ABSTRACT
Survival of various immune cell populations has been proposed to preferentially rely on a particular anti-apoptotic BCL-2 family member, for example, naive T cells require BCL-2, while regulatory T cells require MCL-1. Here we examined the survival requirements of multiple immune cell subsets in vitro and in vivo, using both genetic and pharmacological approaches. Our findings support a model in which survival is determined by quantitative participation of multiple anti-apoptotic proteins rather than by a single anti-apoptotic protein. This model provides both an insight into how the sum of relative levels of anti-apoptotic proteins BCL-2, MCL-1 and A1 influence survival of T cells, B cells and dendritic cells, and a framework for ascertaining how these different immune cells can be optimally targeted in treatment of immunopathology, transplantation rejection or hematological cancers.
Subject(s)
Gene Expression Regulation/immunology , Minor Histocompatibility Antigens/genetics , Models, Immunological , Myeloid Cell Leukemia Sequence 1 Protein/genetics , Proto-Oncogene Proteins c-bcl-2/genetics , Animals , Antineoplastic Agents/pharmacology , B-Lymphocytes/cytology , B-Lymphocytes/drug effects , B-Lymphocytes/immunology , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , CD4-Positive T-Lymphocytes/cytology , CD4-Positive T-Lymphocytes/drug effects , CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/cytology , CD8-Positive T-Lymphocytes/drug effects , CD8-Positive T-Lymphocytes/immunology , Cell Survival , Dendritic Cells/cytology , Dendritic Cells/drug effects , Dendritic Cells/immunology , Flow Cytometry , Immunity, Innate , Immunophenotyping , Mice , Mice, Inbred C57BL , Mice, Transgenic , Minor Histocompatibility Antigens/immunology , Myeloid Cell Leukemia Sequence 1 Protein/immunology , Organ Specificity , Proto-Oncogene Proteins c-bcl-2/immunology , Signal Transduction , Sulfonamides/pharmacologyABSTRACT
The endoplasmic reticulum (ER) stress response constitutes cellular reactions triggered by a wide variety of stimuli that disturb folding of proteins, often leading to apoptosis. ER stress-induced apoptotic cell death is thought to be an important contributor to many human pathological conditions. The molecular mechanism of this apoptosis process has been highly controversial with both the receptor and the mitochondrial pathways being implicated. Using knockout mouse models and RNAi-mediated gene silencing in cell lines, our group and others had demonstrated the importance of the mitochondrial apoptotic pathway in ER stress-induced cell death, particularly the role of the pro-apoptotic BH3-only BCL-2 family members, BIM and PUMA. However, a recent report suggested a central role for the death receptor, DR5, activated in a ligand-independent manner, and the initiator caspase, caspase-8, in ER stress-induced cell death. This prompted us to re-visit our previous observations and attempt to reproduce the newly published findings. Here we report that the mitochondrial apoptotic pathway, activated by BH3-only proteins, is essential for ER stress-induced cell death and that, in contrast to the previous report, DR5 as well as caspase-8 are not required for this process.
