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Phosphorylation-independent ubiquitylation and endocytosis of Fc gammaRIIA

Patricia Mero1, Christine Y Zhang, Zhen-Yu Huang

  • 1Molecular and Cellular Biology Research, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada.

The Journal of Biological Chemistry
|September 9, 2006
PubMed

Insights

Fc gammaRIIA receptor ubiquitylation, not phosphorylation, drives endocytosis. Inhibitors targeting the ubiquitin system blocked Fc gammaRIIA receptor endocytosis, revealing a novel pathway for immunoreceptor internalization.

Area of Science:

  • Immunology
  • Cell Biology
  • Molecular Biology

Background:

  • Fc gammaRIIA receptor signaling is initiated by tyrosine phosphorylation mediated by Src family kinases.
  • The role of ubiquitylation in Fc gammaRIIA receptor endocytosis remains incompletely understood.

Purpose of the Study:

  • To investigate the molecular mechanisms governing Fc gammaRIIA receptor ubiquitylation and endocytosis.
  • To determine the relationship between Fc gammaRIIA receptor phosphorylation, ubiquitylation, and endocytosis.

Main Methods:

  • Utilized Src family kinase inhibitor PP1, genistein, and proteasomal inhibitor MG132.
  • Assessed Fc gammaRIIA receptor phosphorylation, ubiquitylation, and endocytosis in ts20 cells.
  • Investigated the role of the immunoreceptor tyrosine-based activation motif (ITAM) and clathrin-dependent pathways.

Main Results:

  • PP1 inhibited Fc gammaRIIA phosphorylation and phagocytosis but not ubiquitylation or endocytosis.
  • Genistein and MG132 inhibited Fc gammaRIIA ubiquitylation and endocytosis without affecting phosphorylation.
  • A specific ITAM region was essential for ubiquitylation and endocytosis, which occurs at the plasma membrane.
  • Endocytosis is clathrin-dependent but AP-2 independent.

Conclusions:

  • Fc gammaRIIA receptor endocytosis is primarily regulated by ubiquitylation, not phosphorylation.
  • A novel ubiquitylation-dependent pathway mediates Fc gammaRIIA receptor internalization.
  • This pathway involves the ITAM, occurs at the plasma membrane, and utilizes clathrin machinery.

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