S6K1 overexpression enhances autophagy in breast cancer cells by inducing the translation of CLU.

Background: Ribosomal protein S6 kinase B1 (S6K1) is frequently amplified and correlates with drug resistance and poor prognosis in patients with breast cancer. Although S6K1 functions primarily in the process of translation, the genome-wide translational profiles regulated by S6K1 remain unclear. This study sought to clarify the pivotal role of S6K1 in translational regulation and investigate its novel targets in breast cancer.

Methods: Ribosome profiling sequencing (Ribo-seq) was performed to explore genome-wide translational profiles regulated by S6K1 in breast cancer cells. Integrated multiomics analyses, including Ribo-seq, RNA sequencing, and mass spectrometry, were employed to identify a new target of S6K1 translational regulation, the autophagy-related gene clusterin (CLU). Western blotting and immunofluorescence were utilized to confirm that S6K1 regulated CLU translation, thus influencing autophagy in breast cancer cells. Bafilomycin A1 (a late-stage autophagy inhibitor) was used to demonstrate that S6K1 regulated autophagosome formation in breast cancer cells through affecting the translation of CLU.

Results: S6K1 depletion resulted in the downregulation of global messenger RNA (mRNA) translation and affected translation in multiple pathways that play crucial roles in carcinogenesis, with autophagy-related pathways being the most prominently affected. The role of S6K1 in autophagy was further confirmed in breast cancer cells, and CLU was identified as a novel target regulated by S6K1 at the translational level. Additionally, the overexpression of S6K1 promoted the translation of CLU, thus facilitating the formation of autophagosomes.

Conclusions: This study demonstrated that the overexpression of S6K1 promoted autophagy in breast cancer cells by facilitating the translation of the autophagy-related gene CLU.