Elsevier

Experimental Cell Research

Volume 315, Issue 9, 15 May 2009, Pages 1584-1592
Experimental Cell Research

Review
Trafficking and function of the tetraspanin CD63

https://doi.org/10.1016/j.yexcr.2008.09.020Get rights and content

Abstract

Tetraspanins comprise a large superfamily of cell surface-associated membrane proteins characterized by four transmembrane domains. They participate in a variety of cellular processes, like cell activation, adhesion, differentiation and tumour invasion. At the cell surface, tetraspanins form networks with a wide diversity of proteins called tetraspanin-enriched microdomains (TEMs). CD63 was the first characterized tetraspanin. In addition to its presence in TEMs, CD63 is also abundantly present in late endosomes and lysosomes. CD63 at the cell surface is endocytosed via a clathrin-dependent pathway, although recent studies suggest the involvement of other pathways as well and we here present evidence for a role of caveolae in CD63 endocytosis. In late endosomes, CD63 is enriched on the intraluminal vesicles, which by specialized cells are secreted as exosomes through fusion of endosomes with the plasma membrane. The complex localization pattern of CD63 suggests that its intracellular trafficking and distribution must be tightly regulated. In this review we discuss the latest insights in CD63 trafficking and its emerging function as a transport regulator of its interaction partners. Finally, the involvement of CD63 in cancer will be discussed.

Section snippets

The tetraspanin family

The tetraspanin family was first recognized in 1990, when sequences from Cluster of Differentiation (CD) 37 and CD81 were compared to the tumour-associated gene CD63 [1]. This revealed sequence homology and a conserved predicted structure of 4 hydrophobic transmembrane domains, a small and a large extracellular loop and 2 short intracellular amino- and carboxyl tails. A typical tetraspanin consists of 200–300 amino acids and contains 4–8 conserved extracellular cysteines of which 2 are present

Tetraspanin trafficking

Like most transmembrane proteins, tetraspanins are synthesized in the endoplasmic reticulum (ER). The transmembrane regions of tetraspanins are important for ER exit, since deletion of one or more transmembrane domains of CD9, CD151, CD82 and uroplakin Ib resulted in ER retention, even when their extracellular domain was properly folded [7], [8], [9], [10]. Many tetraspanins are palmitoylated, which occurs in the Golgi complex [11]. After palmitoylation, tetraspanins often form homodimers,

CD63

The CD63 gene is located on human chromosome 12q13 and was the first characterized tetraspanin. Originally, however, CD63 was discovered as a protein present on the cell surface of activated blood platelets, known as platelet glycoprotein 40 (Pltgp40) [30] and in early stage human melanoma cells, where it was known as melanoma antigen 491 (ME491) [31], [32]. CD63, being a tetraspanin, interacts with many different proteins either directly or indirectly. Interaction partners include integrins

Trafficking of CD63

CD63 is a ubiquitously expressed protein that is localized within the endosomal system and at the cell surface (Fig. 1). In most cells the major pool of CD63 resides in late endosomes/MVBs and lysosomes, which is why it is also referred to as a lysosomal membrane protein. Lysosomal membrane proteins that exit the TGN can travel to lysosomes via either a direct TGN-to-endosome pathway or an indirect route, involving passage over the plasma membrane and subsequent endocytosis (Fig. 1). In

CD63 in caveolae

An alternative pathway for clathrin-mediated endocytosis is provided by caveolae. These typical flask-like shaped 50–100 nm diameter plasma membrane invaginations mediate endocytosis in a dynamin-dependent, but clathrin-independent manner [55]. The best characterized entry via caveolae is for Simian virus 40 (SV40) [56]. Furthermore, Echovirus (EV1) is using α2β1-integrin to gain entry into the cell via caveolae [57]. Other proteins, such as cholera toxin and albumin can also be endocytosed via

AP-3 dependent transport of CD63

Transport of CD63 from early endosomes to late endosomes and lysosomes may involve at least two different pathways: 1. incorporation into ILVs (see previous paragraph) or 2. the AP-3 pathway. In previous immuno-electron microscopy studies, we localized AP-3 to buds emerging from tubular endosomal membranes (Fig. 1) that contain proteins for distinct destinations in the cell, i.e. TGN, plasma membrane and lysosomes [51], [59] and which we called ‘tubular sorting endosomes’ (TSE). We postulated

Cell surface expression of CD63

An increasing number of studies indicate that in certain conditions the cell surface expression of CD63 is tightly regulated, which likely is important for its functioning within TEMs. Here we discuss syntenin-1 and L6-antigen, two proteins that mediate cell surface levels of CD63.

Possible functions of CD63 in intracellular trafficking

Although the intracellular function of CD63 remains to be established, a number of studies performed in different cell types implicate a role for CD63 in intracellular transport of other proteins.

CD63 and cancer

CD63 was first discovered as an abundantly expressed surface antigen in early stage melanoma cells [31]. However, during further malignant melanoma progression CD63 expression is reduced, while cells become more invasive, suggesting a negative correlation between cell surface expression of CD63 and tumour invasiveness. Indeed, silencing of CD63 by RNAi in melanoma cells results in increased cell motility and matrix-degrading ability [67], whereas in a reversed approach, in which a CD63-negative

Concluding remarks

In this review, we have summarized current insights in CD63 functioning and trafficking. Although AP-2-mediated uptake of CD63 via clathrin coated pits is well established, recent studies suggest the existence of alternative pathways of CD63 trafficking from the cell surface to endosomes/lysosomes. Syntenin-1 might divert CD63 from the clathrin-mediated endocytosis pathway to another pathway that has yet to be described in detail, while our own data indicate that CD63 may be internalized via

Acknowledgments

We thank Hans Geuze, Harry Heijnen and Vincent Schoonderwoert for critical reading of this manuscript, Andrew Peden for kindly providing us with the Mocha CD63 cells, Viola Oorschot for technical support and Marc van Peski and René Scriwanek for preparation of the figures. We also thank Harry Heijnen and Vincent Schoonderwoert for sharing non-published data with us. The anti-CD63 antibody was purchased from the Developmental Studies Hybridoma Bank, the anti-caveolin-1 antibody from Transduction

References (73)

  • S. Saksena et al.

    ESCRTing proteins in the endocytic pathway

    Trends Biochem. Sci.

    (2007)
  • L. Pelkmans

    Secrets of caveolae- and lipid raft-mediated endocytosis revealed by mammalian viruses

    Biochim. Biophys. Acta

    (2005)
  • M.S. Kwon et al.

    CD63 as a biomarker for predicting the clinical outcomes in adenocarcinoma of lung

    Lung cancer (Amsterdam, Netherlands)

    (2007)
  • I. Sordat et al.

    Complementary DNA arrays identify CD63 tetraspanin and alpha3 integrin chain as differentially expressed in low and high metastatic human colon carcinoma cells

    Lab. Invest.; J Tech. Methods Pathol.

    (2002)
  • M.E. Hemler

    Tetraspanin proteins mediate cellular penetration, invasion, and fusion events and define a novel type of membrane microdomain

    Annu. Rev. Cell Dev. Biol.

    (2003)
  • M.E. Hemler

    Tetraspanin functions and associated microdomains

    Nat. Rev. Mol. Cell. Biol

    (2005)
  • S. Levy et al.

    The tetraspanin web modulates immune-signalling complexes

    Nat. Rev.

    (2005)
  • R. Nishiuchi et al.

    Potentiation of the ligand-binding activity of integrin alpha3beta1 via association with tetraspanin CD151

    Proc. Natl. Acad. Sci. U. S. A.

    (2005)
  • K. Toyo-oka et al.

    Association of a tetraspanin CD9 with CD5 on the T cell surface: role of particular transmembrane domains in the association

    Int. Immunol.

    (1999)
  • K.S. Cannon et al.

    Quality control of transmembrane domain assembly in the tetraspanin CD82

    EMBO J.

    (2001)
  • L. Tu et al.

    Integrity of all four transmembrane domains of the tetraspanin uroplakin Ib is required for its exit from the ER

    J. Cell Sci.

    (2006)
  • X. Yang et al.

    Palmitoylation of tetraspanin proteins: modulation of CD151 lateral interactions, subcellular distribution, and integrin-dependent cell morphology

    Mol. Biol. Cell.

    (2002)
  • O.V. Kovalenko et al.

    Evidence for specific tetraspanin homodimers: inhibition of palmitoylation makes cysteine residues available for cross-linking

    Biochem. J.

    (2004)
  • M. Andre et al.

    Glycosylation status of the membrane protein CD9P-1

    Proteomics

    (2007)
  • J.P. Luzio et al.

    Lysosomes: fusion and function

    Nat. Rev. Mol. Cell. Biol.

    (2007)
  • E. van Meel et al.

    Imaging and imagination: understanding the endo-lysosomal system

    Histochem. Cell. Biol.

    (2008)
  • F. Berditchevski et al.

    Tetraspanins as regulators of protein trafficking

    Traffic (Copenhagen, Denmark)

    (2007)
  • C. Thery et al.

    Exosomes: composition, biogenesis and function

    Nat. Rev.

    (2002)
  • W. Stoorvogel et al.

    The biogenesis and functions of exosomes

    Traffic (Copenhagen, Denmark)

    (2002)
  • C. Harding et al.

    Endocytosis and intracellular processing of transferrin and colloidal gold-transferrin in rat reticulocytes: demonstration of a pathway for receptor shedding

    Eur. J. Cell Biol.

    (1984)
  • K. Denzer et al.

    Follicular dendritic cells carry MHC class II-expressing microvesicles at their surface

    J. Immunol.

    (2000)
  • G. Raposo et al.

    B lymphocytes secrete antigen-presenting vesicles

    J. Exp. Med.

    (1996)
  • H. Valadi et al.

    Exosome-mediated transfer of mRNAs and microRNAs is a novel mechanism of genetic exchange between cells

    Nat. Cell Biol.

    (2007)
  • S. Viaud et al.

    Exosomes for the treatment of human malignancies

    Horm Metab. Res. Hormon- und Stoffwechselforschung

    (2008)
  • M. Iero et al.

    Tumour-released exosomes and their implications in cancer immunity

    Cell Death Differ.

    (2008)
  • H.T. Maecker et al.

    The tetraspanin superfamily: molecular facilitators

    FASEB J.

    (1997)
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