Regular exercise suppresses steatosis-associated liver cancer development by degrading E2F1 and c-Myc via circadian gene upregulation

Regular exercise is believed to suppress cancer progression. However, the precise molecular mechanisms by which exercise prevents cancer development remain unclear. In this study, using a steatosis-associated liver cancer mouse model, we found that regular exercise at a speed of 18 m/min for 20 min daily suppressed liver cancer development. To explore the underlying mechanisms, we examined the gene expression profiles in the livers of the exercise and non-exercise groups. We extracted RNA from non-tumor and tumor tissues from each mouse liver and performed bulk RNA-seq analysis. The expressions of circadian genes, such as Per1 and Cry2, were upregulated in the exercise group. We further found that the expression of a series of E2F1 and c-Myc target genes that directly affect the proliferation of cancer cells was downregulated in the exercised group. However, the expression of these genes was transcriptionally unchanged but degraded at the post-translational level by exercise. Cry2, which is regulated by the Skp1-Cul1-FBXL3 (SCFFBXL3) ubiquitin ligase complex by binding to FBXL3, can form a complex with E2F1 and c-Myc, which we think is the mechanism to degrade them. Our study revealed a previously unknown mechanism by which exercise prevents cancer development. To analyze effects of excercise on tumor promotion, we used liver carcinogenesis model mice by 7,12-dimethylbenz(a)anthracene (DMBA) trearment and high fat diet (HFD) feeding. Total RNA was extracted from the frozen liver tissues of exercised and non-exercised mice.