Biology subjects

Seager, R.

Publications and source records attributed to Seager, R..

6 recordsLinked to original sources

bioRxiv2026

MFF SUMOylation regulates neuronal mitochondrial morphology and facilitates AMPK-induced mitochondrial fragmentation

Mitochondrial dysfunction and fragmentation in neurons are characteristics of many neurodegenerative conditions. AMP-activated protein kinase (AMPK) is a cellular energy sensor which is hyperactivated in Alzheimers disease. Under stress conditions, AMPK-mediates phosphorylation of the outer mitochondrial membrane protein mitochondrial fission factor (MFF), leading to SUMOylation at Lys151. MFF SUMOylation promotes fission and subsequent mitochondrial fragmentation. Here, using primary neuronal culture, we investigate the role of MFF SUMOylation in mitochondrial morphology and function. We show that MFF SUMOylation is required to maintain neuronal mitochondrial length under basal conditions in axons and dendrites. Using the AMPK activator (AICAR) to induce mitochondrial fission, show that preventing MFF SUMOylation reduces AICAR-induced fragmentation of dendritic mitochondria. These findings reconcile observations of AMPK hyperactivation and mitochondrial fragmentation by revealing the AMPK-MFF-SUMO pathway to be crucial in neuronal mitochondrial fission.

neuroscience↗

bioRxiv2025

PINK1 SUMOylation regulates basal mitophagy

The mitochondrial kinase PTEN-induced kinase 1 (PINK1) initiates mitophagy in response to mitochondrial damage, yet mechanisms that constrain its activation under basal conditions remain incompletely defined. Here, we identify a non-canonical SUMO-2/3 modification of PINK1 that suppresses basal mitophagy. We show that the mitochondrial E3 ligase mitochondrial-anchored protein ligase (MAPL/MUL1) promotes PINK1 SUMO-2/3 modification, while MAPL depletion reduces SUMOylation and enhances basal mitophagy. Targeted deSUMOylation increases PINK1 stabilisation and augments mitophagy. These findings reveal a novel SUMO-based checkpoint for basal PINK1 activation and mitochondrial quality control.

cell biology↗

bioRxiv2023

Coordinated interplay between palmitoylation, phosphorylation and SUMOylation regulates kainate receptor surface expression.

Kainate receptors (KARs) are key regulators of neuronal excitability and synaptic transmission. KAR surface expression is tightly controlled in part by post-translational modifications (PTMs) of the GluK2 subunit. We have shown previously that agonist activation of GluK2-containing KARs leads to phosphorylation of GluK2 at S868, which promotes subsequent SUMOylation at K886 and receptor endocytosis. Furthermore, GluK2 has been shown to be palmitoylated. However, how the interplay between palmitoylation, phosphorylation and SUMOylation orchestrate KAR trafficking remains unclear. Here, we used a library of site-specific GluK2 mutants to investigate the interrelationship between GluK2 PTMs, and their impact on KAR surface expression. We show that GluK2 is basally palmitoylated and that this is decreased by kainate stimulation. Moreover, a non-palmitoylatable GluK2 mutant (C858/C871A) shows enhanced S868 phosphorylation and K886 SUMOylation under basal conditions and is insensitive to KA-induced internalisation. These results indicate that GluK2 palmitoylation contributes to stabilising KAR surface expression and that dynamic depalmitoylation promotes downstream phosphorylation and SUMOylation to mediate activity-dependent KAR endocytosis. Significance StatementPost-translational modifications (PTMs) are biochemical switches that control substrate protein properties and interactions. In consequence, PTMs are critical regulators of essentially all cellular pathways and are vital for eukaryotic cell survival. In the brain, among other roles, PTMs influence neuronal growth, differentiation, synaptic activity and plasticity. Kainate receptors (KARs) play core roles in all these processes and previous work has shown that the GluK2 subunit of KARs is subject to multiple PTMs. Here, using GluK2 as an exemplar protein, we delineate the sequence, coordination, and consequences of the PTMs palmitoylation, phosphorylation and SUMOylation on KAR surface expression. Our data show how the complex interplay between PTMs dynamically regulates synaptic proteins and neuronal function.

neuroscience↗

bioRxiv2023

SUMOylation of MFF is required for stress-induced mitochondrial fission

Mitochondrial fission regulates mitochondrial morphology, function, mitophagy and apoptosis. Fission is mediated by the GTPase dynamin related protein-1 (DRP1) and its recruitment to the outer mitochondrial membrane by DRP1 receptors. Mitochondrial fission factor (MFF) is considered the major pro-fission receptor, whereas the mitochondrial dynamics proteins (MiD49/51) sequester inactive DRP1 and facilitate the MFF-DRP1 interaction by forming a trimeric DRP1-MiD-MFF complex. Here, we identify MFF as a target of poly-SUMOylation at a single residue (Lys151). Following bioenergetic stress, AMPK phosphorylates MFF to promote its SUMOylation, a critical step in stress-induced fragmentation. MFF SUMOylation is not required for DRP1 recruitment from the cytosol but causes a rearrangement of the trimeric fission complex to displace MiD proteins. This alleviates MiD inhibition of DRP1 to facilitate formation of a fission-competent complex. Thus, our data demonstrate that MFF SUMOylation fine-tunes the ratio of MiD to DRP1 for the dynamic control of stress-induced mitochondrial fragmentation.

cell biology↗

bioRxiv2020

Sustained postsynaptic kainate receptor activation downregulates AMPA receptor surface expression and induces hippocampal LTD

Here we report that sustained activation of GluK2 subunit-containing kainate receptors leads to AMPA receptor endocytosis and a novel form of long-term depression (KAR-LTDAMPAR) in hippocampal neurons. The KAR-evoked loss of surface AMPA receptors requires KAR channel activity and is occluded by the blockade of PKC or PKA. Moreover, in acute hippocampal slices, kainate invoked LTD of AMPA EPSCs. These data, together with our previously reported KAR-LTPAMPAR, demonstrate that KARs bidirectionally regulate synaptic AMPARs and synaptic plasticity.

neuroscience↗

bioRxiv2019

Parkin-mediated ubiquitination contributes to the constitutive turnover of mitochondrial fission factor (Mff)

The mitochondrial outer membrane protein Mitochondrial Fission Factor (Mff) plays a key role in both physiological and pathological fission. It is well established that in stressed or functionally impaired mitochondria the PINK1 recruits the ubiquitin ligase Parkin which ubiquitinates Mff to facilitate the removal of defective mitochondria and maintain the integrity mitochondrial network. Here we show that, in addition to this clearance pathway, Parkin also ubiquitinates Mff in a PINK1-dependent manner under basal, non-stressed conditions to regulate constitutive Mff turnover. We further show that removing Parkin with shRNA knockdown does not completely prevent Mff ubiquitination under these conditions indicating that at least one other ubiquitin ligase contributes to Mff proteostasis. These data demonstrate that Parkin plays a role in physiological maintenance of mitochondrial membrane protein composition in healthy mitochondria through constitutive low-level activation.

cell biology↗