ABSTRACT
Hepatoblastoma is a primary liver cancer that affects children, due to the sensitivity of this tumor to insulin-like growth factor 1 (IGF-1). In this paper we show that azathioprine (AZA) is capable of inhibiting IGF1-mediated signaling cascade in HepG2 cells. The efficiency of AZA on inhibition of proliferation differs in the evaluated cell lines as follows: HepG2 (an experimental model of hepatoblastoma)>Hep3B (derived from a hepatocellular carcinoma)>HuH6 (derived from a hepatoblastoma)>>HuH7 (derived from a hepatocellular carcinoma)=Chang Liver cells (a non-malignant cellular model). The effect of AZA in HepG2 cells has been proven to derive from activation of Ras/ERK/TSC2, leading to activation of mTOR/p70S6K in a sustained manner. p70S6K phosphorylates IRS-1 in serine 307 which leads to the uncoupling between IRS-1 and p85 (the regulatory subunit of PI3K) and therefore causing the lack of response of HepG2 to IGF-1. As a consequence, proliferation induced by IGF-1 is inhibited by AZA and autophagy increases leading to senescence of HepG2 cells. Our results suggest that AZA induces the autophagic process in HepG2 activating senescence, and driving to deceleration of cell cycle but not to apoptosis. However, when simultaneous to AZA treatment the autophagy was inhibited by bafilomycin A1 and the degradation of regulatory proteins of cell cycle (e.g. Rb, E2F, and cyclin D1) provoked apoptosis. In conclusion, AZA induces resistance in hepatoblastoma cells to IGF-1, which leads to autophagy activation, and causes apoptosis when it is combined with bafilomycin A1. We are presenting here a novel mechanism of action of azathioprine, which could be useful in treatment of IGF-1 dependent tumors, especially in its combination with other drugs.
Subject(s)
Apoptosis/drug effects , Azathioprine/administration & dosage , Insulin-Like Growth Factor I/toxicity , Liver Neoplasms/chemically induced , Liver Neoplasms/pathology , Macrolides/administration & dosage , Antimetabolites, Antineoplastic/administration & dosage , Apoptosis/physiology , Cell Line, Tumor , Drug Therapy, Combination , Enzyme Inhibitors/administration & dosage , Hep G2 Cells , Humans , Liver Neoplasms/drug therapyABSTRACT
Increased protein synthesis is regulated, in part, by two eukaryotic translation initiation factors (eIFs): eIF4E and eIF2alpha. One or both of these factors are often overexpressed in several types of cancer cells; however, no data are available at present regarding eIF4E and eIF2alpha levels in brain tumors. In this study, we analyzed the expression, subcellular localization and phosphorylation states of eIF4E and eIF2alpha in 64 brain tumors (26 meningiomas, 16 oligodendroglial tumors, and 22 astrocytomas) and investigated the correlation with the expression of MIB-1, p53, and cyclin D1 proteins as well. There are significant differences in the phosphorylated eIF4E levels between the tumors studied, being the highest in meningiomas and the lowest in the oligodendroglial tumors. Relative to subcellular localization, eIF4E is frequently found in the nucleus of the oligodendroglial tumors and rarely in the same compartment of the meningiomas, whereas eIF2alpha showed an inverse pattern. Finally, cyclin D1 levels directly correlate with the phosphorylation status of both factors. The different expression, phosphorylation, or/and subcellular distribution of eIF2alpha and eIF4E within the brain types of tumors studied could indicate that different pathways are activated for promoting cell cycle proliferation, for instance, leading to increased cyclin D1 expression.
