Sensitization of U937 leukemia cells to doxorubicin by the MG132 proteasome inhibitor induces an increase in apoptosis by suppressing NF-kappa B and mitochondrial membrane potential loss

Pablo César Ortiz-Lazareno,Jorge Ramiro Domínguez-Rodríguez,Alejandro Bravo-Cuellar,Ruth De Célis,Georgina Hernández-Flores,José Manuel Lerma-Díaz,Oscar González-Ramella,Paulina Gómez-Lomelí,Adriana Aguilar-Lemarroy,Luis Felipe Jave-Suárez

doi:10.1186/1475-2867-14-13

Abstract

BackgroundThe resistance of cancerous cells to chemotherapy remains the main limitation for cancer treatment at present. Doxorubicin (DOX) is a potent antitumor drug that activates the ubiquitin-proteasome system, but unfortunately it also activates the Nuclear factor kappa B (NF-кB) pathway leading to the promotion of tumor cell survival. MG132 is a drug that inhibits I kappa B degradation by the proteasome-avoiding activation of NF-кB. In this work, we studied the sensitizing effect of the MG132 proteasome inhibitor on the antitumor activity of DOX.MethodsU937 human leukemia cells were treated with MG132, DOX, or both drugs. We evaluated proliferation, viability, apoptosis, caspase-3, -8, and −9 activity and cleavage, cytochrome c release, mitochondrial membrane potential, the Bcl-2 and Bcl-XL antiapoptotic proteins, senescence, p65 phosphorylation, and pro- and antiapoptotic genes.ResultsThe greatest apoptosis percentage in U937 cells was obtained with a combination of MG132 + DOX. Likewise, employing both drugs, we observed a decrease in tumor cell proliferation and important caspase-3 activation, as well as mitochondrial membrane potential loss. Therefore, MG132 decreases senescence, p65 phosphorylation, and the DOX-induced Bcl-2 antiapoptotic protein. The MG132 + DOX treatment induced upregulation of proapoptotic genes BAX, DIABLO, NOXA, DR4, and FAS. It also induced downregulation of the antiapoptotic genes BCL-XL and SURVIVIN.ConclusionMG132 sensitizes U937 leukemia cells to DOX-induced apoptosis, increasing its anti-leukemic effectiveness.

Highlights

The resistance of cancerous cells to chemotherapy remains the main limitation for cancer treatment at present
Reduction of viability in U937 leukemia cells by MG132 + DOX treatment First, the U937 cells were evaluated for viability by carrying out a dose–response effect and kinetics with the different treatments
These results clearly confirm the toxic effect exerted by MG132 and the sensitization of U937 leukemia cells to the toxic action of DOX

Summary

Introduction

The resistance of cancerous cells to chemotherapy remains the main limitation for cancer treatment at present. They represent the most common cancer in children and the leading cause of infant death from cancer worldwide [1,2] This type of tumor is treated with chemotherapy, but its effectiveness is sometimes limited by the generation of drug resistance as well as by multiple side effects [3,4,5,6]. Major efforts are being conducted to identify the mechanisms underlying tumor resistance to anticancer drugs In this regard, DOX can activate the ubiquitinproteasome system that regulates the Nuclear factor kappa-B (NF-кB) transcription factor, which promote proliferation and survival in tumor cells [11,12]; overactivation of NF-кB has been shown in several tumor types [13]. Chemotherapeutic agents such as DOX exhibit a dual role that induces apoptosis in tumor cells and paradoxically, DOX could activate a protection mechanism, preventing apoptosis [23,24,25]

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