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 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.

Summary These studies were undertaken to assess the relative expression and autocrine activation of the epidermal growth factor receptor (EGFR) in normal and transformed prostatic epithelial cells and to determine whether EGFR activation plays a functional role in androgenstimulated growth of prostate cancer cells in vitro. EGFR expression was determined by Western blot analysis and ELISA immunoassays. Immunoprecipitation of radiophosphorylated EGFR and evaluation of tyrosine phosphorylation was used to assess EGFR activation. The human androgen-independent prostate cancer cell lines PC3 and DU145 exhibited higher levels of EGFR expression and autocrine phosphorylation than normal human prostatic epithelial cells or the human androgen-responsive prostate cancer cell line LNCaP. PC3 and DU145 cells also showed higher levels of autonomous growth under serum-free defined conditions. Normal prostatic epithelial cells expressed EGFR but did not exhibit detectable levels of EGFR phosphorylation when cultured in the absence of exogenous EGF. Addition of EGF stimulated EGFR phosphorylation and induced proliferation of normal cells. LNCaP cells exhibited autocrine phosphorylation of EGFR but did not undergo significant proliferation when cultured in the absence of exogenous growth factors. A biphasic growth curve was observed when LNCaP cells were cultured with dihydrotestosterone (DHT). Maximum proliferation occurred at 1 nM DHT with regression of the growth response at DHT concentrations greater than 1 nm. However, neither EGFR expression nor phosphorylation was altered in LNCaP cells after androgen stimulation. In addition, DHT-stimulated growth of LNCaP cells was not inhibited by anti-EGFR. These studies show that autocrine activation of EGFR is a common feature of prostatic carcinoma cells in contrast to normal epithelial cells. However, EGFR activation does not appear to play a functional role in androgen-stimulated growth of LNCaP cells in vitro.