title: Phosphorylation controls CLIMP-63-mediated anchoring of the endoplasmic reticulum to microtubules.
abstract: The microtubule-binding 63-kDa cytoskeleton-linking membrane protein (CLIMP-63) is an integral membrane protein that links the endoplasmic reticulum (ER) to microtubules. Here, we tested whether this interaction is regulated by phosphorylation. Metabolic labeling with (32)P showed that CLIMP-63 is a phosphoprotein with increased phosphorylation during mitosis. CLIMP-63 of mitotic cells is unable to bind to microtubules in vitro. Mitotic phosphorylation can be prevented by mutation of serines 3, 17, and 19 in the cytoplasmic domain of CLIMP-63. When these residues are mutated to glutamic acid, and hence mimic mitotic phosphorylation, CLIMP-63 does no longer bind to microtubules in vitro. Overexpression of the phospho-mimicking mitotic form of CLIMP-63 in interphase cells leads to a collapse of the ER around the nucleus, leaving the microtubular network intact. The results suggest that CLIMP-63-mediated stable anchoring of the ER to microtubules is required to maintain the spatial distribution of the ER during interphase and that this interaction is abolished by phosphorylation of CLIMP-63 during mitosis.
authors.affiliation: Biozentrum, University of Basel, Switzerland.
authors.forename: Cécile
authors.initials: C
authors.lastname: Vedrenne
authors.forename: Dieter R
authors.initials: DR
authors.lastname: Klopfenstein
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Hauri
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism
chemical_list: C081876:CKAP4 protein, human; D008565:Membrane Proteins; D010768:Phosphoserine