Phosphorylation controls CLIMP-63-mediated anchoring of the endoplasmic reticulum to microtubules

Mol Biol Cell. 2005 Apr;16(4):1928-37. doi: 10.1091/mbc.e04-07-0554. Epub 2005 Feb 9.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Line
  • Chlorocebus aethiops
  • Endoplasmic Reticulum / metabolism*
  • Humans
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Microtubules / metabolism*
  • Mitosis
  • Molecular Sequence Data
  • Mutation / genetics
  • Phosphorylation
  • Phosphoserine / metabolism


  • CKAP4 protein, human
  • Membrane Proteins
  • Phosphoserine