Gene and protein expression of mTOR and LC3 in hepatocellular carcinoma, colorectal liver metastasis and "normal" liver tissues

PLoS One. 2020 Dec 23;15(12):e0244356. doi: 10.1371/journal.pone.0244356. eCollection 2020.

Abstract

The physiological role of autophagy in the progression of liver diseases is still debated. To understand the clinical relevance of autophagy in primary e secondary hepatic tumors, we analyzed the expression of mTOR (mammalian target of rapamycin), a key regulator of autophagy; Raptor (regulatory-associated protein of mTOR); ULK1 (Unc-51 like kinase 1) determinant in the autophagy initiation; LC3 (microtubule-associated protein 1A/1B-light chain 3), a specific marker of autophagosomes; and p62, a selective autophagy receptor. Samples from subjects with chronic hepatitis (n.58), cirrhosis (n.12), hepatocellular carcinoma (HCC, n.56), metastases (n.48) from colorectal cancer and hyperplasia or gallbladder stones (n.7), the latter considered as controls, were examined. Gene expression analysis was carried out in n.213 tissues by absolute q-PCR, while protein expression by Western Blot in n.191 lysates, including tumoral, surrounding tumoral and normal tissues. Nonparametric statistical tests were used for comparing expression levels in the above-mentioned groups. Subgroup analysis was performed considering viral infection and chemotherapy treatment. The mTOR transcriptional level was significantly lower in metastases compared to HCC (P = 0.0001). p-mTOR(Ser2448) and LC3II/LC3I protein levels were significantly higher in metastases compared to HCC (P = 0.008 and P<0.0001, respectively). ULK(Ser757) levels were significantly higher in HCC compared to metastases (P = 0.0002) while the HCV- and HBV- related HCC showed the highest p62 levels. Chemotherapy induced a down-regulation of the p-mTOR(Ser2448) in metastases and in non-tumor surrounding tissues in treated patients compared to untreated (P = 0.001 and P = 0.005, respectively). Conclusions: the different expression of proteins considered, owning their interaction and diverse tissue microenvironment, indicate an impairment of the autophagy flux in primary liver tumors that is critical for the promotion of tumorigenesis process and a coexistence of autophagy inhibition and activation mechanisms in secondary liver tumors. Differences in mTOR and LC3 transcripts emerged in tumor-free tissues, therefore particular attention should be considered in selecting the control group.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Carcinoma, Hepatocellular / genetics
  • Carcinoma, Hepatocellular / metabolism*
  • Carcinoma, Hepatocellular / secondary
  • Case-Control Studies
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / metabolism*
  • Diagnosis, Differential
  • Down-Regulation
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Liver Neoplasms / genetics
  • Liver Neoplasms / metabolism*
  • Liver Neoplasms / secondary
  • Male
  • Microtubule-Associated Proteins / genetics*
  • Microtubule-Associated Proteins / metabolism*
  • Middle Aged
  • Phosphorylation
  • TOR Serine-Threonine Kinases / genetics*
  • TOR Serine-Threonine Kinases / metabolism*
  • Tumor Microenvironment

Substances

  • MAP1LC3A protein, human
  • Microtubule-Associated Proteins
  • MTOR protein, human
  • TOR Serine-Threonine Kinases

Grants and funding

MB: 2017-prot. BIRD175781 University of Padova The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.