T lymphocytes undergo apoptosis in response to a variety of stimuli, including exposure to UV radiation and ␥-irradiation. While the mechanism by which stress stimuli induce apoptosis is not well understood ,

CD28 is an accessory receptor that is involved in biological responses such as anergy, apoptosis, and cytokine production in T cells (13-16). The requirement for dual receptor ligation to activate the JNK cascade is unique for T cells and raises the important question of whether both receptors contribute to the JNK cascade, e.g. by activating a component that is shared by both receptor types. In this regard, it is known that both anti-CD3 and anti-CD28 mAbs induce GTP/GDP exchange on Ras (8, 17). Whereas Ras acts upstream of the JNK cascade in some receptor protein-tyrosine kinase signaling pathways, not all stimuli that activate JNKs in lymphocytes depend on Ras (18 -22). It is important to determine whether Ras is involved in the T cell response, because it provides us with a potential target by which to study the synergy between the TCR/CD3 and CD28 receptors in this cascade. The role of JNK in T cell activation is not well understood. Several lines of evidence suggest, however, that JNKs may be involved in inducing the transcriptional activation of AP-1 response elements in TCR-responsive genes (10). JNKs play a role in the expression as well as transcriptional activation of AP-1 binding proteins (19 -27). The JNK cascade leads to transcriptional activation of c-Jun by phosphorylation of serine residues (i.e. Ser 63 and Ser 73 ) in its transactivation domain (18, 28 -31). c-Jun, in turn, up-regulates its own expression by interacting with the c-Jun promoter (25, 31). In addition, JNKs up-regulate c-Fos expression by phosphorylation of the ternary complex factor, p62 TCF (Elk-1), which binds the c-fos promoter (23, 25). Both c-Fos and c-Jun contribute to the expression of the IL-2 gene, which, as for JNK activation, is dependent on co-ligation of CD3 and CD28 (10,16,32,33). This suggests that JNK may play a role in transcriptional activation of the IL-2 promoter. To this end, it is known that in the absence of CD28 co-stimulation, TCR ligation may lead to the induction of an-* This work was supported by United States Public Health Service Grants CA-09120 -21, GM41576, and AI-34567 (UCLA Asthma, Allergy and Immunologic Disease Center funded by the NIAID and NIEHS) and the Concern Foundation of Los Angeles. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.‡ To whom correspondence should be addressed: UCLA School of Medicine, Dept. of Medicine, CIA, 52-175 CHS, 10833 Le Conte Ave., Los Angeles, CA 1 The abbreviations used are: TCR, T cell receptor; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; MEKK-1, mitogen-activated protein kinase kinase kinase; TCF, ternary complex factor; AP-1, activating protein-1; NFAT, nuclear factor of activated T cells; PCR, polymerase chain reaction; RT-PCR, reverse transcription-PCR; mAb, monoclonal antibody; IL, interleukin; DA-MEKK-1 and DN-MEKK-1, dominant active and dominant ...

SummaryCD40 plays an important role in B cell activation, proliferation, and Ig class switching. The signal transduction pathway mediated by CD40 was studied using monoclonal antibody (mAb) 626.1 to CD40. Burkitt's lymphoma and Epstein-Barr virus-transformed B cell lines and tonsilar B lymphocytes were treated with the anti-CD40 mAb for various lengths of time. The early events triggered by CD40 were examined by monitoring the changes in tyrosine phosphorylation of cellular proteins with anti-phosphotyrosine mAb. Dephosphorylation of specific proteins ranging between 50-110 kD and the appearance of a 28-kD tyrosine phosphorylated protein were seen within 30 s in human B cell lines. The dephosphorylation was reversed and the 28-kD protein was dephosphorylated in cells stimulated for 1 min. In resting B cells, the appearance of the 28-kD phosphoprotein was observed in 30 s after the addition of the anti-CD40 mAb. The tyrosine phosphorylation of this protein persisted. The patterns of protein tyrosine phosphorylation differed from those induced by an anti-immunoglobulin M mAb. The changes in the state of tyrosine phosphorylation induced by the anti-CD40 mAb were obviated by mAb to CD45, a protein tyrosine phosphatase (PTP) or by the addition of sodium orthovanadate, a broad PTP inhibitor. They were also blocked by protein tyrosine kinase (FFK) inhibitors, herbimycin A and genistein, and PKC and protein serine/threonine kinase inhibitors, H7 and HA1004. In addition, the alteration in the tyrosine phosphorylation ofPTKs Lyn, Fyn, and Syk was directly demonstrated. Engagement of CD40 for 30 s induced a transient decrease in tyrosine phosphorylation of these PTKs. These results indicate that the early events in CD40 signaling involve the complex interaction between PTP and protein kinases. C D40 is a 47-50-kD glycoprotein expressed on B cells and some normal and neoplastic epithelial cells including follicular dendritic cells and thymic epithelium (1-8). The cDNA sequences of both human and murine CD40 show that these glycoproteins are type I transmembrane proteins and contain cysteine-rich extracellular domains followed by serine/threonine-rich regions preceding the transmembrane domain (9, 10). They have significant homology to the members of the nerve growth factor receptor family (9-11).CD40 plays an important role in B cell activation, differentiation, and survival. Heterologous Abs and mAbs to CD40 induce B cell proliferation (1, 2, 4, 12, 13) and the engagement of CD40 by mAb provides a stimulatory signal synergistic with those delivered by IL-4 or Ab to either surface IgM (slgM) 1 or CD20 (2,14,15). An anti-CD40 mAb in the presence of IL-4 promotes long-term B cell growth (16). CD40 also plays a role in the induction of homotypic adhesion (17,18). A mAb to CD40 induces bcl-2 expression and Parts of these results have been presented in abstract form at the Annual Meeting AAP/ASCI/AFCR in

Fas is expressed constitutively by colonic epithelial cells, and its ligand is expressed by intraepithelial and lamina propria lymphocytes. Fas ligation induces apoptosis in colonic epithelial cells and is implicated in the epithelial damage seen in ulcerative colitis. To understand the pleiotropic effects of Fas in the intestinal mucosa, we have examined signaling pathways activated by Fas in HT-29 colonic epithelial cells. HT-29 cells were stimulated with anti-Fas in the presence or absence of interferon-γ (IFN-γ). Activation of mitogen-activated protein kinase pathways was assessed by kinase assay, Western blots, and promoter-reporter assays. Electromobility shift assays were used to assess activator protein-1 (AP-1) binding activity. IFN-γ increases expression of Fas on HT-29 cells. Signaling via Fas receptor, as determined by induction of c-Jun NH2-terminal kinase (JNK) activity and transcriptional activation of AP-1, is enhanced in IFN-γ-primed cells. Dominant-interfering mutants of the JNK pathway do not block Fas-mediated apoptosis. Signaling through Fas results in activation of JNK and AP-1 binding activity that is increased in the presence of IFN-γ. Inhibition of JNK does not block Fas-mediated apoptosis in these cells. Fas-Fas ligand interactions in the intestinal mucosa may lead to complex signal transduction cascades and gene regulation that culminate in apoptosis, cytokine secretion, or other novel functions.

OSM, IL-1 and TNF-alpha induce KS cell growth by inducing the expression of various bFGF isoforms. Moreover, bFGF production by KS and HUVEC is dependent on the activation of the ERK and JNK cascades, which result in the transcriptional activation of the bFGF promoter.