A serine protease triggers the initial step of transmembrane signalling in cytotoxic T cells

"Hit the primary": A paradigm shift in the treatment of metastatic prostate cancer?

Patients with metastatic prostate cancer (PC) represent a heterogeneous group with survival rates varying between 13 and 75 months. The current standard treatment in this setting is hormonal therapy, with or without docetaxel-based chemotherapy. In the era of individualized medicine, however, maximizing treatment options, especially in long-term surviving patients with limited disease burden, is of capital importance. Emerging data, mainly from retrospective surgical series, show survival benefits in men diagnosed with metastatic PC following definitive therapy for the prostate. Whether the irradiation of primary tumor in a metastatic disease might improve the therapeutic ratio in association with systemic treatments remains investigational. In this scenario, modern radiation therapy (RT) can play a significant role owing to its intrinsic capability to act as a more general immune response modifier, as well as to the potentially better toxicity profile compared to surgery. Preclinical data, clinical experience, and challenges in local treatment in de novo metastatic PC are reviewed and discussed.

Optimizing cancer treatments to induce an acute immune response: radiation Abscopal effects, PAMPs, and DAMPs

Clinical results indicate improved survival in poorly differentiated prostate cancer patients following a treatment schedule that maximizes hormone therapy prior to radiation. This may be because of a systemic immune response, called an abscopal effect. A literature review showed an association between acute infection and abscopal cancer remission. This led to the theory that, in the presence of endogenous cancer-specific antigens exposed by cancer necrosis, an innate immune response can adapt to respond to those antigens via a cross-talk mechanism. This theory was validated in an animal model. An acute innate immune T-cell response was stimulated using cluster vaccination with Poly(I:C). In the presence of exogenous cancer-specific antigens, this immune response became adaptive, creating an abscopal effect that resulted in cancer resolution. These concepts may be of clinical value, improving outcomes by inducing systemic abscopal effects.

Neuropeptide enzyme hydrolysis in allergic human saliva

The activity of neuropeptide-degrading enzymes, and possible variations in this activity under allergic conditions, was examined in human saliva obtained from allergic volunteers and from an age- and sex-matching group of healthy controls, using leucine enkephalin as model substrate. The results obtained indicate that, under experimental conditions, the substrate was partially hydrolyzed by all three classes of enzymes known to degrade it in human saliva: aminopeptidases, dipeptidylaminopeptidases and dipeptidylcarboxypeptidases. In the presence of saliva obtained from allergic donors, a large increase in the activity of aminopeptidases, and a more limited increase in the activity of dipeptidylaminopeptidases, induced an increase of substrate hydrolysis with respect to that measured in the controls. The activity of all substrate-active enzymes, the allergy-associated variations in this activity, and the amount of substrate hydrolyzed, were found to be different in male and female saliva. Specifically, in the controls the gender-related differences in substrate hydrolysis were mainly caused by the higher activity of aminopeptidases observed in male as compared to female saliva. In contrast, in allergic saliva, a greater increase in the activity of aminopeptidases in female saliva reduced the gender-related differences in the pattern of hydrolysis, which was also different from that observed in the controls.

Separation by heparin-affinity chromatography of catalytically active and inactive forms of trypsin which retain the (Na-K)ATPase stimulating property

The possibility that different structural determinants on trypsin, other than catalytic sites, are involved in the cell membrane (Na-K)ATPase stimulating property was investigated by submitting bovine trypsin to two purification procedures: gel filtration on Sephadex G-50 and heparin-Sepharose chromatography. The latter procedure was also chosen in consideration of the known affinity for heparin displayed by serine proteinases. Trypsin peaks eluted from both columns were analysed by measuring esterolytic and proteolytic activities, the beef heart (Na-K)ATPase stimulating property and amino acid content. Fluorescence emission spectra and both non-denaturing and SDS-gel electrophoresis were also performed to test structural modifications on trypsin peaks. Four peaks eluted from Sephadex G-50 with variable estero-proteolytic and (Na-K)ATPase stimulating activities; the latter was also present in two peaks which displayed the lowest estero-proteolytic activities. All peaks proved to be trypsin in amino acid composition. Two peaks eluted from the heparin-Sepharose column with distinct biological activities: a first minor peak, eluted with the void volume, was catalytically inactive but it retained the (Na-K)ATPase stimulating activity. The second, major peak eluted mostly with 0.5 mol/l NaCl, displayed only esteroproteolytic activities, but no (Na-K)ATPase-stimulating activity. It overlapped control trypsin in both electrophoretic patterns, fluorescence emission spectrum and amino acid composition. The first peak showed differences with the parent compound, as revealed by the amino acid composition and tryptophan fluorescence emission spectrum. Marked differences were also observed in the electrophoretic pattern which only showed bands of low molecular mass mostly confined to the anode. NH2-terminus analysis confirmed that the first peak contained trypsin fragments originated from the parent compound after passage through the heparin column. It is hypothesized that trypsin binding to heparin causes structural alteration of the proteinase and primes the catalytic cleavage of fragments which lose heparin affinity and elute in the void volume. The results also confirm that the proteolytic mechanism is not involved in trypsin-mediated (Na-K)ATPase stimulation and indicate that heparin-Sepharose chromatography is a useful tool to separate catalytically active and inactive forms of trypsin.

The esterases: perspectives and problems

Many proteins capable of hydrolysing esters are present in biological material of all kinds (microorganisms, plants, invertebrates and vertebrates). Some serve, as indicated by their substrate specificity and distribution within organisms, a defined biological function. However for most esterases a rather general substrate specificity is found indicating that they may have a broad biological function. Their properties will be briefly reviewed with particular emphasis on inhibitors. The mechanism of hydrolysis of esters by many carboxylesterases (B-esterases) is well established largely due to the reaction of OP compounds with their catalytic centre. For others, such as enzymes hydrolysing (i) OP compounds and/or (ii) carboxyl esters which are not inhibited by a time and temperature dependent reaction by OP compounds, reaction mechanisms are still conjecture. The purpose of this presentation is to explore similarities and differences between the esterases and to discuss possible routes for progress in the A-esterase group.

Inhibition of interleukin 2 driven proliferation of mouse CTLL2 cells, by selected carbamate and organophosphate insecticides and congeners of carbaryl

The anticholinesterase (antiCHE) insecticides, a large family of pesticides used extensively throughout the world, inhibit serine hydrolases by carbamylating or phosphorylating a serine residue at the catalytic site. These insecticides are viewed as potential inhibitors of serine hydrolase-dependent immune functions including interleukin 2 (IL2) signalling. Previous studies in our laboratory have demonstrated that carbaryl (an antiCHE insecticide) produces a marked concentration-dependent inhibition of IL2 driven 1) proliferation of mouse CTLL2 cells, 2) proliferation of human natural killer (NK) cells, and 3) enhancement of target cell killing by human NK cells. In the present study, we examined the potential of 8 antiCHE insecticides (4 carbamates and 4 organophosphates) to inhibit IL2-dependent proliferation of mouse CTLL2 cells. The order of potency for T cell inhibition was carbaryl = dichlorvos > methiocarb > carbofuran > paraoxon > mevinphos > aldicarb = monocrotophos. In view of the relatively high inhibitory potency of carbaryl (a carbamate with low cholinergic toxicity), 3 metabolites and 5 congeners of carbaryl were tested for potency to inhibit CTLL2 proliferation. The data indicate a significant contribution of the 1-naphthol leaving group to inhibition of T cell proliferation by carbaryl, and are consistent with inhibition of a serine hydrolase(s) as a mechanism contributing to the observed inhibition of IL2-dependent proliferation.

Inhibition of interleukin-2-stimulated enhancement of human natural killer (NK) cell activity by carbaryl, an anticholinesterase insecticide

The potency of the anticholinesterase (antiCHE) insecticides as serine hydrolase inhibitors, and evidence for serine hydrolase activity in interleukin-2 (IL2) signalling suggest that the natural killer (NK) cell may be a target for dysregulation by antiCHE insecticides. NK cells are large granular lymphocytes (LGL) that respond to IL2 by proliferating and increasing their cytolytic efficiency. In the present study, we assessed the effects of carbaryl (CA, an antiCHE insecticide) and alpha-naphthol (NA, the major metabolite of CA) on both target cell killing per se and IL2 enhancement of target cell killing by human NK cells. Human LGL, collected from the peripheral blood of normal donors, were cultured for 4 days with human recombinant IL2 (HRIL2), then assayed by a 51Chromium (51Cr) release assay for lytic activity against human K562 cells. When added at the beginning of the culture period, CA inhibited enhancement of cytolytic efficiency in a concentration-dependent manner; at concentrations (0.5 and 5.0 microM) compatible with no cholinergic toxicity. Reduction of the effector/target cell (E/T) ratio in the 51Cr release assay markedly enhanced the observed inhibition by CA. In one experiment, inhibition increased from 6% to 20%, 17% to 35%, and 53% to 73% at 0.5, 5.0, and 50 microM CA, respectively, when E/T was reduced from 10:1 to 2.5:1. This result is consistent with reduced cytolytic efficiency of individual NK cells exposed to CA. NA had no effect at 0.5 or 5.0 microM but caused some inhibition at 50 microM. Neither CA nor NA produced LGL death. When CA or NA was added directly to the 51Cr release assay, inhibition was not observed. The mechanism of inhibition of IL2-stimulated enhancement of target cell killing is not yet known, however, the results are consistent with impairment of IL2 signalling, by CA.

Proteinases and proteinase inhibitors as modulators of animal cell growth

1. Three distinct lines of evidence indicate that proteinases are involved in the growth of cultured animal cells. 2. Endogenous growth-related proteinases have been identified, and exogenous proteinases can also stimulate cell proliferation, probably by different mechanisms. In some cases, higher concentrations of proteinases are cytotoxic. 3. Proteinase inhibitors, not surprisingly, inhibit cell growth, but can also be mitogenic at sub-inhibitory concentrations. 4. There must, therefore, be at least three major cellular processes in which proteinases or proteinase inhibitors can operate to exert a direct effect on cell proliferation. 5. Details of one action of an exogenous proteinase, typified by thrombin and the thrombin receptor, are becoming clear at the molecular level, but thrombin probably activates at least two intracellular signalling systems, as well as acting as a growth inhibitor in some situations. 6. Much remains to be investigated in other examples.

Immunosuppressive factor in cow follicular fluid

The activity of the immunosuppressive fraction and proteinase inhibitor isolated from cow follicular fluid was investigated. The immunosuppressive factor was separated from the accompanying proteinase inhibitor by Sepharose 6B and Sephacryl S-200 column chromatography. In vitro, the fraction significantly reduced mitogen-induced lymphocyte proliferation. In vivo, the fraction inhibited mouse plaque formation. However, the factor had no effect on the development of intact or zona free embryos. The active components have a molecular mass of about 110,000.

Cell death mechanisms and the immune system

The immune system provides good models for cell death, a phenomenon now recognized to be of fundamental importance in many fields of biology. Cell death is strikingly polymorphic: it can proceed via necrosis (as in complement-mediated cell death) or apoptosis, but the latter displays different patterns (in the receptor-mediated death of some thymocytes, in cell death mediated by TNF alpha or by cytotoxic T cells), perhaps reflecting different pathways of control of a common core mechanism. Even though there are differences in the morphological and metabolic changes associated with the different patterns of apoptosis, some recurrent sequences of events are observed in almost all dying cells. The metabolic state of a cell often seems to play a major role in determining if and how this cell will die in given external circumstances. The nature of molecules causally involved in the dying cell can now be approached in some systems.

Trypsin inhibitors prevent the progesterone-initiated increase in intracellular calcium required for the human sperm acrosome reaction

Inhibitors of trypsin-like enzymes, benzamidine hydrochloride and 4'-acetamidophenyl 4-guanidinobenzoate (also an inhibitor of other serine proteases), were tested for their effects on the acrosome reaction (AR) of human sperm initiated by progesterone or the calcium ionophore ionomycin. The AR was assayed by indirect immunofluorescence and transmission electron microscopy. The trypsin inhibitors, when added 10 min prior to stimulation by progesterone, significantly inhibited the AR in comparison with progesterone treatment alone. Transmission electron microscopic examination of the sperm after progesterone treatment indicated that the inhibitors blocked the membrane fusion events of the AR. By contrast, when ionomycin (at final concentrations of 3 microM) was added to sperm preincubated in inhibitors, sperm underwent morphologically normal AR, acrosomal matrix loss was not inhibited, and the percentage of acrosome-reacted sperm was the same as that obtained in the absence of inhibitors. Using the cell calcium indicator fura-2, we further demonstrated that both trypsin inhibitors prevented the progesterone-stimulated rise in intracellular Ca2+ ([Ca2+]int) required for the AR, but did not affect [Ca2+]int in unstimulated sperm. These results suggest that sperm trypsin-like activity may be directly or indirectly involved in increasing sperm [Ca2+]int during stimulation by progesterone.

Mechanism of killing by virus-induced cytotoxic T lymphocytes elicited in vivo

The mechanism of lysis by in vivo-induced cytotoxic T lymphocytes (CTL) was examined with virus-specific CTL from mice infected with lymphocytic choriomeningitis virus (LCMV). LCMV-induced T cells were shown to have greater than 10 times the serine esterase activity of T cells from normal mice, and high levels of serine esterase were located in the LCMV-induced CD8+ cell population. Serine esterase was also induced in purified T-cell preparations isolated from mice infected with other viruses (mouse hepatitis, Pichinde, and vaccinia). In contrast, the interferon inducer poly(I.C) only marginally enhanced serine esterase in T cells. Serine esterase activity was released from the LCMV-induced T cells upon incubation with syngeneic but not allogeneic LCMV-infected target cells. Both cytotoxicity and the release of serine esterase were calcium dependent. Serine esterase released from disrupted LCMV-induced T cells was in the form of the fast-sedimenting particles, suggesting its inclusion in granules. Competitive substrates for serine esterase blocked killing by LCMV-specific CTL, but serine esterase-containing granules isolated from LCMV-induced CTL, in contrast to granules isolated from a rat natural killer cell tumor line, did not display detectable hemolytic activity. Fragmentation of target cell DNA was observed during the lytic process mediated by LCMV-specific CTL, and the release of the DNA label [125I]iododeoxyuridine from target cells and the accompanying fragmentation of DNA also were calcium dependent. These data support the hypothesis that the mechanism of killing by in vivo-induced T cells involves a calcium-dependent secretion of serine esterase-containing granules and a target cell death by a process involving nuclear degradation and DNA fragmentation.

Novel structures CTLA-2 alpha and CTLA-2 beta expressed in mouse activated T cells and mast cells and homologous to cysteine proteinase proregions

Differential screening of a subtracted cDNA library led to the detection of two distinct but homologous mouse cDNA, called CTLA-2 alpha and CTLA-2 beta. The corresponding transcripts have a tissue distribution restricted to T lymphocytes, where they are inducible upon activation, and to mast cells. The open-frame regions of both cDNA encode proteins homologous to cysteine proteinase precursors, remarkably, however, only to the proregion of these. The ctla-2 alpha and ctla-2 beta genes both map to the C1 band of mouse chromosome 13. Sequence comparisons suggest that the proregion of an ancestor proteinase gene evolved to the ctla-2 genes by successive duplications, first to autonomy, then to amplification. These results raise the question of the possible role of cysteine proteinase proregions, of cysteine proteinases themselves and of inhibitors thereof in activated T lymphocytes; from a different point of view, they also show that some protease proregions may have evolved as autonomous modules.

Suppression of streptococcal cell wall-induced arthritis by a potent protease inhibitor, bis(5-amidino-2-benzimidazolyl)methane

Bis(5-amidino-2-benzimidazolyl)methane, a powerful synthetic trypsin inhibitor, proved to be highly effective in suppressing the arthritis induced by streptococcal cell wall fragments in Lewis rats. It reduced not only the degree of synovitis, osteitis, and hematopoietic hyperplasia in the distal extremities, but also the degree of associated granulomatous inflammation in the liver. The results suggest that trypsin-like proteases play an important role in this arthritis model and that inhibitors may be useful in the treatment of similar arthritic conditions in humans.

Rapid changes in target cell lysosomes induced by cytotoxic T cells: indication of target suicide?

Although many studies have attempted to elucidate how cytotoxic T (Tc) lymphocytes cause the death of target cells, the mechanism is still controversial. In the present study the effect on the integrity of the lysosomes of the target cell has been investigated. We show here that the specific recognition and attachment of cloned type A influenza-specific Tc cells to A/X31 influenza virus-infected target cells caused rapid change in the amount of lysosomal naphthylamidase activity that was bound within the lysosomes, indicating that the lysosomal membranes in the target cells had been totally labilized. Target cells infected with type B influenza virus served as controls. We therefore suggest that the viral specificity of Tc lymphocytes allows for recognition and intimate membrane contact with suitably infected targets. This intimate contact induces sufficient perturbation of the target cell plasma membrane so as to cause total labilization of the target cell lysosomes which could account for intracellular lysis.

A T cell- and natural killer cell-specific, trypsin-like serine protease. Implications of a cytolytic cascade

A new trypsin-like serine protease was cloned from both a murine cytotoxic T lymphocyte and a human PHA-stimulated peripheral blood lymphocyte cDNA library. In both the mouse and human system, this transcript had a T cell- and NK-specific distribution, being detected in cytotoxic T lymphocytes (CTL), some T-helper clones, and NK, but not in a variety of normal tissues. T-cell activation with Con A plus IL-2 induced mouse spleen cells to express this gene with kinetics correlating with the acquisition of cytolytic capacity. Both the mouse and human nucleotide sequences of this gene encoded an amino acid sequence with 25-40% identity to members of the serine protease family. The active-site "charge-relay" residues (His-57, Asp-102, and Ser-195 of the chymotrypsin numbering system) are conserved, as well as the trypsin-specific Asp (position 189 in trypsin). We reviewed the evidence of this serine protease's role in lymphocyte lysis and proposed a "lytic cascade." We discussed the biological and clinical implications of a cascade, proposing these enzymes as markers for cytolytic cells and as targets for rational drug therapy. Genetic and acquired deficits in the lethal hit-delivery system are considered as a basis for approaching some immunodeficiency states, including severe EBV infections, T-gamma leukemias, and T8+ lymphocytosis syndromes.

A differential molecular biology search for genes preferentially expressed in functional T lymphocytes: the CTLA genes

One approach to the isolation of molecules involved in T cell-mediated cytolysis stems from the postulate of a possible correlation between molecular phenotype and molecular functional involvement. Accordingly, CTL-specific molecules have been looked for, using a strategy based on the differential screening of a subtracted cDNA library. This led to the isolation and characterization of the following structures, expressed mostly (but no exclusively) in CTLs and inducible upon lymphocyte activation: CTLA-1 and CTLA-3 (serine-proteases), CTLA-4 (a member of the Ig superfamily) and CTLA-2 alpha and beta (homologues to the proregion of cysteine-proteases). The theoretical and practical limitations and the prospects of this type of approach are discussed.