Activation and signal transduction via mitogen-activated protein (MAP) kinases in T lymphocytes

Pulsatile MEK Inhibition Improves Anti-tumor Immunity and T Cell Function in Murine Kras Mutant Lung Cancer

KRAS is one of the driver oncogenes in non-small-cell lung cancer (NSCLC) but remains refractory to current modalities of targeted pathway inhibition, which include inhibiting downstream kinase MEK to circumvent KRAS activation. Here, we show that pulsatile, rather than continuous, treatment with MEK inhibitors (MEKis) maintains T cell activation and enables their proliferation. Two MEKis, selumetinib and trametinib, induce T cell activation with increased CTLA-4 expression and, to a lesser extent, PD-1 expression on T cells in vivo after cyclical pulsatile MEKi treatment. In addition, the pulsatile dosing schedule alone shows superior anti-tumor effects and delays the emergence of drug resistance. Furthermore, pulsatile MEKi treatment combined with CTLA-4 blockade prolongs survival in mice bearing tumors with mutant Kras. Our results set the foundation and show the importance of a combinatorial therapeutic strategy using pulsatile targeted therapy together with immunotherapy to optimally enhance tumor delay and promote long-term anti-tumor immunity.

Suppression of T lymphocyte activation by 3-chloro-1,2-propanediol mono- and di-palmitate esters in vitro

This study investigated whether and how 3-chloro-1,2-propanediol (3-MCPD) fatty acid esters, a group of food contaminants formed during processing, might inhibit the immune system through suppressing T lymphocyte activation for the first time. Three 3-MCPD esters including 1-palmitoyl-3-chloropropanediol (1-pal), 2-palmitoyl-3-chloropropanediol (2-pal), and1,2-dipalmitoyl-3-chloropropanediol (dipal) were selected as the probe compounds to test the possible effects of fatty acid structure on their potential immune inhibitory effect. The results showed that 1-pal and 2-pal, but not dipal, significantly suppressed ConA-induced T lymphocyte proliferation, cell cycle activity, Th1 and Th2 cytokine secretion, CD4⁺ T cell populations, and the ratio of CD4⁺/CD8⁺ T cells under the experimental conditions. Moreover, Western blotting and immunofluorescence analyses revealed that 1-pal and 2-pal could inhibit the activation of ConA-stimulated mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways. In addition, 1-pal significantly suppressed DNFB-induced delayed-type hyper sensitivity (DTH) reaction characterized by the increased ear thickness and IFN-γ production in mice. These observations indicated that 3-MCPD esters exerted a negative effect on T lymphocyte-mediated immunity, and the immunosuppressive activities of 3-MCPD monopalmitates were stronger than 3-MCPD dipalmitate.

Immune Effects of Chemotherapy, Radiation, and Targeted Therapy and Opportunities for Combination With Immunotherapy

There have been significant advances in cancer treatment over the past several years through the use of chemotherapy, radiation therapy, molecularly targeted therapy, and immunotherapy. Despite these advances, treatments such as monotherapy or monomodality have significant limitations. There is increasing interest in using these strategies in combination; however, it is not completely clear how best to incorporate molecularly targeted and immune-targeted therapies into combination regimens. This is particularly pertinent when considering combinations with immunotherapy, as other types of therapy may have significant impact on host immunity, the tumor microenvironment, or both. Thus, the influence of chemotherapy, radiation therapy, and molecularly targeted therapy on the host anti-tumor immune response and the host anti-host response (ie, autoimmune toxicity) must be taken into consideration when designing immunotherapy-based combination regimens. We present data related to many of these combination approaches in the context of investigations in patients with melanoma and discuss their potential relationship to management of patients with other tumor types. Importantly, we also highlight challenges of these approaches and emphasize the need for continued translational research.

Estrogen attenuates lipopolysaccharide-induced nitric oxide production in macrophages partially via the nongenomic pathway

Steroid hormones exert genotropic effects through members of the nuclear hormone receptor family. In the present study, we examined the effects of 17β-estradiol (E2) on nitric oxide (NO) production following lipopolysaccharide (LPS) stimulation and investigated the mechanisms in mouse bone marrow-derived macrophages (BMMs). E2 alone did not affect NO production. In contrast, E2 inhibited LPS-induced production of NO in BMMs. Using a cell-impermeable E2 conjugated to BSA (E2-BSA), which has been used to investigate the nongenomic effects of estrogen, we found that the increase in NO production induced by LPS was also attenuated. In addition, the intracellular estrogen receptor blocker, ICI 182780, only partially antagonized the total effects of E2 on LPS-stimulated NO production capacity. E2 also attenuated the LPS activation of p38 mitogen-activated protein kinase (MAPK) but not that of extracellular-regulated protein kinase 1/2 (ERK1/2) and c-Jun NH2-terminal kinase (JNK). This attenuation was not abrogated by ICI 182780. Moreover, the p38 inhibitor, SB 203580, greatly reduced the LPS-induced NO production, and the remaining NO levels were no longer regulated by E2. Additionally, E2-BSA inhibited LPS-mediated changes in p38 MAPK activation to the same extent as E2. Moreover, E2 and E2-BSA inhibited LPS-induced activation of nuclear factor-kappa B (NF-κB) and activator protein 1 (AP-1). This inhibitory effect of E2 was only partially antagonized by ICI 182780. Taken together, these results suggest that E2 has an inhibitory effect on LPS-induced NO production in BMMs through inhibition of p38 MAPK phosphorylation, and blockade of NF-κB and AP-1 activation. These effects are mediated at least in part via a nongenomic pathway.

Role of PPARγ in the salutary effects of 17β-estradiol on Kupffer cell cytokine production following trauma-hemorrhage

Studies have shown that administration of 17β-estradiol prevents trauma-hemorrhage-induced increase in proinflammatory cytokine production by Kupffer cells and associated multiple organ injury. Since activation of peroxisome proliferator-activated receptor γ (PPARγ) following ischemic conditions has been shown to be protective, we examined if PPARγ plays any role in the salutary effects of 17β-estradiol on Kupffer cell cytokine production following trauma-hemorrhage. Male mice underwent trauma-hemorrhage (mean blood pressure 40 mmHg for 90 min, then resuscitation). 17β-estradiol (50 µg/kg) or vehicle with or without PPARγ antagonist GW9662 was injected subcutaneously at the middle of resuscitation. At 2 h after trauma-hemorrhage, plasma interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels, Kupffer cell IL-6 and TNF-α production and mRNA expression, and PPARγ, nuclear factor (NF)-κB and activator protein (AP)-1 DNA binding activity were determined. Kupffer cell IL-6 and TNF-α production, as well as plasma IL-6 and TNF-α levels, increased following trauma-hemorrhage. Moreover, NF-κB and AP-1 DNA binding activity and IL-6 and TNF-α mRNA expression were also enhanced under such conditions. However, 17β-estradiol administration normalized all these parameters. Although PPARγ activity decreased after trauma-hemorrhage, administration of 17β-estradiol following trauma-hemorrhage elevated PPARγ activity above the normal level. Inhibition of PPARγ by co-administration of GW9662, however, abolished the salutary effects of 17β-estradiol on plasma cytokine and Kupffer cells. Thus, activation of PPARγ appears to play an important role in mediating the salutary effects of 17β-estradiol on plasma cytokine levels and Kupffer cell cytokine production after trauma-hemorrhage, which are likely mediated via NF-κB and AP-1.

Mycobacterial antigen(s) induce anergy by altering TCR- and TCR/CD28-induced signalling events: insights into T-cell unresponsiveness in leprosy

Present study investigates the role of Mycobacterium leprae (M. leprae) antigens on TCR- and TCR/CD28-induced signalling leading to T-cell activation and further correlates these early biochemical events with T-cell anergy, as prevailed in advanced stages of leprosy. We observed that both whole cell lystae (WCL) and soluble fraction of M. leprae sonicate (MLSA) not only inhibited TCR, thapsigargin and ionomycin induced calcium fluxes by diminishing the opening of calcium channels, but also TCR- or TCR/CD28-induced proximal signalling events like phosphorylation of Zap-70 and protein kinase-C (PKC) activity. Study of TCR- and TCR/CD28-induced downstream signals revealed that M. leprae antigens curtail phosphorylation of both Erk1/2 and p38MAPK, consequently altering terminal signalling events like reduced binding of NFAT on IL-2 promoter and transcription of IL-2 gene, diminished expression of activation markers (CD25 and CD69). Furthermore, M. leprae fractions significantly inhibited IL-2 secretion and T-cell blastogenesis in healthy individuals. Altogether, results suggest that M. leprae interferes with TCR/CD28-induced upstream as well as downstream signalling events resulting in reduced IL-2 production and thus inhibition in T-cell proliferation, which might be responsible for T-cell unresponsiveness leading to stage of immunosuppression and consequently, for the progression of disease.

Biochemical signaling pathways for memory T cell recall

Memory T cells exhibit low activation thresholds and rapid effector responses following antigen stimulation, contrasting naive T cells with high activation thresholds and no effector responses. Signaling mechanisms for the distinct properties of naive and memory T cells remain poorly understood. Here, I will discuss new results on signal transduction in naive and memory T cells that suggest proximal control of activation threshold and a distinct biochemical pathway to rapid recall. The signaling and transcriptional pathways controlling immediate effector function in memory T cells closely resemble pathways for rapid effector cytokine production in innate immune cells, suggesting memory T cells use innate pathways for efficacious responses.

Estradiol's salutary effects on keratinocytes following trauma-hemorrhage are mediated by estrogen receptor (ER)-alpha and ER-beta

Although administration of 17beta-estradiol (estrogen) following trauma-hemorrhage attenuates the elevation of cytokine production and mitogen-activated protein kinase (MAPK) activation in epidermal keratinocytes, whether the salutary effects of estrogen are mediated by estrogen receptor (ER)-alpha or ER-beta is not known. To determine which estrogen receptor is the mediator, we subjected C3H/HeN male mice to trauma-hemorrhage (2-cm midline laparotomy and bleeding of the animals to a mean blood pressure of 35 mmHg and maintaining that pressure for 90 min) followed by resuscitation with Ringer's lactate (four times the shed blood volume). At the middle of resuscitation we subcutaneously injected ER-alpha agonist propyl pyrazole triol (PPT; 5 microg/kg), ER-beta agonist diarylpropionitrile (DPN; 5 microg/kg), estrogen (50 microg/kg), or ER antagonist ICI 182,780 (150 microg/kg). Two hours after resuscitation, we isolated keratinocytes, stimulated them with lipopolysaccharide for 24 h (5 microg/mL for maximum cytokine production), and measured the production of interleukin (IL)-6, IL-10, IL-12, and TNF-alpha and the activation of MAPK. Keratinocyte cytokine production markedly increased and MAPK activation occurred following trauma-hemorrhage but were normalized by administration of estrogen, PPT, and DPN. PPT and DPN administration were equally effective in normalizing the inflammatory response of keratinocytes, indicating that both ER-alpha and ER-beta mediate the salutary effects of estrogen on keratinocytes after trauma-hemorrhage.

Mitogen activated protein kinase (MAPK) mediates non-genomic pathway of estrogen on T cell cytokine production following trauma-hemorrhage

Although studies have shown 17beta-estradiol (E2) administration following trauma-hemorrhage (T-H) attenuates alterations in T cell cytokine production, it remains unknown whether such effects of E2 are mediated via genomic or non-genomic pathways. In this study, we determined the non-genomic effects of E2 on splenic T cell cytokine production and the role of MAPK following T-H. Male Sprague-Dawley rats underwent T-H (mean BP 40 mmHg for 90 min, then resuscitation). E2, E2 conjugated with BSA (E2-BSA, 1 mg/kg E2) with or without an estrogen receptor antagonist (ICI 182 780), or vehicle was administered during resuscitation. Two hours thereafter, T cell production of IL-2 and IFN-gamma and activation of MAPK (p38, ERK-1/2 and JNK) were determined. The effect of selective MAPK inhibitors on cytokine production was also examined in vitro. IL-2 and IFN-gamma production capacity and MAPK activation decreased in T cells following T-H. However, E2 administration normalized these parameters. Although E2-BSA administration also attenuated suppression in cytokine production, the values were lower compared to sham. In contrast, E2-BSA prevented T-H-induced suppression in MAPK activation to the same extent as E2. Co-administration of ICI 182 780 abolished E2-BSA effects. These findings suggest E2 effects on T cell cytokine production following T-H are mediated at least in part via non-genomic pathway and these non-genomic effects are likely mediated via MAPK pathways.

Salutary effects of 17beta-estradiol on T-cell signaling and cytokine production after trauma-hemorrhage are mediated primarily via estrogen receptor-alpha

Although 17beta-estradiol (E2) administration following trauma-hemorrhage prevents the suppression in splenocyte cytokine production, it remains unknown whether the salutary effects of 17beta-estradiol are mediated via estrogen receptor (ER)-alpha or ER-beta. Moreover, it is unknown which signaling pathways are involved in 17beta-estradiol's salutary effects. Utilizing an ER-alpha- or ER-beta-specific agonist, we examined the role of ER-alpha and ER-beta in E2-mediated restoration of T-cell cytokine production following trauma-hemorrhage. Moreover, since MAPK, NF-kappaB, and activator protein (AP)-1 are known to regulate T-cell cytokine production, we also examined the activation of MAPK, NF-kappaB, and AP-1. Male rats underwent trauma-hemorrhage (mean arterial pressure 40 mmHg for 90 min) and fluid resuscitation. ER-alpha agonist propyl pyrazole triol (PPT; 5 microg/kg), ER-beta agonist diarylpropionitrile (DPN; 5 microg/kg), 17beta-estradiol (50 microg/kg), or vehicle (10% DMSO) was injected subcutaneously during resuscitation. Twenty-four hours thereafter, splenic T cells were isolated, and their IL-2 and IFN-gamma production and MAPK, NF-kappaB, and AP-1 activation were measured. T-cell IL-2 and IFN-gamma production was decreased following trauma-hemorrhage, and this was accompanied with a decrease in T-cell MAPK, NF-kappaB, and AP-1 activation. PPT or 17beta-estradiol administration following trauma-hemorrhage normalized those parameters, while DPN administration had no effect. Since PPT, but not DPN, administration following trauma-hemorrhage was as effective as 17beta-estradiol in preventing the T-cell suppression, it appears that ER-alpha plays a predominant role in mediating the salutary effects of 17beta-estradiol on T cells following trauma-hemorrhage, and that such effects are likely mediated via normalization of MAPK, NF-kappaB, and AP-1 signaling pathways.

Estrogen-mediated activation of non-genomic pathway improves macrophages cytokine production following trauma-hemorrhage

Although 17beta-estradiol (E2) attenuates the alterations in Kupffer cells and splenic macrophages (MPhi) cytokine production following trauma-hemorrhage, the mechanism by which this occurs remains unknown. Utilizing a cell-impermeable E2 conjugated with BSA (E2-BSA), we examined the non-genomic effects of E2 on the above two cell population cytokine production, MAPK and transcription factors activation following trauma-hemorrhage. Male Sprague-Dawley rats underwent trauma-hemorrhage (mean BP 40 mmHg for 90 min, then resuscitation). E2, E2-BSA (1 mg/kg E2) with or without an estrogen receptor antagonist (ICI 182,780), or vehicle was administrated during resuscitation. Two hrs thereafter, Kupffer cells and SMPhi production of IL-6, TNF-alpha, and IL-10, activation of MAPK (p38, ERK-1/2, and JNK), and transcription factors (NF-kappaB and AP-1) were determined. IL-6, TNF-alpha, and IL-10 productive capacity, MAPK, and transcription factors activation increased in Kupffer cells while they decreased in SMPhi following trauma-hemorrhage. However, E2 administration normalized all of these alterations. Although E2-BSA also attenuated the alterations in cytokine production/transcription factors, the values were higher in Kupffer cells and lower in SMPhi compared to shams. In contrast, E2-BSA prevented trauma-hemorrhage-mediated changes in MAPK activation to the same extent as E2. Co-administration of ICI 182,780 abolished E2-BSA effects. Although some MAPK inhibitors suppressed cytokine production, the inhibitor effectiveness was dependent on cytokine, cell type and animal condition (trauma-hemorrhage or sham). Thus, E2 effects on Kupffer cells and SMPhi cytokine production and transcription factors activation following trauma-hemorrhage are mediated at least in part via non-genomic pathway and these non-genomic effects are likely mediated via MAPK pathways.

Saikosaponin-d inhibits T cell activation through the modulation of PKCtheta, JNK, and NF-kappaB transcription factor

The effects of saikosaponin-d, a triterpene saponin derived from Bupleurum falcatum L. (Umbelliferae), on the signaling pathways of T cell activation were examined. The results showed that saikosaponin-d potently suppressed both early (CD69) and late (CD71) expressions of mouse T cells stimulated with Con A or PMA. It interfered with PKCtheta translocation from cytosol to membrane fraction and inhibited the phosphorylations of IkappaBalpha and JNK, but not ERK, in PMA-activated mouse T cells. Additionally, it inhibited PMA and ionomycin-stimulated IL-2 production in mouse T cells. In summary, these results indicate that the mechanism by which saikosaponin-d inhibits T cell activation would involve the suppression of CD69 and CD71 expressions and IL-2 production, and the modulation of PKC pathway through PKCtheta, JNK, and NF-kappaB transcription factor. This may herald a novel approach for further studies of saikosaponin-d as a candidate for use in the treatment of inflammatory and autoimmune diseases.

The immunosuppressive effect of Gamisanghyulyunbueum through inhibition of mitogen-activated protein kinase and nuclear factor activation in MOLT-4 cells

Gamisanghyulyunbueum (GSHYBE) has been used clinically to treat skin related disease in South Korea. We investigated GSHYBE-mediated changes in downstream T cell signal transduction. To determine the mechanism of inhibition, we have studied many of the major pathways in phytohemagglutinin (PHA)-activated T cell. We show that among the mitogen-activated protein kinase family activation of phosphorylation of extra cellular signal-regulated kinase 1/2 (ERK1/2, p44/42) and p38, but not c-jun NH2-terminal kinase is inhibited. In activated MOLT-4 cells, the nuclear localization of nuclear factor of activated T cells (NFATc) was blocked by GSHYBE (1 mg/ml). Also, degradation of inhibitor kappaB-alpha and transactivation by nuclear factor-kappaB (NF-kappaB)/Rel A were impaired by GSHYBE (1 mg/ml). Furthermore, interlukin (IL)-2, IL-4 and Interferen (IFN)-gamma secretion by PHA activated MOLT-4 cells and peripheral blood mononuclear cells (PBMC) were significantly diminishes following GSHYBE treatment (1 mg/ml). Also, oral administration of GSHYBE inhibited IL-2 secretion in skin allergic reaction. In conclusion, our data indicate that GSHYBE treatment of T cells inhibits ERK1/2 and p38 activation and nuclear translocation of NFATc, NF-kappaB, resulting in diminished secretion of IL-2.

DNFB activates MAPKs and upregulates CD40 in skin-derived dendritic cells

BACKGROUND

The intracellular mechanisms involved in the activation of DCs during sensitization in allergic contact dermatitis (ACD) are not known.

OBJECTIVE

Here, we investigated the effect of a strong sensitizer, 2,4-dinitrofluorobenzene (DNFB) on the activity of MAPKs in a dendritic cell (DC) line generated from fetal mouse skin (FSDC), and the results were correlated with the expression of a costimulatory molecule upregulated upon DC maturation, CD40.

METHODS

Phosphorylation of ERK1/2 (pERK1/2) and p38 MAPK (pp38 MAPK), and CD40 protein levels, were determined by Western blot. Cellular localization of pERK1/2 and pp38 MAPK were determined by immunocytochemistry using phospho-specific antibodies.

RESULTS

Although with different kinetics, DNFB activated ERK1/2 and p38 MAPK, and induced the translocation of the phosphorylated forms of the kinases to the nucleus. In addition, DNFB upregulated significantly CD40 protein levels in FSDC. However, 2,4-dichloronitrobenzene (DCNB), an inactive analogue of DNFB, did not affect significantly the phosphorylation of MAPKs and CD40 protein levels. SB203580 and SB202190, inhibitors of the p38 MAPK activity, inhibited DNFB-induced CD40 upregulation, although this effect did not reach statistical significance. In contrast, PD 98059 and U0126, inhibitors of mitogen or extracellular signal-regulated kinase (MEK), had no effect on the CD40 upregulation induced by DNFB.

CONCLUSIONS

Taken together, these results indicate that the strong sensitizer DNFB activates ERK1/2 and p38 MAPK signaling pathways, and upregulates CD40 protein levels. However, MAPKs do not play a major role in the induction of CD40, one of the phenotypic markers of DC maturation.

Signaling control of memory T cell generation and function

Memory T cells exhibit low activation thresholds and mediate rapid effector responses when recalled by antigen; contrasting the higher activation threshold, slower responses and predominant IL-2 production by naive T cells. While the sequence of intracellular events coupling the T cell-receptor (TCR) to naive T cell activation is well characterized, biochemical control of memory T cell differentiation and function remains undefined. In this review, we will discuss recent developments in T cell-receptor signal transduction as they pertain to memory T cells, and will discuss how signal dampening may drive memory generation, and more efficient spatial organization of signaling molecules may promote rapid recall responses.

Combined alcohol and burn injury differentially regulate p-38 and ERK activation in mesenteric lymph node T cell

Recent studies from our laboratory have suggested that acute alcohol ingestion prior to burn injury enhances gut bacterial translocation by suppressing T cell-mediated intestinal immune defense. To determine the mechanism responsible for suppressed T cell function, we examined the activation of mitogen-activated protein kinases (MAPK) members p-38 and ERK-1/2. Both p-38 and ERK-1/2 are known to play a significant role in the T cell proliferation and their cytokine production. Rats were gavaged with ethanol to achieve a blood alcohol level of approximately 100 mg/dl, before they were subjected to a 25% total body surface area burn injury. Two days after injury, rats were sacrificed and mesenteric lymph node (MLN) T cells were isolated and their ability to proliferate in response to anti-CD3 was determined. For p-38 and ERK-1/2 determination, T cells were divided into two groups. Cells in one group were stimulated with anti-CD3 for 3 min and lysed. The cells in the second group were cultured for approximately 18 h in the presence of anti-CD3 and lysed. MAPK status in 18-h cultured cells allowed us to determine whether or not the changes in p-38 and ERK-1/2 are transient or persist in the proliferating cells. Two days after injury, anti-CD3-mediated MLN T cell proliferation was more suppressed in rats gavaged with alcohol prior to burn injury compared to rats receiving either burn injury alone or sham-injured rats regardless of their exposure. Western blot analyses showed significant inhibition of ERK-1/2 phosphorylation in both freshly isolated and 18-h cultured T cells from alcohol and burn-injured rats compared to the sham rat T cells. The inhibition of p-38 phosphorylation in T cells derived from alcohol and burn-injured rats was found to be transient as no significant difference in p-38 phosphorylation was noted between the 18 h incubated MLN T cells of sham and alcohol and burn-injured rats. Taken together, our findings suggest that low levels of ERK-1/2 activation is likely to play a significant role in MLN T cell proliferative suppression in alcohol and burn-injured rats.

Identification of a protein that interacts with the golli-myelin basic protein and with nuclear LIM interactor in the nervous system

The myelin basic protein (MBP) gene encodes the classic MBPs and the golli proteins, which are related structurally to the MBPs but are not components of the myelin sheath. A yeast two-hybrid approach was used to identify molecular partners that interact with the golli proteins. A mouse cDNA was cloned that encoded a protein of 261 amino acids and called golli-interacting protein (GIP). Database analysis revealed that GIP was the murine homolog of human nuclear LIM interactor-interacting factor (NLI-IF), a nuclear protein whose function is just beginning to be understood. It is a member of a broad family of molecules, found in species ranging from yeast to human, that contain a common domain of approximately 100 amino acids. Immunocytochemical and Northern blot analyses showed co-expression of GIP and golli in several neural cell lines. GIP and golli also showed a similar developmental pattern of mRNA expression in brain, and immunohistochemical staining of GIP and golli showed co-expression in several neuronal populations and in oligodendrocytes in the mouse brain. GIP was localized predominantly in nuclei. GIP co-immunoprecipitated with golli in several in vitro assays as well as from PC12 cells under physiologic conditions. GIP was the first member of this family shown to interact with nuclear LIM interactor (NLI). NLI co-immunoprecipitated with GIP and golli from lysates of N19 cells transfected with NLI, further confirming an interaction between golli, GIP, and NLI. The ability of GIP to interact with both golli and NLI, and the nuclear co-localization of GIP and golli in many cells, indicates a role for the golli products of the MBP gene in NLI- associated regulation of gene expression.

Mammalian transcription factor LSF is a target of ERK signaling

LSF is a mammalian transcription factor that is rapidly and quantitatively phosphorylated upon growth induction of resting, peripheral human T cells, as assayed by a reduction in its electrophoretic mobility. The DNA-binding activity of LSF in primary T cells is greatly increased after this phosphorylation event (Volker et al. [1997]: Genes Dev 11:1435-1446). We demonstrate here that LSF is also rapidly and quantitatively phosphorylated upon growth induction in NIH 3T3 cells, although its DNA-binding activity is not significantly altered. Three lines of experimentation established that ERK is responsible for phosphorylating LSF upon growth induction in both cell types. First, phosphorylation of LSF by ERK is sufficient to cause the reduced electrophoretic mobility of LSF. Second, the amount of ERK activity correlates with the extent of LSF phosphorylation in both primary human T cells and NIH 3T3 cells. Finally, specific inhibitors of the Ras/Raf/MEK/ERK pathway inhibit LSF modification in vivo. This phosphorylation by ERK is not sufficient for activation of LSF DNA-binding activity, as evidenced both in vitro and in mouse fibroblasts. Nonetheless, activation of ERK is a prerequisite for the substantial increase in LSF DNA-binding activity upon activation of resting T cells, indicating that ERK phosphorylation is necessary but not sufficient for activation of LSF in this cell type.

IL-2 activation of a PI3K-dependent STAT3 serine phosphorylation pathway in primary human T cells

Interleukin-2 (IL-2) is the major growth factor of activated T lymphocytes. By inducing cell cycle progression and protection from apoptosis in these cells, IL-2 is involved in the successful execution of an immune response. Upon binding its receptor, IL-2 activates a variety of signal transduction pathways, including the Ras/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) and Janus kinase (JAK)/STAT cascades. In addition, activation of phosphatidylinositol 3-kinase (PI3K) and several of its downstream targets has also been shown. However, the coupling of STAT3 serine phosphorylation to PI3K in response to IL-2 has yet to be shown in either T cell lines or primary human T cells. This report shows that the PI3K inhibitors LY294002 and wortmannin block activation of MEK and ERK by IL-2 in primary human T cells. Moreover, these inhibitors significantly reduce IL-2-triggered STAT3 serine phosphorylation without affecting STAT5 serine phosphorylation. Analysis of the effects of these inhibitors on cell cycle progression and apoptosis strongly suggests that PI3K-mediated events, which includes STAT3 activation, are involved in IL-2-mediated cell proliferation but not cell survival. Finally, results presented illustrate that in primary human T cells, activation of Akt is insufficient for IL-2-induced anti-apoptosis. Thus, these results demonstrate that IL-2 stimulates PI3K-dependent events that correlate with cell cycle progression, but not anti-apoptosis, in activated primary human T cells.

Characterization of the dual-specificity phosphatasePYST2 and its transcripts

PYST2 is a member of a structurally homologous subfamily of MAP kinase phosphatases. A computer-based analysis of the PYST2 locus revealed that it harbors two alternative open reading frames promoted by two conserved promoter regions. Using Northern blot analysis and reverse transcription-polymerase chain reaction followed by sequencing and alignment of the products, we confirmed the existence of two mRNAs that were transcribed from this genomic region. Western blot analysis indicated that these transcripts were translated. Functional bioinformatic analysis of both transcripts revealed that exon 2 exists in only one of the PYST2 transcripts, designated PYST2-L, and has the consensus elements of the phosphatase catalytic domain (PCD). We found that the translation from the PYST2-L transcript starts 46 codons upstream from the (already-known) PYST2 5' sequence. Furthermore, the existence of three PYST2-L transcripts was indicated. These transcripts differ only in their 5' untranslated regions (5'UTRs). Unlike PYST2-L, the other mRNA (PYST2-S) is devoid of any known PCD. Analysis of the predicted Pyst2-S protein revealed the presence of the vertebrate metallothionein signature I, the mammalian defensin, and the zinc-containing alcohol dehydrogenase motifs. These motifs might confer on this protein the ability to sense changes in the cellular environment. From these and previous results, we speculate that Pyst2-S may function as a negative regulator of Pyst2-L.

Two separate domains in the golli myelin basic proteins are responsible for nuclear targeting and process extension in transfected cells

The golli products of the myelin basic protein (MBP) gene are expressed in neurons and oligodendrocytes (OLs). In certain neuronal populations, golli proteins undergo translocation between the nucleus and cytoplasm/processes during development. The proteins consist of two domains, a golli domain of 133 amino acids and an MBP domain of variable length. One objective of this study was to identify the sequences responsible for nuclear targeting. Site-directed mutagenesis and deletion analyses were used to generate a series of golli-green fluorescent protein (GFP) DNA constructs that were transfected into OL and neuronal cell lines to follow localization by confocal microscopy. The results indicated that a 36-residue stretch in the MBP domain is essential for nuclear targeting, and the sequence appears to be a nontraditional localization signal motif. The studies also revealed that overexpression of golli proteins could induce dramatic changes in cell morphology. In OL lines, overexpression of intact golli proteins, or golli peptide alone, caused an increase in the length and number of processes, and the elaboration of membrane sheets. In the neuronal lines, there was a dramatic increase in number and length of extensions. The results, consistent with the timing of golli expression in cells during neural development, suggest that golli proteins may be involved in process formation/extension in OLs and neurons during development. These studies have defined two functional domains in the golli protein. Sequences in the MBP domain target the protein into the nucleus and sequences within the golli domain induce process sheet extension in OLs and neurons.

Serial triggering of T cell receptors results in incremental accumulation of signaling intermediates

Triggering of the T cell receptor (TCR) leads to the production of intracellular intermediates with half-life of a few minutes. Signaling kinetics of events originating from serial TCR triggering and its relation to antigen dose was investigated. In this study we documented incremental accumulation of short-lived intermediates of the extracellular signal-regulated kinase (ERK) family, produced during successive TCR triggering. The rate and extent of the intermediate accumulation are essentially determined by the level of TCR engagement and are augmented by costimulation. ERK-1 and ERK-2 exhibit different rates of accumulation following serial receptor triggering. The data indicate that the quantitative kinetic differences in downstream signaling pathways induce qualitatively distinct biological outcomes. Although CD69, interleukin-2, and interferon-gamma (IFN-gamma) were primarily produced by high antigen doses that supported high MAPK phosphorylation, maximal interleukin-5 expression is induced by low and intermediate stimulus doses that do not support significant accumulation of activated ERK. We further demonstrated that the rate of phosphorylated ERK accumulation correlates with the duration of delay between T cell stimulation and the onset of IFN-gamma response, with stronger stimuli giving a more rapid IFN-gamma response. This delay might reflect the time required for the accumulation of signaling intermediates up to a threshold level that is necessary for activation. Thus, the data suggest that signaling events originating from serially triggered TCR are not simply sustained but are gradually accumulated and are integrated in a corresponding response.

Gene expression profiling in chronic myeloid leukemia patients treated with hydroxyurea

Using array technology that allows the simultaneous detection of gene expression of hundreds of genes, four patients with chronic myeloid leukemia (CML) were investigated at diagnosis and after starting administration of hydroxyurea. To detect the gene expression of peripheral blood mononuclears and granulocytes Human Cancer cDNA Array (CLONTECH) with 588 gene probes was used. Gene expression mononuclear and granulocyte profiles of patients at diagnosis were compared with the control profiles. The significant expression changes observed in most patients seemed to be important. Increased expression of c-jun N-terminal kinase 2 (JNK2), integrin alpha E, MMP-8, MMP-9 was detected in both fractions of most patients. In some samples PCNA, HDGF, MAPK p38, CD59 increased expressions were found. Significant down-regulation of expression in patients was detected in genes CDK4 inhibitor A, PURA, notch1 in mononuclears; STAT2, STAT5, RAR-alpha, MCL-1, junB, caspase 4 in granulocytes; CDK6, GADD153, ERBB-3, cadherin 5 in both fractions. Expression profiles detected in patients at diagnosis did not differ markedly from those after one-week treatment with hydroxyurea. Only in a few genes were significant changes after hydroxyurea administration observed and inter-individual expression differences were rather common.

Reprogrammed gene expression in a somatic cell-free extract

We have developed a somatic cell-free system that remodels chromatin and activates gene expression in heterologous differentiated nuclei. Extracts of stimulated human T cells elicit chromatin binding of transcriptional activators of the interleukin-2 (IL-2) gene, anchoring and activity of a chromatin-remodeling complex and hyperacetylation of the IL-2 promoter in purified exogenous resting T-cell nuclei. The normally repressed IL-2 gene is transcribed in nuclei from quiescent human T cells and from various non-T-cell lines. This demonstrates that somatic cell extracts can be used to reprogram gene expression in differentiated nuclei. In vitro reprogramming may be useful for investigating regulation of gene expression and for producing replacement cells for the treatment of a wide variety of diseases.

Occurrence of DNA sequences specifically recognized by drugs in human promoters

Several DNA-binding drugs are being developed to create tailored molecules which can discriminate among the different sequences of the whole genome. By discriminating among specific sites in DNA, these molecules may provide optimal drug therapy. The complete sequencing of the human genome offers a wealth of DNA targets to be analyzed as potential drug-binding sites. To increase our understanding of DNA-drug interactions and their selectivity, we have studied the relative and absolute occurrence of CG-rich sequences, of various lengths, in human gene promoters. In several promoters, including those of oncogenes, cell cycle regulation factors, tumor suppressors and housekeeping genes, the presence of potential binding sites containing CpG steps (in which many drugs are known to intercalate) is variable, but in many cases these sites are not randomly distributed. Sequences 6-7 base pairs in length, like CGCCCG or CGCCCCG, occur only once in some promoters, thus they may be potentially specific therapeutic targets.

Modulation of human lymphocyte proliferative response with aging

Previously, we have demonstrated age-associated alterations in transmembrane signaling. One of the most reproducible alterations found in the immune response with aging is the decrease of lymphocyte proliferation on stimulation with various different mitogens. Here, we confirm that proliferative responses to stimulation with phytohaemagglutin (PHA), recombinant human IL-2, or anti-CD3 monoclonal antibody are all greater in the young (20-25 years) than old (60-87 years) population. We attempted to modulate the proliferative response using various agents acting at different levels of transmembrane signaling (pertussis toxin, cholera toxin, isoproterenol, PMA, Ca ionophore A23187), as well as at the level of the lymphocyte plasma membrane (methyl-beta-cyclodextrin, MBCD), or by using antioxidant vitamins (Vitamin E or C). None of these agents was able to restore effectively the proliferative response of lymphocytes from the aged to the level of young subjects. Even the combination of A23187 and PMA acting directly on calcium metabolism and protein kinase C activity was insufficient to restore the decreased mitogenic capacity of T cells from elderly subjects. Cyclodextrin, which decreases the cholesterol content of the membrane, increased the proliferative response of lymphocytes of elderly subjects, but not to the level of the young. Vitamin E had a very strong inhibitory effect on lymphocyte stimulation in both the age groups, except in combination with MBCD in T cells of the elderly, while Vitamin C had no significant modulatory effect. MAPK ERK and p38 activation was found to be decreased with aging in T cells after anti-CD3 mAb stimulation. Vitamin E but not Vitamin C strongly inhibited MAPK ERK or p38 activation. The direct activation of certain molecules or the modulation of the cholesterol content of the membrane seems to be effective immunomodulatory interventions with aging.

The alternatively spliced domain TnFnIII A1A2 of the extracellular matrix protein tenascin-C suppresses activation-induced T lymphocyte proliferation and cytokine production

Several lines of evidences have suggested that T cell activation could be impaired in the tumor environment, a condition referred to as tumor-induced immunosuppression. We have previously shown that tenascin-C, an extracellular matrix protein highly expressed in the tumor stroma, inhibits T lymphocyte activation in vitro, raising the possibility that this molecule might contribute to tumor-induced immunosuppression in vivo. However, the region of the protein mediating this effect has remained elusive. Here we report the identification of the minimal region of tenascin-C that can inhibit T cell activation. Recombinant fragments corresponding to defined regions of the molecule were tested for their ability to inhibit in vitro activation of human peripheral blood T cells induced by anti-CD3 mAbs in combination with fibronectin or IL-2. A recombinant protein encompassing the alternatively spliced fibronectin type III domains of tenascin-C (TnFnIII A-D) vigorously inhibited both early and late lymphocyte activation events including activation-induced TCR/CD8 down-modulation, cytokine production, and DNA synthesis. In agreement with this, full length recombinant tenascin-C containing the alternatively spliced region suppressed T cell activation, whereas tenascin-C lacking this region did not. Using a series of smaller fragments and deletion mutants issued from this region, we have identified the TnFnIII A1A2 domain as the minimal region suppressing T cell activation. Single TnFnIII A1 or A2 domains were no longer inhibitory, while maximal inhibition required the presence of the TnFnIII A3 domain. Altogether, these data demonstrate that the TnFnIII A1A2 domain mediate the ability of tenascin-C to inhibit in vitro T cell activation and provide insights into the immunosuppressive activity of tenascin-C in vivo.

Signaling alterations in activation-induced nonresponsive CD8 T cells

Costimulation-dependent production and autocrine use of IL-2 by activated CD8 T cells results in initial clonal expansion, but this is transient. The cells quickly become anergic, unable to produce IL-2 in response to Ag and costimulation, irrespective of the form of costimulation. This activation-induced non-responsiveness (AINR) differs from "classical" anergy in that it results despite the cells receiving both signal 1 and signal 2. AINR cells can still proliferate in response to exogenous IL-2, but can no longer produce it. Other TCR-mediated events including cytolytic function and IFN-gamma production are not affected in the AINR state. To characterize the mechanism(s) responsible for lack of IL-2 production in CD8 T cells in the AINR state, microspheres bearing immobilized anti-TCR Abs or peptide-MHC complexes, B7-1, and ICAM-1 were used to provide well-defined stimuli to the cells. Comparison of normal and AINR cells revealed that in AINR cells extracellular signal-regulated kinase (ERK) is upregulated more transiently, Janus kinase activation is substantially reduced, and activation of p38 is eliminated. PMA and ionomycin restored proliferation and IL-2 production in AINR cells, indicating a signaling defect upstream of Ras and protein kinase C. Inhibitors of ERK (PD98059) and of p38 kinase (SB202190) blocked IL-2 mRNA expression and proliferation of both peptide-MHC/B7-1/ICAM-1-stimulated normal cells and PMA/ionomycin-stimulated AINR cells. Together these results demonstrate that activation of at least ERK and p38 is essential for IL-2 production by CD8 T cells and that up-regulation of these mitogen-activated protein kinases, along with Janus kinase, is defective in AINR cells.

Protein phosphorylation in mitochondria from human placenta

The aim of this study was to investigate whether mitochondria from human placenta contain phosphorylated proteins and kinases. Interestingly, the placenta contains two types of mitochondria with different sizes. These are 'heavy' mitochondria which sediment at a much lower g force than 'light' mitochondria. Mitochondria were incubated with [gamma32]P-ATP and labelled proteins analysed by electrophoresis and autoradiography. A major protein band of 20 kDa was detected with minor bands at 22, 38 and 85 kDa. The 20 kDa band was attenuated by 83 per cent by the co-incubation of mitochondria with Herbimycin, a tyrosine kinase inhibitor. A 20 kDa protein was also identified using an anti-tyrosine phosphate antibody and detection of this protein was significantly higher in heavy mitochondria as opposed to light mitochondria. Protein kinase A enzyme activity was also detected in mitochondria at a level not significantly different than that found in whole non-fractionated cells. These data indicate that mitochondria from human placenta contains kinase activity and phosphoproteins. These molecules may have functions in signalling systems in this organelle. Phosphoprotein signalling systems may be differentially modulated in heavy mitochondria as compared with light mitochondria.

Rapid induction of naive T cell apoptosis by ecto-nicotinamide adenine dinucleotide: requirement for mono(ADP-ribosyl)transferase 2 and a downstream effector

Lymphocytes express a number of NAD-metabolizing ectoenzymes, including mono(ADP-ribosyl)transferases (ART) and ADP ribosylcyclases. These enzymes may regulate lymphocyte functions following the release of NAD in injured or inflammatory tissues We report here that extracellular NAD induces apoptosis in BALB/c splenic T cells with an IC(50) of 3-5 microM. Annexin V staining of cells was observed already 10 min after treatment with NAD in the absence of any additional signal. Removal of GPI-anchored cell surface proteins by phosphatidylinositol-specific phospholipase C treatment rendered cells resistant to NAD-mediated apoptosis. RT-PCR analyses revealed that resting BALB/c T cells expressed the genes for GPI-anchored ART2.1 and ART2.2 but not ART1. ART2-specific antisera blocked radiolabeling of cell surface proteins with both [(32)P]NAD and NAD-mediated apoptosis. Further analyses revealed that natural knockout mice for Art2.a (C57BL/6) or Art2.b (NZW) were resistant to NAD-mediated apoptosis. Labeling with [(32)P]NAD revealed strong cell surface ART activity on T cells of C57BL/6 and little if any activity on cells of NZW mice. T cells of (C57BL/6 x NZW)F(1) animals showed strong cell surface ART activity and were very sensitive to NAD-induced apoptosis. As in BALB/c T cells, ART2-specific antisera blocked cell surface ART activity and apoptosis in (C57BL/6 x NZW)F(1) T cells. The fact that T cells of F(1) animals are sensitive to rapid NAD-induced apoptosis suggests that this effect requires the complementation of (at least) two genetic components. We propose that one of these is cell surface ART2.2 activity (defective in the NZW parent), the other a downstream effector of ADP-ribosylation (defective in the C57BL/6 parent).

Inhibition of LPS-induced cytokines by Bcl-xL in a murine macrophage cell line

The antiapoptotic molecule Bcl-xL has been implicated in the differentiation and survival of activated macrophages in inflammatory conditions. In this report, the role of Bcl-xL in LPS-induced cytokine gene expression and secretion was studied. Bcl-xL-transfected RAW 264 macrophages were protected from gliotoxin-induced apoptosis, indicating the presence of functional Bcl-xL. Overexpression of Bcl-xL in this macrophage cell line was also associated with a marked inhibition of LPS-induced TNF-alpha, JE/monocyte chemoattractant protein 1, and macrophage inflammatory protein 2 secretion. Inhibition of LPS-induced cytokine secretion was paralleled by a decrease in levels of steady-state mRNA for the above cytokines and for IL-1beta. Decreased production of TNF-alpha in Bcl-xL transfectants was not due to increased mRNA degradation, as the mRNA half-lives were the same in Bcl-xL transfectants and control macrophages. Although the composition of NF-kappaB complexes detected by EMSA and supershift analysis in nuclear lysates derived from Bcl-xL transfectants and control cells was indistinguishable, LPS-induced inhibitory kappaBalpha degradation, as well as NF-kappaB binding and AP-1 activation, were slightly decreased by ectopic expression of Bcl-xL. More strikingly, LPS-induced phosphorylation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase was strongly repressed by Bcl-xL overexpression, offering a possible mechanism for the inhibition of LPS-induced cytokine production. These data provide the first evidence for a novel role for Bcl-xL as an anti-inflammatory mediator in macrophages.

Negative regulation of the nuclear factor kappa B-inducing kinase by a cis-acting domain

Nuclear factor kappaB (NF-kappaB)-inducing kinase (NIK) participates in the activation of NF-kappaB, a family of eukaryotic transcription factors that mediate cell growth and transformation. NIK activates the IkappaB kinase both in vivo and in vitro, although how the activity of NIK is regulated has remained unclear. Here we show that the N-terminal region of NIK contains a negative-regulatory domain (NRD), which is composed of a basic motif and a proline-rich repeat motif. Deletion of these motifs leads to a marked enhancement of NIK function. We further demonstrate that the N-terminal NRD interacts with the C-terminal region of NIK, thereby inhibiting the binding of NIK to its substrate IkappaB kinase. Consistently, when expressed alone, the NRD potently inhibits NIK-mediated NF-kappaB signaling. These results provide a new insight into the mechanism of NIK regulation.

Gene expressions of lipopolysaccharide receptors, toll-like receptors 2 and 4, are differently regulated in mouse T lymphocytes

Toll-like receptors (TLRs) are a family of mammalian proteins homologous to Drosophila Toll. Human TLR2 was shown to mediate the responsiveness to lipopolysaccharide (LPS). On the other hand, gene mutations of mouse TLR4 (mTLR4) in LPS-hyporesponsive strains have suggested that mTLR4 is essential for LPS-signaling in mice, but the role of mTLR2 has not been explored. This report describes molecular cloning of the mTLR2 cDNA. Overexpression of mTLR2 and mouse CD14 conferred LPS-inducibility of c-Jun N-terminal kinase phosphorylation and nuclear factor-κB activation to COS7 cells, suggesting that mTLR2 is a signaling receptor for LPS. BothmTLR2 and mTLR4 genes were expressed in T cells. Treatment with anti-CD3ɛ, PMA plus ionomycin, or interleukin-2 (IL-2)/IL-15 increased mTLR2 but not mTLR4 messenger RNA (mRNA) in some T cell lines. Specific inhibitors of mitogen-activated extracellular signal-regulated kinase and fusion protein 38 (p38) kinase inhibited mTLR2 mRNA up-regulation by PMA plus ionomycin. This suggests that extracellular signal-regulated kinase and p38 kinase pathways were involved. Additionally, LPS treatment of EL-4 cell line decreasedIL-4 gene expression. Our results indicate that both mTLR2 and mTLR4 are involved in LPS signaling, but their expressions are regulated differently in T cells, and that LPS may directly affect T-cell functions by binding to TLRs.

Janus kinases and signal transducers and activators of transcription: their roles in cytokine signaling, development and immunoregulation

Cytokines play a critical role in the normal development and function of the immune system. On the other hand, many rheumatologic diseases are characterized by poorly controlled responses to or dysregulated production of these mediators. Over the past decade tremendous strides have been made in clarifying how cytokines transmit signals via pathways using the Janus kinase (Jak) protein tyrosine kinases and the Signal transducer and activator of transcription (Stat) proteins. More recently, research has focused on several distinct proteins responsible for inhibiting these pathways. It is hoped that further elucidation of cytokine signaling through these pathways will not only allow for a better comprehension of the etiopathogenesis of rheumatologic illnesses, but may also direct future treatment options.

Production of tumor necrosis factor alpha in human T lymphocytes by staphylococcal enterotoxin B correlates with toxin-induced proliferation and is regulated through protein kinase C

The superantigen staphylococcal enterotoxin B (SEB) simultaneously binds both the major histocompatibility complex (MHC) class II receptor on monocytes and the T-cell receptor (TCR) on T lymphocytes, resulting in a range of cell responses including induction of tumor necrosis factor alpha (TNF-alpha). In this study, we have used mixed cultures of human peripheral blood monocytes and lymphocytes to investigate biochemical events controlling SEB induction of TNF-alpha. TNF-alpha production induced by SEB in mixed cultures is more closely associated with T cells than with monocytes: (i) a TCR-binding-site mutant of SEB (N23F) is less active in TNF-alpha induction than an MHC class II receptor-binding-site mutant (F44R), and (ii) flow cytometric analysis indicated that SEB induced TNF-alpha production in T cells but not in monocytes. Pretreatment of cells with inhibitors of signal transduction pathways was employed to further define events in SEB-induced TNF-alpha production. Neither protein kinase A inhibitors nor two protein tyrosine kinase inhibitors altered SEB-induced TNF-alpha production. In contrast, SEB induced protein kinase C (PKC) translocation, and pretreatment of cultures with inhibitors of PKC blocked TNF-alpha induction. Alteration of levels of diacylglycerol (DAG), an activator of PKC, by treatment with inhibitors of phospholipase C or DAG kinase also altered SEB-induced TNF-alpha production. These data suggest that PKC activation plays a critical role in SEB-induced TNF-alpha production in human T cells.

Mitogen-activated protein kinase mediation of hemolysate-induced contraction in rabbit basilar artery

OBJECT

Mitogen-activated protein kinase (MAPK) is an important signaling factor in vascular proliferation and contraction, which are the two features of cerebral vasospasm that follow subarachnoid hemorrhage. The authors studied the possible involvement of MAPK in hemolysate-induced signal transduction and contraction in rabbit basilar artery (BA).

METHODS

Isometric tension was used to record the contractile response of rabbit BA to hemolysate, and Western blots were obtained using antibodies for MAPK. The following results are reported. 1) Hemolysate produced a concentration-dependent contraction of rabbit BA; however, preincubation of arteries with the MAPK kinase (MEK) inhibitor PD-98059 markedly reduced this contraction. The administration of PD-98059 also relaxed, in a concentration-dependent fashion, the sustained contraction induced by 10% hemolysate. 2) The Janus tyrosine kinase 2 inhibitor AG-490, preincubated with arterial rings, reduced the contractile response to hemolysate but failed to relax the sustained contraction induced by this agent. The Src-tyrosine kinase inhibitor damnacanthal and the phosphatidylinositol 3-kinase inhibitor wortmannin failed to reduce hemolysate-induced contraction. 3) Hemolysate produced a time-dependent elevation of MAPK immunoreactivity as seen on Western blots of rabbit BA. The MAPK was enhanced 1 minute after hemolysate exposure and the effect reached maximum levels at 5 minutes. The immunoreactivity of MAPK decayed slowly over time, but the level of this kinase was still higher than the basal level, even at 2 hours after exposure to hemolysate. Preincubation of arteries with the MEK inhibitor PD-98059 abolished the effect of hemolysate on MAPK immunoreactivity.

CONCLUSIONS

Hemolysate produced contraction of rabbit BA, possibly by activation of MAPK, and therefore MAPK inhibitors may be useful in the treatment of cerebral vasospasm.

Cutting Edge: Negative Regulation of Human T Cell Activation by the Receptor-Type Protein Tyrosine Phosphatase CD148

T cell activation represents a balance between positive and negative signals delivered via distinct cell surface molecules. Many cytoplasmic protein tyrosine phosphatases are involved in regulating cellular responses by antagonizing the action of protein tyrosine kinases. CD148 is a receptor-type protein tyrosine phosphatase expressed by all human mononuclear cells. We have investigated the effect of CD148 on TCR-mediated activation of human T cells. Overexpression of wild-type, but not a phosphatase-deficient, CD148 in Jurkat T cells inhibited TCR-mediated activation, evidenced by reduced expression of the early activation Ag CD69, inhibition of tyrosine phosphorylation of many intracellular proteins including the critical protein tyrosine kinase ZAP-70, and impairment of mitogen-activated protein kinase activation. Taken together, these results suggest that CD148 is an important phosphatase involved in negatively regulating the proximal signaling events during activation of Ag-specific T cells.