Expression of the costimulatory receptor CD30 is regulated by both CD28 and cytokines.

Costimulation was originally defined and characterized during primary T cell activation. The signaling events that regulate subsequent antigen encounters by T cells are less well defined. In this study we examined the role of CD30 in T cell activation and defined factors that regulate expression of CD30 on T cells. We demonstrate that CD30 expression is restricted to activated T cells and regulated by CD28 signal transduction. In contrast to CD28-expressing TCR Tg cells, CD28-deficient TCR Tg cells did not express CD30 when cultured with peptide and APCs. However, rIL-4 reconstituted CD30 expression on CD28-deficient TCR Tg cells. Blockade of CD28 interactions or depletion of IL-4 inhibited the induction of CD30, suggesting that both CD28 and IL-4 play important roles in the induction of CD30 expression on wild-type cells. However, CD28 signaling did not up-regulate CD30 expression solely through its ability to augment IL-4 production because IL-4-deficient T cells stimulated with anti-CD3 and anti-CD28 expressed CD30. Induction of CD30 in the absence of IL-4 was not due to the IL-4-related cytokine IL-13. CD30, when expressed on an activated T cell, can act as a signal transducing receptor that enhances the proliferation of T cells responding to CD3 crosslinking. Collectively, the data suggest that T cell expression of CD30 is dependent on the presence of CD28 costimulatory signals or exogenous IL-4 during primary T cell activation. Once expressed on the cell surface, CD30 can serve as a positive regulator of mature T cell function.

Induction of nuclear factor kappaB by the CD30 receptor is mediated by TRAF1 and TRAF2.

CD30 is a lymphoid cell-specific surface receptor which was originally identified as an antigen expressed on Hodgkin's lymphoma cells. Activation of CD30 induces the nuclear factor kappaB (NF-kappaB) transcription factor. In this study, we define the domains in CD30 which are required for NF-kappaB activation. Two separate elements of the cytoplasmic domain which were capable of inducing NF-kappaB independently of one another were identified. The first domain (domain 1) mapped to a approximately 120-amino-acid sequence in the membrane-proximal region of the CD30 cytoplasmic tail, between residues 410 and 531. A second, more carboxy-terminal region (domain 2) was identified between residues 553 and 595. Domain 2 contains two 5- to 10-amino-acid elements which can mediate the binding of CD30 to members of the tumor necrosis factor receptor-associated factor (TRAF) family of signal transducing proteins. Coexpression of CD30 with TRAF1 or TRAF2 but not TRAF3 augmented NF-kappaB activation through domain 2 but not domain 1. NF-kappaB induction through domain 2 was inhibited by coexpression of either full-length TRAF3 or dominant negative forms of TRAF1 or TRAF2. In contrast, NF-kappaB induction by domain 1 was not affected by alterations in TRAF protein levels. Together, these data support a model in which CD30 can induce NF-kappaB by both TRAF-dependent and -independent mechanisms. TRAF-dependent induction of NF-kappaB appears to be regulated by the relative levels of individual TRAF proteins in the cell.

A conserved family of cellular genes related to the baculovirus iap gene and encoding apoptosis inhibitors.

The baculovirus inhibitor of apoptosis gene, iap, can impede cell death in insect cells. Here we show that iap can also prevent cell death in mammalian cells. The ability of iap to regulate programmed cell death in widely divergent species raised the possibility that cellular homologs of iap might exist. Consistent with this hypothesis, we have isolated Drosophila and human genes which encode IAP-like proteins (dILP and hILP). Like IAP, both dILP and hILP contain amino-terminal baculovirus IAP repeats (BIRs) and carboxy-terminal RING finger domains. Human ilp encodes a widely expressed cytoplasmic protein that can suppress apoptosis in transfected cells. An analysis of the expressed sequence tag database suggests that hilp is one of several human genes related to iap. Together these data suggest that iap and related cellular genes play an evolutionarily conserved role in the regulation of apoptosis.

CD30 contains two binding sites with different specificities for members of the tumor necrosis factor receptor-associated factor family of signal transducing proteins.

CD30 is a member of the tumor necrosis factor (TNF) receptor family of proteins. CD30 can regulate proliferation of lymphocytes and may also play an important role in human immunodeficiency virus replication. However, little is known about CD30 signal transduction. We performed a yeast two-hybrid library screen with the cytoplasmic domain of CD30 and isolated multiple independent cDNAs encoding human tumor necrosis factor receptor-associated factor (TRAF) 1, TRAF2, and CRAF1 (TRAF3). The ability of TRAF1, TRAF2, and CRAF1 to associate with CD30 was confirmed using an in vitro coprecipitation assay, further demonstrating that the interaction was specific and direct. The TRAF-binding domain of CD30 was mapped to the COOH-terminal 36 amino acid residues, which contained two independent binding sites. CRAF1 bound only a single site, which contained the sequence PEQET, whereas TRAF1 and TRAF2 were capable of binding to either the PEQET site or an additional downstream domain. These data indicate that the TRAF protein binding pattern of CD30 differs from other TNF receptor family members and suggest that signaling specificity through TNF receptor family proteins may be achieved through differences in their abilities to bind TRAF proteins.