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Protein import defects induce mitophagy without membrane depolarization

ABSTRACT: Upon mitochondrial dysfunction, mitophagy has been described to be activated by a breakdown of membrane potential leading to PINK1 accumulation on the outer membrane and engulfment of mitochondria for degradation. However, recent findings have indicated that mitophagy may also be triggered in the absence of membrane potential alterations. Here, we report mechanistic details on how inhibition of protein import induces mitophagy independent of mitochondrial membrane depolarization. Carrying out a genome-wide CRISPR/Cas9 screen for regulators of mitophagy, we found that the pre-sequence translocase-associated motor complex PAM controls mitophagy induction. Loss of PAM caused defects in protein import and was sufficient to induce mitophagy without depolarization. Quantitative interaction and aggregation proteomics revealed that PAM was highly sensitive to proteostasis perturbation; upon misfolding conditions, PAM dissociated from the import machinery, sequestered into the insoluble fraction and caused mitophagy despite an intact membrane potential. Our findings extend the current mitophagy model and provide mechanistic insight into how proteostasis perturbation leads to mitophagy induction. They reveal the PAM complex as key folding sensor integrating proteostasis, import and mitophagy.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Permanent Cell Line Cell, Cell Culture

DISEASE(S): Cervix Carcinoma

SUBMITTER: Jonas Michaelis

LAB HEAD: Christian Münch

PROVIDER: PXD022560 | Pride | 2022-09-03

REPOSITORIES: Pride

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	20200114_GT_SB_SB6_F1.raw	Raw
	20200114_GT_SB_SB6_F2.raw	Raw
	20200114_GT_SB_SB6_F3.raw	Raw
	20200114_GT_SB_SB6_F4.raw	Raw
	20200114_GT_SB_SB6_F5.raw	Raw

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PAM complex sequesters from TIM translocon and becomes part of an insoluble protein fraction under protein folding stress

Project description:Upon mitochondrial dysfunction, mitophagy has been described to be activated by a breakdown of membrane potential leading to PINK1 accumulation on the outer membrane and engulfment of mitochondria for degradation. However, recent findings have indicated that mitophagy may also be triggered in the absence of membrane potential alterations. Here, we report mechanistic details on how inhibition of protein import induces mitophagy independent of mitochondrial membrane depolarization. Carrying out a genome-wide CRISPR/Cas9 screen for regulators of mitophagy, we found that the pre-sequence translocase-associated motor complex PAM controls mitophagy induction. Loss of PAM caused defects in protein import and was sufficient to induce mitophagy without depolarization. Quantitative interaction and aggregation proteomics revealed that PAM was highly sensitive to proteostasis perturbation; upon misfolding conditions, PAM dissociated from the import machinery, sequestered into the insoluble fraction and caused mitophagy despite an intact membrane potential. Our findings extend the current mitophagy model and provide mechanistic insight into how proteostasis perturbation leads to mitophagy induction. They reveal the PAM complex as key folding sensor integrating proteostasis, import and mitophagy.

2022-09-03 | PXD022524 | Pride

PAM complex sequesters from TIM translocon and becomes part of an insoluble protein fraction under protein folding stress

2022-09-03 | PXD022530 | Pride

Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy

Project description:Mitophagy is essential to maintain mitochondrial function and prevent diseases. It activates upon mitochondria depolarization, which causes PINK1 stabilization on the mitochondrial outer membrane. Strikingly, a number of conditions, including mitochondrial protein misfolding, can induce mitophagy without a loss in membrane potential. The underlying molecular details remain unclear. Here, we report that a loss of mitochondrial protein import, mediated by the pre-sequence translocase-associated motor complex PAM, is sufficient to induce mitophagy in polarized mitochondria. A genome-wide CRISPR/Cas9 screen for mitophagy inducers identifies components of the PAM complex. Protein import defects are able to induce mitophagy without a need for depolarization. Upon mitochondrial protein misfolding, PAM dissociates from the import machinery resulting in decreased protein import and mitophagy induction. Our findings extend the current mitophagy model to explain mitophagy induction upon conditions that do not affect membrane polarization, such as mitochondrial protein misfolding.

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Human mitochondrial protein import proteomics - Proteinase K control

Project description:Most mitochondrial proteins are encoded in the nucleus and require mitochondrial import after translation in the cytosol. A number of mutations in the mitochondrial protein import machinery have been shown to lead to human pathologies. However, a lack suitable tools to measure mitochondrial protein uptake has prevented determination of import rates across the mitochondrial proteome and identification of specific proteins affected by perturbation. Here, we introduce a pulsed-SILAC based proteomics approach that includes a booster signal to selectively increase the sensitivity for mitochondrial proteins, enabling dynamic analysis of mitochondrial protein uptake at the global scale. We applied this method to determine protein uptake kinetics and examined how inhibitors of different mitochondrial import machineries affect protein uptake in sub-mitochondrial compartments. Monitoring changes in translation and protein uptake upon mitochondrial membrane depolarization revealed that protein uptake was extensively modulated the import- and translation machineries, via activation of the integrated stress response. Strikingly, uptake changes were not uniform with three groups of protein identified that showed no changes in uptake, or changes driven by reduced translation or import capacity. This study provides with a quantitative proteomics method to monitor mitochondrial protein uptake at a global scale to provide with insight into uptake rearrangements upon perturbation.

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Investigating B cell stimulation in ubiquilin-1 KO mice

Project description:Ubiquilins are a family of proteins involved in proteasomal degradation of mislocalized membrane proteins. Here, Greer et al. demonstrate that Ubqln1 is required for BCR-driven B cell proliferation through maintenance of protein synthesis following stimulation. In the absence of Ubqln1, mitochondrial proteins accumulate in the cytosol, which may account for the observed proteostasis. BCR stimulation of murine B cells induced a long-lasting mitochondrial depolarization that did not occur in response to LPS. We hypothesize that in the absence of Ubqln1, mitochondrial depolarization leads to an accumulation of mitochondrial membrane proteins in the cytosol, which leads to translational inhibition and a cell cycle block.

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Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy

Project description:Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy

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Parallel kinase pathways stimulate actin polymerization at depolarized mitochondria

Project description:Mitochondrial damage (MtD) represents a dramatic change in cellular homeostasis, necessitating metabolic changes and stimulating mitophagy. One rapid response to MtD is rapid peri-mitochondrial actin polymerization, termed ADA (acute damage-induced actin). The activation mechanism for ADA is unknown. Here, we use mitochondrial depolarization or the complex I inhibitor metformin to induce ADA. We show that two parallel signaling pathways are required for ADA. In one pathway, increased cytosolic calcium activates in turn PKC-β, Rac, WAVE regulatory complex, and Arp2/3 complex. In the other pathway, a drop in cellular ATP activates in turn AMPK (through LKB1), Cdc42, and FMNL formins. We also identify putative guanine nucleotide exchange factors for Rac and Cdc42, Trio and Fgd1 respectively, whose phosphorylation states increase upon mitochondrial depolarization and whose suppression inhibits ADA. The depolarization-induced calcium increase is dependent on the mitochondrial sodium-calcium exchanger NCLX, suggesting initial mitochondrial calcium efflux. We also show that ADA inhibition results in enhanced mitochondrial shape changes upon mitochondrial depolarization, suggesting that ADA inhibits these shape changes. These depolarization-induced shape changes are not fragmentation but a circularization of the inner mitochondrial membrane, dependent on the inner mitochondrial membrane protease Oma1. ADA inhibition increases proteolytic processing of an Oma1 substrate, the dynamin GTPase Opa1. These results show that ADA requires the combined action of Arp2/3 complex and formin proteins to polymerize a network of actin filaments around mitochondria, and that the ADA network inhibits the rapid mitochondrial shape changes that occur upon mitochondrial depolarization.

2022-03-15 | PXD031699 | Pride

Signaling from the secretory granule to the nucleus: Uhmk1 and PAM

Project description:Neurons and endocrine cells package peptides in secretory granules (large dense core vesicles; LDCVs) for storage and stimulated release. Studies of PAM, an essential secretory granule membrane enzyme, revealed a pathway that can relay information from secretory granules to the nucleus, resulting in alterations in gene expression. The cytosolic domain of PAM, a type 1 membrane enzyme essential for the production of amidated peptides, is basally phosphorylated by Uhmk1 and other Ser/Thr kinases. Proopiomelanocortin processing in AtT-20 corticotrope tumor cells was increased when Uhmk1 expression was reduced. Uhmk1 was concentrated in the nucleus, but cycled rapidly between nucleus and cytosol. Endoproteolytic cleavage of PAM releases a soluble cytosolic domain (CD) fragment that localizes to the nucleus. Localization of PAM-CD to the nucleus was decreased when PAM-CD with phosphomimetic mutations was examined and when active Uhmk1 was simultaneously over-expressed. Membrane-tethering Uhmk1 did not eliminate its ability to exclude PAM-CD from the nucleus, suggesting that cytosolic Uhmk1 could cause this response. Microarray analysis demonstrated the ability of PAM to increase expression of a small subset of genes, including aquaporin 1 (Aqp1) in AtT-20 cells. Aqp1 mRNA levels were higher in wildtype mice than in mice heterozygous for PAM, indicating that a similar relationship occurs in vivo. Expression of PAM-CD also increased Aqp1 levels while expression of Uhmk1 diminished Aqp1 expression. The outlines of a pathway that ties secretory granule metabolism to the transcriptome are thus apparent. Three separate clones of AtT-20 mouse corticotrope tumor cells stably transfected with doxycycline-inducible rat PAM-1 (clones 14, 6_1, 6_2) were treated with cotrol or doxycycline medium for 48 hours. Total mRNA was isolated and hybridized to an Illumina MouseWG-6 v 2.0 whole genome BeadChip.

2010-07-29 | E-GEOD-22509 | biostudies-arrayexpress

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