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Potential role for a novel AP180-related protein during endocytosis in MDCK cells

Linda Kusner1, Cathleen Carlin

  • 1Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.

American Journal of Physiology. Cell Physiology
|October 9, 2003
PubMed

Insights

Researchers discovered a new protein, AP180-3, in kidney cells that is similar to a brain protein. This protein, AP180-3, interacts with clathrin and AP-2, suggesting a role in cellular transport beyond the brain.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Protein Biochemistry

Background:

  • Clathrin assembly protein AP180 was initially identified as a brain-specific protein crucial for synaptic vesicle dynamics.
  • AP180 regulates vesicle size and maintains a readily releasable pool of synaptic vesicles during high-frequency activity.

Purpose of the Study:

  • To investigate the presence and function of AP180-related proteins in non-neuronal cells, specifically polarized epithelial cells.
  • To characterize a novel high-molecular-weight homolog of AP180 in Madin-Darby canine kidney (MDCK) cells.

Main Methods:

  • Sequence analysis of AP180-3 expressed in MDCK cells.
  • Immunohistochemistry and immunodetection to determine protein localization and expression.
  • Biochemical assays to assess complex formation with AP-2 and clathrin.

Main Results:

  • MDCK cells express two AP180-related proteins: CALM (AP180-2) and a novel homolog, AP180-3.
  • AP180-3 shares high homology with brain AP180 and contains conserved functional motifs (ENTH domain, AP-2 binding site, DLL repeats).
  • AP180-3 forms complexes with AP-2 and clathrin, whose membrane recruitment is modulated by phosphorylation; it localizes to cytoplasmic vesicles in MDCK cells and kidney tubule cells.

Conclusions:

  • A novel high-molecular-weight AP180 homolog, AP180-3, is expressed in polarized epithelial cells and kidney tubule cells, not just brain tissue.
  • AP180-3 participates in clathrin-mediated endocytosis by forming complexes with AP-2 and clathrin.
  • These findings expand the known expression and potential roles of AP180-related proteins in cellular processes.

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