title: Climp-63-mediated binding of microtubules to the ER affects the lateral mobility of translocon complexes.
abstract: Microtubules are frequently seen in close proximity to membranes of the endoplasmic reticulum (ER), and the membrane protein CLIMP-63 is thought to mediate specific interaction between these two structures. It was, therefore, of interest to investigate whether these microtubules are in fact responsible for the highly restricted lateral mobility of the translocon complexes in M3/18 cells as described before. As determined by fluorescence recovery after photobleaching, the breakdown of microtubules caused by drug treatment or by overexpression of the microtubule-severing protein spastin, resulted in an increased lateral mobility of the translocons that are assembled into polysomes. Also, the expression of a CLIMP-63 mutant lacking the microtubule-binding domain resulted in a significant increase of the lateral mobility of the translocon complexes. The most striking increase in the diffusion rate of the translocon complexes was observed in M3/18 cells transfected with a siRNA that effectively knocked down the expression of the endogenous CLIMP-63. It appears, therefore, that interaction of microtubules with the ER results in the immobilization of translocon complexes that are part of membrane-bound polysomes, and may play a role in the mechanism that segregates the rough and smooth domains of the ER.
authors.affiliation: Department of Cell Biology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Nikonov
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Hauri
authors.forename: Brett
authors.initials: B
authors.lastname: Lauring
authors.forename: Gert
authors.initials: G
authors.lastname: Kreibich
mesh_terms: D000251:Adenosine Triphosphatases / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D001692:Biological Transport / Q000235:genetics; D019556:COS Cells; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011132:Polyribosomes / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D000074181:Spastin
chemical_list: C081876:CKAP4 protein, human; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D000251:Adenosine Triphosphatases; D000074181:Spastin; C400283:SPAST protein, human