title: Aspergillus nidulans Ambient pH Signaling Does Not Require Endocytosis.
abstract: Aspergillus nidulans (Pal) ambient pH signaling takes place in cortical structures containing components of the ESCRT pathway, which are hijacked by the alkaline pH-activated, ubiquitin-modified version of the arrestin-like protein PalF and taken to the plasma membrane. There, ESCRTs scaffold the assembly of dedicated Pal proteins acting downstream. The molecular details of this pathway, which results in the two-step proteolytic processing of the transcription factor PacC, have received considerable attention due to the key role that it plays in fungal pathogenicity. While current evidence strongly indicates that the pH signaling role of ESCRT complexes is limited to plasma membrane-associated structures where PacC proteolysis would take place, the localization of the PalB protease, which almost certainly catalyzes the first and only pH-regulated proteolytic step, had not been investigated. In view of ESCRT participation, this formally leaves open the possibility that PalB activation requires endocytic internalization. As endocytosis is essential for hyphal growth, nonlethal endocytic mutations are predicted to cause an incomplete block. We used a SynA internalization assay to measure the extent to which any given mutation prevents endocytosis. We show that none of the tested mutations impairing endocytosis to different degrees, including slaB1, conditionally causing a complete block, have any effect on the activation of the pathway. We further show that PalB, like PalA and PalC, localizes to cortical structures in an alkaline pH-dependent manner. Therefore, signaling through the Pal pathway does not involve endocytosis.
authors.affiliation: Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Madrid, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lucena-Agell
authors.affiliation: Division of Cell Biology, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom.
authors.forename: Antonio
authors.initials: A
authors.lastname: Galindo
authors.affiliation: Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Madrid, Spain Section of Microbiology, Imperial College London, London, United Kingdom.
authors.forename: Herbert N
authors.initials: HN
authors.lastname: Arst
authors.affiliation: Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Madrid, Spain penalva@cib.csic.es.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Peñalva
mesh_terms: D001233:Aspergillus nidulans / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D005656:Fungal Proteins; C092394:PacC protein, Aspergillus; D014157:Transcription Factors; D003546:Cysteine Endopeptidases; C097042:PalB protein, Aspergillus nidulans
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