The PtdIns3P-binding Protein Phafin 2 Mediates Epidermal Growth Factor Receptor Degradation by Promoting Endosome Fusion

Traffic. 2012 Nov;13(11):1547-63. doi: 10.1111/j.1600-0854.2012.01400.x. Epub 2012 Aug 8.


Phosphatidylinositol 3-phosphate (PtdIns3P) orchestrates endosomal cargo transport, fusion and motility by recruiting FYVE or PX domain-containing effector proteins to endosomal membranes. In an attempt to discover novel PtdIns3P effectors involved in the termination of growth factor receptor signalling, we performed an siRNA screen for epidermal growth factor (EGF) degradation, targeting FYVE and PX domain proteins in the human proteome. This screen identified several potential regulators of EGF degradation, including HRS (used as positive control), PX kinase, MTMR4 and Phafin2/PLEKHF2. As Phafin2 has not previously been shown to be required for EGF receptor (EGFR) degradation, we performed further functional studies on this protein. Loss of Phafin2 was found to decrease early endosome size, whereas overexpression of Phafin2 resulted in enlarged endosomes. Moreover, both the EGFR and the fluid-phase marker dextran were retained in abnormally small endosomes in Phafin2-depleted cells. In yeast two-hybrid analysis we identified Phafin2 as a novel interactor of the endosomal-tethering protein EEA1, and Phafin2 colocalized strongly with EEA1 in microdomains of the endosome membrane. Our results suggest that Phafin2 controls receptor trafficking and fluid-phase transport through early endosomes by facilitating endosome fusion in concert with EEA1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Endocytosis
  • Endosomes / metabolism*
  • Endosomes / ultrastructure
  • Epidermal Growth Factor / metabolism
  • ErbB Receptors / metabolism*
  • HeLa Cells
  • High-Throughput Screening Assays
  • Humans
  • Intracellular Signaling Peptides and Proteins / chemistry
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Organelle Size
  • Protein Interaction Domains and Motifs
  • Protein Tyrosine Phosphatases, Non-Receptor / chemistry
  • Protein Tyrosine Phosphatases, Non-Receptor / genetics
  • Protein Tyrosine Phosphatases, Non-Receptor / metabolism
  • Protein-Serine-Threonine Kinases / chemistry
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Proteolysis
  • Proteome / chemistry
  • Proteome / metabolism
  • RNA, Small Interfering
  • Two-Hybrid System Techniques
  • Up-Regulation
  • Vesicular Transport Proteins / chemistry
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism*


  • Intracellular Signaling Peptides and Proteins
  • Nerve Tissue Proteins
  • Proteome
  • RNA, Small Interfering
  • Vesicular Transport Proteins
  • early endosome antigen 1
  • phafin2 protein, human
  • Epidermal Growth Factor
  • ErbB Receptors
  • PXK protein, human
  • Protein-Serine-Threonine Kinases
  • MTMR4 protein, human
  • Protein Tyrosine Phosphatases, Non-Receptor