There is something about BOK we just don't get yet

Mcl-1 and Bok transmembrane domains: Unexpected players in the modulation of apoptosis

The Bcl-2 protein family comprises both pro- and antiapoptotic members that control the permeabilization of the mitochondrial outer membrane, a crucial step in the modulation of apoptosis. Recent research has demonstrated that the carboxyl-terminal transmembrane domain (TMD) of some Bcl-2 protein family members can modulate apoptosis; however, the transmembrane interactome of the antiapoptotic protein Mcl-1 remains largely unexplored. Here, we demonstrate that the Mcl-1 TMD forms homooligomers in the mitochondrial membrane, competes with full-length Mcl-1 protein with regards to its antiapoptotic function, and induces cell death in a Bok-dependent manner. While the Bok TMD oligomers locate preferentially to the endoplasmic reticulum (ER), heterooligomerization between the TMDs of Mcl-1 and Bok predominantly takes place at the mitochondrial membrane. Strikingly, the coexpression of Mcl-1 and Bok TMDs produces an increase in ER mitochondrial-associated membranes, suggesting an active role of Mcl-1 in the induced mitochondrial targeting of Bok. Finally, the introduction of Mcl-1 TMD somatic mutations detected in cancer patients alters the TMD interaction pattern to provide the Mcl-1 protein with enhanced antiapoptotic activity, thereby highlighting the clinical relevance of Mcl-1 TMD interactions.

Genetic effects on planum temporale asymmetry and their limited relevance to neurodevelopmental disorders, intelligence or educational attainment

Previous studies have suggested that altered asymmetry of the planum temporale (PT) is associated with neurodevelopmental disorders, including dyslexia, schizophrenia, and autism. Shared genetic factors have been suggested to link PT asymmetry to these disorders. In a dataset of unrelated subjects from the general population (UK Biobank, N = 18,057), we found that PT volume asymmetry had a significant heritability of roughly 14%. In genome-wide association analysis, two loci were significantly associated with PT asymmetry, including a coding polymorphism within the gene ITIH5 that is predicted to affect the protein's function and to be deleterious (rs41298373, p = 2.01 × 10-15), and a locus that affects the expression of the genes BOK and DTYMK (rs7420166, p = 7.54 × 10-10). DTYMK showed left-right asymmetry of mRNA expression in post mortem PT tissue. Cortex-wide mapping of these SNP effects revealed influences on asymmetry that went somewhat beyond the PT. Using publicly available genome-wide association statistics from large-scale studies, we saw no significant genetic correlations of PT asymmetry with autism spectrum disorder, attention deficit hyperactivity disorder, schizophrenia, educational attainment or intelligence. Of the top two individual loci associated with PT asymmetry, rs41298373 showed a tentative association with intelligence (unadjusted p = .025), while the locus at BOK/DTYMK showed tentative association with educational attainment (unadjusted Ps < .05). These findings provide novel insights into the genetic contributions to human brain asymmetry, but do not support a substantial polygenic association of PT asymmetry with cognitive variation and mental disorders, as far as can be discerned with current sample sizes.

Role of B-Cell Lymphoma 2 Ovarian Killer (BOK) in Acute Toxicity of Human Lung Epithelial Cells Caused by Cadmium Chloride

Background

B-cell lymphoma 2 (BCL-2) ovarian killer (BOK) is a Bcl-2 family member with sequence homology to pro-apoptotic BAX and BAK, but its physiological and pathological roles remain largely unclear. Exposure of cells to cadmium may cause DNA damage, decrease DNA repair capacity, and increase genomic instability.

Material/Methods

The present study investigated the effects of BOK on the toxicity of cadmium chloride (CdCl₂) to human bronchial epithelial (16HBE) cells. We constructed BOK over-expressing (16HBE-BOK) cells and BOK knockdown (16HBE-shBOK) cells using the BOK-ORF plasmid and BOK-siRNA. qRT-PCR for BOK mRNA expression. We used Trypan blue exclusion assay for cell growth, MTT colorimetric assays for cells inhibition rate, and Comet assays for detecting damaged DNA.

Results

CdCl₂, at various concentrations and exposure times, increased BOK mRNA. 16HBE-BOK cells (BOK over-expressing) proliferated more than 16HBE cells after 72 h; 16HBE-shBOK (BOK knockdown) cells proliferated less. In addition, BOK deficiency enhanced cell death induced by CdCl₂. Similarly, CdCl₂- and H₂O₂-induced DNA damage was greater in BOK-deficient cells.

Conclusions

These findings support a role for BOK in CdCl₂-induced DNA damage and cell death.

Role and Regulation of Pro-survival BCL-2 Proteins in Multiple Myeloma

Apoptosis plays a key role in protection against genomic instability and maintaining tissue homeostasis, and also shapes humoral immune responses. During generation of an antibody response, multiple rounds of B-cell expansion and selection take place in germinal centers (GC) before high antigen affinity memory B-cells and long-lived plasma cells (PC) are produced. These processes are tightly regulated by the intrinsic apoptosis pathway, and malignant transformation throughout and following the GC reaction is often characterized by apoptosis resistance. Expression of pro-survival BCL-2 family protein MCL-1 is essential for survival of malignant PC in multiple myeloma (MM). In addition, BCL-2 and BCL-XL contribute to apoptosis resistance. MCL-1, BCL-2, and BCL-XL expression is induced and maintained by signals from the bone marrow microenvironment, but overexpression can also result from genetic lesions. Since MM PC depend on these proteins for survival, inhibiting pro-survival BCL-2 proteins using novel and highly specific BH3-mimetic inhibitors is a promising strategy for treatment. This review addresses the role and regulation of pro-survival BCL-2 family proteins during healthy PC differentiation and in MM, as well as their potential as therapeutic targets.

Contribution of BH3-domain and Transmembrane-domain to the Activity and Interaction of the Pore-forming Bcl-2 Proteins Bok, Bak, and Bax

Central to intrinsic apoptosis signaling is the release of cytochrome c from mitochondria, which depends on the pro-apoptotic effector proteins Bax, Bak or Bok. These pore-forming effector proteins share four Bcl-2 homology (BH) domains, a functionally essential and conserved sequence of hydrophobic amino acids in their BH3-domain and a C-terminal transmembrane-domain whose specific function remains rather unknown. To elucidate the molecular basis of Bok-mediated apoptosis we analyzed apoptosis induction by transmembrane-domain deficient BokΔTM compared to the respective Bax and Bak proteins and proteins in which the first leucine in the BH3-stretch was mutated to glutamic acid. We show that deletion of the C-terminal transmembrane-domain reduces the pro-apoptotic function of each protein. Mutation of the first leucine in the BH3-domain (L78E) blocks activity of Bak, while mutation of the homologue residues in Bax or Bok (L63E and L70E respectively) does not affect apoptosis induction. Unexpectedly, combined mutation of the BH3-domain and deletion of the transmembrane-domain enhances the pro-apoptotic activity of Bok(L70E)ΔTM by abolishing the interaction with anti-apoptotic proteins, especially the primary Bok-inhibitory protein Mcl-1. These results therefore suggest a specific contribution of the transmembrane-domain to the pro-apoptotic function and interaction of Bok.