer cells undergoing EMT remains elusive. Here, we identify a mechanism in which the EMT inducer Twist1 elicits cancer cell movement through activation of RAC1. Twist1 cooperates with BMI1 to suppress let-7i expression, which results in upregulation of NEDD9 and DOCK3, leading to RAC1 activation and enabling mesenchymal-mode movement in three-dimensional environments. Moreover, the suppression of let-7i contributes to Twist1-induced stem-like properties. Clinically, activation of the Twist1-let-7i-NEDD9 axis in head and neck cancer patients correlates with tumour invasiveness and worse outcome. Our results uncover an essential mechanism to explain how Twist1 induces the motile stem-like cancer cell phenotype beyond simply suppressing E-cadherin.

No abstract