New adenovirus vectors for protein production and gene transfer.

Based on two new adenovirus expression cassettes, we have constructed a series of Ad transfer vectors for the overexpression of one or two genes either in a dicistronic configuration or with separate expression cassettes. Inclusion of the green or blue fluorescent protein in the vectors accelerates the generation of adenovirus recombinants and facilitates the functional characterization of genes both in vitro and in vivo by allowing easy quantification of gene transfer and expression. With our optimized tetracycline-regulated promoter (TR5) we have generated recombinant adenoviruses expressing proteins, that are either cytotoxic or which interfere with adenovirus replication, at levels of 10-15% of total cell protein. Proteins that are not cytotoxic can be produced at levels greater than 20% of total cell protein. As well, these levels of protein production can be achieved with or without adenovirus replication. This yield is similar to what can be obtained with our optimized human cytomegalovirus-immediate early promoter-enhancer (CMV5) for constitutive protein expression in non-complementing cell lines. Using the green fluorescent protein as a reporter, we have shown that a pAdCMV5-derived adenovirus vector expresses about 6-fold more protein in complementing 293 cells and about 12-fold more in non- complementing HeLa cells than an adenovirus vector containing the standard cytomegalovirus promoter. Moreover, a red-shifted variant of green fluorescent protein incorporated in one series of vectors was 12-fold more fluorescent than the S65T mutant, making the detection of the reporter protein possible at much lower levels of expression.

Role of XIAP protein, a human member of the inhibitor of apoptosis (IAP) protein family, in phytohemagglutinin-induced apoptosis of human T cell lines.

A new family of human genes xiap, hiap-1 and hiap-2, which are homologous to the baculovirus iap (inhibitor of apoptosis) genes cp-iap and op-iap, has been recently cloned and shown to suppress apoptosis after serum withdrawal or exposure to a free radical inducer. In order to examine the role of one of these human genes, namely xiap, in lymphoid cells, we studied XIAP expression, after PHA stimulation in three different human T cell lines. We report here that stimulation with PHA resulted in the human T cell lines undergoing apoptosis, as assessed by DNA fragmentation and by propidium iodide (PI) staining and flow cytometry. When XIAP protein expression was evaluated by Western blot, we observed that the induction of apoptosis by PHA was associated with a parallel decrease of XIAP expression. We also provide evidence that stably transfected Jurkat cells containing the xiap open reading frame became resistant to PHA-induced apoptosis. These data suggest a role for XIAP protein in the regulation of apoptosis in lymphoid cells.

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.

Regulation of p56lck kinase expression and control of DNA synthesis in activated human B lymphocytes.

In this study, we analyzed the expression and regulation of src kinase p56lck expression during human B lymphocyte activation. We show that upon mitogenic stimulation with anti-IgM antibodies and interleukin-2, specific mRNA for p56lck becomes detectable in B cells after 24 h of activation and is followed by an increase in p56lck protein expression on days 2 and 3. This up-regulation is specific for p56lck since expression of other src kinases such as fyn, lyn, or yes was not modified. Furthermore, immune complex kinase assays show that p56lck protein expressed on day 2 is associated with kinase activity. Experiments using lck-specific antisense oligonucleotides show that the G0-G1 transition does not require p56lck, whereas DNA synthesis is dependent upon its expression. Thus, our data demonstrate that p56lck expression is up-regulated during human B cell stimulation and this kinase plays an important role during the control of late steps of B lymphocyte activation such as S phase entry.

ADP-ribosylation of the ras-related, GTP-binding protein RhoA inhibits lymphocyte-mediated cytotoxicity.

The Rho proteins are identified as a subgroup of the Ras superfamily of low molecular weight GTP-binding proteins. We have studied the expression of these proteins in human cytotoxic natural killer cells and found that RhoA is the most abundantly expressed member of the Rho family. The Rho proteins are specific substrates for ADP-ribosylation catalyzed by the C3 exoenzyme from Clostridium botulinum. We report here that introduction of recombinant C3 in electropermeabilized natural killer cells or in cytotoxic T lymphocytes resulted in a dose-dependent inhibition of their cytolytic function. Furthermore, a single substrate is efficiently ADP-ribosylated by C3 in extracts from cytotoxic cells. Biochemical analyses indicate that this substrate is RhoA, and subcellular fractionation experiments demonstrate that it is essentially present in the cytosol of the cells. Western blot analysis, however, revealed that a small proportion of the Rho protein can be found associated with the cell membrane as well as with the cytotoxic granules. These results indicate that the low molecular weight GTP-binding protein RhoA is present in cytotoxic lymphocytes and plays a critical role in cell-mediated cytotoxicity.

Cyclic AMP upregulates mRNA and surface expression of IL-2R alpha p55(Tac) in normal human NK cell clones.

The effects of cAMP upon cell proliferation, cytotoxic activity, and regulation of IL-2R expression was investigated in normal human, IL-2-dependent natural killer (NK) cell clones. We report here that addition to the cultures of Bt2cAMP, a cell permeant analogue of cAMP, results in inhibition of IL-2-dependent proliferation, as assessed by [3H]Thymidine incorporation, in both NK and T cell clones. In addition, Bt2cAMP was shown to block the cytotoxic activity of NK cell clones at the level of the lytic phase. Contrasting with these inhibitory effects, cAMP induces an upregulation of the membrane expression of the IL-2R alpha chain (p55, Tac) in normal NK cell clones, which correlates with an accumulation of Tac mRNA. This is clearly at variance with T cell clones in which no such effect of cAMP alone is observed. In both cell types however, cAMP appears to synergize with IL-2 to increase IL-2R alpha mRNA expression. In addition, we demonstrate, using a cDNA probe to the IL-2R beta, that expression of this second component of the high affinity IL-2R, does not appear to be co-regulated together with IL-2R alpha in response to cAMP or/and IL-2 in cultured NK cells. Thus the effects of cAMP on human NK cell clones are complex. cAMP is inhibitory of proliferation and cytolytic function, whereas it is stimulatory of IL-2R alpha expression in these cells.

In vitro responsiveness to interleukins and theophylline of CD16+, CD56- natural killer cells in a patient with chronic granular lymphocyte disorder.

We report here the case of a 55-year-old patient with chronic granular lymphocyte disorder associated with moderate neutropenia. The majority of peripheral blood lymphocytes displayed a CD3-, CD8-, CD16+, CD56(NKH1)- phenotype. The patient's cells showed high spontaneous cytotoxic activity against K562 targets and developed the ability to kill the natural killer (NK)-resistant target Daudi following activation with interleukin 2 (IL-2). Simultaneously, IL-2 induced proliferation of these cells, albeit to a low level. The effects of IL-2 are likely to be mediated through the IL-2R beta chain (p70) which is expressed on these cells in the absence of the IL-2R alpha chain (p55, Tac). IL-4 was demonstrated to be inhibitory of both the cytotoxic and proliferative effects of IL-2. Thus, despite an unusual CD56- phenotype, the expanded lymphocyte population in this patient display functional and phenotypic properties of normal, non-activated NK cells. These cells probably represent the counterpart of a minor NK cell subpopulation, present in normal individuals at a low frequency, and which has never been fully characterized functionally. In addition, we show that the cytolytic activity of this NK cell population can be blocked in vitro in the presence of a cAMP analog or of theophylline, possibly providing new means of investigating the role of NK cell cytotoxicity on the pathogenesis of associated symptoms in such patients.

Functional consequences of cAMP accumulation in human natural killer cells. Implications for IL-2 and IL-4 signal transduction.

To approach the mechanisms whereby IL-2 activates human NK cells, we have compared the effects of IL-4 and of Bt2cAMP on this activation. Both agents block completely the proliferation induced by IL-2 on highly purified CD3-negative human NK cells. We also report that the net LAK response of PBL is inhibited by IL-4 and cAMP. However, kinetics analysis showed that IL-4 appears to inhibit an early stage of IL-2-induced activation of NK cells. IL-4 does not affect the cytotoxicity of freshly isolated NK cells against the K562 target and is ineffective on IL-2-preactivated cells. In contrast, cAMP primarily blocks the lytic effector phase, whether cells have been cultured in IL-2 or not, and its effect appears independent of time of addition. These differences between the activity of IL-4 and cAMP suggested that cAMP was not directly involved in IL-4 signal transduction in human NK cells. Consistent with this interpretation, we did not observe any variation in the level of intracellular cAMP concentrations when NK cells were stimulated with IL-4, or when they are stimulated with IL-2 or IL-2 plus IL-4. In addition, we also demonstrate that NK cell cytotoxic activation induced by IL-2 is still demonstrable in the presence of Bt2cAMP under conditions in which NK cell proliferation is blocked. These results clearly indicate that the differentiative effect of IL-2 on NK cells is independent of cell proliferation. Furthermore, the p70-75 IL-2R-initiated signal transduction pathway that leads to increased cytotoxicity appears not to be susceptible to inhibition by cAMP in human NK cells.