Lipid Transfer Proteins and Membrane Contact Sites in Human Cancer.

Lipid-transfer proteins (LTPs) were initially discovered as cytosolic factors that facilitate lipid transport between membrane bilayers in vitro. Since then, many LTPs have been isolated from bacteria, plants, yeast, and mammals, and extensively studied in cell-free systems and intact cells. A major advance in the LTP field was associated with the discovery of intracellular membrane contact sites (MCSs), small cytosolic gaps between the endoplasmic reticulum (ER) and other cellular membranes, which accelerate lipid transfer by LTPs. As LTPs modulate the distribution of lipids within cellular membranes, and many lipid species function as second messengers in key signaling pathways that control cell survival, proliferation, and migration, LTPs have been implicated in cancer-associated signal transduction cascades. Increasing evidence suggests that LTPs play an important role in cancer progression and metastasis. This review describes how different LTPs as well as MCSs can contribute to cell transformation and malignant phenotype, and discusses how "aberrant" MCSs are associated with tumorigenesis in human

Comprehensive Genetic Characterization of Mitochondrial Ca2+ Uniporter Components Reveals Their Different Physiological Requirements In Vivo.

Mitochondrial Ca2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca2+ uniporter has opened it up to genetic analysis in model organisms. Here, we report a comprehensive genetic characterization of all known uniporter components conserved in Drosophila. While loss of pore-forming MCU or EMRE abolishes fast mitochondrial Ca2+ uptake, this results in only mild phenotypes when young, despite shortened lifespans. In contrast, loss of the MICU1 gatekeeper is developmentally lethal, consistent with unregulated Ca2+ uptake. Mutants for the neuronally restricted regulator MICU3 are viable with mild neurological impairment. Genetic interaction analyses reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that this results from uniporter-independent functions. Our data reveal the interplay among components of the mitochondrial Ca2+ uniporter and shed light on their physiological requirements in vivo.This work is supported by MRC core funding (MC_UU_00015/4, MC-A070-5PSB0, and MC_UU_00015/6) and an ERC starting grant (DYNAMITO; 309742) to A.J.W., as well as by the Italian Ministry of Health “Ricerca Finalizzata” (GR-2011-02351151) to E.Z. T.P.G. and J.J.L. are supported by MRC studentships awarded via the MRC MBU. V.L.H. was funded by an EMBO Long-Term Fellowship (ALTF 740-2015) co-funded by the European Commission FP7 (Marie Curie Actions, LTFCOFUND2013, GA-2013-609409)

Comprehensive Genetic Characterisation of Mitochondrial Ca2+ Uniporter Components Reveals Their Different Physiological Requirements in Vivo

Mitochondrial Ca2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca2+ uniporter has opened it up to genetic analysis in model organisms. Here, we report a comprehensive genetic characterisation of all known uniporter components conserved in Drosophila. While loss of pore-forming MCU or EMRE abolishes fast mitochondrial Ca2+ uptake, this results in only mild phenotypes when young, despite shortened lifespans. In contrast, loss of the MICU1 gatekeeper is developmental lethal, consistent with unregulated Ca2+ uptake. Mutants for the neuronally-restricted regulator MICU3 are viable with mild neurological impairment. Genetic interaction analyses reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that this results from uniporter-independent functions. Our data interrogates the interplay between components of the mitochondrial Ca2+ uniporter, and sheds light on their physiological requirements in vivo.This work is supported by MRC core funding (MC_UU_00015/4, MC-A070-5PSB0 and MC_UU_00015/6) and ERC Starting grant (DYNAMITO; 309742) to A.J.W., and the Italian Ministry of Health “Ricerca Finalizzata” [GR-2011-02351151] to E.Z. T.P.G. and J.J.L. are supported by MRC Studentships awarded via the MRC MBU. V.L.H. was funded by an EMBO Long-Term Fellowship (ALTF 740-2015) co-funded by the European Commission FP7 (Marie Curie Actions, LTFCOFUND2013, GA-2013-609409). Stocks were obtained from the Bloomington Drosophila Stock Center which is supported by grant NIH P40OD018537, and material was obtained from the Drosophila Genomics Resource Center, which is supported by NIH grant 2P40OD010949

Mitochondrially-targeted APOBEC1 is a potent mtDNA mutator affecting mitochondrial function and organismal fitness in Drosophila

Abstract: Somatic mutations in the mitochondrial genome (mtDNA) have been linked to multiple disease conditions and to ageing itself. In Drosophila, knock-in of a proofreading deficient mtDNA polymerase (POLG) generates high levels of somatic point mutations and also small indels, but surprisingly limited impact on organismal longevity or fitness. Here we describe a new mtDNA mutator model based on a mitochondrially-targeted cytidine deaminase, APOBEC1. mito-APOBEC1 acts as a potent mutagen which exclusively induces C:G>T:A transitions with no indels or mtDNA depletion. In these flies, the presence of multiple non-synonymous substitutions, even at modest heteroplasmy, disrupts mitochondrial function and dramatically impacts organismal fitness. A detailed analysis of the mutation profile in the POLG and mito-APOBEC1 models reveals that mutation type (quality) rather than quantity is a critical factor in impacting organismal fitness. The specificity for transition mutations and the severe phenotypes make mito-APOBEC1 an excellent mtDNA mutator model for ageing research

High-content phenotypic screen to identify small molecule enhancers of Parkin-dependent ubiquitination and mitophagy

Mitochondrial dysfunction and aberrant mitochondrial homeostasis are key aspects of Parkinson's disease (PD) pathophysiology. Mutations in PINK1 and Parkin proteins lead to autosomal recessive PD, suggesting that defective mitochondrial clearance via mitophagy is key in PD etiology. Accelerating the identification and/or removal of dysfunctional mitochondria could therefore provide a disease-modifying approach to treatment. To that end, we performed a high-content phenotypic screen (HCS) of ∼125,000 small molecules to identify compounds that positively modulate mitochondrial accumulation of the PINK1-Parkin-dependent mitophagy initiation marker p-Ser65-Ub in Parkin haploinsufficiency (Parkin +/R275W) human fibroblasts. Following confirmatory counter-screening and orthogonal assays, we selected compounds of interest that enhance mitophagy-related biochemical and functional endpoints in patient-derived fibroblasts. Identification of inhibitors of the ubiquitin-specific peptidase and negative regulator of mitophagy USP30 within our hits further validated our approach. The compounds identified in this work provide a novel starting point for further investigation and optimization

The Drosophila inner-membrane protein PMI controls crista biogenesis and mitochondrial diameter.

International audienceCristae are mitochondrial inner-membrane structures that concentrate respiratory chain complexes and hence regulate ATP production. Mechanisms controlling crista morphogenesis are poorly understood and few crista determinants have been identified. Among them are the Mitofilins that are required to establish crista junctions and ATP-synthase subunits that bend the membrane at the tips of the cristae. We report here the phenotypic consequences associated with the in vivo inactivation of the inner-membrane protein Pantagruelian Mitochondrion I (PMI) both at the scale of the whole organism, and at the level of mitochondrial ultrastructure and function. We show that flies in which PMI is genetically inactivated experience synaptic defects and have a reduced life span. Electron microscopy analysis of the inner-membrane morphology demonstrates that loss of PMI function increases the average length of mitochondrial cristae in embryonic cells. This phenotype is exacerbated in adult neurons in which cristae form a dense tangle of elongated membranes. Conversely, we show that PMI overexpression is sufficient to reduce crista length in vivo. Finally, these crista defects are associated with impaired respiratory chain activity and increases in the level of reactive oxygen species. Since PMI and its human orthologue TMEM11 are regulators of mitochondrial morphology, our data suggest that, by controlling crista length, PMI influences mitochondrial diameter and tubular shape

A comprehensive genetic characterisation of the mitochondrial Ca2+ uniporter in Drosophila

Abstract Mitochondrial Ca 2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca 2+ uniporter has opened it up to genetic analysis in model organisms. Here we report a comprehensive genetic characterisation of the known uniporter components conserved in Drosophila . While loss of MCU or EMRE abolishes fast mitochondrial Ca 2+ uptake, this results in surprisingly mild phenotypes. In contrast, loss of the regulatory gatekeeper component MICU1 has a much more severe phenotype, being developmental lethal, consistent with unregulated Ca 2+ uptake. Mutants for MICU3 are viable with mild neurological phenotypes. Genetic interaction studies reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that the lethality results from MCU-independent functions. This study helps shed light on the physiological requirements of the mitochondrial Ca 2+ uniporter, and provides a suite of tools to interrogate their interplay in homeostasis and disease conditions

Comprehensive Genetic Characterization of Mitochondrial Ca2+ Uniporter Components Reveals Their Different Physiological Requirements In Vivo.

Mitochondrial Ca2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca2+ uniporter has opened it up to genetic analysis in model organisms. Here, we report a comprehensive genetic characterization of all known uniporter components conserved in Drosophila. While loss of pore-forming MCU or EMRE abolishes fast mitochondrial Ca2+ uptake, this results in only mild phenotypes when young, despite shortened lifespans. In contrast, loss of the MICU1 gatekeeper is developmentally lethal, consistent with unregulated Ca2+ uptake. Mutants for the neuronally restricted regulator MICU3 are viable with mild neurological impairment. Genetic interaction analyses reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that this results from uniporter-independent functions. Our data reveal the interplay among components of the mitochondrial Ca2+ uniporter and shed light on their physiological requirements in vivo.This work is supported by MRC core funding (MC_UU_00015/4, MC-A070-5PSB0, and MC_UU_00015/6) and an ERC starting grant (DYNAMITO; 309742) to A.J.W., as well as by the Italian Ministry of Health “Ricerca Finalizzata” (GR-2011-02351151) to E.Z. T.P.G. and J.J.L. are supported by MRC studentships awarded via the MRC MBU. V.L.H. was funded by an EMBO Long-Term Fellowship (ALTF 740-2015) co-funded by the European Commission FP7 (Marie Curie Actions, LTFCOFUND2013, GA-2013-609409)

Partial loss of MCU mitigates pathology in vivo across a diverse range of neurodegenerative disease models.

Mitochondrial calcium (Ca2+) uptake augments metabolic processes and buffers cytosolic Ca2+ levels; however, excessive mitochondrial Ca2+ can cause cell death. Disrupted mitochondrial function and Ca2+ homeostasis are linked to numerous neurodegenerative diseases (NDs), but the impact of mitochondrial Ca2+ disruption is not well understood. Here, we show that Drosophila models of multiple NDs (Parkinson's, Huntington's, Alzheimer's, and frontotemporal dementia) reveal a consistent increase in neuronal mitochondrial Ca2+ levels, as well as reduced mitochondrial Ca2+ buffering capacity, associated with increased mitochondria-endoplasmic reticulum contact sites (MERCs). Importantly, loss of the mitochondrial Ca2+ uptake channel MCU or overexpression of the efflux channel NCLX robustly suppresses key pathological phenotypes across these ND models. Thus, mitochondrial Ca2+ imbalance is a common feature of diverse NDs in vivo and is an important contributor to the disease pathogenesis. The broad beneficial effects from partial loss of MCU across these models presents a common, druggable target for therapeutic intervention

Partial loss of MCU mitigates pathology in vivo across a diverse range of neurodegenerative disease models

Summary: Mitochondrial calcium (Ca2+) uptake augments metabolic processes and buffers cytosolic Ca2+ levels; however, excessive mitochondrial Ca2+ can cause cell death. Disrupted mitochondrial function and Ca2+ homeostasis are linked to numerous neurodegenerative diseases (NDs), but the impact of mitochondrial Ca2+ disruption is not well understood. Here, we show that Drosophila models of multiple NDs (Parkinson’s, Huntington’s, Alzheimer’s, and frontotemporal dementia) reveal a consistent increase in neuronal mitochondrial Ca2+ levels, as well as reduced mitochondrial Ca2+ buffering capacity, associated with increased mitochondria-endoplasmic reticulum contact sites (MERCs). Importantly, loss of the mitochondrial Ca2+ uptake channel MCU or overexpression of the efflux channel NCLX robustly suppresses key pathological phenotypes across these ND models. Thus, mitochondrial Ca2+ imbalance is a common feature of diverse NDs in vivo and is an important contributor to the disease pathogenesis. The broad beneficial effects from partial loss of MCU across these models presents a common, druggable target for therapeutic intervention