CD30, also known as TNFRSF8, is a cell membrane protein of the tumor necrosis factor receptor family and tumor marker.This receptor is expressed by activated, but not by resting, T and B cells. TRAF2 and TRAF5 can interact with this receptor and mediate the signal transduction that leads to the activation of NFkB. It is a positive regulator of apoptosis, and also has been shown to limit the proliferative potential of autoreactive CD8 effector T cells and protect body against autoimmunity (Pleiotropic signal transduction mediated by human CD30: a member of the tumor necrosis factor receptor (TNFR) family, 2002).
CD30 is associated with anaplastic large cell lymphoma. It is expressed in embryonal carcinoma (Hodgkin's lymphoma and CD30 signal transduction, 2003) and is also expressed on classical Hodgkin lymphoma (Expression and a role of CD30 in regulation of T-cell activity, 2003).
Human CD30 gene is located to 1p36.22 chromosome and it is transcribed in a product of about 3.8 kb. The gene contains 15 exons and spans 78.930 bp (from 12.123.656 to 12.202.585) oriented at the forward strand.
The CD30 gene encodes a protein of 595aa. CD30 exists as a 120-kDa membrane glycoprotein chain that originate from a 90-kDa precursor form. Extracellular domain of CD30 contains binding sites for CD30 ligand, whereas cytoplasmic domain tumor necrosis factor receptor-associated factor (TRAF) proteins, which play a crucial role in signal transduction (CD30 molecule (Ki-1 Ag): more than just a marker of CD30+ lymphoma, 1995).
TNFR family is characterized by a series of three or four cysteine-rich pseudorepeats in extracytoplasmic region. The protein analysis of human CD30 demonstrates that this molecule has an 18-residue leader peptide, followed by a 365aa extracytoplasmic domain, a 24aa transmembrane region, and a cytoplasmic domain of 188aa.
The human CD30 extracytoplasmic domain can be divided into six cysteine-rich motifs of approximately 40aa that contain six cysteines with the exception of motif 1B and 3B, which are truncated.
A hinge region of approximately 50aa, which contains multiple serine, threonine and proline residues and is O-glycosylated, connect the two cysteine-rich domains. There are two sites for N-linked glycosylation.
The intracellular domain of human CD30 is long and its sequence diverges significantly from the intracellular sequences of all other TNFR family members. Within this domain, two short peptide sequences, PHYPEQET and LSVEEEGKE bind the TNFR associated factors 1 (TRAF1). Within the intracellular domain a conserved motif for ATP-binding (GxGxxG) found in many protein kinases, is also present. Finally, potential phosphorylation sites for tyrosine kinase and serine/threonine kinase are located in the extracellular and intracellular domains, respectively (CD30 in normal and neoplastic cells, 1999).
Protein Aminoacids Percentage
SYNTHESIS AND TURNOVER
CD30 was originally described as a surface molecule on Hodgkin's and Reed-Stenberg cells (H-RS) of Hodgkin's disease (HD). It is expressed also in neoplastic cells of certain types of non-Hodgkin's lymphomas, such us CD30+ anaplastyc large cell lymphoma (ALCL), angioimmunoblastic-like lymphoma and HTLV-1 + adult T cell leukemia/lymphoma (ATLL).
Normally there are no CD30-expressing cells in the blood, whereas they are present in scanty numbers as large mononuclear cells with evident nucleolus mainly around the B cell follicles of lymphoid tissues and, to a lesser degree, at the edge of germinal centers. This cells are mostly proliferating and express either B or T cell antigens, or have a null phenotype. CD30 expression is a feature of activated lymphoid cells (CD30 molecule (Ki-1 Ag): more than just a marker of CD30+ lymphoma.,1995).
Its turnover is estimated at about 7 days in mice and about 60 days in humans (CD30 (Ki-1) molecule expression in human embryonal epithelial cells of the basal layer of the developing epidermis and epidermal buds and its potential significance for embryogenesis,2005).
Signal transduction is exclusively mediated by protein interaction with adapter molecules like members of the TNFR-associated factor (TRAF) family and TRAF-binding proteins. In the cytoplasmic tail of CD30 there are different domains responsible of interaction with TRAF molecules and NFkB activation. CD30 shows two separate NFkB activating sites, one membrane proximal region between the sites 410 and 531 (D1 domain), and a second carboxy-terminal region between 553 and 595. The carboxy-terminal region has been show to associate with TRAF1, TRAF2, TRAF3 and TRAF5. There are no interaction between CD30 and TRAF6. The carboxy-terminal region contains two separate TRAF binding sites, the 558PHYPEQET565 motif (D2 domain) responsible for binding TRAF2, TRAF3 and TRAF5 proteins and the 576MLSVEEEG583 motif (D3 domain) for association with TRAF1 and TRAF2. These aminoacid motifs seem to be conserved in other cytokine receptors. The membrane-proxymal D1 domain is sufficient for activation of NFkB in CD30 mutants lacking the TRAF-binding domain 2 and 3. Deletion of the last 19 aminoacids of the D1 domain or substitution of alanine for either threonine residues 524 or 529 abolishes NFkB activation. there is no binding between TRAF2 and TRAF5 and the D1 domain, suggesting a TRAF independent NFkB activation by CD30 or the involvement of a yet unknown TRAF molecule. CD30 mediated signaling pathways and entailed signaling molecules resulting in apoptosis, cell cycle arrest and other effects are being investigated. Interaction with the ligand and binding to the antibody enhance proliferation of D3-activated T-lymphocytes and HDLM-2 cells, a phenotypic T-cell like HD-derived cell line. Pro-survival signaling of CD30 in HD cells is accompanied by activation of the NFkB trascription factor. In contrast, experiments show that stimulation of the ALCL-derived cells resulte in a drastic decrease of cell growth, which is due to CD30-mediated cell death; CD30 induce opposite effects in HD and ALCL cells. As the CD30 antigen does not contain a death domain which is typical or other death-inducing receptors, the signaling pathways leading to cell death are also disputed. CD30-mediated growth inhibition and cell death are observed in various CD30+ lymphomas. In the large granular lymphoma, several CD30-mediated signaling pathways are described leading either to increased susceptibility to apoptosis by enhanced expression of CD95, DR-3 and TRAIL or to a certain protection against apoptosis by upregulation of TRAF1 and the cellular inhibitor of apoptosis protein 2 (cIAP2) (Pleiotropic signal transduction mediated by human CD30: a member of the tumor necrosis factor receptor (TNFR) family,2002).
Overexpression of CD30 is the hallmark of Hodgkin and Reed-Sternberg (H-RS) cells and drives constitutive NFkB activation that is the molecular basis for the pathophysiology of Hodgkin's lymphoma (AP-1 mediated relief of repressive activity of the CD30 promoter microsatellite in Hodgkin and Reed-Sternberg cells).
It is used in order to confirm the diagnosis of anaplastic large cell lymphoma, classic Hodgkin's lymphoma, embryonal carcinoma and other lymphoma diagnosis. The membrane bound CD30 molecule can be proteolytically cleaved, thereby generating a soluble form (sCD30) of about 85kDa. Low serum levels of sCD30 were found in healthy humans, whereas increased sCD30 serum concentrations were detected under pathophysiological situations such us systemic lupus erythematosus, rheumatoid arthritis, certain viral infections and adult T cell leukemia/lymphoma (Soluble CD30 serum level--an adequate marker for allograft rejection of solid organs?).
The majority of the monoclonal antibodies (mAbs) against human CD30 recognize epitopes within the extracytoplasmic domain. Crosslinking CD30 via these epitopes may result in:
* the proteolytic degradation of the protein, through a metalloprotease dependent pathway and the ultimate release of sCD30 products into the extracellular compartement;
* its functional activation.
The latter results in the engagement of multiple intracellular molecules leading to the firing intracellular transduction pathway(s). However, not all the anti-CD30 mAbs can cause the effects and many of them are unable to produce any detectable biological changes.
CD30 is a target for immunotherapy beacause its restricted expression in normal tissues; the CD30 molecule appears to be an ottimal target for selectively eliminating CD30-expressing neoplastic cells by specific toxin-conjugated mAbs. Preliminary studies clearly demonstrated that anti-CD30 immunotoxins specifically inhibited protein synthesis by Hodgin's cell lines and displayed a powerful in vivo anti-tumor effect in SCID mice bearing human Hodgkin's and ALCL tumors. On this basis and following the demonstration that in vivo injection of the anti-CD30 Ber-H2mAb was able to optimally target CD30-expressing tumor cells, Ber-H2/saporin immunotoxin was administered to patients with advanced HD refractory to conventional therapies. This innovative treatment resulted in a remarkable, although transient, regression of tumor masses ranging from 50% to more than 75% in a considerable number of patients. Although host immunoreaction to the immunotoxin prevent edits subsequent administration for more than 2 to 3 weeks, with consequent re-growth of the tumor masses, this therapeutic approach appears very promising, especially for the elimination of minimal residual disease following high-dose chemotherapeutic regimens.