Function of fusion regulatory proteins (FRPs) in immune cells and virus-infected cells

Crit Rev Immunol. 2000;20(3):167-96.


Two molecules that regulate cell fusion have been identified and designated fusion regulatory protein-1 (FRP-1) and FRP-2. FRP-1 is a complex composed of a glycosylated heavy chain and a nonglycosylated light chain that are disulfide linked. FRP-1 heavy chain is identical to 4F2/CD98 heavy chain, whereas FRP-2 is identical to integrin alpha3 subunit. The FRP-1 heavy chain is a multifunctional molecule: that is, fusion regulator, amino acid transporter, integrin regulator, comitogenic factor, Na+-Ca2+ exchanger, oncogenic protein, and so on. Several aspects of the structure and function of the FRP-1 system are reviewed: fusion regulatory molecular mechanisms, cross-talk between the FRP-1 and integrin, the FRP-1 system as amino acid transporter, and FRP-1-mediated T-cell activation. The FRP-1 system is involved in virus-mediated cell fusion and multinucleated giant cell formation of blood monocytes. Monoclonal antibodies against human FRP-1 heavy chain induce polykaryocytes that have properties as osteoclasts. Multiple steps participate in molecular mechanisms regulating cell fusion. The FRP-1 heavy chain supports amino acid transport activity and the FRP-1 light chains have recently been cloned as amino acid transporters that require association with the heavy chain to exhibit their activity. Novel pathways for monocyte-dependent regulation of T-cell activation have recently been found that are mediated by the FRP-1 system. In conclusion, the FRP-1 molecules are essential factors for basic cellular functions.

Publication types

  • Review

MeSH terms

  • Amino Acids / metabolism
  • Antigens, CD / chemistry
  • Antigens, CD / immunology*
  • Antigens, CD / metabolism
  • Antigens, CD / physiology*
  • Biological Evolution
  • Biological Transport, Active
  • Carrier Proteins / chemistry
  • Carrier Proteins / immunology*
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology*
  • Cell Fusion
  • Fusion Regulatory Protein-1
  • HIV / physiology*
  • Humans
  • Integrin alpha3
  • Integrins / chemistry
  • Integrins / immunology*
  • Integrins / metabolism
  • Integrins / physiology*
  • Leukocytes, Mononuclear / immunology*
  • Models, Biological
  • Newcastle disease virus / physiology*


  • Amino Acids
  • Antigens, CD
  • Carrier Proteins
  • Fusion Regulatory Protein-1
  • Integrin alpha3
  • Integrins