Biology subjects

Tait, S.

Publications and source records attributed to Tait, S..

6 recordsLinked to original sources

bioRxiv2023

Mitochondrial outer membrane integrity regulates a ubiquitin-dependent NF-κB inflammatory response

Mitochondria are often essential for apoptosis through mitochondrial outer membrane permeabilization (MOMP). This central event enables cytochrome c release leading to caspase activation and rapid cell death. Recently, MOMP has been shown to be inherently pro-inflammatory, for instance, by enabling mitochondrial DNA-dependent activation of cGAS-STING signalling. Alongside having emerging functions in health and disease, MOMP associated inflammation can also elicit anti-tumour immunity. Nonetheless, how MOMP triggers inflammation and how the cell counteracts this remains poorly defined. We find that upon MOMP, mitochondria are ubiquitylated in a promiscuous manner targeting proteins localised to both inner and outer mitochondrial membranes. Mitochondrial ubiquitylation serves to recruit the essential adaptor molecule, NEMO, leading to activation of pro-inflammatory NF-{kappa}B signalling. We find that disruption of mitochondrial outer membrane integrity through different means leads to engagement of a similar pro-inflammatory signalling platform. Thus, mitochondrial integrity directly controls inflammation, such that permeabilised mitochondria initiate NF-{kappa}B signalling. This event may be important for the various pathophysiological functions of MOMP-associated inflammation.

cell biology↗

bioRxiv2022

Intracellular BAPTA directly inhibits PFKFB3, thereby impeding mTORC1-driven Mcl-1 translation and killing Mcl-1-addicted cancer cells

Intracellular Ca2+ signals control several physiological and pathophysiological processes. The main tool to chelate intracellular Ca2+ is intracellular BAPTA (BAPTAi), usually introduced into cells as a membrane-permeant acetoxymethyl ester (BAPTA-AM). We previously demonstrated that BAPTAi enhanced apoptosis induced by venetoclax, a Bcl-2 antagonist, in diffuse large B-cell lymphoma (DLBCL). These findings implied a novel interplay between intracellular Ca2+ signaling and anti-apoptotic Bcl-2 function. Hence, we set out to identify the underlying mechanisms by which BAPTAi enhances cell death in B-cell cancers. In this study, we observed that BAPTAi alone induced apoptosis in lymphoma cell models that were highly sensitive to S63845, an Mcl-1 antagonist. BAPTAi provoked a rapid decline in Mcl-1 protein levels by inhibiting mTORC1-driven MCL-1 translation. Overexpression of nondegradable Mcl-1 rescued BAPTAi-induced cell death. We further examined how BAPTAi diminished mTORC1 activity and found that BAPTAi impaired glycolysis by directly inhibiting 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) activity, an up to now unkown effect of BAPTAi. All aforementioned effects of BAPTAi were also elicited by a BAPTAi analog with low affinity for Ca2+. Thus, our work reveals PFKFB3 inhibition as an unappreciated Ca2+-independent mechanism by which BAPTAi impairs cellular metabolism and ultimately the survival of Mcl-1-dependent cancer cells. Our work has two important implications. First, direct inhibition of PFKFB3 emerged as a key regulator of mTORC1 activity and a promising target in the treatment of Mcl-1-dependent cancers. Second, cellular effects caused by BAPTAi are not necessarily related to Ca2+ signaling. Our data support the need for a reassessment of the role of Ca2+ in cellular processes when findings were based on the use of BAPTAi.

cell biology↗

bioRxiv2021

Increased apoptotic priming of glioblastoma enables therapeutic targeting by BH3-mimetics

IDH wild-type glioblastoma (GBM) is the most prevalent malignant primary brain tumour in adults. GBM typically has a poor prognosis, mainly due to a lack of effective treatment options leading to tumour persistence or recurrence. Tackling this, we investigated the therapeutic potential of targeting anti-apoptotic BCL-2 proteins in GBM. Levels of anti- apoptotic BCL-xL and MCL-1 were consistently increased in GBM compared with non- malignant cells and tissue. Moreover, we found that relative to their differentiated counterparts, patient-derived GBM stem-like cells also displayed higher expression of anti- apoptotic BCL-2 family members. Surprisingly, high anti-apoptotic BCL-xL and MCL-1 expression correlated with heightened susceptibility of GBM to BCL-2 family protein- targeting BH3-mimetics. This is indicative of increased apoptotic priming. Indeed, GBM displayed an obligate requirement for MCL-1 expression in both tumour development and maintenance. Investigating this apoptotic sensitivity, we found that sequential inhibition of BCL-xL and MCL-1 led to robust anti-tumour responses in vivo, in the absence of overt toxicity. These data demonstrate that BCL-xL and MCL-1 pro-survival function is a fundamental prerequisite for GBM survival that can be therapeutically exploited by BH3- mimetics.

cancer biology↗

bioRxiv2020

BRD4-mediated repression of p53 is a target for combination therapy in AML

Acute Myeloid Leukemia (AML) is a typically-lethal molecularly heterogeneous disease, with few broad-spectrum therapeutic targets. Unusually, most AML retain wild-type TP53, encoding the pro-apoptotic tumor suppressor p53. MDM2 inhibitors (MDM2i), which activate wild-type p53, and BET inhibitors (BETi), targeting the BET-family co-activator BRD4, both show encouraging pre-clinical activity, but limited clinical activity as single agents. Here, we report synergistic toxicity of combined MDM2i and BETi towards AML cell lines, primary human blasts and mouse models, resulting from BETis ability to evict an unexpected repressive form of BRD4 from p53 target genes, and hence potentiate MDM2i-induced p53 activation. These results indicate that wild-type TP53 and a transcriptional repressor function of BRD4 together represent a potential broad-spectrum synthetic therapeutic vulnerability for AML.

cell biology↗

bioRxiv2019

Distributed Biomanufacturing of Liquefied Petroleum Gas

Liquefied Petroleum Gas (LPG) is a major domestic and transport fuel. Its combustion lessens NOx, greenhouse gas and particulates emissions compared to other fuels. Propane - the major constituent of LPG - is a clean, high value drop-in fuel that can help governments develop integrated fuels and energy policies with low carbon burden, providing solutions to the multi-faceted challenges of future energy supply. We show that bio-LPG (bio-propane and bio-butane) can be produced by microbial conversion of waste volatile fatty acids that can be derived from anaerobic digestion, industrial waste, or CO2 via photosynthesis. Bio-LPG production was achieved photo-catalytically, using biomass propagated from bioengineered bacteria including E. coli, Halomonas (in non-sterile seawater), and Synechocystis (photosynthetic). These fuel generation routes could be implemented rapidly in advanced and developing nations of the world to meet energy needs, global carbon reduction targets and clean air directives.

bioengineering↗

bioRxiv2018

Activated BAX/BAK enable mitochondrial inner membrane permeabilisation and mtDNA release during cell death

During apoptosis, pro-apoptotic BAX and BAK are activated, causing mitochondrial outer membrane permeabilisation (MOMP), caspase activation and cell death. However, even in the absence of caspase activity, cells usually die following MOMP. Such caspase-independent cell death is accompanied by inflammation that requires mitochondrial DNA (mtDNA) activation of cGAS-STING signaling. Because the mitochondrial inner membrane is thought to remain intact during apoptosis, we sought to address how matrix mtDNA could activate the cytosolic cGAS-STING signaling pathway. Strikingly, using super-resolution imaging, we show that mtDNA is efficiently released from mitochondria following MOMP. In a temporal manner, we find that following MOMP, BAX/BAK-mediated mitochondrial outer membrane pores gradually widen over time. This allows extrusion of the mitochondrial inner membrane into the cytosol whereupon it permeablises allowing mtDNA release. Our data demonstrate that mitochondrial inner membrane permeabilisation can occur during cell death in a BAX/BAK-dependent manner. Importantly, by enabling the cytosolic release of mtDNA, inner membrane permeabilisation underpins the immunogenic effects of caspase-independent cell death.

cell biology↗