High-protein diets alleviate tumour growth and drug resistance by promoting AKT aggregation and turnover

Background Despite the long-standing recommendations of high-protein diets for patients with cancer, the precise mechanisms of this dietary approach in benefiting tumour suppression and enhancing sensitivity to chemotherapy remain elusive. Objective To investigate the effect and underlying mechanism of high-protein diets in promoting cancer drug resistance. Characterisation of AKT regulation in this setting will provide new strategies to combat liver cancer. Design The role of high-protein diets in cancer drug resistance was analysed in cells and in syngeneic mouse models. In vivo and in vitro kinase and ubiquitination assays were employed to detect AKT phosphorylation and ubiquitination modifications. Clustered regularly interspaced short palindromic repeats (CRISPR)-based screen was used to identify the E3 ligase for AKT. Generation of Akt1 T72E knock-in mice and Traf5 knockout mice was employed. Results High-protein diets repress tumour growth and sensitise tumour to chemotherapies. Specifically, S6K1 directly phosphorylates AKT, leading to acute inactivation and long-term instability of AKT protein. S6K1 promotes AKT aggregation and facilitates its interaction with TRAF5, resulting in AKT degradation in response to amino acid stimuli. Traf5 knockout mice exhibit high AKT protein levels, insulin resistance and counteracting protein diet-induced tumour repression. While a reversible phenomenon has been observed in the constitutive phosphor-mimetic Akt1 T72E knock-in mice, which manifest retarded liver tumourigenesis in C-Myc transgenic mice. Conclusions Our results highlight a fine-tuned regulation of AKT by S6K1-mediated phosphorylation and TRAF5-dictated ubiquitination and degradation, offering a strategy for integrating chemotherapy with high-protein diets to enhance cancer treatment efficacy.