Rap_GAP Domain of TSC2 Contributes to Tumor Suppression Through mTOR Signaling in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is an aggressive disease with a high degree of tumor heterogeneity. Genetic lesions of mTOR-related genes, including and hyperactivation of mTOR signaling, are common in HCC. However, the association of genetic alterations with hepatocarcinogenesis remains unclear. In this study, continuous truncating mutations occurred within or upstream of the Rap_GAP domain in clinical HCC samples. To elucidate whether hyperactivation of mTOR signaling in HCC is caused by truncating mutations, HCC cell models carrying the deletion (CRISPR/Cas9) or the truncating mutation (mutagenesis) were established. Our findings showed that either deletion or mutant could lead to loss-of-function and hyperactivation of mTOR signaling. Furthermore, hyperactivation of mTOR signaling was relieved by rapamycin. Immunohistochemistry of clinical samples confirmed frequent loss in HCC. Thus, our study revealed that genetic alterations cause loss of function and result in the hyperactivation of mTOR, and high frequency of truncating mutations around RAP_GAP domain may be one of the reasons for the hyperactivation of mTOR in HCC patients.