Molecular Pathways Leading to Induction of Cell Death and Anti-Proliferative Properties by Tacrolimus and mTOR Inhibitors in Liver Cancer Cells.

BACKGROUND/AIMS: Orthotopic liver transplantation (OLT) is the recommended treatment for patients at early stages of hepatocarcinoma (HCC) with portal hypertension and/or increased bilirubinemia, but without vascular-associated diseases. Tumor recurrence, which is the main drawback for the survival of patients submitted to OLT for HCC, has been related to tumor-related variables and the immunosuppressive therapies. We have previously shown that Tacrolimus (FK506) exerts a more potent pro-apoptotic and anti-proliferative effects than the mammalian target of rapamycin (mTOR) inhibitors (Sirolimus and Everolimus) in liver cancer cells. This study identified the role of the immunosuppressant partners such as FK506-binding proteins (FKBPs) in the induction of cell death and arrest of cell proliferation by immunosuppressants in two representative liver cancer cells.

METHODS

The regulation of endoplasmic reticulum (ER) stress, apoptosis/autophagy, cell proliferation, and FKBPs expression was determined in Tacrolimus-, Sirolimus- and Everolimus-treated primary human hepatocytes, and hepatoma HepG2 and Huh7 cell lines. The functional repercussion of FKBPs on cell death and proliferation was also addressed using the siRNA technology. The assessed antitumoral properties of the immunosuppressants were associated to microRNAs (miRNAs) pattern.

RESULTS

The enhanced pro-apoptotic and anti-proliferative properties of Tacrolimus versus mTOR inhibitors were associated with increased protein kinase RNA-like endoplasmic reticulum kinase (PERK)-related ER stress, P-p53/p53 ratio and p21 protein expression that may counterbalance the risk of proliferative upregulation caused by enhanced P-Cdk4/Cdk4 activation in liver cancer cells. The inhibition of the mTOR pathway by Sirolimus and Everolimus was related to an induction of autophagy; and at a high dose, these drugs impaired translation likely at a very early step of the elongation phase. Tacrolimus and mTOR inhibitors increased the protein expression of FKBP12 and FKBP51 that appeared to play pro-survival role. Interestingly, the administration of immunosuppressants yields a specific pattern of miRNAs. Tacrolimus and mTOR inhibitors decreased miR-92a-1-5p, miR-197-3p, miR-483-3p and miR-720, and increased miR-22-3p, miR-376a-3p, miR-663b, miR-886-5p, miR-1300 and miR-1303 expressions in HepG2 cells.

CONCLUSION

The more potent pro-apoptotic and anti-proliferative properties of Tacrolimus versus mTOR inhibitors were associated with an increased activation of PERK and p53 signaling, and p21 protein expression. FKBP12 and FKBP51 appeared to be the most relevant partners of Tacrolimus and mTOR inhibitors exerting a pro-survival effect in HepG2 cells. The observed effects of immunosuppressants were related to a specific miRNA signature in liver cancer cells.