Persistent effect of mTOR inhibition on preneoplastic foci progression and gene expression in a rat model of hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is a heterogeneous disease in which tumor subtypes can be identified based on the presence of adult liver progenitor cells. Having previously identified the mTOR pathway as critical to progenitor cell proliferation in a model of liver injury, we investigated the temporal activation of mTOR signaling in a rat model of hepatic carcinogenesis. The model employed chemical carcinogens and partial hepatectomy to induce progenitor marker-positive HCC. Immunohistochemical staining for phosphorylated ribosomal protein S6 indicated robust mTOR complex 1 (mTORC1) activity in early preneoplastic lesions that peaked during the first week and waned over the subsequent 10 days. Continuous administration of rapamycin by subcutaneous pellet for 70 days markedly reduced the development of focal lesions, but resulted in activation of the PI3K signaling pathway. To test the hypothesis that early mTORC1 activation was critical to the development and progression of preneoplastic foci, we limited rapamycin administration to the 3-week period at the start of the protocol. Focal lesion burden was reduced to a degree indistinguishable from that seen with continuous administration. Short-term rapamycin did not result in the activation of PI3K or mTORC2 pathways. Microarray analysis revealed a persistent effect of short-term mTORC1 inhibition on gene expression that resulted in a genetic signature reminiscent of normal liver. We conclude that mTORC1 activation during the early stages of hepatic carcinogenesis may be critical due to the development of preneoplastic focal lesions in progenitor marker-positive HCC. mTORC1 inhibition may represent an effective chemopreventive strategy for this form of liver cancer.

MicroRNAs in Animal Models of HCC

“…Interestingly, a global proteomic analysis from glutathione S-transferase-P (GST-P) positive laser micro-dissected nodules identified G6PD among protein markers discriminating R-H model-derived focal lesion from normal liver with or without progenitor cell activation, demonstrating LCM coupled with mass-spectrometry-based proteomics as an effective approach to characterize preneoplastic lesions and to identify early diagnostic markers for effective clinical intervention. In addition, mTOR pathway was found activated at early stages of carcinogenesis and, consistently, its transient inhibition by rapamycin treatment impaired the growth of focal lesions and induced a less aggressive phenotype attenuating the loss of differentiating functions, as detected by both transcriptomic and proteomic genome-wide analyses [177,178]. The AKT/mTOR pathway is frequently activated in HCC, characterizing a subgroup of patients with a high proliferation signature and sorafenib resistance [179][180][181].…”

Stability of histone post-translational modifications in samples derived from liver tissue and primary hepatic cells

“…The critical role of histone modifications in the regulation of gene expression, as well as their dynamic nature, led us to explore their stability and propensity for change in several models of liver biology in the rat. Our laboratory’s interest in late gestation liver development and its relationship to hepatic carcinogenesis has focused, in part, on the regulation of gene expression [ 33 , 34 , 35 , 36 , 37 ]. Our studies have indicated that the mechanisms for nutrient-mediated transcriptional control in the developing liver are, to a large degree, independent of well characterized, canonical transcript factor signaling pathways.…”

“…Our studies have indicated that the mechanisms for nutrient-mediated transcriptional control in the developing liver are, to a large degree, independent of well characterized, canonical transcript factor signaling pathways. This observation has led to our interest in chromatin structure as a critical regulator of fetal hepatocyte gene expression and the related contribution of progenitor cells to hepatocellular carcinogenesis [ 33 ]. This, in turn, motivated our interest in histone modifications.…”

A five‑gene based risk score with high prognostic value in colorectal cancer

“…Microarray technology allows comprehensive analysis of gene expression profiles in different diseases, which has been demonstrated in a variety of hematological tumors and solid tumors including lung ( 6 ), liver ( 7 ), pancreas ( 8 ), and breast ( 9 ). Biomarkers discovered by microarrays have a great potential in the prediction of clinical outcomes and survival as well as classification in different sub-types ( 10 – 12 ).…”