p53 haploinsufficiency and increased mTOR signaling define a subset of aggressive hepatocellular carcinoma.

p53 mutations occur frequently in human hepatocellular carcinoma (HCC). Activation of the mammalian target of rapamycin (mTOR) pathway is also associated with HCC. However, it is still unknown whether these changes together initiate HCC and can be targeted as a potential therapeutic strategy.We generated mouse models in which mTOR was hyperactivated by loss of tuberous sclerosis complex 1 (Tsc1) with or without p53 haplodeficiency. Primary cells were isolated from mouse livers. Oncogenic signaling was assessed in vitro and in vivo, with or without targeted inhibition of a single molecule or multiple molecules. Transcriptional profiling was used to identify biomarkers predictive of HCC. Human HCC materials were used to corroborate the findings from mouse models.p53 haploinsufficiency facilitates mTOR signaling via the Pten/PI3k/Akt axis, promoting HCC tumorigenesis and lung metastasis. Inhibition of PI3K/Akt reduced mTOR activity, which effectively enhanced the anticancer effort of an mTOR inhibitor. Abcc4 was found to be responsible for p53 haploinsufficiency- and Tsc1 loss-driven HCC tumorigenesis. Moreover, in clinical HCC samples, Abcc4 specifically identified an aggressive subtype. The mTOR inhibitor rapamycin significantly reduced hepatocarcinogenesis triggered by Tsc1 loss and p53 haploinsufficiency in vivo, as well as the biomarker Abcc4.Our data advance the current understanding of the activation of the Pten/PI3K/Akt/mTOR axis and its downstream target Abcc4 in hepatocarcinogenesis driven by p53 reduction and Tsc1 loss. Targeting mTOR, an unexpected vulnerability in p53 (haplo)deficiency HCC, can be exploited therapeutically to treat Abcc-4-positive HCC patients.

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