ABSTRACT
Apoptosis is a cell death programme primordial to cellular homeostasis efficiency. This normal cell suicide program is the result of the activation of a cascade of events in response to death stimuli. Apoptosis occurs in normal cells to maintain a balance between cell proliferation and cell death. A deregulation of this balance due to modifications in the apoptosic pathway leads to different human diseases including cancers. Apoptosis resistance is one of the most important hallmarks of cancer and some new therapeutical strategies focus on inducing cell death in cancer cells. Nevertheless, cancer cells are resistant to treatment inducing cell death because of different mechanisms, such as DNA mutations in gene coding for pro-apoptotic proteins, increased expression of anti-apoptotic proteins and/or pro-survival signals, or pro-apoptic gene silencing mediated by DNA hypermethylation. In this context, aberrant DNA methylation patterns, hypermethylation and hypomethylation of gene coding for proteins implicated in apoptotic pathways are possible causes of cancer cell resistance. This review highlights the role of DNA methylation of apoptosis-related genes in cancer cell resistance.
ABSTRACT
This multicenter study assesses the value of O(6)-methylguanine-DNA methyltransferase (MGMT) status for predicting overall survival in glioblastoma patients. Five methods are used, to identify the approach with the best prognostic value. Eighty-one tumors were obtained from patients with glioblastomas treated by surgery and radiotherapy with concomitant temozolomide (TMZ) followed by adjuvant TMZ. MGMT promoter methylation was assessed by qualitative methyl-specific polymerase chain reaction (MSP), semiquantitative methyl-specific polymerase chain reaction (SQ-MSP), and pyrosequencing, while MGMT expression was measured at the RNA level by quantitative real-time PCR (Q-RT-PCR) and at the protein level by immunohistochemistry (IHC). MGMT promoter methylation as evaluated by MSP, SQ-MSP, and pyrosequencing was significantly correlated with overall survival. The best predictive value was obtained by pyrosequencing of one specific CpG position. Overall survival was 14 and 25 months for patients with percentages of methylation below and above the median, respectively. In contrast, MGMT status determined by Q-RT-PCR and IHC showed little or no correlation with overall survival, respectively. These results confirm the prognostic value of MGMT promoter methylation in glioblastoma patients initially treated with TMZ. SQ-MSP allowed better discrimination than classical MSP, and pyrosequencing represented a good option.
Subject(s)
DNA Modification Methylases/metabolism , DNA Repair Enzymes/metabolism , Glioblastoma/diagnosis , Glioblastoma/enzymology , Tumor Suppressor Proteins/metabolism , Adult , Aged , Aged, 80 and over , DNA Methylation , DNA Modification Methylases/genetics , DNA Repair Enzymes/genetics , Female , Glioblastoma/mortality , Humans , Kaplan-Meier Estimate , Male , Middle Aged , Probability , Prognosis , Reverse Transcriptase Polymerase Chain Reaction , Statistics, Nonparametric , Time Factors , Tumor Suppressor Proteins/geneticsABSTRACT
We have investigated the mechanism responsible for mitochondria permeabilization occurring during cell apoptosis. We have developed an in vivo model of apoptotic rat liver. Mitochondria appeared as an homogenous population in control liver. On the contrary, mitochondria varied in size, morphology, and the matrical density in apoptotic liver. Mitochondria were purified from control and apoptotic livers. In control conditions, a single mitochondrial population was identified; whereas three populations of mitochondria were purified from apoptotic liver. Our data show that these apoptotic populations correspond to early, intermediate, and late apoptotic mitochondria, which are characterized by an increasing extent of permeabilization of their outer membrane and a gradual enrichment in oligomerized Bax protein. Remarkably, a new ionic channel was observed in apoptotic but not in control mitochondria. The biophysical and pharmacological properties of this channel are in good agreement with those reported for a previously described mitochondrial apoptosis-induced channel (MAC) (Pavlov, E. V., Priault, M., Pietkiewicz, D., Cheng, E. H., Antonsson, B., Manon, S., Korsmeyer, S. J., Mannella, C. A., and Kinnally, K. W. (2001) J. Cell Biol. 155, 725-731). However, MAC activity was only observed in the late apoptotic mitochondrial population. Thus, our study establishes that MAC activity is related to the overall apoptotic process but corresponds to a late event.
Subject(s)
Apoptosis , Ion Channels/chemistry , Ion Channels/physiology , Liver/pathology , Mitochondria/pathology , Mitochondrial Proteins/chemistry , Mitochondrial Proteins/physiology , Animals , Anions , Biophysical Phenomena , Biophysics , Caspase 3 , Caspases/metabolism , Cell Membrane/metabolism , Electrophoresis, Polyacrylamide Gel , Electrophysiology , Immunoblotting , Intracellular Membranes/metabolism , Ions , Liver/metabolism , Liver/ultrastructure , Microscopy, Electron , Mitochondria/metabolism , Permeability , Proto-Oncogene Proteins c-bcl-2/metabolism , Rats , Time Factors , bcl-2-Associated X ProteinABSTRACT
Caspases are one of the key effector molecules in apoptosis. Caspase-3 activity (identified by cleavage of the peptide DEVD) was analysed in bone marrow blasts (minimum 70%) from 45 acute myeloid leukaemia (AML) patients. 12 patients (25%) exhibited high levels of specific DEVDase activity. These blast cells, despite having activated caspase-3, displayed none of the classical caspase-dependent morphological characteristics of apoptosis, such as degradation of DNA fragmentation factor 45, DNA fragmentation, and appeared to be more resistant to drug-induced apoptosis. Our results suggest that in these AML cells, resistance to apoptosis occurred downstream of caspase-3 activation.
