title: Sip1, a conserved AP-1 accessory protein, is important for Golgi/endosome trafficking in fission yeast.
abstract: We had previously identified the mutant allele of apm1(+) that encodes a homolog of the mammalian μ 1A subunit of the clathrin-associated adaptor protein-1 (AP-1) complex and demonstrated that the AP-1 complex plays a role in Golgi/endosome trafficking, secretion, and vacuole fusion in fission yeast. Here, we isolated a mutant allele of its4(+)/sip1(+), which encodes a conserved AP-1 accessory protein. The its4-1/sip1-i4 mutants and apm1-deletion cells exhibited similar phenotypes, including sensitivity to the calcineurin inhibitor FK506, Cl(-) and valproic acid as well as various defects in Golgi/endosomal trafficking and cytokinesis. Electron micrographs of sip1-i4 mutants revealed vacuole fragmentation and accumulation of abnormal Golgi-like structures and secretory vesicles. Overexpression of Apm1 suppressed defective membrane trafficking in sip1-i4 mutants. The Sip1-green fluorescent protein (GFP) co-localized with Apm1-mCherry at Golgi/endosomes, and Sip1 physically interacted with each subunit of the AP-1 complex. We found that Sip1 was a Golgi/endosomal protein and the sip1-i4 mutation affected AP-1 localization at Golgi/endosomes, thus indicating that Sip1 recruited the AP-1 complex to endosomal membranes by physically interacting with each subunit of this complex. Furthermore, Sip1 is required for the correct localization of Bgs1/Cps1, 1,3-β-D-glucan synthase to polarized growth sites. Consistently, the sip1-i4 mutants displayed a severe sensitivity to micafungin, a potent inhibitor of 1,3-β-D-glucan synthase. Taken together, our findings reveal a role for Sip1 in the regulation of Golgi/endosome trafficking in coordination with the AP-1 complex, and identified Bgs1, required for cell wall synthesis, as the new cargo of AP-1-dependent trafficking.
authors.affiliation: Laboratory of Molecular Pharmacogenomics, School of Pharmaceutical Sciences, Kinki University, Higashi-Osaka, Japan.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yu
authors.forename: Ayako
authors.initials: A
authors.lastname: Kita
authors.forename: Masako
authors.initials: M
authors.lastname: Udo
authors.forename: Yuta
authors.initials: Y
authors.lastname: Katayama
authors.forename: Mami
authors.initials: M
authors.lastname: Shintani
authors.forename: Kwihwa
authors.initials: K
authors.lastname: Park
authors.forename: Kanako
authors.initials: K
authors.lastname: Hagihara
authors.forename: Nanae
authors.initials: N
authors.lastname: Umeda
authors.forename: Reiko
authors.initials: R
authors.lastname: Sugiura
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure; D054714:Echinocandins / Q000494:pharmacology; D011992:Endosomes / Q000378:metabolism*; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D055666:Lipopeptides / Q000494:pharmacology; D000077551:Micafungin; D012568:Schizosaccharomyces / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism
chemical_list: D054714:Echinocandins; D055666:Lipopeptides; D029702:Schizosaccharomyces pombe Proteins; D018808:Transcription Factor AP-1; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase; D055372:AMP-Activated Protein Kinases; D000077551:Micafungin