Biology subjects

Cobbaut, M.

Publications and source records attributed to Cobbaut, M..

3 recordsLinked to original sources

bioRxiv2025

The penetrant chordoid glioma PRKCA mutation is an oncogenic gain-of-function kinase inactivation eliciting early onset chondrosarcoma in mice.

The penetrant PRKCA D463H mutation, a biomarker and potential driver in chordoid glioma, was found to provoke the development of chondrosarcomas in heterozygous knock-in mice. This mutation entirely abrogates kinase activity, but strikingly no oncogenic phenotype is observed for the related inactivating mutation D463N indicating that the lack of activity is not the driver. In cells, the D463H mutant closely mirrored PKC WT behaviours and retained ATP binding, contrary to the related D463N mutant. Mechanistically, the PKC D463H mutant protein was found to display quantitative alterations to the PKC interactome, enhancing association with epigenetic regulators. This aligned with transcriptomic changes which resembled an augmented PKC expression program, with enhanced BRD4, Myc and TGF{beta} signatures. D463H dependent reduced sensitivity to the BET inhibitors JQ1 and AZD5153 indicates the functional importance of these pathways. The data show that D463H is a dominant gain-of-function oncogenic mutant, operating through a non-catalytic allosteric mechanism. One Sentence SummaryA PKC catalytic inactivating mutation confers gain-of-function properties - a paradigm shift in kinase actions.

cancer biology↗

bioRxiv2024

Capture, mutual inhibition and release mechanism for aPKC-Par6 and its multi-site polarity substrate Lgl

The mutually antagonistic kinase-substrate relationship between the apical aPKC-Par6 heterodimer and the basolateral substrate Lgl is key to the establishment and maintenance of cell polarity across metazoa. Although aPKC-Par6 can phosphorylate Lgl at three serine sites to exclude it from the apical domain, paradoxically, aPKC-Par6 and Lgl can also form a stable kinase-substrate complex whose function remains unclear and with conflicting roles proposed for Par6. We report the structure of human aPKC{iota}-Par6 bound to full-length Llgl1, captured through an aPKC{iota} docking site and a Par6PDZ contact. This soluble tripartite complex traps a phospho-S663 Llgl1 intermediate bridging between aPKC and Par6, impeding phosphorylation progression. Thus, aPKC{iota} is effectively inhibited by Llgl1pS663 whilst Llgl1 is captured by aPKC{iota}-Par6. Mutational disruption of Lgl-aPKC interaction impedes complex assembly and Lgl phosphorylation, whereas disrupting the Lgl-Par6PDZ contact promotes complex dissociation and completion of Lgl phosphorylation cycle. We incorporate these findings into a Par6PDZ-regulated substrate capture-and-release model that we demonstrate requires binding by Cdc42-GTP and the apical partner Crumbs to drive complex disassembly. Our results provide an explanation for the opposing roles of Par6 underpinning the spatial control of aPKC-Par6 activity by Lgl relevant to polarised membrane contexts across multi-cellular organisms.

biochemistry↗

bioRxiv2023

Control of atypical PKC{iota} membrane dissociation by tyrosine phosphorylation within a PB1-C1 interdomain interface

Atypical PKCs are cell polarity kinases that operate at the plasma membrane where they function within multiple molecular complexes to contribute to the establishment and maintenance of polarity. In contrast to the classical and novel PKCs, atypical PKCs do not respond to diacylglycerol cues to bind the membrane compartment. Until recently it was not clear how aPKCs are recruited; whether aPKCs can directly interact with membranes or whether they are dependent on other protein interactors to do so. Two recent studies identified the pseudo-substrate region and the C1 domain as direct membrane interaction modules, however their relative importance and coupling are unknown. We combined molecular modelling and functional assays to show that the regulatory module of aPKC{iota}, comprising the PB1 pseudo-substrate and C1 domains, forms a cooperative and spatially continuous invariant membrane interaction platform. Furthermore, we show the coordinated orientation of membrane-binding elements within the regulatory module requires a key PB1-C1 interfacial {beta}-strand (BSL). We show this element contains a highly conserved Tyr residue that can be phosphorylated and that negatively regulates the integrity of the regulatory module, leading to membrane release. We thus expose a novel regulatory mechanism of aPKC{iota} membrane binding and release during cell polarization.

biochemistry↗