Actomyosin organization at adherens junctions

Actomyosin-undercoated adherens junctions are critical for epithelial cell integrity and remodeling. Actomyosin associates with adherens junctions through αE-catenin complexed with β-catenin and E-cadherin in vivo; however, in vitro biochemical studies in solution showed that αE-catenin complexed with β-catenin binds to F-actin less efficiently than αE-catenin that is not complexed with β-catenin. Although a “catch-bond model” partly explains this inconsistency, the mechanism for this inconsistency between the in vivo and in vitro results remains elusive. We herein demonstrate that afadin binds to αE-catenin complexed with β-catenin and enhances its F-actin–binding activity in a novel mechanism, eventually inducing the proper actomyosin organization through αE-catenin complexed with β-catenin and E-cadherin at adherens junctions

MitoBlue as a tool to analyze the mitochondria-lysosome communication

MitoBlue is a fluorescent bisamidine that can be used to easily monitor the changes in mitochondrial degradation processes in different cells and cellular conditions. MitoBlue staining pattern is exceptional among mitochondrial dyes and recombinant fluorescent probes, allowing the dynamic study of mitochondrial recycling in a variety of situations in living cells. MitoBlue is a unique tool for the study of these processes that will allow the detailed characterization of communication between mitochondria and lysosomesWe are thankful for the support given by the Spanish grants BFU2013-43513-R, SAF2016-76689-R, CTQ2015-70698-R, RTI2018-099877-B-I00, CTQ2013-49317-EXP, CTQ2013-41339-P, CTQ2016-75870-P, CTQ2015-71896-REDT (Red de Fotoquímica Biológica) and Instituto de Salud Carlos III (ISCIII; RETIC ARADYALRD16/0006/0012), Junta de Andalucía (PI0250-2016 and UMA18-FEDERJA-007), Orfeo-cinqa network CTQ2016-81797-REDC; the Xunta de Galicia (2015-CP082, ED431C 2017/19, Centro Singular de investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the European Union (European Regional Development Fund - ERDF), and the European Research Council (Advanced Grant No. 340055) are gratefully acknowledged. M.E.V. also acknowledges the support provided by the Fundación AECC (IDEAS197VAZQ grant)S

Membrane dynamics and organelle biogenesis—lipid pipelines and vesicular carriers

Abstract Discoveries spanning several decades have pointed to vital membrane lipid trafficking pathways involving both vesicular and non-vesicular carriers. But the relative contributions for distinct membrane delivery pathways in cell growth and organelle biogenesis continue to be a puzzle. This is because lipids flow from many sources and across many paths via transport vesicles, non-vesicular transfer proteins, and dynamic interactions between organelles at membrane contact sites. This forum presents our latest understanding, appreciation, and queries regarding the lipid transport mechanisms necessary to drive membrane expansion during organelle biogenesis and cell growth

Mitochondrial Ubiquitin Ligase MITOL Ubiquitinates Mutant SOD1 and Attenuates Mutant SOD1-induced Reactive Oxygen Species Generation

We have previously identified a novel mitochondrial ubiquitin ligase, MITOL, which is localized in the mitochondrial outer membrane and is involved in the control of mitochondrial dynamics. In this study, we examined whether MITOL eliminates misfolded proteins localized to mitochondria. Mutant superoxide dismutase1 (mSOD1), one of misfolded proteins, has been shown to localize in mitochondria and induce mitochondrial dysfunction, possibly involving in the onset and progression of amyotrophic lateral sclerosis. We found that in the mitochondria, MITOL interacted with and ubiquitinated mSOD1 but not wild-type SOD1. In vitro ubiquitination assay revealed that MITOL directly ubiquitinates mSOD1. Cycloheximide-chase assay in the Neuro2a cells indicated that MITOL overexpression promoted mSOD1 degradation and suppressed both the mitochondrial accumulation of mSOD1 and mSOD1-induced reactive oxygen species (ROS) generation. Conversely, the overexpression of MITOL CS mutant and MITOL knockdown by specific siRNAs resulted in increased accumulation of mSOD1 in mitochondria, which enhanced mSOD1-induced ROS generation and cell death. Thus, our findings indicate that MITOL plays a protective role against mitochondrial dysfunction caused by the mitochondrial accumulation of mSOD1 via the ubiquitin–proteasome pathway