Kinases and phosphatases in T-cell activation

Toxicological disruption of signaling homeostasis: tyrosine phosphatases as targets

The protein tyrosine phosphatases (PTPs) consist of a diverse group of enzymes whose activity opposes that of the tyrosine kinases. As such, the PTPs have critical roles in maintaining signaling quiescence in resting cells and in restoring homeostasis by effecting signal termination. Interest in these enzymes has increased in recent years following the discovery that the activity of PTPs is modulated through redox mechanisms during signaling. The molecular features that enable redox regulation of PTPs during physiological signaling also render them highly susceptible to oxidative and electrophilic inactivation by a broad spectrum of structurally disparate xenobiotic compounds. The loss of PTP activity results in a profound disregulation of protein phosphotyrosine metabolism, leading to widespread and persistent activation of signaling cascades in the cell.

In vitro assays for cell death determination

In this paper, we focused on commonly used in vitro assays for estimation of cell death: morphological analyses of cell death, cytotoxic assays based on enzymes activity determination, flow cytometry, and western blot techniques. We discussed advantages and disadvantages of several assays used in the modern research for estimation of cell death.

The role of cytokine in regulation of the natural killer cell activity

Natural killer (NK) cells are characterized by a CD3-CD16+ CD56+ immunophenotype and have a central role in the innate immune system. They are defined by their capacity to kill certain tumor-target cells or virus infected cells without prior sensitization or MHC-restriction. The activity of the NK cells is determined by the balance between activation and inhibitory receptor molecules expressed on the surface of NK cells. However, several cytokines and chemokines can significantly modulate their activity, inducing increase of NK cell activity. Immunomodulation mediated by NK cells is very important mechanism in tumor immunity, as well as in other immunodepressions of the immune system. In this study, we summarize the role of several cytokines, including IFN, IL-1, IL-2, IL-4, IL-7, IL-12 and IL-17, on NK cell function. The NK cells, after activation, depending on cytokine environment, can differentiate into NK1 cells that produce Th1 cytokine type (IFN-?, IL-2, IL-12) or NK2 cells that produce Th2 type cytokines, enhance exocytosis and release of previously formed molecules from NK cells (granzyme, perforin). We also describe that the release of cytokines and mediators show local or distance effects, or induce apoptosis (mostly by secreted TNF-?) after binding appropriated killer cell receptors from TNF receptor superfamily.

T lymphocyte activation signals

Activation of T lymphocytes results in immediate biochemical changes including increases in intracellular calcium levels, activation of protein kinase C (PKC) and changes in tyrosine phosphorylation. In T cells recent studies have indicated that activation of the guanine nucleotide-binding proteins p21ras is mediated by PKC, which suggests that the p21ras proteins may regulate intracellular signalling events downstream of PKC. The p21ras proteins can be activated in T cells by signals generated by triggering of the T cell antigen receptor (TCR), the CD2 antigen and the interleukin 2 receptor. Experiments using a PKC pseudosubstrate inhibitor indicate that PKC does not mediate TCR-induced activation of p21ras. These results imply that an alternative signal transduction pathway not involving PKC can regulate the activity of p21ras proteins in T cells.

New alleles of chicken CD8 alpha and CD3d found in Chinese native and western breeds

Chinese native chicken breeds provide useful resources for the study of genetic diversity. In this study, the alleles of CD8 alpha and CD3d cDNA from Chinese native and introduced western breeds of chicken were analyzed at the sequence level. Six alleles were found, due to 13 amino acid replacements in the extracellular domain of the CD8 alpha sequence. There were four alleles detected in the Chinese strains, and alleles 5 and 6 were identified for the first time. Allele 6 was shared by Langshan, Beijing Fatty and Recessive White Feather chickens. Allele 2, found in the Bigbone strain, was the same as that found in the Leghorn strain H.B15.H7, and allele 3 in the Xianju breed was also the same as in the Leghorn strain H.B15.H12. Two Leghorn lines (RPL line 7 and AY519197) and the Camellia possessed an allele (alleles 1, 4 and 5), respectively, that was not found in the other lines. Nine out of 13 amino acid replacements were situated in the putative major histocompatibility complex (MHC) class I binding CDR1 (positions 30, 33 and 34), CDR2 (positions 58, 62, 63 and 65) and CDR3 (positions 90 and 106). Except for the Xianju breed, the CD8 alpha cDNA of Chinese native chicken breeds shared high homology. Two alleles were found in CD3d. Three additional nucleotides were found at positions 64, 65 and 66 in the newly discovered allele 2. This led to a difference of four amino acids (at residues 22, 23, 24 and 25) in the extracellular domain of CD3d cDNA from the Gushi, Recessive White Feather and ISA chickens compared with these of the White Leghorn and T11.15 (NM_205512). Five hybridoma clones (1C9, 1H5, 4B11, 6G5 and 13C5) against chicken CD8 alpha were generated by DNA immunization. Two monoclonal antibodies (mAbs), 6G5 and 4B11, showed reactivity to the splenocytes from five Chinese native chicken breeds, the Recessive White Feather chicken and the Leghorn (AY519197), while mAbs 1C9, 1H5 and 13C5 showed no reaction with these breeds.

The serine proteinase thrombin promotes migration of human renal carcinoma cells by a PKA-dependent mechanism

In this study, we demonstrated that thrombin activates protein kinase C (PKC), mitogen activated protein kinases (MAP kinases), transcription factor nuclear factor-kappa B (NF-kappa B), and cAMP-dependent protein kinase (PKA) in the human renal carcinoma cell line A-498. In addition, it enhanced the migratory capacity, but had no effect on the proliferation of A-498 cells. The effect of thrombin on migration could be blocked by the PKA inhibitor H-89 but was not influenced by inhibition of PKC, MAP kinases or NF-kappa B. We concluded, that thrombin acts as a regulator on human A-498 renal carcinoma cell migration including PKA.

Phorbol ester-induced disruption of the CD4-Lck complex occurs within a detergent-resistant microdomain of the plasma membrane. Involvement of the translocation of activated protein kinase C isoforms

Recent studies have highlighted the existence of discrete microdomains at the cell surface that are distinct from caveolae. The function of these microdomains remains unknown. However, recent evidence suggests that they may participate in a subset of transmembrane signaling events. In hematopoietic cells, these low density Triton-insoluble (LDTI) microdomains (also called caveolae-related domains) are dramatically enriched in signaling molecules, such as cell surface receptors (CD4 and CD55), Src family tyrosine kinases (Lyn, Lck, Hck, and Fyn), heterotrimeric G proteins, and gangliosides (GM1 and GM3). Human T lymphocytes have become a well established model system for studying the process of phorbol ester-induced down-regulation of CD4. Here, we present evidence that phorbol 12-myristate 13-acetate (PMA)-induced down-regulation of the cell surface pool of CD4 occurs within the LDTI microdomains of T cells. Localization of CD4 in LDTI microdomains was confirmed by immunoelectron microscopy. PMA-induced disruption of the CD4-Lck complex was rapid (within 5 min), and this disruption occurred within LDTI microdomains. Because PMA is an activator of protein kinase C (PKC), we next evaluated the possible roles of different PKC isoforms in this process. Our results indicate that PMA induced the rapid translocation of cytosolic PKCs to LDTI microdomains. We identified PKCalpha as the major isoform involved in this translocation event. Taken together, our results support the hypothesis that LDTI microdomains represent a functionally important plasma membrane compartment in T cells.

Human CD5 Signaling and Constitutive Phosphorylation of C-Terminal Serine Residues by Casein Kinase II

CD5 is a lymphocyte surface glycoprotein with a long cytoplasmic domain suitable for phosphorylation and signal transduction, which is involved in the modulation of Ag-specific receptor-mediated activation and differentiation signals. In this study, we use Jurkat T cell transfectants of CD5 cytoplasmic tail mutants to reveal phosphorylation sites relevant to signal transduction. Our results show that casein kinase II (CKII) is responsible for the constitutive phosphorylation of CD5 molecules at a cluster of three serine residues located at the extreme C terminus (S458, S459, and S461). Furthermore, the yeast two-hybrid system demonstrates the specific association between the C-terminal regions of the CD5 cytoplasmic tail and the regulatory β subunit of CKII. We demonstrate that CKII associates with and phosphorylates the C-terminal region of CD5, a conserved domain known to be relevant for the generation of second lipid messengers, and thereby enables at least one component of its signaling funcion.

Proteinase-activated receptor-2-mediated signaling and inhibition of DNA synthesis in human pancreatic cancer cells

CONCLUSION

Proteinase-activated receptor-2 (PAR-2)-mediated effects contribute to the intracellular signaling network in pancreatic tumor cells. A role of PAR-2 as negative regulator in human pancreatic tumor growth might be implied.

BACKGROUND

Using the human pancreatic tumor cell line MIA PaCa-2, we evaluated cellular effects of trypsin and the PAR-2-activating peptide SLIGRL on [Ca2+]i mobilization, Ins(1,4,5)P3 level, and protein kinase (PKC) activation. Furthermore, PAR-2 involvement in the regulation of cell proliferation has been estimated by measurement of [3H]thymidine incorporation in MIA PaCa-2 cells.

RESULTS

Trypsin and the PAR-2 synthetic peptide agonist SLIGRL induced [Ca2+]i mobilization, transient increase in inositol (1,4,5) triphosphate level, and PKC translocation in MIA PaCa-2 cells. In addition, SLIGRL induced a decrease in DNA synthesis in MIA PaCa-2 cells.

Protein kinase C is involved in cholecystokinin octapeptide-induced proliferative action in rat glioma C6 cells

Chotecystoknin octapeptide (CCK-8) has been shown to stimulate DNA synthesis in rat glioma C6 cells by activation of CCKB type receptors. However, the signalling pathways contributing to this proliferative action in C6 cells have not been investigated thus far. This study demonstrated that stimulation of rat glioma C6 cells with CCK-8S resulted in activation of protein kinase C isozymes betaI, betaII, gamma and zeta. The participation of protein kinase C in the CCK-8S-induced effect on C6 cell growth was demonstrated by measurement of [3H]thymidine incorporation and estimation of cell number. The data indicate that CCK-8S stimulates growth in rat glioma C6 cells by a protein kinase C-dependent mechanism.

Cholecystokinin B-type receptor signaling is involved in human pancreatic cancer cell growth

Cholecystokinin (CCK) is known to stimulate pancreatic cancer cell growth, but no detailed CCK receptor subtype characterization and investigation of CCK receptor-mediated cellular responses in human pancreatic cancer cells have been reported thus far. In this study, CCK binding sites were identified in human pancreatic cancer cells (MIA-PaCa-2) using radioligand binding studies. Pharmacological characterization demonstrated a single class of high-affinity CCK sites on MIA-PaCa-2 cells (326 +/- 18 pM, receptor density 16.9 +/- 2.3 fmol/mg protein). These CCK binding sites displayed a typical CCKB binding profile as shown in competition studies by using different CCK-related compounds and non-peptide CCK antagonists discriminating between CCKA and CCKB sites. CCKB receptor-connected effector systems have been characterized in MIA-PaCA-2 cells, and their involvement in CCK-8S-induced proliferative effects on MIA-PaCa-2 cells has been demonstrated.

Thrombin receptor activation results in calcium signaling and protein kinase C-dependent stimulation of DNA synthesis in HEp-2g laryngeal carcinoma cells

BACKGROUND

Recently, the expression of the "tethered ligand" thrombin receptor in carcinosarcoma and melanoma cells has been shown. However, the role of the thrombin receptor in tumor cell metabolism still is undefined.

METHODS

In this article, the "tethered ligand" thrombin receptor was identified on human epidermoid carcinoma cells (HEp-2g cell line) by using immunofluorescence studies with a monoclonal antithrombin receptor antibody and radioligand binding. Furthermore, the effects of alpha-thrombin and thrombin receptor activating peptides (TRAP)-6 on calcium mobilization, protein kinase C (PKC) translocation, and DNA synthesis were estimated.

RESULTS

Pharmacologic characterization using [3H]TRAP-6 as a radioligand demonstrated a single class of high affinity binding sites (dissociation constant [KD] = 7.2 +/- 2.2 x 10(-7) M) and a binding capacity of 27 +/- 3.4 fmol/mg protein. The function of these binding sites was demonstrated by alpha-thrombin- and TRAP-6-induced mobilization of free intracellular calcium, and translocation of PKC from cytosol to cell membrane. Moreover, alpha-thrombin and TRAP-6 induced an increase in [3H]thymidine incorporation in HEp-2g cells that could be blocked by the PKC inhibitor bisindolylmaleimide.

CONCLUSIONS

To the authors' knowledge, the results of this study demonstrate for the first time functional thrombin receptors in epidermoid carcinoma cells. The thrombin receptor appears to be involved in growth regulation in HEp-2g cells by a PKC-dependent mechanism.

A primatized MAb to human CD4 causes receptor modulation, without marked reduction in CD4+ T cells in chimpanzees: in vitro and in vivo characterization of a MAb (IDEC-CE9.1) to human CD4

A Primatized anti-CD4 monoclonal antibody (MAb), CE9.1, with V-domain from cynomolgus macaque (showing 92% homology with human consensus sequence V-domains), and a human IgG1 constant region, was characterized in vitro and in vivo in chimpanzees. This MAb binds human CD4 with Kd of 1.0 nM and was also able to bind to human IgG Fc receptors (Fc gamma R). However, despite being of the IgG1 subclass, CE9.1 did not bind to complement component C1q, nor did it mediate complement-dependent cytotoxicity. Examination of T cells from a number of species showed restricted reactivity for CE9.1, recognizing only human and chimpanzee CD4. In both human and chimpanzee MLRs, it had an IC50 of about 10.0 ng/mL. Therefore, a chimpanzee in vivo model was used to characterize CE9.1, CE9.1 caused transient decrease in the number of lymphocytes bearing the CD4 receptor starting at doses of 0.3 mg/kg in an in vivo dose ranging study in one chimpanzee. This effect was reversed within approximately 7 days. In a multiple high-dose study in which 10.0 mg/kg of CE9.1 was administered at intervals of 1-3 months, there was a dramatic loss of CD4 marker with a reciprocal increase in the number of CD3+ CD8- CD4- cells. The CD4 receptor was totally undetectable on these lymphocytes for 1-2 weeks, with a gradual, but complete, reversal within 4 weeks. We interpret these observations as receptor modulation because, although there was apparent loss of CD4+ lymphocytes, an equivalent number of CD3+CD8- T lymphocytes were present in circulation in all four chimpanzees treated with 10.0 mg/kg CE9.1. Even at this high dose, only limited reduction of CD4+ T lymphocytes was observed in these animals. These observations are in sharp contrast to what has been reported in rodents or in human clinical studies using other IgG1 mAbs to human CD4. CD8 counts, although variable, remained unaffected by CE9.1 treatment. No adverse events were observed following administration of CE9.1 to chimpanzees, and there was no detectable host immune responses to the Primatized MAb.

Association of ERK2 mitogen-activated protein kinase with human immunodeficiency virus particles

Here we report the presence of a protein kinase activity associated with human immunodeficiency virus type 1 (HIV-1) particles. We observed phosphorylation of five major proteins by the endogenous protein kinase activity. Phosphoamino acid analysis revealed phosphorylated serine and threonine residues. In addition, we observed autophosphorylation of two proteins in the presence of gamma-ATP in an in-gel phosphorylation assay. These two proteins are not linked by a disulfide bond, suggesting that two different protein kinases are associated with HIV-1 virions. Our results indicate the presence of ERK2 mitogen-activated protein kinase and of a 53,000-molecular-weight protein kinase associated with virions. Moreover, the use of different HIV strains derived from T cells and promonocytic cells, as well as the use of human T-cell leukemia virus type 1 particles, demonstrates that ERK2 is strongly associated with retrovirus particles in a cell-independent manner. Exogenous substrates, such as histone proteins, and a viral substrate, such as Gag protein, are phosphorylated by virus-associated protein kinases.

Protein-tyrosine phosphatase activity regulates osteoclast formation and function: inhibition by alendronate

Alendronate (ALN), an aminobisphosphonate used in the treatment of osteoporosis, is a potent inhibitor of bone resorption. Its molecular target is still unknown. This study examines the effects of ALN on the activity of osteoclast protein-tyrosine phosphatase (PTP; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48), called PTPepsilon. Using osteoclast-like cells generated by coculturing mouse bone marrow cells with mouse calvaria osteoblasts, we found by molecular cloning and RNA blot hybridization that PTPepsilon is highly expressed in osteoclastic cells. A purified fusion protein of PTPepsilon expressed in bacteria was inhibited by ALN with an IC50 of 2 microM. Other PTP inhibitors--orthovanadate and phenylarsine oxide (PAO)-inhibited PTPepsilon with IC50 values of 0.3 microM and 18 microM, respectively. ALN and another bisphosphonate, etidronate, also inhibited the activities of other bacterially expressed PTPs such as PTPsigma and CD45 (also called leukocyte common antigen). The PTP inhibitors ALN, orthovanadate, and PAO suppressed in vitro formation of multinucleated osteoclasts from osteoclast precursors and in vitro bone resorption by isolated rat osteoclasts (pit formation) with estimated IC50 values of 10 microM, 3 microM, and 0.05 microM, respectively. These findings suggest that tyrosine phosphatase activity plays an important role in osteoclast formation and function and is a putative molecular target of bisphosphonate action.

Human protein tyrosine phosphatase-sigma: alternative splicing and inhibition by bisphosphonates

Two forms of the transmembrane human protein tyrosine phosphatase (PTP sigma), generated by alternative splicing, were identified by cDNA cloning and Northern hybridization with selective cDNA probes. The larger form of PTP sigma is expressed in various human tissues, human osteosarcoma, and rat tibia. The hPTP sigma cDNA codes for a protein of 1911 amino acid residues and is composed of a cytoplasmic region with two PTP domains and an extracellular region that can be organized into three tandem repeats of immunoglobulin-like domains and eight tandem repeats of fibronectin type III-like domains. In the brain, the major transcript of PTP sigma is an alternatively spliced mRNA, in which the coding region for the fibronectin type III-like domains number four to seven are spliced out, thus coding for a protein of 1502 amino acid residues similar to the rat PTP sigma and rat PTP-NE3. Using in situ hybridization, we assigned hPTP sigma to chromosome 6, arm 6q and band 6q15. The bacterial-expressed hPTP sigma exhibits PTPase activity that was inhibited by orthovanadate (IC50 = 0.02 microM) and by two bisphosphonates used for the treatment of bone diseases, alendronate (ALN) (IC50 = 0.5 microM) and etidronate (IC50 = 0.2 microM). In quiescent calvaria osteoblasts, micromolar concentrations of vanadate, ALN and etidronate stimulate cellular proliferation. These findings show tissue-specific alternative splicing of PTP sigma and suggest that PTPs are putative targets of bisphosphonate action.

Characterization of a novel co-stimulatory molecule: a 155-160kD B cell surface protein provides accessory help to CD4+ T cells to proliferate and differentiate

Optimal activation of T cells to clonally expand requires at least two distinct biological signals; one is generated by the interaction of the T cell receptor (TcR) with peptides bound to MHC molecules. The other signal(s) is (are) generated by a functionally defined event called the co-stimulatory pathway. We have characterized the co-stimulatory property of a murine B lymphocyte membrane protein (155-160 kD) on resting CD4+ T cells. The study involved the isolation of a 155-160 kD protein (B1) from the membranes of LPS-stimulated B cells. When reconstituted into lipid vesicles, B1 exerted a dose-dependent proliferative response to CD4+ T cells, resulting in the predominant secretion of IL-4 and IL-5 after cross-linking receptors with anti-CD3 mAb. This protein is a phosphoglycoprotein which gives a single spot on two-dimensional gel electrophoresis under reducing conditions and as a distinct peak on reverse phase-HPLC. The B1 binds to the T cell surface as is demonstrated by electron microscopic autoradiography and scanning electron microscopy, as well as competitive binding assays. It does not cross-react with antibodies directed against ICAM-1, LFA-1 alpha, B7, HSA and VCAM-1, suggesting the novelty of the protein. Activation of CD4+ T cells with B1 in the presence of anti-CD3 resulted in the translocation of protein kinase C (PKC). The B1 is barely detectable on the surface of resting B cells and digestion of this protein with V8 protease and peptide N-glycosidase F resulted in distinct protein bands on an autoradiogram.

Bioluminescent assay for human lymphocyte blast transformation

One of the basic tests of in vitro evaluation of immune cell functional activity is a proliferative response of lymphocytes on the action of external stimuli such as mitogenic lectines, antigens, etc. We compared two methods used to assess the lymphocyte functional status. (1) [3H]thymidine incorporation and (2) bioluminescence for determination of intracellular ATP in blast cells. Comparison has been done for healthy donors and patients with proven low immunological status. The proposed bioluminescent method for evaluation of the proliferative response was shown to be sensitive enough for diagnostic purposes. This method allows one to process a large number of samples at the same time and correlates highly with the radionuclide test use hazardous radioactive materials.

Partial characterization of a 52 kDa CsA/FK506/rapamycin binding protein

Identification and characterization of the cellular proteins that specifically bind to the immunosuppressive drugs, cyclosporine (CsA), FK506, and rapamycin is necessary to understand their mechanism of action. We have isolated and partially characterized a 52 kDa binding protein (BP) from calf thymus. Using 12 peptide substrates we observed very low or no cis-trans peptidyl prolyl isomerase activity. We further tested the protein for catalytic activity including kinase activity, phosphatase activity, protein kinase C regulation, and LCK tyrosine kinase regulation. The 52 kDa BP was capable of blocking the cyclic AMP dependent, protein kinase mediated, phosphorylation of histones and casein. The protein did not demonstrate kinase activity, nor did it affect the activity of protein kinase C or LCK tyrosine kinase. Microsequencing of the 52 kDa BP was performed. A comparison of known sequences indicated that the protein is unique and has not been previously characterized.

Cyclic AMP sensitive signalling by the CD28 marker requires concomitant stimulation by the T-cell antigen receptor (TCR/CD3) complex

We have previously demonstrated that activation of cAMP-dependent protein kinase (cAK) type I (cAKI, RI alpha 2-C beta 2) mediates the inhibitory effects of cAMP on T-cell replication induced through the TCR/CD3 complex. In the present study we have investigated the effect of cAMP on T-cell DNA synthesis, tyrosine phosphorylation of a 100 kDa protein (pp100) and IL2 mRNA expression, induced through stimulation of the TCR/CD3- and/or the CD28 molecules. Our results demonstrate that tyrosine phosphorylation of pp100 stimulated by anti-CD3 is inhibited by cAMP both in the presence and absence of the phorbol ester PMA, and reflects the changes seen in IL2 mRNA expression and T-cell replication. Combined stimulation with anti-CD3 and anti-CD28, which gives a synergistic response in T-cell replication, gave pp100 phosphorylation and IL2 mRNA expression sensitive to cAMP-dependent inhibition. When PMA was added in addition to anti-CD3 and anti-CD28, the inhibitory effect of cAMP on both T-cell replication and pp100 phosphorylation was completely abolished. The fact that pp100 phosphorylation in response to TCR/CD3-, CD28- and PMA stimulation and cAMP mediated inhibition are identical to the effects of the same stimuli on T-cell proliferation, makes this protein an interesting candidate in downstream signalling from these receptors. In addition, our results are compatible with a model where cAMP, through activation of cAKI, eliminates both the PTK and PKC activating capability of the T-cell receptor at a site(s) proximal to PKC activation. Furthermore, the CD28 molecule which activates PTKs, enters the PTK cascade at a point distal to the target(s) for cAKI action. Therefore, during CD28 signalling PKC activation can be achieved either by TCR/CD3 stimulation (inhibited by cAMP), or directly by PMA (not inhibited by cAMP).

Partial cloning and sequencing of the gene encoding the porcine T-cell receptor delta-chain constant region

The polymerase chain reaction (PCR) was utilized to clone the pig T-cell receptor (TCR) delta-chain constant region-encoding gene (C delta). A cDNA was generated from total RNA preparations of normal pig peripheral blood lymphocytes (PBLs) and a miniature pig peripheral blood cell line (PBLCL 62.G4). The cDNA was used to amplify the porcine TCR C delta gene by PCR using primers chosen by comparing other known C delta sequences for sequence identity. Clones were sequenced and used to determine the primary structure of the porcine TCR C delta chain. A comparison of the nucleotide and deduced amino acid (aa) sequences with the known human, mouse, sheep and cattle sequences revealed that the primary structure of the pig TCR C delta chain has been highly conserved. The immunoglobulin (Ig) domain has two conserved Cys residues and contains a high degree of sequence identity, whereas the hinge region is marked by a high level of diversity. The transmembrane and cytoplasmic regions are also highly conserved, including the presence of the two basic aa, Arg and Lys, in the transmembrane domain. Southern blot analysis has confirmed the presence of one TCR C delta gene in the porcine genome, consistent with similar findings in other species. Thus, the successful cloning and sequencing of the porcine TCR C delta gene should facilitate our understanding of the role of gamma delta T-lymphocytes in the swine immune system.

Effect of deoxyribonucleosides on the hypersensitivity of human peripheral blood lymphocytes to UV-B and UV-C irradiation

We have previously shown that non-cycling (unstimulated) human lymphocytes from normal donors show extreme hypersensitivity to UV-B irradiation, and are killed by an excisable lesion which is not a pyrimidine dimer or 6-4 photoproduct. In this paper we show that addition of the 4 deoxyribonucleosides to the medium, each at 10(-5) M, substantially increased the survival of non-cycling normal human T-lymphocytes following UV-B irradiation and substantially reduced the frequency of excision-related strand breaks in human mononuclear cells. Addition of ribonucleosides to the medium did not enhance excision-break rejoining. The survival of fibroblasts, of cycling T-lymphocytes and of unstimulated xeroderma pigmentosum T-lymphocytes was not enhanced by deoxyribonucleosides. This suggests that the hypersensitivity is due to reduced rejoining of excision breaks as a consequence of low intracellular deoxyribonucleotide pools and that it can be redressed by supplementation of the medium with deoxyribonucleosides or upregulation of ribonucleotide reductase following mitogen stimulation. We suggest that UV-B forms an additional DNA lesion which is not a pyrimidine dimer or 6-4 photoproduct, which is relatively common, and at which incision is particularly efficient. In fibroblasts, repair of this lesion is completed with high efficiency, whereas in normal unstimulated T-lymphocytes, rapid incision exacerbates the effects of the reduced rate of strand rejoining and leads to cell death.

Signal transduction of interleukin 2 in human natural killer cells: involvement of the p56lck tyrosine kinase

Despite numerous reports, the role of the protein tyrosine kinase p56lck in IL-2 signal transduction has remained controversial. We show here, using IL-2-dependent human natural killer cell lines, that p56lck is regulated by IL-2 in two different ways: (1) IL-2 induces a rapid increase of p56lck kinase activity as assessed in vitro; and (2) following IL-2 stimulation, p56lck undergoes phosphorylation on serine residues that is reflected by a modification of its electrophoretic mobility in SDS-PAGE. Furthermore, dose response experiments, and blocking studies performed with anti-IL-2R alpha antibodies, indicated that binding of IL-2 to the IL-2R beta chain was sufficient to produce these modifications of p56lck. In contrast, activation of the CD2 pathway stimulated the kinase activity of p56lck, but did not induce a significant shift in NK cells, as opposed to T lymphocytes. Western blot analyses, and immunoprecipitations of cell lysates from 32P-preloaded NK cells demonstrated that seven major proteins are tyrosine phosphorylated in response to IL-2. These phosphoproteins, with apparent molecular weights of 190, 150, 120, 110, 85, 65 and 56, which may not all be p56lck substrates, undergo phosphorylation and dephosphorylation with different kinetics. Furthermore, pp120 was identified as rasGAP, by Western blot and immunoprecipitation experiments. rasGAP and some of its co-precipitating molecules become phosphorylated in response to IL-2, presumably by p56lck, which would thus provide a link between IL-2R and downstream events critical for NK cell proliferation and function.

Ala-->Gly mutation in the putative catalytic loop confers temperature sensitivity on Ros, insulin receptor, and insulin-like growth factor I receptor protein-tyrosine kinases

Temperature-sensitive mutations in the avian sarcoma virus UR2 oncogene ros, encoding a receptor protein-tyrosine kinase (PTK), were identified. The Ala385-->Gly change mapping within the highly conserved RDLAARN motif in the Ros kinase domain was responsible for the temperature-sensitive phenotype. Based on the sequence homology of all known protein kinases and the crystalline structure of the cAMP-dependent protein kinase, this conserved region probably represents the PTK catalytic loop. The same mutation when introduced into the human insulin and insulin-like growth factor I receptors made these PTKs temperature sensitive in both biological function and kinase activity. Our results support the presumed catalytic role of this highly conserved sequence in PTKs. Due to its highly conserved nature, we predict that the same mutation would probably confer temperature sensitivity on other PTKs.

CD45-mediated regulation of LFA1 function in human natural killer cells. Anti-CD45 monoclonal antibodies inhibit the calcium mobilization induced via LFA1 molecules

The TA218 and T205 monoclonal antibodies (mAb) were selected on the basis of their ability to inhibit the non-major histocompatibility complex-restricted lysis of the murine mastocytoma P815 cell line mediated by CD3-CD16+ natural killer (NK) cells. Both mAb were found to react with CD45 molecules, as demonstrated by immunoprecipitation after surface iodination and western blot analysis. A panel of tumor target cells susceptible to lysis by polyclonal or clonal CD3-CD16+ NK cells was used to study the mAb-mediated inhibitory effect. The inhibition of cytolysis mediated by TA218 and T205 mAb was found to consistently parallel the inhibition mediated (with the same tumor target cells) by the anti-LFA1 alpha mAb TS.1.22 or by the anti-LFA1 beta mAb TS.1.18. However, different from the anti-LFA1 mAb, T205 or TA218 mAb did not inhibit the binding of activated CD3-CD16+ effector NK cells to the same tumor target cells. This finding supported the concept that the anti-CD45 mAb-mediated inhibition could occur at a post-binding stage. In polyclonal or clonal CD3-CD16+ NK cells T205 or TA218 mAb were found to reduce by 50-70% the intracellular Ca++ ([Ca++]i) mobilization induced by anti-LFA1 alpha or anti-LFA1 beta mAb. On the other hand, TA218 and T205 mAb did not inhibit the Ca++ mobilization induced by anti-CD16 mAb or phytohemagglutinin, thus suggesting that, in NK cells, CD45 molecules may exert a selective inhibitory effect on the signal transduction mediated by LFA1 molecules. In line with this hypothesis, the cytolytic activity of human NK clones was triggered in the presence of the hybridoma cells secreting either anti-CD16 or anti-LFA1 alpha mAb (as "triggering targets"). This effect of anti-LFA1 alpha, but not of anti-CD16 hybridoma was susceptible to inhibition by the anti-CD45 mAb T205 or TA218. Further, experiments on cloned NK cells indicated that T205 or TA218 mAb induced a strong decrease in the constitutive phosphorylation of the LFA1 alpha chain (but not of HLA class I antigens). Taken together, these studies suggest that in human NK lymphocytes, CD45 molecule may regulate both the activation state and the function of the LFA1 molecule.

Selective activation of resting human gamma delta T lymphocytes by interleukin-2

In rheumatoid arthritis and other inflammatory diseases we and others have found that gamma delta T cells express activation antigens, suggesting that they are involved in the pathogenesis of these disorders. In this study we have stimulated peripheral blood mononuclear cells from normal donors with recombinant interleukin-2 (rIL-2) to see whether such a stimulus alone could activate gamma delta T cells. Short-term exposure (24-96 h) to rIL-2 selectively stimulated the gamma delta but not the alpha beta T cells to express activation antigens (CD69, CD25 and HLA-DR). Long-term culture (2 weeks) in rIL-2-containing medium caused a selective increase in the proportion of the gamma delta T cells and a corresponding reduction of the fraction of alpha beta T cells. Limiting dilution analysis revealed that approximately 1/60 of the gamma delta T cells responded to IL-2 in contrast to only 1/250 of the alpha beta T cells. Comparison of the expression of the IL-2 receptor (IL-2R) alpha and beta chains showed that there was a similar expression of the alpha chain on gamma delta and alpha beta T cells whereas the relative density of the beta chain was more than twice as high on gamma delta T cells. Both the IL-2-induced proliferation of gamma delta T cells and the expression of activation antigens on these cells could be inhibited by an anti-IL-2R beta monoclonal antibody (mAb) but not by an anti-IL-2R alpha mAb. Expression of CD69 on gamma delta T cells was dependent neither on the presence of B cells, monocytes, nor alpha beta T cells. Finally, we found that the IL-2-induced expression of CD69 was inhibited by activation of cAMP-dependent protein kinase and by inhibition of the Src-family of the tyrosine protein kinase, but not by inhibition of protein kinase C or by activation of the CD45 associated tyrosine phosphatase. The ability of gamma delta T cells to be activated by IL-2 is a feature which they have in common with natural killer cells. Moreover, it may be possible that the expression of activation antigens on gamma delta T cells in inflammatory diseases is an epiphenomenon secondary to IL-2 produced by activated alpha beta T cells.

Isolation of interleukin 2-induced immediate-early genes

Clonal expansion of antigen-reactive T lymphocytes is driven by the lymphokine interleukin 2 (IL-2). To further elucidate the mechanisms of IL-2 action, we have utilized a differential hybridization procedure to clone IL-2-induced immediate-early genes from an IL-2-stimulated human T-cell cDNA library. To increase the frequency of IL-2-induced transcripts represented in the library, the protein synthesis inhibitor cycloheximide was included during the 2-hr IL-2 stimulation to superinduce gene expression, and the uridine analogue 4-thiouridine was utilized to enable selective purification of newly synthesized transcripts. From the enriched library, we have isolated eight IL-2-induced genes, six of which represent previously unrecognized human sequences. Northern blot analysis revealed that the induction of seven of the genes is specific to the IL-2-mediated G1 "progression" phase of the cell cycle, in that only one gene is also induced during the T-cell receptor-triggered G0-G1 "competence" phase. These results indicate that the effects of IL-2 are mediated by the specific induction of a number of immediate-early genes and provide a means with which to further delineate the mechanisms whereby IL-2 stimulates T-lymphocyte proliferation and differentiation. The methods described in this report should also be of general utility in the dissection of the signaling pathways activated by diverse cytokine receptors.

Neuroimmune modulation: signal transduction and catecholamines

In recent years, much interest has centered on the commonalities and bi-directional interactions between the nervous system and the immune system. This review focuses on mechanisms through which, catecholamines, a class of neuro-endocrine molecules, modulate immune functions. Catecholamines can be immune suppressive and inhibit lymphocyte activation of both T and B cells as well as the generation of immune-mediated anti-tumor responses. Some of these catecholamine-regulated activities appear to be modulated through the second messenger, cyclic AMP, whereas others appear to be catecholamine-dependent but cyclic AMP independent. Further delineation of the interacting ligand-receptor complexes, populations of responding cells and signal transduction mechanisms leading to the activation of specifically involved genes and gene products, will lead to enhanced understanding of the integratory functions of the nervous system in immune responses, the biology of stress, the role of stress-associated molecular mechanisms in perturbations of physiological homeostasis and the development of a new biological psychiatry with accompanying rational therapeutic modalities.

CD3 and CD2 antigen-mediated CD3 gamma-chain phosphorylation in permeabilized human T cells. Regulation by cytosolic phosphatases

The role of cytosolic and membrane-associated phosphatases in regulating dephosphorylation of the CD3 antigen gamma-chain has been investigated using streptolysin-O-permeabilized T lymphoblasts and Jurkat T leukaemia cells. Permeabilization of T cells caused a rapid extrusion of cytosolic type 2A phosphatases, but a membrane-associated phosphorylase phosphatase activity remained inside the cells. This activity had the properties characteristic of type 2A phosphatases, being resistant to inhibition by type 1 phosphatase inhibitors, though it was inhibited in a time-dependent manner by ATP or by non-hydrolysable ATP analogues, but not by GTP, CTP, ITP or PPi. The membrane-associated type 2A phosphatase in permeabilized cells did not dephosphorylate the CD3 antigen gamma-chain, suggesting that cytosolic phosphatases dephosphorylate the gamma-chain in situ. Cross-linking the CD2 and CD3 antigens with a bivalent monoclonal antibody in the absence of cytosolic phosphatases induced marked phosphorylation of the CD3 gamma-chain, immunoprecipitated using a novel gamma-chain peptide analogue directed antiserum (TG1). Phosphorylation was inhibited by a protein kinase C (PKC) pseudosubstrate inhibitor, indicating that CD2/CD3-induced gamma-chain phosphorylation is a PKC-mediated event. Activation of T cells either with phorbol 12,13-dibutyrate or by CD2-CD3 cross-linking caused [32P]Pi incorporation into the same gamma-chain Ser residues. The site-mapping data suggested that PKC in situ may incorporate phosphate at the CD3 gamma-chain Ser-123 and Ser-126 residues, but that phosphate is rapidly lost from Ser-123 by cytosolic phosphatase action. Our findings underline the importance of the dual actions of kinases and phosphatases as potential regulators of T cell antigen-receptor complex function.

Mechanisms of induction of primary virus-specific cytotoxic T lymphocyte responses

We have investigated the ability of various antigen-presenting cell (APC) types to induce primary anti-viral cytotoxic T lymphocyte (CTL) responses by single in vitro stimulation. Of these APC types, only dendritic cells (DC) and RMA-S lymphoma cells could induce primary CTL responses, but by divergent mechanisms. DC were capable of generating primary virus-specific CTL, either by presenting viral peptide or processed infectious virus. In contrast, RMA-S cells could not present endogenous antigen, e.g. after virus infection, but this cell line very efficiently presented exogenous viral peptides to induce primary virus-specific CTL in vitro. Spleen cells, lipopolysaccharide-induced B cell blasts or the non-mutated RMA cells did not have the ability to trigger unprimed T cells by single in vitro stimulation. We have investigated several characteristics important for primary CTL response induction by DC and RMA-S cells (summarized in Fig. 6). Primary CTL response induction by DC or RMA-S cells was blocked by anti-LFA-1 or anti-CD8 monoclonal antibodies (mAb). DC rapidly aggregated with unprimed T cells, which was independent of LFA-1 and CD8 molecules. RMA-S cells did not form conjugates with unprimed T cells. Despite their abundant major histocompatibility complex (MHC) class I cell-surface expression, DC did not bind much exogenously added viral peptide. In contrast, the MHC class I molecules on RMA-S cells bound a large quantity of exogenously administered peptide. Powerful adhesion by DC and high expression of relevant MHC/peptide complexes on RMA-S cells are important features in the initial contact with unprimed T lymphocytes. In a later stage of contact, both DC and RMA-S cells activate LFA-1 (and CD8) molecules at the T cell surface to strengthen and maintain the contact between T cell and APC.

The effect of disodium cromoglycate on in vitro proliferation of peripheral blood mononuclear cells from allergic and healthy donors

The effect of disodium cromoglycate on in vitro proliferative responses of peripheral blood mononuclear cells from healthy individuals, allergic patients with moderate serum IgE and patients with atopic dermatitis and high levels of serum IgE was investigated. Peripheral blood mononuclear cells were stimulated with mitogens (phytohaemagglutinin, Concanavalin A), recombinant interleukin-2, calcium ionophore + phorbol 12-myristate 13-acetate, purified protein derivative of tuberculin and allergens. It was possible to induce in vitro specific, allergen-triggered responses only in allergic individuals with moderate serum IgE and not in individuals with atopic dermatitis and high serum IgE. Generally, whenever the stimulatory signal(s) caused a significant proliferative response, disodium cromoglycate inhibited the proliferation. This inhibition was seen for all activation agents and for both healthy and allergic individuals. By contrast, for certain non- or low-responders (both healthy and allergic individuals) disodium cromoglycate seemed to amplify the proliferation to various activation signals. Only non- or low-responder cells derived from atopic dermatitis patients showed a biphasic kinetic response pattern when stimulated with the drug in combination with recombinant interleukin-2, recombinant interleukin-2 + ionophore or specific allergens.

Involvement of a protein kinase C and protein phosphatases in adhesion of CD4+ T cells to and detachment from extracellular matrix proteins

For immune surveillance and function to be effective, T lymphocytes constantly recirculate via lymph and blood between lymphoid organs and body tissues. To enable efficient cell movement and migration, cell adhesion to components of the basement membrane and the extracellular matrix (ECM) must be a rapid and transitory process. Whether phosphorylation and dephosphorylation of cellular proteins are involved in this phenomena was explored by monitoring the adhesion of T cells to immobilized ECM proteins. A short exposure of 51Cr-labeled human CD4+ T cells to phorbol esters in vitro induced a rapid beta 1-integrin-mediated adhesion to both fibronectin and laminin, as determined by inhibition with anti-integrin antibodies. Adhesion was reversible; detachment from the immobilized ECM ligands occurred between 20 and 120 min without further intervention. This T cell adhesion was regulated by the activation of protein kinase C because (a) staurosporine and H-7 inhibitors of protein kinase C suppressed T cell adhesion, and (b) PMA-induced down-regulation of intracellular levels of protein kinase C was associated with the abrogation of the T cell adhesiveness to fibronectin and laminin. Furthermore, inhibition of protein phosphatases activity by okadaic acid delayed the detachment of the T cells from fibronectin or laminin. Thus, we suggest that T cell-ECM interactions such as adhesion and detachment are regulated, respectively, by protein kinase C and protein phosphatases.

Mouse T-lymphocyte activation by Urtica dioica agglutinin. II.--Original pattern of cell activation and cytokine production induced by UDA

Urtica dioica agglutinin (UDA) is a T-lymphocyte-specific polyclonal activator that differs from ConA, the classical mouse T-cell mitogen, by inducing a late and limited proliferation of a distinct T-cell subset recruited among both CD4+ and CD8+ lymphocytes. We investigated the possibility that the particular kinetics may originate from UDA-specific activation processes in which the known early mandatory signals were completed only after an extended delay. We report that the time of contact required between lectin and the cell membrane to acquire the capacity to proceed into cell cycle was much longer (36-40 h) for UDA than for ConA (8-10 h). Addition of phorbol ester, which artificially induces PKC translocation, or ionomycin, which provokes Ca2+ mobilization, did not accelerate the proliferative kinetics, suggesting that these early mandatory signals are not the limiting factors in the delayed proliferation. The induction of c-myc was retarded in the UDA group, and there was a good correlation between the kinetics of c-myc induction and the kinetics of cell proliferation. The comparison of the level of transcription of the genes encoding different cytokines revealed additional differences between the two mitogens: the whole wave of cytokine gene expression was delayed with UDA. In particular, IL2, IL3 and IFN gamma gene expression was retarded compared to the ConA-induced single wave. An even later transcriptional wave took place at around 72 h for IL4 and IL5. Finally, this particular kinetics corresponded to an unusually high level of IL3 and IFN gamma and a low level of IL4 and IL5 gene transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

Internalization, lysosomal degradation and new synthesis of surface membrane CD4 in phorbol ester-activated T-lymphocytes and U-937 cells

Protein kinase C activating phorbol esters downregulated membrane CD4 by endocytosis in U-937 and human T-cells. Half-time for internalization (approximately 15 min at 50 ng/ml PMA) was determined by FACS. CD4-bound 125I-labeled anti-CD4 mAb was rapidly degraded in PMA-activated cells, whereas degradation was low in resting cells. Endocytosis and/or degradation of anti-CD4 mAb was suppressed by H7, and by inhibitors of membrane traffic (Monensin) and lysosome function (methylamine, chloroquine). Immunocytochemistry localized CD4 to the surface of unstimulated T-cells. Upon PMA stimulation occasional labeling was seen in endosomes but whole cell CD4 decreased dramatically. However, methylamine-treated PMA blasts showed accumulation of CD4 in lysosomes and accordingly, pulse-chase experiments in biolabeled cell cultures suggested a manifest reduction of CD4 half-life in response to PMA. Despite their low surface CD4 density, PMA blasts exhibited uptake and accelerated degradation of anti-CD4 mAb. Also, inhibitors of protein synthesis enhanced the PMA-induced downregulation, and membrane CD4 reappeared on fully activated as well as unstimulated cells treated with trypsin. Ongoing CD4 synthesis in activated cells was further evidenced by metabolic labeling and Northern blot analysis demonstrating unaltered or slightly increased CD4 protein and mRNA levels resulting from PMA. Our findings demonstrate that phorbol esters downregulate the cellular CD4 pool by endocytosis and subsequent lysosomal degradation of membrane CD4. Transport of CD4 to the cell surface and CD4 synthesis is unaffected by activation.

Induction of high-affinity paf receptor expression during T cell activation

Activated human T cells via the CD2 or the CD3 pathways exhibited a higher capacity than resting T lymphocytes to incorporate and metabolize [3H]pafacether (paf) at 37 degrees C. Resting T lymphocytes lacked specific binding capacity for paf, yet high-affinity paf receptors (paf-R) were induced on CD3- or CD2-dependent activation. This up-regulation in the number of paf-R became apparent by day 1 of culture, reached a maximum of about 25,000 sites cell by days 4 to 6 and subsequently declined. Interestingly, human recombinant interleukin-2 in a dose-dependent manner prevented the decrease of high-affinity paf-R expression on T cells. By contrast, the receptor affinity was constant throughout the culture period. Thus, paf-R at different stages of T cell activation were indistinguishable with respect to receptor-ligand interaction, and differed only in their number. Together, these data demonstrate that after activation human T cells develop membrane high-affinity paf-binding sites. They also suggest for the first time that expression of the paf-R are coupled to T cell activation and/or differentiation.

The protein tyrosine kinase p56lck inhibits CD4 endocytosis by preventing entry of CD4 into coated pits

The lymphocyte glycoprotein CD4 is constitutively internalized and recycled in nonlymphoid cells, but is excluded from the endocytic pathway in lymphocytic cells (Pelchen-Matthews, A., J. E. Armes, G. Griffiths, and M. Marsh. 1991. J. Exp. Med. 173: 575-587). Inhibition of CD4 endocytosis is dependent on CD4 expressing an intact cytoplasmic domain and is only observed in cells where CD4 can interact with the protein tyrosine kinase p56lck, a member of the src gene family. We have expressed p56lck, p60c-src, or chimeras of the two proteins in CD4- transfected NIH-3T3 or HeLa cells. Immunoprecipitation of CD4 and in vitro kinase assays showed that p56lck and the lck/src chimera, which contains the NH2 terminus of p56lck, can associate with CD4. In contrast, p60c-src and the src/lck chimera, which has the NH2 terminus of p60c-src, do not associate with CD4. Endocytosis assays using radioiodinated anti-CD4 monoclonal antibodies demonstrated that coexpression of CD4 with p56lck, but not with p60c-src, inhibited CD4 endocytosis, and that the extent of the inhibition depended directly on the relative levels of CD4 and p56lck expressed. The uptake of mutant CD4 molecules which cannot interact with p56lck was not affected. Measurement of the fluid-phase endocytosis of HRP or the internalization of transferrin indicated that the effect of p56lck was specific for CD4, and did not extend to other receptor-mediated or fluid-phase endocytic processes. Immunogold labeling of CD4 at the cell surface and observation by electron microscopy demonstrated directly that p56lck inhibits CD4 endocytosis by preventing its entry into coated pits.

Immune modification due to chemical interference with transmembrane signalling: application to polycyclic aromatic hydrocarbons

Triggering of the T-cell antigen receptor complex and some other surface molecules is coupled to the phosphodiesterase (phospholipase C)-mediated hydrolysis of membrane phosphoinositides, in particular, phosphatidylinositol-4,5-biphosphate (PiP2). PiP2 hydrolysis generates two products, inositol 1,4,5-triphosphate and diacylglycerol, which act in concert as second messengers to increase the free intracellular calcium concentration and activate protein kinase C, respectively, thereby stimulating subsequent events leading to cellular activation and proliferation. Transmembrane signalling in T-lymphocytes represents a potential target for designated drugs as well as immunotoxicants. Immunotoxic effects of polycyclic aromatic hydrocarbons are discussed in the view of interaction with transmembrane signalling in the T-lymphocyte.

A comparison of the response of unstimulated and stimulated T-lymphocytes and fibroblasts from normal, xeroderma pigmentosum and trichothiodystrophy donors to the lethal action of UV-C

Unstimulated T-lymphocytes from normal donors are significantly more sensitive to the lethal effects of UV-C than either stimulated T-lymphocytes or fibroblasts as judged by colony-forming ability. Data from other studies suggest that excision repair is more effective in stimulated than unstimulated T-lymphocytes leading to the prediction that these differences in survival should be minimal in cells established from excision defective donors. The prediction was met with XP6BR, a donor of unknown complementation group. For 3 XP's from complementation group D, however, enhanced survival in stimulated T-cells was observed. With cells from an excision-defective TTD who was included in complementation group D of XP both fibroblasts and unstimulated T-lymphocytes were hypersensitive. For a second excision defective TTD patient who was excluded from complementation group D, the unstimulated T-lymphocytes were more resistant than those of normal donors although the fibroblasts were hypersensitive. These results suggest that the in vitro response of stimulated T-lymphocytes or fibroblasts may not reflect the in vivo response of cells, as measured by the response of unstimulated T-lymphocytes.

T cell receptor activation of a ribosomal S6 kinase activity

Stimulation of the T cell receptor-CD3 complex activates multiple signal transduction pathways, including serine/threonine and tyrosine protein kinases. Stimulation of the human T cell line Jurkat via the T cell receptor-CD3 complex with anti-CD3 monoclonal antibody or incubation with the tumor promoter phorbol 12-myristate 13-acetate caused increases in S6 kinase and microtubule-associated protein 2 (MAP) kinase activities. An S6 kinase activity that was able to phosphorylate exogenous 40S ribosomal S6 protein was recovered in immunoprecipitates obtained using a 90-kDa ribosomal S6 kinase-specific antiserum and thus represents activation of a member of the 90-kDa ribosomal S6 kinase family. Stimulation of the S6 kinase activity correlated with an increase in a kinase activity able to phosphorylate exogenous 90-kDa ribosomal S6 kinase (rsk) attributed to a MAP kinase activity. These increases in S6 and MAP kinase activities further correlated with the appearance of a 42-kDa phosphoprotein detected by anti-phosphotyrosine immunoblotting. However, while the tyrosine phosphorylation of the 42-kDa protein and the MAP kinase activity are dependent on protein kinase C activity, residual S6 kinase activity can be detected following protein kinase C depletion and subsequent anti-CD3 stimulation. Thus, T cell activation through the T cell receptor-CD3 complex results in activation of a member of the 90-kDa S6 kinase family which correlates with, but can be independent of, MAP kinase activation.

Interaction of a synthetic peptide of the interferon alpha 2 C-terminal part with human blood leukocytes. II. Effect on protein tyrosine phosphorylation

Tyrosine phosphorylation in human blood lymphocytes was studied as a function of stimulation with concanavalin A (ConA) and treatment of the cells with interferon alpha 2 (IFN alpha 2) and/or an IFN-derived C-terminal synthetic peptide 2438 (amino acid residues 124-138). Both IFN alpha 2 and the peptide 2438 decreased the level of protein tyrosine phosphorylation in the ConA-stimulated cells. In unstimulated cells, IFN alpha 2 increased, and the peptide 2438 decreased the level of the tyrosine phosphorylation. A possible correlation of these effects with stimulation of cell proliferation is discussed.

Modulation of the effector functions of cytolytic T-lymphocytes with synthetic peptide inhibitors of protein kinases

The hypothesis was tested that it is possible to influence cellular responses of intact cells using synthetic peptide substrates, pseudosubstrates, and inhibitors of protein kinases. Using cytotoxic T-cells (CTL), we demonstrate here that some basic amino acid-containing synthetic peptide substrates of protein kinases [e.g., of cGMP-dependent protein kinase (peptide PKG-S), synthetic peptide inhibitor of cGMP-dependent protein kinase (peptide PKG-I), and peptide corresponding to the tyrosine phosphorylation site in pp60src (peptide RR-src)] were strongly inhibitory in T-cell receptor (TCR) and T-cell growth factor, interleukin 2 (IL-2)-triggered proliferation of CTL. These peptides also inhibited other cellular responses of CTL. Peptides which contain basic amino acids, but do not have substrate specificity determinants for protein kinase, were not inhibitory. The inhibition with peptides is not due to their toxicity, since no cell death was observed by the trypan blue exclusion test and by lactate dehydrogenase release. Use of the granule exocytosis assay provided opportunities to clarify the mechanism of the peptide action. Tested peptides inhibited not only cell-surface ligand-induced CTL activation, but also affected cell-surface receptor-independent CTL activation (granule exocytosis and gamma-interferon secretion) induced by the synergistic action of the protein kinase C activator (PMA) and ionophore A23187. It was found that minor changes in amino acid composition or amino acid position in the synthetic peptides dramatically change their ability to affect lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

T lymphocyte adhesion to the fibronectin and laminin components of the extracellular matrix is regulated by the CD4 molecule

The adhesion of T cells to components of the extracellular matrix (ECM) is mediated by the beta 1 subfamily of integrin receptors, designated VLA. It has been recently demonstrated that the binding of VLA receptors to protein components of the ECM is rapidly augmented by the activation of the T cells without, however, any actual change in the level of expression of the VLA receptors for fibronectin (FN) or laminin (LN). Thus, it is likely that activation of existing VLA receptors is required for binding. The activation must be regulated by T cell surface molecules capable of transducing signals into the cell. We studied the role of the CD4 molecule in the binding of rat CD4+ T cells to the FN and LN components of the ECM. We now report that the CD4 molecule appears to play a major role in regulating T cell interactions with ECM. This conclusion is based on the following observations: (a) monoclonal antibodies directed against the CD4 molecule inhibited T cell adhesion to both FN and LN; (b) down-regulation of the CD4 molecule resulted in partial loss of the ability of CD4+ T cells to adhere to FN and LN; (c) a CD4+ T cell clone adhered to both FN and LN while a CD4-CD8- clone expressing an identical T cell receptor bound weakly to both proteins and (d) treatment of the CD4+ T cells with an inhibitor of the CD4-associated tyrosine protein kinase activity inhibited T cell adhesion to both ECM proteins.

A protein kinase C inhibitory activity is present in the human T lymphoblast cell line Jurkat

The human lymphoblast cell line Jurkat is widely used as a model system for studying signal transduction pathways during lymphocyte activation. We report the presence of a potent endogenous inhibitor of protein kinase C (PKC) in the cytosolic fraction of Jurkat cells. This inhibitor is not diffusible and is thermolabile; it is assumed to be a protein. It was separated from PKC by ion-exchange chromatography on DEAE-cellulose. The inhibitory activity was partially reversed by increasing the concentration of the PKC substrate; increasing that of PKC activators (calcium and phospholipids) was without effect. PKC activity was inhibited by more than 90% in the crude cytosolic fraction but the inhibition could be completely reversed by diluting the cell extract. This inhibitory activity could not be detected in the cytosol from normal lymphocytes or from lymphoblasts from leukemic patients.