N52 monodeamidated Bcl‑xL shows impaired oncogenic properties in vivo and in vitro

Bcl-xL Is Spontaneously Inserted into Preassembled Nanodiscs and Stimulates Bax Insertion in a Cell-Free Protein Synthesis System

The antiapoptotic protein Bcl-xL is a major regulator of cell death and survival, but many aspects of its functions remain elusive. It is mostly localized in the mitochondrial outer membrane (MOM) owing to its C-terminal hydrophobic α-helix. In order to gain further information about its membrane organization, we set up a model system combining cell-free protein synthesis and nanodisc insertion. We found that, contrary to its proapoptotic partner Bax, neosynthesized Bcl-xL was spontaneously inserted into nanodiscs. The deletion of the C-terminal α-helix of Bcl-xL prevented nanodisc insertion. We also found that nanodisc insertion protected Bcl-xL against the proteolysis of the 13 C-terminal residues that occurs during expression of Bcl-xL as a soluble protein in E. coli. Interestingly, we observed that Bcl-xL increased the insertion of Bax into nanodiscs, in a similar way to that which occurs in mitochondria. Cell-free synthesis in the presence of nanodiscs is, thus, a suitable model system to study the molecular aspects of the interaction between Bcl-xL and Bax during their membrane insertion.

Inhibition of Autophagy Negates Radiofrequency-Induced Adaptive Response in SH-SY5Y Neuroblastoma Cells

In the last years, radiofrequency (RF) has demonstrated that it can reduce DNA damage induced by a subsequent treatment with chemical or physical agents in different cell types, resembling the adaptive response, a phenomenon well documented in radiobiology. Such an effect has also been reported by other authors both in vitro and in vivo, and plausible hypotheses have been formulated, spanning from the perturbation of the cell redox status, to DNA repair mechanisms, and stress response machinery, as possible cellular mechanisms activated by RF pre-exposure. These mechanisms may underpin the observed phenomenon, and require deeper investigations. The present study aimed to determine whether autophagy contributes to RF-induced adaptive response. To this purpose, SH-SY5Y human neuroblastoma cells were exposed for 20 h to 1950 MHz, UMTS signal, and then treated with menadione. The results obtained indicated a reduction in menadione-induced DNA damage, assessed by applying the comet assay. Such a reduction was negated when autophagy was inhibited by bafilomycin A1 and E64d. Moreover, CRISPR SH-SY5Y cell lines defective for ATG7 or ATG5 genes did not show an adaptive response. These findings suggest the involvement of autophagy in the RF-induced adaptive response in human neuroblastoma cells; although, further investigation is required to extend such observation at the molecular level.

Keeping Cell Death Alive: An Introduction into the French Cell Death Research Network

Since the Nobel Prize award more than twenty years ago for discovering the core apoptotic pathway in C. elegans, apoptosis and various other forms of regulated cell death have been thoroughly characterized by researchers around the world. Although many aspects of regulated cell death still remain to be elucidated in specific cell subtypes and disease conditions, many predicted that research into cell death was inexorably reaching a plateau. However, this was not the case since the last decade saw a multitude of cell death modalities being described, while harnessing their therapeutic potential reached clinical use in certain cases. In line with keeping research into cell death alive, francophone researchers from several institutions in France and Belgium established the French Cell Death Research Network (FCDRN). The research conducted by FCDRN is at the leading edge of emerging topics such as non-apoptotic functions of apoptotic effectors, paracrine effects of cell death, novel canonical and non-canonical mechanisms to induce apoptosis in cell death-resistant cancer cells or regulated forms of necrosis and the associated immunogenic response. Collectively, these various lines of research all emerged from the study of apoptosis and in the next few years will increase the mechanistic knowledge into regulated cell death and how to harness it for therapy.

Introducing protein deamidation: Landmark discoveries, societal outreach, and tentative priming workflow to address deamidation

Our current knowledge on protein deamidation results from a journey that started almost 100 years ago, when a handful of researchers first described the non-enzymatic "desamidation" of glutamine, and the effect of different anions on the catalytic rate of the reaction. Since then, the field has tremendously expended and now finds outreach in very diverse areas. In light of all the recent articles published in these areas, it seemed timely to propose an integrated review on the subject, including a short historical overview of the landmark discoveries in the field, highlighting the current global positioning of protein deamidation in biology and non-biology fields, and concluding with a workflow for those asking if a protein can deamidate, and identify the residues involved. This review is essentially intended to provide newcomers in the field with an overview of how deamidation has penetrated our society and what tools are currently at hand to identify and quantify protein deamidation.

Contribution of Yeast Studies to the Understanding of BCL-2 Family Intracellular Trafficking

BCL-2 family members are major regulators of apoptotic cell death in mammals. They form an intricate regulatory network that ultimately regulates the release of apoptogenic factors from mitochondria to the cytosol. The ectopic expression of mammalian BCL-2 family members in the yeast Saccharomyces cerevisiae, which lacks BCL-2 homologs, has been long established as a useful addition to the available models to study their function and regulation. In yeast, individual proteins can be studied independently from the whole interaction network, thus providing insight into the molecular mechanisms underlying their function in a living context. Furthermore, one can take advantage of the powerful tools available in yeast to probe intracellular trafficking processes such as mitochondrial sorting and interactions/exchanges between mitochondria and other compartments, such as the endoplasmic reticulum that are largely conserved between yeast and mammals. Yeast molecular genetics thus allows the investigation of the role of these processes on the dynamic equilibrium of BCL-2 family members between mitochondria and extramitochondrial compartments. Here we propose a model of dynamic regulation of BCL-2 family member localization, based on available evidence from ectopic expression in yeast.

1D continuous gel electrophoresis composition for the separation of deamidated proteins

Deamidation is a spontaneous modification of peptides and proteins that has potent repercussions on their activity and stability in vivo and in vitro. Being able to implement easy techniques to detect and quantify protein deamidation is a major goal in this field. Here we focus on electrophoretic methods that can be deployed to assess protein deamidation. We provide an update on the use of Taurine/Glycinate as trailing ions to assist the detection of several examples of deamidated proteins, namely the small GTPases RhoA, Rac1 and Cdc42, but also the oncogene Bcl-xL and calcium-binding Calmodulin. We also report on the use of imidazole as a counter ion to improve the focusing of deamidated bands. Finally, we provide examples of how these gels proved useful to compare on full-length proteins the effect of ions and pH on the catalytic rates of spontaneous deamidation. Taken together, the electrophoretic method introduced here proves useful to screen at once the effect of various conditions of pH, ionic strength and buffer ions on protein stability. Direct applications can be foreseen to tailor buffer formulations to control the stability of proteins drug products.

Improved Electrophoretic Separation to Assist the Monitoring of Bcl-xL Post-Translational Modifications

Bcl-x_L is an oncogene of which the survival functions are finely tuned by post-translational modifications (PTM). Within the Bcl-2 family of proteins, Bcl-x_L shows unique eligibility to deamidation, a time-related spontaneous reaction. Deamidation is still a largely overlooked PTM due to a lack of easy techniques to monitor Asn→Asp/IsoAsp conversions or Glu→Gln conversions. Being able to detect PTMs is essential to achieve a comprehensive description of all the regulatory mechanisms and functions a protein can carry out. Here, we report a gel composition improving the electrophoretic separation of deamidated forms of Bcl-x_L generated either by mutagenesis or by alkaline treatment. Importantly, this new gel formulation proved efficient to provide the long-sought evidence that even doubly-deamidated Bcl-x_L remains eligible for regulation by phosphorylation.

Bcl-xL deamidation and cancer: Charting the fame trajectories of legitimate child and hidden siblings

Bcl-2 family proteins control programmed cell death through a complex network of interactions within and outside of this family, that are modulated by post-translational modifications (PTM). Bcl-x_L, an anti-apoptotic member of this family, is overexpressed in a number of cancers, plays an important role in tumorigenesis and is correlated with drug resistance. Bcl-x_L is susceptible to a number of different PTMs. Here, we focus on deamidation. We will first provide an overview of protein deamidation. We will then review how the apoptotic and autophagic functions of Bcl-x_L are modified by this PTM, and how this impacts on its oncogenic properties. Possible therapeutic outcomes will also be discussed. Finally, we will highlight how the specific case of Bcl-x_L deamidation provides groundings to revisit some concepts related to protein deamidation in general.

Bax mitochondrial relocation is linked to its phosphorylation and its interaction with Bcl-xL

The heterologous expression of Bax, and other Bcl-2 family members, in the yeast Saccharomyces cerevisiae, has proved to be a valuable reporter system to investigate the molecular mechanisms underlying their interaction with mitochondria. By combining the co-expression of Bax and Bcl-xL mutants with analyzes of their localization and interaction in mitochondria and post-mitochondrial supernatants, we showed that the ability of Bax and Bcl-xL to interact is dependent both on Bax phosphorylation - mimicked by a substitution S184D - and by Bax and Bcl-xL localization. This, and previous data, provide the molecular basis for a model of dynamic equilibrium for Bax localization and activation, regulated both by phosphorylation and Bcl-xL.

A brewing understanding of the regulation of Bax function by Bcl-xL and Bcl-2

Bcl-2 family members form a network of protein-protein interactions that regulate apoptosis through permeabilization of the mitochondrial outer membrane. Deciphering this intricate network requires streamlined experimental models, including the heterologous expression in yeast. This approach had previously enabled researchers to identify domains and residues that underlie the conformational changes driving the translocation, the insertion and the oligomerization of the pro-apoptotic protein Bax at the level of the mitochondrial outer membrane. Recent studies that combine experiments in yeast and in mammalian cells have shown the unexpected effect of the anti-apoptotic protein Bcl-xL on the priming of Bax. As demonstrated with the BH3-mimetic molecule ABT-737, this property of Bcl-xL, and of Bcl-2, is crucial to elaborate about how apoptosis could be reactivated in tumoral cells.