Lymphocyte granule-mediated cytolysis requires serine protease activity

Identification of a novel fish granzyme involved in cell-mediated immunity

Granzymes (Gzms) are serine proteases released from cytoplasmic granules within cytotoxic T lymphocytes and natural killer (NK) cells. Gzms induce apoptosis within virus-infected and transformed cells. In fish as well as mammals, Gzms appear to play a major role in inducing target cell death. However, information on the function of fish Gzms is limited, although Gzm-like genes have been reported in several species. We identified and characterized a fish Gzm (termed gcGzm) in ginbuna crucian carp, Carassius auratus langsdorfii. The primary structure of gcGzm resembled mammalian GzmB, and gcGzm clustered with mammalian GzmB by phylogenetic tree analysis. gcGzm was secreted from HEK293T cells transfected with gcgzm cDNA and was predominantly expressed in CD8(+) T cells, as in mammals. Expression of gcgzm mRNA was greatly enhanced by allo-sensitization and infection with the intracellular pathogen Edwardsiella tarda, indicating that gcGzm is involved in cell-mediated immunity. However, its enzymatic activity was different from mammalian Gzms because gcGzm did not cleave the known substrates for mammalian Gzms. Thus we conclude that the newly discovered gcGzm is a novel secretory serine protease involved in cell-mediated immunity in fish, with similar structure to human GzmB but different substrate specificity.

rAAV human trial experience

Recombinant AAV vectors have been used in clinical trials since the mid-1990s, with over 300 subjects enrolled in studies. Although there are not yet licensed AAV products, there are several clear examples of clinical efficacy, and recombinant AAV vectors have a strong safety record after administration both locally and systemically. This chapter provides a review of two types of studies that have shown efficacy, including studies for Leber's congenital amaurosis, a hereditary retinal degenerative disorder in which subretinal administration of AAV has shown efficacy in terms of improvement in multiple measures of visual/retinal function; and of Parkinson's disease which has also shown improvement in clinical and imaging studies after gene transfer to the CNS. The chapter also provides a detailed review of the results of studies of gene therapy for hemophilia, in which short-term efficacy was achieved, but expression of the donated gene failed to persist, likely due to an immune response to the vector. Safety issues relating to AAV-mediated gene transfer are discussed, including a detailed review of the single death to have occurred in an AAV gene therapy trial (likely unrelated to the AAV vector), and of issues related to integration and insertional mutagenesis, risk of germline transmission, and risks related to immune responses to either vector or transgene product. Finally, protocols for determining the presence of vector DNA in body fluids using real-time quantitative PCR, and for isolating, cryopreserving, and testing peripheral blood mononuclear cells for interferon-γ (IFN-γ) responses to capsid are described in detail.

Delivery and therapeutic potential of human granzyme B

Granzyme B (GzmB) is used by cytotoxic lymphocytes as a molecular weapon for the defense against virus-infected and malignantly transformed host cells. It belongs to a family of small serine proteases that are stored in secretory vesicles of killer cells. After secretion of these cytolytic granules during killer cell attack, GzmB is translocated into the cytosol of target cells with the help of the pore-forming protein perforin. GzmB has adopted similar protease specificity as caspase-8, and once delivered, it activates major executioner apoptosis pathways. Since GzmB is very effective in killing human tumor cell lines that are otherwise resistant against many cytotoxic drugs and since GzmB of human origin can be recombinantly expressed, its use as part of a 'magic bullet' in tumor therapy is a very tempting idea. In this review, we emphasize the peculiar characteristics of GzmB that make it suited for use as an effector domain in potential immunoconjugates. We discuss what is known about its uptake into target cells and the trials performed with GzmB-armed immunoconjugates, and we assess the prospects of its potential therapeutic value.

The Proinflammatory Cytokine Interleukin-18 Alters Multiple Signaling Pathways to Inhibit Natural Killer Cell Death

The proinflammatory cytokine, interleukin-18 (IL-18), is a natural killer (NK) cell activator that induces NK cell cytotoxicity and interferon-gamma (IFN-gamma) expression. In this report, we define a novel role for IL-18 as an NK cell protective agent. Specifically, IL-18 prevents NK cell death initiated by different and distinct stress mechanisms. IL-18 reduces NK cell self-destruction during NK-targeted cell killing, and in the presence of staurosporin, a potent apoptotic inducer, IL-18 reduces caspase-3 activity. The critical regulatory step in this process is downstream of the mitochondrion and involves reduced cleavage and activation of caspase-9 and caspase-3. The ability of IL-18 to regulate cell survival is not limited to a caspase death pathway in that IL-18 augments tumor necrosis factor (TNF) signaling, resulting in increased and prolonged mRNA expression of c-apoptosis inhibitor 2 (cIAP2), a prosurvival factor and caspase-3 inhibitor, and TNF receptor-associated factor 1 (TRAF1), a prosurvival protein. The cumulative effects of IL-18 define a novel role for this cytokine as a molecular survival switch that functions to both decrease cell death through inhibition of the mitochondrial apoptotic pathway and enhance TNF induction of prosurvival factors.

Selective chemical functional probes of granzymes A and B reveal granzyme B is a major effector of natural killer cell-mediated lysis of target cells

The mechanism of target cell lysis in cytotoxic lymphocyte-mediated death is not well understood, and the role of granzymes in this process is unclear. Chemical functional probes were thus prepared for the major granzymes A and B to deconvolute their role in natural killer cell-mediated lysis of target cells. These biotinylated and substrate specificity-based diphenyl phosphonates allowed facile evaluation of selectivity through activity-based profiling in cell lysates and intact cells. Both inhibitors were found to be extremely selective in vitro and in cells. Use of these inhibitors in cell-based assays revealed granzyme A to be a minor effector and granzyme B to be a major effector of target cell lysis by natural killer cells. These studies indicate that the proapoptotic granzyme B functions also as a pronecrotic effector of target cell death.

Characterization of structural determinants of granzyme B reveals potent mediators of extended substrate specificity

Granzymes are trypsin-like serine proteases mediating apoptotic cell death that are composed of two genetically distinct subfamilies: granzyme A-like proteases resemble trypsin in their active site architecture, while granzyme B-like proteases are quite distinct. Granzyme B prefers substrates containing P4 to P1 amino acids Ile/Val, Glu/Met/Gln, Pro/Xaa, and aspartic acid N-terminal to the proteolytic cleavage. By investigating the narrow extended specificity of the granzyme B-like proteases the mediators of their unique specificity are being defined. The foci of this study were the structural determinants Ile99, Tyr174, Arg192, and Asn218. Even modest mutations of these residues resulted in unique extended specificity profiles as determined using combinatorial substrate libraries and individual fluorogenic substrates. As with other serine proteases, Ile99 completely defines and predicts P2 specificity, primarily through the binding constant Km. Asn218 variants have minor effects alone but in combination with mutations at Arg192 and Ile99 alter P2 through P4 extended specificity. For each variant, the activity on its cognate substrate was equal to that of granzyme B for the same substrate. Thus, mutations at these determinants change extended selectivity preferentially over catalytic power. Additionally Asn218 variants result in increased activity on the wild type substrate, while the N218A/I99A variant disrupts the additivity between P2 and P4 specificity. This defines Asn218 not only as a determinant of specificity but also as a structural component required for P2 and P4 independence. This study confirms four determinants of granzyme B extended substrate specificity that constitute a canon applicable to the study of the remaining family members.

Reduction of perforin, granzyme B, and cytokine interferon gamma by ethanol in male Fischer 344 rats

BACKGROUND

Chronic alcohol consumption can impair the immune system and predispose individuals to an increased risk of cancer and infection. Natural killer (NK) cells are the first line of defense against viral, bacterial, and fungal infections and play an important role in cellular resistance to malignancy and tumor metastasis. We have shown previously that ethanol administration suppresses NK cell cytolytic activity in male Fischer rats. This study analyzed the effects of ethanol on perforin, granzyme B, and the cytokine interferon (IFN)-gamma, factors that modulate NK cell cytolytic activity, to understand the molecular mechanism involved in ethanol's suppression of NK cell activity.

METHODS

A group of male Fischer rats was fed an ethanol-containing diet (8.7% v/v), whereas a control group was pair-fed an isocaloric diet. At the end of 2 weeks, animals were decapitated, and spleen tissues were immediately removed and used for analysis of NK cell cytolytic activity, perforin, granzyme B, and IFN-gamma messenger RNA (mRNA) or protein levels. The mRNA levels of perforin, granzyme B, and IFN-gamma were evaluated by quantitative real-time polymerase chain reaction, and protein levels of these factors were analyzed by Western blot, enzyme-linked immunosorbent assay, or enzymatic activity assay.

RESULTS

Ethanol reduced the NK cell cytolytic activity and decreased the mRNA expression of perforin, granzyme B, and IFN-gamma in ethanol-fed animals when compared with pair-fed animals. Ethanol also significantly reduced the protein levels of perforin and IFN-gamma and the enzyme activity of granzyme B in alcohol-fed animals as compared with pair-fed animals.

CONCLUSIONS

These data suggest that chronic ethanol consumption may suppress NK cell cytolytic activity in male Fischer rats by decreasing the production, activity, or both of granzyme B, perforin, and IFN-gamma.

Granzymes (lymphocyte serine proteases): characterization with natural and synthetic substrates and inhibitors

Natural killer (NK) and cytotoxic T-lymphocytes (CTLs) kill cells within an organism to defend it against viral infections and the growth of tumors. One mechanism of killing involves exocytosis of lymphocyte granules which causes pores to form in the membranes of the attacked cells, fragments nuclear DNA and leads to cell death. The cytotoxic granules contain perforin, a pore-forming protein, and a family of at least 11 serine proteases termed granzymes. Both perforin and granzymes are involved in the lytic activity. Although the biological functions of most granzymes remain to be resolved, granzyme B clearly promotes DNA fragmentation and is directly involved in cell death. Potential natural substrates for Gr B include procaspases and other proteins involved in cell death. Activated caspases are involved in apoptosis. The search continues for natural substrates for the other granzymes. The first granzyme crystal structure remains to be resolved, but in the interim, molecular models of granzymes have provided valuable structural information about their substrate binding sites. The information has been useful to predict the amino acid sequences that immediately flank each side of the scissile peptide bond of peptide and protein substrates. Synthetic substrates, such as peptide thioesters, nitroanilides and aminomethylcoumarins, have also been used to study the substrate specificity of granzymes. The different granzymes have one of four primary substrate specificities: tryptase (cleaving after Arg or Lys), Asp-ase (cleaving after Asp), Met-ase (cleaving after Met or Leu), and chymase (cleaving after Phe, Tyr, or Trp). Natural serpins and synthetic inhibitors (including isocoumarins, peptide chloromethyl ketones, and peptide phosphonates) inhibit granzymes. Studies of substrate and inhibitor kinetics are providing valuable information to identify the most likely natural granzyme substrates and provide tools for the study of key reactions in the cytolytic mechanism.

Granzyme A loading induces rapid cytolysis and a novel form of DNA damage independently of caspase activation

Cytotoxic lymphocytes trigger apoptosis by releasing perforin and granzymes (Grn). GrnB activates the caspase apoptotic pathway, but little is known about GrnA-induced cell death. Perforin was used to load recombinant GrnA and GrnB and enzymatically inactive variants into target cells. GrnA induces single-strand DNA breaks that can be labeled with Klenow polymerase and visualized on alkaline gels. GrnA-induced DNA damage but not cytolysis requires GrnA proteolysis. GrnA-induced membrane perturbation, nuclear condensation, and DNA damage are unimpaired by caspase blockade. GrnA fails to induce cleavage of caspase-3, lamin B, rho-GTPase, or PARP. GrnA-induced cytotoxicity and cleavage of PHAP II, a previously identified GrnA substrate, are unimpaired in Jurkat cells that overexpress bcl-2. Therefore, GrnA activates a novel apoptotic pathway.

Definition and redesign of the extended substrate specificity of granzyme B

Granzyme B is a protease involved in the induction of rapid target cell death by cytotoxic lymphocytes. Definition of the substrate specificity of granzyme B allows for the identification of in vivo substrates in this process. By using the combinatorial methods of synthetic substrate libraries and substrate-phage display, an optimal substrate for granzyme B that spans over six subsites was determined to be Ile-Glu-Xaa-(Asp downward arrowXaa)-Gly, with cleavage of the Asp downward arrowXaa peptide bond. Granzyme B proteolysis was shown to be highly dependent on the length and sequence of the substrate, supporting the role of granzyme B as a regulatory protease. Arginine 192 was identified as a determinant of P3-Glu and P1-Asp substrate specificity. Mutagenesis of arginine 192 to glutamate reversed the preference for negatively charged amino acids at P3 to positively charged amino acids. The preferred substrate sequence matches the activation sites of caspase 3 and caspase 7 and thus is consistent with the role of granzyme B in activation of these proteases during apoptosis. The caspase substrate poly(ADP)-ribose polymerase is cleaved by granzyme B in a cell-free assay at two sites that resemble the granzyme B specificity determined by the combinatorial methods. Many caspase substrates contain granzyme B cleavage sites and are proposed as potential granzyme B targets, suggesting a redundant function with certain caspases.

Synthesis and kinetic studies of diphenyl 1-(N-peptidylamino)alkanephosphonate esters and their biotinylated derivatives as inhibitors of serine proteases and probes for lymphocyte granzymes

Diphenyl 1-(N-peptidylamino)alkanephosphonate esters are highly reactive, specific, and aqueously stable irreversible inhibitors which can be used to probe the functions of many serine proteases, including the lymphocyte granzymes. We synthesized 16 peptide phosphonates with Ala, Met, Phe, or Val P1 amino acid residues, including two biotinylated derivatives for future functional and biochemical characterization of granzymes. The reactivity of the inhibitors was characterized with human leukocyte elastase (HLE), porcine pancreatic elastase (PPE), bovine chymotrypsin, and the granzymes of natural killer (NK) cells, which include a number of proteolytic activities (Asp-ase, Met-ase, etc.) that cleave peptide substrates with these residues in the P1 position. The reactivity and specificity of the phosphonates depended on the length and sequence of the peptidyl moiety and on the leaving group. Z-Ala-Ala-AlaP(OPh)2 was a good inhibitor of HLE and PPE (k(obsd)/[I] = 38 and 30 M(-1) s(-1), respectively) and had little reactivity with chymotrypsin. Z-Phe-Pro-Phe-P(OPh)2 was a good inhibitor of chymotrypsin (k(obsd)/[I] = 17,000 M(-1) s(-1)) and had little reactivity with the elastases. The leaving group of Z-MetP(OPh-4-Cl)2 made it a more effective chymotrypsin inhibitor than Z-MetP(OPh)2 (k(obsd)/[I] values of 142 and 30 M(-1) s(-1), respectively). With granzymes, the compounds reacted with a fraction of the Met-ase, chymase, and Ser-ase activities and lacked reactivity with Asp-ase and tryptase. Z-MetP(OPh-4-Cl)2 was an excellent inhibitor of Met-ase 1. Bi-Aca-Aca-Phe-Leu-PheP(OPh)2 appears to react specifically with one chymase while leaving other chymases untouched. Perforin-dependent lysis mediated by cytotoxic lymphocyte granules was inactivated by Z-Ala-Ala-AlaP(OPh)2, Z-MetP(OPh-4-Cl)2, Z-Leu-PheP(OPh)2, and Bi-Aca-Aca-Phe-Leu-PheP(OPh)2. The biochemical properties and biological efficacy of these inhibitors make them suitable for cellular and physiological studies of granzyme function.

Perforin-enhancing protein, a low molecular weight protein of cytotoxic lymphocyte granules, enhances perforin lysis

Perforin is a 68 kD protein found in the granules of cytotoxic lymphocytes and is used by lymphocytes to form lethal pores in the membranes of the cells they kill. We and others have found that when perforin is purified, its lytic activity is markedly reduced. ELISAs indicated that our final recovery of perforin protein was excellent. We decided to determine if depletion of other granule proteins contributed to the loss of lytic activity. We isolated perforin to the point where lytic activity was diminished and added back granule proteins that had no lytic activity or detectable (antigenic) perforin. Perforin was isolated by Cu2+-immobilized metal affinity chromatography (IMAC) followed by phenyl-Superose hydrophobic interaction chromatography (HIC). Its lytic activity was enhanced by a low molecular weight (<15 kD) protein, perforin enhancing protein (PEPr). We have isolated PEPr by two methods, HIC and MonoQ. Nonlytic PEPr restored perforin to close to its original lytic activity. A protein similar if not identical to PEPr was also detectable as an 125I-labeled protein associated with lytic perforin. We propose that PEPr acts in conjunction with perforin to form lethal pores and suggest that PEPr may be the rat equivalent of the human cytotoxic lymphocyte protein, granulysin.

Peptide thioester substrates for serine peptidases and metalloendopeptidases

Peptide thioesters are sensitive substrates of various serine peptidases and metalloendopeptidases. Thioester substrates generally have high enzymatic hydrolysis rates and low background hydrolysis rates, and the hydrolysis rates can be easily monitored in the presence of thiol reagents such as 4,4'-dithiodipyridine or 5,5'-dithiobis (2-nitrobenzoic acid). Peptide thioester substrates have been invaluable for the study of enzyme specificity and enzyme inhibitors, especially in cases where no other practical synthetic substrates are available. Tripeptide substrates of the type Boc-Ala-Ala-AA-SBzl, where AA is nearly all of the 20 common amino acids, have now been synthesized and should be useful for the subsite mapping of new serine peptidases and the study of crude cell preparations containing serine peptidases.

Nongranular proteolytic enzymes of rat IL-2-activated natural killer cells. II. Purification and identification of rat A-NKP 1 and A-NKP 2 as constituents of the multicatalytic proteinase (proteasome) complex

We have recently described nongranular, cytosolic, high-molecular-weight trypsin-like (A-NKP 1) and chymotrypsin-like (A-NKP 2) proteases of interleukin-2-activated rat natural killer (A-NK) cells. A functional correlation between the inactivation of A-NKP 2 and the inhibition of rat A-NK cell-mediated cytotoxicity was found. Herein we describe the 6,000-fold purification of A-NKP 2 to apparent homogeneity following: isopycnic sucrose gradient fractionation of postnuclear supernatants, molecular sieve chromatography, and heparin-Sepharose chromatography. We also report the novel finding that A-NKP 2 as well as A-NKP 1, derived from either rat A-NK cells or the rat NK leukemic cell line CRNK-16, are constituents of the multicatalytic proteinase (MCP/proteasome) complexes of these cells. Characteristic biochemical, biophysical, and electron microscopic/ultrastructural similarity to the rat liver proteasome was observed. However, Western blot analysis using polyclonal antibodies to the rat liver proteasome clearly indicated differences in the rat hepatic proteasome and the CRNK-16-derived proteasomal subunits. The identification, characterization, and purification of A-NKP 1 and A-NKP 2, described herein, now allow for further investigation of the potential role of these proteasome components in NK cell function. Moreover, the proteasome of NK and A-NK cells can now be compared and contrasted to the granzymes of lytic granules with respect to their role in cell-mediated cytotoxicity.

Sulfonyl fluoride serine protease inhibitors inactivate RNK-16 lymphocyte granule proteases and reduce lysis by granule extracts and perforin

Cytolytic granules purified from natural killer lymphocytes (NK) contain a pore-forming protein (perforin) and a number of serine proteases. When these proteases are inhibited by serine protease-specific isocoumarin reagents the serine proteases are inactivated and the cytolytic activity of the granules is decreased. Paradoxically, it has been found that the general serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) frequently cannot block killing even though it inhibits many of the serine proteases. At the same time it has been reported that "purified" perforin alone can lyze cells. To address these inconsistencies we first compared the ability of PMSF and four new sulfonyl fluoride serine protease inhibitors to inhibit proteases and cell lysis. We determined the effects on lysis and the second order inhibition rate constants for five granule protease activities: ly-tryptase, ly-chymase, Met-ase (methionine cleaving), Ser-ase (serine cleaving) and Asp-ase (aspartic acid cleaving). One compound, 2-(Z-NH(CH2)2CONH)C6SO2F, was a potent inhibitor of Met-ase activity (k(obsd)/[I] = 162 M-1 s-1), ly-chymase activity (k(obsd)/[I] = 147 M-1 s-1), and granule-mediated as well as perforin-mediated lysis. PMSF was a poor inhibitor of granule proteases (k(obsd)/[I]'s less than 7 M-1 s-1 for four activities and no inhibition of Ser-ase); the lack of reactivity is consistent with the failure of PMSF to block granule lytic activity. We also prepared enriched perforin by anion exchange chromatography and showed that a ly-chymase and a Met-ase associated with perforin. By inhibiting these proteases we also inhibited lytic activity.

Human and murine cytotoxic T lymphocyte serine proteases: subsite mapping with peptide thioester substrates and inhibition of enzyme activity and cytolysis by isocoumarins

The active site structures of human Q31 granzyme A, murine granzymes (A, B, C, D, E, and F), and human granzymes (A, B, and 3) isolated from cytotoxic T lymphocytes (CTL) were studied with peptide thioester substrates, peptide chloromethyl ketone, and isocoumarin inhibitors. Human Q31, murine, and human granzyme A hydrolyzed Arg- or Lys-containing thioesters very efficiently with kcat/KM of 10(4)-10(5) M-1 s-1. Murine granzyme B was found to have Asp-ase activity and hydrolyzed Boc-Ala-Ala-Asp-SBzl with a kcat/KM value of 2.3 X 10(5) M-1 s-1. The rate was accelerated 1.4-fold when the 0.05 M NaCl in the assay was replaced with CaCl2. The preparation of granzyme B also had significant activity toward Boc-Ala-Ala-AA-SBzl substrates, where AA was Asn, Met, or Ser [kcat/KM = (4-5) X 10(4) M-1 s-1]. Murine granzymes C, D, and E did not hydrolyze any thioester substrate but contained minor contaminating activity toward Arg- or Lys-containing thioesters. Murine granzyme F had small activity toward Suc-Phe-Leu-Phe-SBzl, along with some contaminating trypsin-like activity. Human Q31 granzyme A, murine, and human granzyme A were inhibited quite efficiently by mechanism-based isocoumarin inhibitors substituted with basic groups (guanidino or isothiureidopropoxy). Although the general serine protease inhibitor 3,4-dichloroisocoumarin (DCI) inactivated these tryptases poorly, it was the best isocoumarin inhibitor for murine granzyme B (kobs/[I] = 3700-4200 M-1 s-1). Murine and human granzyme B were also inhibited by Boc-Ala-Ala-Asp-CH2Cl; however, the inhibition was less potent than that with DCI. DCI, 3-(3-amino-propoxy)-4-chloroisocoumarin, 4-chloro-3-(3-isothiureidopropoxy)isocoumarin, and 7-amino-4-chloro-3-(3-isothiureidopropoxy)isocoumarin inhibited Q31 cytotoxic T lymphocyte mediated lysis of human JY lymphoblasts (ED50 = 0.5-5.0 microM).

The enzymatic activity of human cytotoxic T-lymphocyte granzyme A and cytolysis mediated by cytotoxic T-lymphocytes are potently inhibited by a synthetic antiprotease, FUT-175

The synthetic antiprotease, FUT-175 (6-amidino-2-naphthyl-4-guanidinobenzoate), was found to be an extraordinarily potent and rapid inhibitor of human Q31 cytotoxic T-lymphocyte granzyme A. The granzyme A was inhibited in a time-dependent manner with kobs/i = 430,000 +/- 80,000 M-1 s-1. Four other FUT-175 analogs were also found to be potent, rapid Q31 granzyme A inhibitors. All five compounds inhibited Q31 cytotoxic T-lymphocyte-mediated cytolysis of human JY lymphoma cells, but at concentrations far in excess of those needed for granzyme A inhibition. The data presented suggest that postmarketing surveillance of FUT-175 should include a review of possible immunosuppressive side-effects, such as increased susceptibility to viral infections and to neoplastic transformations.

Comparison of the effects of purified human alpha 1-antichymotrypsin and alpha 1-proteinase inhibitor on NK cytotoxicity: only alpha 1-proteinase inhibitor inhibits natural killing

While an inhibitory effect on natural killer (NK) cell activity was demonstrated with partially purified alpha 1 Achy, neither highly purified alpha 1 Achy from two healthy donors nor from one patient with giant-cell arteritis, which carries more highly branched glycans, inhibited the NK cytotoxicity. Our purification procedure, based on immunoaffinity chromatography and gel filtration, was not in question since the pure alpha 1-proteinase inhibitor (alpha 1PI) prepared in our laboratory by using a similar procedure continued to inhibit the NK cytotoxicity. If an inhibitory effect not related to antiprotease activity occurs with alpha 1PI, it is surprising that it is not shared by alpha 1 Achy which, like alpha 1PI, belongs to the serpin family and which possesses a strong structural homology with alpha 1PI. Our finding that alpha 1PI is able to affect human NK cytotoxicity while alpha 1 Achy (even with more highly branched glycans) is unable to suggests that events controlling NK activity may involve other enzymes than chymotrypsin-like enzymes.

Prognostic significance of alpha-1-antitrypsin in early stage of colorectal carcinomas

We have previously shown that human colorectal carcinoma cell lines, RCM-1 and CoCM-1, synthesize alpha-1-antitrypsin (alpha 1-AT) in culture. We have studied immunohistochemically the incidence of alpha 1-AT on histologic sections from paraffin-embedded tissues of surgically resected colorectal carcinomas and their metastatic foci, polypectomized adenomas, and normal mucosae. alpha 1-AT was detected in 89 (61%) of 145 carcinomas (including 14 carcinomas in adenoma), and 12 (39%) of 31 adenomas. But only 2 (4%) of 55 normal colorectal mucosae were positive for alpha 1-AT. In metastatic tumor cells of colorectal carcinomas in lymph nodes and other organs, alpha 1-AT positivity was 60% and 82%, respectively. The incidence of alpha 1-AT was markedly higher in advanced adenocarcinomas than in early ones and more frequent in adenocarcinomas of right side (including transverse colon) than those of left side and rectum, regardless of their histological malignancy grades. In mucinous carcinomas the frequency was greater (8 of 9 cases) than in conventional adenocarcinomas. Clinical follow-up of the patients with colorectal carcinomas suggested that alpha 1-AT positivity in Dukes' stage A/B tends to correlate with unfavorable prognosis irrespective of the grade of histologic differentiation of carcinoma, but there is no significant relation in Dukes' stage C/D. Our findings suggest that alpha 1-AT in colorectal carcinoma is related to the invasive and metastatic capacity. It may thus serve as a biologic marker for prognosis of colorectal carcinomas at relatively early stages (Dukes' stage A/B).

An inhibitor specific for the mouse T-cell associated serine proteinase 1 (TSP-1) inhibits the cytolytic potential of cytoplasmic granules but not of intact cytolytic T cells

We have investigated a proteinase inhibitor, designed according to the preferred amino acid sequence that is cleaved by the murine T-cell specific serine proteinase 1 (TSP-1) for its effect on the cytolytic potential of cloned cytotoxic T-cell lines (CTLL) and of cytoplasmic granules, derived from these cells. Pretreatment of effector cells with H-D-Pro-Phe-Arg-chloromethyl-ketone (PFR-CK) prior to the cytotoxicity assay did not result in inhibition of cytolytic activity of three independent CTLL and did not effect their granule-associated TSP-1 activity after extraction with Triton X-100. Furthermore, PFR-CK did not interfere with cytolysis of target cells by CTLL when present for the entire incubation period. In contrast, PFR-CK inhibited in a dose-dependent manner both TSP-1 activity and the hemolytic/cytolytic potential of isolated cytoplasmic granules after their pretreatment with high-salt concentration. We interpret these results to mean that cytolysis of target cells by CTLL involves the granule-associated proteinase TSP-1, which probably becomes active upon exocytosis following effector-target cell interactions.

Mechanism-based isocoumarin inhibitors for serine proteases: use of active site structure and substrate specificity in inhibitor design

Isocoumarins are potent mechanism-based heterocyclic irreversible inhibitors for a variety of serine proteases. Most serine proteases are inhibited by the general serine protease inhibitor 3,4-dichloroisocoumarin, whereas isocoumarins containing hydrophobic 7-acylamino groups are potent inhibitors for human leukocyte elastase and those containing 7-alkylureidogroups are inhibitors for procine pancreatic elastase. Isocoumarins containing basic side chains that resemble arginine are potent inhibitors for trypsin-like enzymes. A number of 3-alkoxy-4-chloro-7-guanidinoisocoumarins are potent inhibitors of bovine thrombin, human factor Xa, human factor XIa, human factor XIIa, human plasma kallikrein, porcine pancreatic kallikrein, and bovine trypsin. Another cathionic derivative, 4-chloro-3-(2-isothiureidoethoxy) isocoumarin, is less reactive toward many of these enzymes but is an extremely potent inhibitor of human plasma kallikrein. Several guanidinoisocoumarins have been tested as anticoagulants in human plasma and are effective at prolonging the prothrombin time. The mechanism of inhibition by this class of heterocyclic inactivators involves formation of an acyl enzyme by reaction of the active site serine with the isocoumarin carbonyl group. Isocoumarins with 7-amino or 7-guanidino groups will then decompose further to quinone imine methide intermediates, which react further with an active site residue (probably His-57) to form stable inhibited enzyme derivatives. Isocoumarins should be useful in further investigations of the physiological function of serine proteases and may have future therapeutic utility for the treatment of emphysema and coagulation disorders.

New human colorectal carcinoma cell lines that secrete proteinase inhibitors in vitro

Two new human cell lines, RCM-1 and CoCM-1, have been established from primary colorectal adenocarcinomas. Both cell lines were unique in that the cultures secreted trypsin inhibitors in vitro. The activities of these inhibitors were accumulated in serum-free media of both cell lines over a period of several days. Two inhibitors (PI-1 and PI-2) were isolated from serum-free conditioned medium in which RCM-1 was grown by anion-exchange and gel filtration high-performance liquid chromatography. PI-1 inhibited trypsin and chymotrypsin strongly, and pancreatic elastase weakly. Its molecular weight was about 57 kilodaltons (Kd) as determined by gel filtration chromatography. It cross-reacted with the antiserum elicited against human alpha 1-antitrypsin in double immunodiffusion. PI-1 corresponding to alpha 1-antitrypsin was also demonstrated immunohistochemically in both cell lines. PI-2 inhibited trypsin strongly, and chymotrypsin, kallikrein and plasmin weakly. It had higher molecular weight (200-300 Kd) than that of PI-1, and did not cross-react with antisera against human alpha 1-antitrypsin, alpha 2-macroglobulin, alpha 1-antichymotrypsin, alpha 2-plasmin inhibitor, inter-alpha-trypsin inhibitor and urinary trypsin inhibitor. RCM-1 and CoCM-1 are the first colorectal adenocarcinoma cell lines that secrete functionally active trypsin inhibitors, including alpha 1-antitrypsin in vitro, and are useful for the study of tumor-cell derived proteinase inhibitors.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.

Localization, implications for function, and gene expression of chymotrypsin-like proteinases of cytotoxic RNK-16 lymphocytes

Rat RNK-16 leukemia cells kill YAC-1, which are the cells lysed by rodent natural killer lymphocytes. We found chymotrypsin-like proteinase ('chymase') activity in the RNK-16 dense granules that also contain cytolytic activity. The chymase activity hydrolyzed the thiobenzyl peptide substrate Suc-Phe-Leu-Phe-SBzl and, in comparison to RNK-16 tryptase activity, was selectively inhibited by three different types of serine proteinase inhibitors. The selective inhibitors were the fungal aldehyde chymostatin, the chloromethylketone Z-Gly-Leu-Phe-CH2Cl, and the mechanism-based or 'suicide' inhibitor 7-amino-4-chloro-3-(2-phenylethoxy)isocoumarin. These proteinase inhibitors also blocked RNK-16 granule-mediated cytolysis. Chymostatin, a reversible inhibitor, delayed granule-mediated cytolysis, whereas the irreversible chloromethylketone and isocoumarin proteinase inhibitors completely abrogated granule-mediated cytolysis. The two irreversible inhibitors displayed biphasic inhibition of the chymase activity, indicating that at least two chymases are present in the granules. By Northern blot analysis, we found that RNK-16 mRNA hybridized strongly with a cDNA probe of CCPI, a mouse cytotoxic T lymphocyte serine proteinase gene. These data imply that chymase activity in the cytotoxic granules is important for cytolytic function and is likely to belong to a new subfamily of serine proteinases.

Lysis by RNK-16 cytotoxic lymphocyte granules. Rate assays and conditions to study control of cytolysis

Dense subcellular granules of cytolytic lymphocytes can mediate rapid lysis of erythrocytes or nucleated cells. The granules contain several different proteases and proteoglycans that regulate cytolysis. We describe a rate assay that we have already used to demonstrate the requirement for serine proteases in granule-mediated lysis. In this assay, 51Cr-labeled erythrocytes are lysed by limiting concentrations of granules from RNK-16 tumor cells. Cytolysis is initiated by the addition of calcium (1 mM final concentration) and stopped at 0.5-1 min intervals by acidification to pH 6.0. The effects of the granule protein concentration, temperature, the concentration of erythrocytes, pH, and the concentration of calcium on the rate of lysis are reported. A preliminary mathematical approach is described and suggested as a means to differentiate 'lag' or activation times from the initial burst of lysis. With this rate assay, we have found four classes of protease inhibitors that block granule-mediated lysis (Hudig et al. (1987) Biochem. Biophys. Res. Commun. 149, 882). The utility of the rate assays is underscored by the observation that reversible protease inhibitors only showed rates of cytolysis whereas irreversible protease inhibitors stopped cytolysis completely. Rate assays are essential for future analyses of the complex physiological regulation of granule-mediated cytotoxicity by proteases, endogenous protease inhibitors and proteoglycans.