RESUMO
T lymphocyte non-Hodgkin's lymphoma (T-NHL) represents an aggressive and largely therapy-resistant subtype of lymphoid malignancies. As deregulated apoptosis is a frequent hallmark of lymphomagenesis, we analyzed gene expression profiles and protein levels of primary human T-NHL samples for various apoptotic regulators. We identified the apoptotic regulator MCL-1 as the only pro-survival BCL-2 family member to be highly expressed throughout all human T-NHL subtypes. Functional validation of pro-survival protein members of the BCL-2 family in two independent T-NHL mouse models identified that the partial loss of Mcl-1 significantly delayed T-NHL development in vivo. Moreover, the inducible reduction of MCL-1 protein levels in lymphoma-burdened mice severely impaired the continued survival of T-NHL cells, increased their susceptibility to chemotherapeutics and delayed lymphoma progression. Lymphoma viability remained unaffected by the genetic deletion or pharmacological inhibition of all alternative BCL-2 family members. Consistent with a therapeutic window for MCL-1 treatment within the context of the whole organism, we observed an only minimal toxicity after systemic heterozygous loss of Mcl-1 in vivo. We conclude that re-activation of mitochondrial apoptosis by blockade of MCL-1 represents a promising therapeutic strategy to treat T-cell lymphoma.
Assuntos
Proteínas Reguladoras de Apoptose/genética , Apoptose , Linfoma de Células T/química , Proteína de Sequência 1 de Leucemia de Células Mieloides/análise , Animais , Proteínas Reguladoras de Apoptose/análise , Sobrevivência Celular , Resistencia a Medicamentos Antineoplásicos , Perfilação da Expressão Gênica , Humanos , Linfoma de Células T/patologia , Camundongos , Proteína de Sequência 1 de Leucemia de Células Mieloides/antagonistas & inibidores , Proteína de Sequência 1 de Leucemia de Células Mieloides/genética , Proteína de Sequência 1 de Leucemia de Células Mieloides/fisiologia , Proteínas Proto-Oncogênicas c-bcl-2/genéticaRESUMO
B-cell lymphoma-2 (Bcl-2) proteins mediate intrinsic-, or mitochondrial-, initiated apoptosis. We have investigated the structure and function of the least characterized Bcl-2 family member, Bcl-B, solving the crystal structure of a Bcl-B:Bim complex to 1.9 Å resolution. Bcl-B is distinguished from other Bcl-2 family members through an insertion of an unstructured loop between helices α5 and α6. Probing Bcl-B interactions with Bcl-2 homology (BH)3 motifs using a combination of biophysical- and cell-based assays revealed a unique BH3-only protein binding profile. Bcl-B has high-affinity interactions with Bim and Bik only. Our results not only delineate the mode of action of Bcl-B but also complete our understanding of the specific interactions between BH3-only proteins and their prosurvival Bcl-2 counterparts. Notably, we conclude that Bim is the universal prosurvival antagonist as no other BH3-only protein binds all six prosurvival proteins and that Mcl-1 and Bcl-x(L) form a distinct prosurvival dyad.
Assuntos
Proteínas Reguladoras de Apoptose/metabolismo , Apoptose , Proteínas de Membrana/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/agonistas , Proteínas Proto-Oncogênicas/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Proteínas Reguladoras de Apoptose/química , Proteínas Reguladoras de Apoptose/genética , Proteína 11 Semelhante a Bcl-2 , Linhagem Celular , Sobrevivência Celular , Humanos , Proteínas de Membrana/química , Proteínas de Membrana/genética , Camundongos , Proteínas Mitocondriais , Conformação Molecular , Dados de Sequência Molecular , Ligação Proteica , Proteínas Proto-Oncogênicas/química , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas c-bcl-2/química , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Alinhamento de SequênciaRESUMO
A group of integral membrane proteins, known as C-tail anchored, is defined by the presence of a cytosolic N-terminal domain that is anchored to the phospholipid bilayer by a single segment of hydrophobic amino acids close to the C-terminus. The mode of insertion into membranes of these proteins, many of which play key roles in fundamental intracellular processes, is obligatorily post-translational, is highly specific and may be subject to regulatory processes that modulate the protein's function. Recent work has demonstrated that tail-anchored proteins translocate their C-termini across the endoplasmic reticulum membrane by a mechanism different from that used for Sec61-dependent post-translational signal-peptide-driven translocation. Here we summarize recent results on the insertion of tail-anchored proteins and discuss possible mechanisms that could be involved.