Nicolas Bidère

Glioblastoma stem-like cells (GSCs) are highly plastic tumor cells that drive initiation, progression and therapeutic resistance. Although lysosomal homeostasis has emerged as a critical determinant of GSC fitness, the molecular mechanisms regulating this compartment remain incompletely understood. Here, using complementary proteomic approaches, we identified a lysosomal signature associated with the kinase CK1α in THP1 monocytic cells. Biochemical analyses revealed that genetic or siRNA-mediated depletion of CK1α altered the overall abundance and maturation of late endosome-lysosome-associated proteins in both THP1 cells and two patient-derived GSCs. This lysosomal remodeling was associated with impaired tumorsphere formation capacity in GSCs. To further explore the therapeutic potential of targeting CK1α, we employed selective molecular glue degraders (MGDs). Acute CK1α degradation efficiently recapitulated lysosomal remodeling and impaired tumorsphere formation in GSCs. While CK1α-targeted MGDs did not sensitize GSCs to lysosomal membrane permeabilization induced by L-leucyl-L-leucine methyl ester (LLOMe), they protected from GPX4 inhibitor-induced ferroptosis. Together, these findings identify CK1α as a regulator of lysosomal fitness and ferroptotic sensitivity, suggesting a connection between CK1α-dependent lysosome remodeling and associated cell death pathways.

Mitochondrial outer membrane permeabilization is a pivotal event in programmed cell death by apoptosis, leading to the activation of the cysteine protease caspase-3 (CASP3) and the release of mitochondrial nucleic acids. This release triggers the activation of the Interferon Regulatory Factor 3 (IRF3) transcription factor and the subsequent IRF3-mediated type I interferon production and cell death. CASP3 ensures apoptosis remains immunologically silent, though the mechanisms are unclear. We report that CASP3 cleaves CYLD, a deubiquitinating enzyme crucial for cell fate and inflammatory signaling. This proteolysis occurs at a site distinct from the previously reported CASP8 site, which is involved in limiting cell lysis and inflammation during extrinsic apoptosis. Although cleaved CYLD retains its enzymatic activity in vitro, knocked-in cells expressing CASP3-resistant CYLD show increased interferon signaling and enhanced cell death. Thus, a proteolytic code regulates CYLD to balance inflammation during programmed cell death.

Inflammatory signal termination is critical for the maintenance of homeostasis. Cyclic dinucleotides (CDNs) are second messengers that trigger inflammatory responses through the activation of the stimulator of IFN genes (STING) signaling platform. No broad-acting direct regulator of intracellular CDNs has been identified in mammals to date. We show that the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a major DNA damage response actor, directly interacts with the intracellular 2′3′-cGAMP CDN through its kinase domain, tempering STING activation. DNA-PKcs also acts on the 3′3′-cGAMP bacterial CDN and pharmacological STING agonists, impacting their bioactivity and ability to mount optimal antiviral responses. STING agonism has been considered as a therapeutic avenue to alleviate immunosuppression in human pathologies. By uncovering DNA-PKcs as a CDN signaling modulator and CDNs as inhibitors of DNA-PKcs kinase activity, we provide critical insights into CDN regulation, with implications for the development of STING-targeting therapeutics.

Activation of the NLRP3 inflammasome by infectious or sterile insults culminates in pyroptosis, a lytic and highly inflammatory form of programmed cell death. A safeguarded two-step process tightly regulates pyroptosis: priming, which drives NF-κB signaling, followed by execution, ultimately leading to plasma membrane rupture. Linear (Met1-linked) ubiquitination, catalyzed by the E3 ligase complex LUBAC, was previously shown to participate in pyroptosis, but the underlying mechanisms are not fully understood. In this study, we show that Met1-linked ubiquitin chains can assemble during both priming and execution phases, independently of the inflammasome sensor NLRP3. Genetic deletion of the LUBAC enzymes or pharmacological inhibition impaired pyroptosis. Conversely, cell death was enhanced without the deubiquitinase OTULIN, which selectively removes linear ubiquitination. Finally, using an optogenetic model to bypass priming, we demonstrate that Met-1-linked ubiquitination is required for the execution phase of pyroptosis. These findings offer insights into the regulation of pyroptotic cell death by linear ubiquitination.

The cGAS-STING pathway is an evolutionarily conserved antimicrobial defense mechanism that senses cytosolic DNA to trigger innate immune responses. cGAS and STING play dual roles in tumorigenesis, promoting antitumor immunity and cell death while fueling tumor growth and metastasis. However, the mechanisms fine-tuning this pathway remain elusive. Using proteomic approaches, we report that Casein Kinase 1 alpha (CK1α) operates as a bimodal regulator of the cGAS-STING pathway. CK1α supports optimal DNA sensing by preventing the proteasomal degradation of cGAS driven by the cullin-RING ubiquitin ligase 3 (CRL3). Conversely, CK1α facilitates STING degradation and signaling termination in response to STING agonists, tempering IRF3 activation. Exploiting these counterposing functions, we show that selective degradation of CK1α with molecular-glue degraders impaired the survival of a triple-negative breast cancer cell line with chronic cGAS-STING activation and synergized with a STING agonist to kill acute myeloid leukemia cells. Thus, CK1α’s dual regulatory role in the cGAS-STING pathway presents a promising target for therapeutic development. TEASER: This study unveils CK1α as a bimodal regulator of the cGAS-STING pathway.

Cytosolic dsDNAs are potent immune-stimulatory molecules that trigger inflammation in several human pathologies ^1,2. A major pathway for the detection of cytosolic dsDNA relies on the cyclic GMP-AMP (cGAMP) synthase (cGAS) that produces the 2’3’-cGAMP cyclic dinucleotide (CDN) for activation of the Stimulator of Interferon Genes (STING) adaptor protein that subsequently drives type I Interferon (IFN) responses ^3,4. Here, we investigated the mechanism regulating intracellular 2’3’-cGAMP levels. We show that the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a major player in the repair of double-strand breaks, directly regulates intracellular levels of 2’3’-cGAMP, thereby reducing STING activation. We describe that the binding of 2’3’-cGAMP to DNA-PKcs occurs in its catalytic cleft, impeding its kinase function. Contrary to other CDN regulatory mechanisms that have been shown to primarily regulate extracellular 2’3’-cGAMP, we show that DNA-PKcs also interacts with the 3’3’-cGAMP bacterial CDN, limiting its capacity to activate STING signaling. Furthermore, we found that DNA-PKcs decreases the potency of pharmacological STING activators. As STING is a major target for therapeutic interventions aiming to boost inflammatory responses in immunosuppressed contexts ⁵, our data bear important implications for drug development and deepens our understanding of inflammatory regulation in response to CDNs.

Centriolar satellites are multiprotein aggregates that orbit the centrosome and govern centrosome homeostasis and primary cilia formation. In contrast to the scaffold PCM1, which nucleates centriolar satellites and has been linked to microtubule dynamics, autophagy, and intracellular trafficking, the functions of its interactant CEP131 beyond ciliogenesis remain unclear. Using a knockout strategy in a non-ciliary T-cell line, we report that, although dispensable for centriolar satellite assembly, CEP131 participates in optimal tubulin glycylation and polyglutamylation, and microtubule regrowth. Our unsupervised label-free proteomic analysis by quantitative mass spectrometry further uncovered mitochondrial and apoptotic signatures. CEP131-deficient cells showed an elongated mitochondrial network. Upon cell death inducers targeting mitochondria, knockout cells displayed delayed cytochrome c release from mitochondria, subsequent caspase activation, and apoptosis. This mitochondrial permeabilization defect was intrinsic, and replicable in vitro with isolated organelles. These findings extend CEP131 functions to life-and-death decisions and propose ways to interfere with mitochondrial apoptosis.