The adaptor SAP controls NK cell activation by regulating the enzymes Vav-1 and SHIP-1 and by enhancing conjugates with target cells.

The adaptor SAP, mutated in X-linked lymphoproliferative disease, has critical roles in multiple immune cell types. Among these, SAP is essential for the ability of natural killer (NK) cells to eliminate abnormal hematopoietic cells. Herein, we elucidated the molecular and cellular bases of this activity. SAP enhanced NK cell responsiveness by a dual molecular mechanism. It coupled SLAM family receptors to the kinase Fyn, which triggered the exchange factor Vav-1 and augmented NK cell activation. SAP also prevented the inhibitory function of SLAM family receptors. This effect was Fyn independent and correlated with uncoupling of SLAM family receptors from the lipid phosphatase SHIP-1. Both mechanisms cooperated to enable conjugate formation with target cells and to stimulate cytotoxicity and cytokine secretion by NK cells. These data showed that SAP secures NK cell activation by a dichotomous molecular mechanism, which is required for conjugate formation. These findings may have implications for the role of SAP in other immune cell types.

Granzyme B-mRNA expression by equine lymphokine activated killer (LAK) cells is associated with the induction of apoptosis in target cells.

Lymphokine-activated killer (LAK) cells are a subset of cytotoxic cells capable of lysing freshly isolated tumor cells. While LAK activity is typically measured using the (51)Cr-release assay, here we used a non-radioactive flow cytometric method to demonstrate equine LAK activity. Equine peripheral blood mononuclear cells (PBMC) were stimulated in vitro with recombinant human interleukin 2 (hIL-2) to generate LAK cells. An equine tumor cell line, EqT8888, labeled with carboxyfluorescein succinimidyl ester (CFSE) was used as target cells. Following incubation of the targets with different concentrations of LAK cells, Annexin V was added to identify the early apoptotic cells. With increasing effector to target cell ratios, EqT8888 apoptosis was increased. We also measured interferon-gamma, granzyme B and perforin mRNA expression in the LAK cell cultures as possible surrogate markers for cytotoxic cell activity and found granzyme B mRNA expression correlated best with LAK activity. Also, we found that the reduced LAK activity of young horses was associated with decreased granzyme B mRNA expression. Our results indicate that fluorescence-based detection of LAK cell activity provides a suitable non-radioactive alternative to (51)Cr-release assays and mRNA expression of granzyme B can be used as surrogate marker for these cytotoxic cells.

Association of CD38 with nonmuscle myosin heavy chain IIA and Lck is essential for the internalization and activation of CD38.

Activation of CD38 in lymphokine-activated killer (LAK) cells involves interleukin-8 (IL8)-mediated protein kinase G (PKG) activation and results in an increase in the sustained intracellular Ca(2+) concentration ([Ca(2+)](i)), cADP-ribose, and LAK cell migration. However, direct phosphorylation or activation of CD38 by PKG has not been observed in vitro. In this study, we examined the molecular mechanism of PKG-mediated activation of CD38. Nonmuscle myosin heavy chain IIA (MHCIIA) was identified as a CD38-associated protein upon IL8 stimulation. The IL8-induced association of MHCIIA with CD38 was dependent on PKG-mediated phosphorylation of MHCIIA. Supporting these observations, IL8- or cell-permeable cGMP analog-induced formation of cADP-ribose, increase in [Ca(2+)](i), and migration of LAK cells were inhibited by treatment with the MHCIIA inhibitor blebbistatin. Binding studies using purified proteins revealed that the association of MHCIIA with CD38 occurred through Lck, a tyrosine kinase. Moreover, these three molecules co-immunoprecipitated upon IL8 stimulation of LAK cells. IL8 treatment of LAK cells resulted in internalization of CD38, which co-localized with MHCIIA and Lck, and blebbistatin blocked internalization of CD38. These findings demonstrate that the association of phospho-MHCIIA with Lck and CD38 is a critical step in the internalization and activation of CD38.

Lymphokine-activated killer T-cell-originated protein kinase phosphorylation of histone H2AX prevents arsenite-induced apoptosis in RPMI7951 melanoma cells.

PURPOSE: Arsenic is a valuable therapeutic tool in cancer treatment. Lymphokine-activated killer T-cell-originated protein kinase (TOPK) is highly expressed in cancer cells, but its specific function is still unknown. We investigated the role of TOPK in arsenic-induced apoptosis in RPMI7951 human melanoma cells. EXPERIMENTAL DESIGN: Expression of TOPK was evaluated in different melanoma cell lines, and liquid chromatography-tandem mass spectrometry analysis was used to identify proteins binding with TOPK. Immunofluorescence, Western blot, and flow cytometry were used to assess the effect of arsenic on TOPK, histone H2AX, and apoptosis in RPMI7951 cells. RESULTS: Melanoma cell lines expressing high levels of TOPK were more resistant to arsenite (As(3+))-induced apoptosis. As(3+) treatment induced phosphorylation of TOPK and histone H2AX in RPMI7951 human melanoma cells. Liquid chromatography-tandem mass spectrometry results indicated that TOPK could bind with histone H2AX, and in vitro and in vivo assays confirmed that TOPK binds with and phosphorylates histone H2AX. As(3+) treatment caused phosphorylation of TOPK, which colocalized with phosphorylated histone H2AX in the nucleus. TOPK small interfering RNA cells exhibited a decreased phosphorylation of histone H2AX with As(3+) treatment. As(3+)-induced apoptosis was decreased in H2AX(-/-) cells but increased in TOPK small interfering RNA cells. CONCLUSIONS: TOPK binds with histone H2AX and inhibits As(3+)-induced apoptosis through phosphorylation of histone H2AX. Melanoma cell lines with high levels of TOPK are more resistant to As(3+)-induced apoptosis. Therefore, inhibition of TOPK activity combined with As(3+) treatment may be helpful in the treatment of melanomas.

[In vitro purging effect of CD3AK/iNOS on leukemia cells].

BACKGROUND & OBJECTIVE: LAK cells have been applied to purge minimal residual leukemia cells in allogeneic hematopoietic stem cell transplantation(AHSCT) in clinic practice. CD3AK cells belong to T lymphocytes activated by anti-CD3McAb. This study was to construct nitric oxide donor CD3AK/iNOS through transfecting inducible nitric oxide synthase (iNOS) gene into human CD3AK cells by retroviral vector, and investigate the cytotoxic activity of CD3AK/iNOS to leukemia cell lines K562 and K562/ADM. METHODS: The amphotropic packaging cell line PA317 transfected with iNOS gene was cultivated to obtain viral supernatant. Human peripheral blood mononuclear cells (PBMNCs) were isolated and activated by anti-CD3McAb and low dose of interleukin-2 (IL-2). CD3AK cells were incubated with viral supernatant. The amount of nitric oxide (NO) and the activity of iNOS in the cultured supernatant of CD3AK/iNOS were evaluated. The cytotoxic activities of CD3AK/iNOS and CD3AK cells to K562 and K562/ADM cells were evaluated by MTT assay. RESULTS: The contents of NO excreted by CD3AK/iNOS and CD3AK cells were (378.60+/-41.57) micromol/L and (98.07+/-22.31) micromol/L, respectively (P<0.001); the activities of iNOS synthesized by CD3AK/iNOS and CD3AK cells were (20.77+/-2.49) U/ml and (9.81+/-1.96) U/ml, respectively (P<0.001). The cytotoxic activities of CD3AK/iNOS cells to K562 and K562/ADM cells were significantly stronger than those of CD3AK [(64.85+/-18.13)% vs. (45.66+/-17.46)%, P<0.05; (63.80+/-9.93)% vs. (47.85+/-12.01)%, P<0.05]. CONCLUSIONS: The content of NO and activity of iNOS synthesized and excreted by CD3AK/iNOS cells are largely increased compared with those of CD3AK cells. CD3AK/iNOS cells have more significant cytotoxic activity to K562 and K562/ADM cells than CD3AK cells, but its cytotoxic activities to K562 and K562/ADM cells are similar.

Characterization of murine cathepsin W and its role in cell-mediated cytotoxicity.

Cathepsin W is a member of the papain-like family of cysteine proteases. In this report, we have isolated the cDNA for murine CtsW (mCtsW) from a splenocyte library. The deduced 371-amino-acid sequence shares 68% identity with human CtsW and includes the conserved catalytic triad cysteine, histidine, and asparagine found in all members of this family. In addition to the fulllength form of mCtsW, we have isolated an alternatively spliced form of the mRNA that lacks a complete catalytic triad. An S1 nuclease protection assay and a Western blot analysis showed that mCtsW is mainly restricted to the CD8(+) T cell and natural killer cell compartments. In addition, we confirmed that, like its human homologue, mCtsW is localized mainly to the endoplasmic reticulum and its expression is up-regulated upon activation. We also characterized the mCtsW locus using bacterial artificial chromosome clones. The gene consists of 10 coding exons and 9 introns spanning 3.2 kb. To elucidate the physiologic role of this protease, we generated mice deficient in mCtsW. Our data establish that mCtsW is not required for cytotoxic lymphocyte-induced target cell death in vitro. In addition, mCtsW deficiency does not alter the susceptibility of cytotoxic lymphocytes to suicide or fratricide after degranulation. Thus, mCtsW does not have a unique role in target cell apoptosis or cytotoxic cell survival in vitro.

Dysregulation of telomerase activity and expression in lymphokine-activated killer cells from advanced cancer patients: possible involvement in cancer-associated immunosuppression mechanism.

There exists cancer-associated immunosuppression, and the generation of lymphokine-activated killer (LAK) cells is impaired in patients with advanced cancer. Telomerase has been reported to be upregulated in the activation of lymphocytes to proliferate against immune stimulation as well as in the malignant transformation of immortal cancer cells. We attempted to clarify the involvement of telomerase in the impairment of LAK cell generation in patients with advanced cancer. LAK cells were generated by stimulation with interleukin (IL)-2 and immobilized anti-CD3 antibody (IL-2/CD3 system) from peripheral blood mononuclear cells of healthy volunteers (he-LAK) or patients with advanced cancer (ca-LAK), and proliferative potential of LAK cells was evaluated on the basis of population doubling level (PDL). Telomere length and telomerase activity of LAK cells were measured by the hybridization with oligonucleotide (TTAGGG)4 and by the telomeric repeat amplification protocol (TRAP) assay, respectively. Effects on telomerase activity in LAK cells of serum from cancer patients, transforming growth factor (TGF)-beta, and IL-10 were also examined. The lifespan of ca-LAK (15.2 +/- 5.1 PDLs) was significantly shorter than that of he-LAK (22.6 +/- 8.3 PDLs) (p = 0.0358). There were no significant differences between he- and ca-LAK in telomere length before IL-2/CD3 stimulation and maximal telomerase activity induced. The telomerase activity induced in ca-LAK failed to elongate sufficiently the telomeric ends (-35.2 +/- 46.2 bp) compared with that in he-LAK (16.8 +/- 41.5 bp) (p = 0.0448). The telomerase activity was initially detectable on day 2 in all he-LAK, whereas 8 (61.5%) of 13 ca-LAK expressed telomerase activity on day 3 or later following the stimulation, showing a significant retardation of telomerase expression (p = 0.0116). The addition to the LAK cell generation system of serum from cancer patients, as well as IL-10, but not transforming growth factor (TGF)-beta, suppressed the telomerase activity. This serum-induced suppression of telomerase activity in LAK cells was abrogated with the addition of anti-IL-10 antibody but not with anti-TGF-beta antibody. It is suggested that the dysregulation of telomerase activity and expression exists in LAK cells of cancer patients, resulting in the impairment of LAK cell generation in patients with advanced cancer. Serum IL-10 may be involved in the impairment of LAK cell generation by the suppression of telomerase activity of lymphocytes in vivo. Thus, the dysregulation mechanism of telomerase activity and expression in lymphocytes of cancer patients may be attributable, in part, to cancer-associated immunosuppression.

DFF45/ICAD can be directly processed by granzyme B during the induction of apoptosis.

Granzyme B (GzmB) is a component of cytotoxic lymphocyte granules that can rapidly initiate apoptosis in target cells. While several procaspases are cleaved and activated by GzmB, the absolute requirement of caspase activation for GzmB-induced apoptosis is controversial. In this report, we demonstrate that GzmB can initiate apoptosis in the absence of caspase-3 activity by directly cleaving DFF45/ICAD to liberate activated DFF40/CAD. DFF45/ICAD cleavage occurs less efficiently in cells that lack caspase-3 activity, suggesting that the caspases normally amplify the GzmB death signal. DFF45/ICAD-deficient mouse embryo fibroblasts are partially resistant to GzmB-induced death, demonstrating the biological importance of DFF45/ICAD for GzmB-mediated apoptosis.

IL-2 activation of NK cells: involvement of MKK1/2/ERK but not p38 kinase pathway.

IL-2 stimulates extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) in various immune cell populations. The functional roles that these kinases play are still unclear. In this study, we examined whether MAPK kinase (MKK)/ERK and p38 MAPK pathways are necessary for IL-2 to activate NK cells. Using freshly isolated human NK cells, we established that an intact MKK/ERK pathway is necessary for IL-2 to activate NK cells to express at least four known biological responses: LAK generation, IFN-gamma secretion, and CD25 and CD69 expression. IL-2 induced ERK activation within 5 min. Treatment of NK cells with a specific inhibitor of MKK1/2, PD98059, during the IL-2 stimulation blocked in a dose-dependent manner each of four sequelae, with inhibition of lymphokine-activated killing induction being least sensitive to MKK/ERK pathway blockade. Activation of p38 MAPK by IL-2 was not detected in NK cells. In contrast to what was observed by others in T lymphocytes, SB203850, a specific inhibitor of p38 MAPK, did not inhibit IL-2-activated NK functions. This data indicate that p38 MAPK activation was not required for IL-2 to activate NK cells for the four functions examined. These results reveal selective signaling differences between NK cells and T lymphocytes; in NK cells, the MKK/ERK pathway and not p38 MAPK plays a critical positive regulatory role during activation by IL-2.

Immunoregulating properties of peptides related to tumor rejection antigens: effect on human monocytes and natural killer cells.

The authors analyzed the effect of several 15-amino acid peptides with sequences related to tumor-rejection antigens, tyrosinase, and the MAGE family on peripheral blood mononuclear cells from healthy donors cultured for periods of 1 to 7 days. Some of these peptides promoted stimulation of monocytes, manifested by phenotypic changes, release of interleukin (IL)-1a, IL-6, and tumor necrosis factor-alpha, and induction of nitric oxide synthase on differentiated CD14++/+ CD16+ DR++ monocytes. An increase in the percentage of cytotoxic monocytes (CD14+/- CD16+) containing granule-associated DNase activity was also observed. Active peptides induced the release of IL-2 and interferon-gamma. Nonspecific natural killer and lymphokine-activated killer cell-mediated cytotoxicity was also observed against classical target cell lines (K-562 and Daudi) and allogenic melanoma cell lines AC and BB, together with an increase in granule-associated DNase in the natural killer cell-enriched population. Monocytes were needed to enhance this innate response, because peptides failed to induce the release of IL-2 on monocyte-depleted peripheral blood mononuclear cells. Data show an enhancement of the rapid innate immune response by peptides related to tumor rejection antigens and suggest that they could also determine the nature of a slow and more definitive specific immune response against tumor cells.

Cloning and expression of a novel MAPKK-like protein kinase, lymphokine-activated killer T-cell-originated protein kinase, specifically expressed in the testis and activated lymphoid cells.

A novel protein kinase, TOPK (T-LAK cell-originated protein kinase), was isolated from a lymphokine-activated killer T (T-LAK) cell subtraction cDNA fragment library. The open reading frame of the TOPK gene encodes a protein of 322 amino acids, possessing a protein kinase domain profile. The cap site analysis of the 5'-end of TOPK mRNA revealed two forms, a major full-length form and a minor spliced form at the 5'-site, both encoding the same protein. A BLAST homology search and phylogenetic analysis indicated that TOPK is related to dual specific mitogen-activated protein kinase kinase (MAPKK). The transfection of the TOPK gene to COS-7 cells up-regulated a phosphorylation of p38 MAPK but not ERK1/2 or SAPK/JNK. Gel precipitation study indicated that TOPK protein can be associated with p38 in vitro. Tissue distribution of TOPK mRNA expression was specific for the testis, T-LAK cells, activated lymphoid cells, and lymphoid tumors. On the other hand, deactivated T-LAK cells did not show TOPK mRNA expression. These data suggest that TOPK is a newly identified member of a novel MEK3/6-related MAPKK that may be enrolled in the activation of lymphoid cells and support testicular functions.

Extracellular granzyme A, complexed to proteoglycans, is protected against inactivation by protease inhibitors.

Granzyme A (GrA) and B (GrB) together with perforin are the main constituents of cytotoxic granules of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. The cytotoxic proteins are released to deliver a lethal hit during contact between the CTL or NK cell and target cell. With the use of an enzyme-linked immunosorbent assay for antigenic levels, we showed in a recent study that plasma of patients with activated CTLs and NK cells contain elevated levels of extracellular GrA. In this study, we determined the form and proteolytic capacity of this extracellular GrA detected in plasma. With the use of various assays, we show that part of the extracellular GrA circulates in the mature conformation and is bound to proteoglycans that protect it against inactivation by protease inhibitors, such as antithrombin III and alpha-2-macroglobulin, whereas another part of GrA circulates as a complex with antithrombin III. Finally, with the use of a novel assay for active GrA, we demonstrate that some plasma samples with high levels of extracellular GrA contain active GrA. These results suggest that various forms of extracellular GrA occur in vivo and that the regulation of GrA activity may be modified by proteoglycans. These data support the notion that granzymes may exert extracellular functions distant from the site of CTL or NK cell interaction with their target cells. (Blood. 2000;95:1465-1472)

Apoptosis induced by granzyme B-glycosaminoglycan complexes: implications for granule-mediated apoptosis in vivo.

Lymphocyte granule-mediated apoptosis occurs by perforin-mediated intracellular delivery of granule-associated serine proteases (granzymes). A granule-associated proteoglycan, namely serglycin, that contains chondroitin 4-sulfate (CS) glycosaminoglycans is present in the granules of cytotoxic cells. Serglycin acts as scaffold for packaging the positively charged granzymes and probably chaperones the proteases secreted extracellularly. To learn how the interaction of granzyme B (GrB) with serglycin might influence the apoptotic potential of this proteases, we have evaluated a model system where desalted CS is combined with isolated human granzyme. CS-GrB complexes were very stable, remaining undissociated in salt concentrations upwards to 500 mM (pH 7.4). On the basis of a capture enzyme immunoassay that accurately detects GrB, equivalent amounts of active free and CS-GrB, delivered by perforin or adenovirus, efficiently induced apoptosis in Jurkat cells and produced a similar time-dependent increase in caspase-3-like activity. CS-GrB processed isolated caspases-3 and -7 less efficiently than free granzyme. However, when added to cytosolic extracts, rates of processing were nearly equivalent for the two forms, suggesting cationic GrB may nonspecifically bind cytosolic proteins, leading to reduce proteolytic activity. Finally, GrB was found to be exocytosed from lymphocyte-activated killer cells as a neutral, high macromolecular weight complex, which possessed apoptotic activity. Collectively, the results indicate that neutral, high m.w. GrB has the capacity to induce cell death and will be useful to study the mechanism of cytotoxic cell-mediated apoptosis in vitro.

The 5' flanking region of the human granzyme H gene directs expression to T/natural killer cell progenitors and lymphokine-activated killer cells in transgenic mice.

Human granzyme H is a neutral serine protease that is expressed predominantly in the lymphokine-activated killer (LAK)/natural killer (NK) compartment of the immune system. The gene that encodes this granzyme is located between the granzyme B and cathepsin G genes on human chromosome 14q11.2. Although the murine orthologue of human granzyme H has not yet been identified, murine granzymes C, D, E, F, and G also lie between the murine granzyme B and cathepsin G genes on murine chromosome 14; murine granzymes C, D, and F are also highly expressed in LAK cells, but minimally in cytotoxic T lymphocytes (CTL). We therefore tested whether the 5' flanking region of human granzyme H contains the cis-acting DNA sequences necessary to target a reporter gene to the LAK/NK compartment of transgenic mice. A 1.2-kb fragment of 5' flanking human granzyme H sequence was linked to an SV40 large T-antigen (TAg) reporter gene and used to create six transgenic founder lines. SV40 TAg was specifically expressed in the LAK cells of these mice, but not in resting T or NK cells, in CTL, or in any other tissues. Most mice eventually developed a fatal illness characterized by massive hepatosplenomegaly and disseminated organ infiltration by large malignant lymphocytes. Cell lines derived from splenic tumors were TAg+ and NK1.1(+) large granular lymphocytes and displayed variable expression of CD3, CD8, and CD16. Although these cell lines contained perforin and expressed granzymes A, B, C, D, and F, they did not exhibit direct cytotoxicity. Collectively, these results suggest that the 5' flanking sequences of the human granzyme H gene target expression to an NK/T progenitor compartment and to activated NK (LAK) cells. Mice and humans may therefore share a regulatory "program" for the transcription of NK/LAK specific granzyme genes.

Cytolytic activities of IL-2 activated NK cells from MMTV/v-Ha-ras transgenic oncomice during tumor progression.

IL-2 activated natural killer (A-NK) cells have the capacity to infiltrate metastatic tumors and lyse tumor cells. Nevertheless, adoptive immunotherapy with lymphokine-activated killer cells has been only modestly effective in the clinic and has not routinely provided long-term survival in patients with established cancer metastases. This may indicate the need for more carefully investigating the role of effector cells of the immune response, including A-NK cells, in models of tumor progression. Herein we describe the use of the MMTV/v-Ha-ras transgenic mouse model as a system for exploring the role of NK cells during tumor progression. We have examined the lytic capacity of A-NK cells generated from tumor-free and tumor-bearing transgenic oncomice against standard A-NK cell targets (YAC-1 and P815) in addition to tumor cells isolated from these animals. A-NK cells generated from mice without obvious tumor burden show higher lytic activity than A-NK cells generated from mice with evident tumors, i.e., those at a more advanced stage of tumor progression. Only long term (8-day) cultures of late passage A-NK cells generated from tumor-bearing mice showed significant increases in lytic activity over those generated from tumor-free mice. These results suggest that experimental protocols using transgenic oncomice at various stages of tumor growth may constitute a novel model for testing the role of A-NK cells for their capacity to interfere with cancer progression.

The role of phorbol ester-sensitive protein kinase C isoforms in lymphokine-activated killer cell-mediated cytotoxicity: dissociation between perforin-dependent and Fas-dependent cytotoxicity.

Treatment of lymphokine-activated killer (LAK) cells with phorbol ester (PMA) caused the downmodulation of LAK activity concomitantly with the inhibition of serine esterase (SE) release, which has been shown as a marker for perforin-dependent cell-mediated cytotoxicity. The reduction of perforin-dependent LAK activity by PMA-treatment appeared to be due to the disappearance of PMA-sensitive protein kinase C (PKC) isoforms such as PKC alpha, gamma, epsilon, theta. In contrast, Fas-mediated LAK activity was refractory against PMA-induced downregulation. Treatment of LAK cells with PMA caused a disappearance of cytotoxicity against Fas L5178Y tumor cells, while cytotoxicity against Fas+ transfectants was not affected by PMA treatment. Moreover, Fas-mediated LAK activity of perforin-knockout mice was not inhibited by PMA treatment. These results clearly demonstrated that Fas-mediated cytotoxicity could be dissociated from perforin-mediated cytotoxicity by their different requirement of PMA-sensitive PKC isoforms.

Human T-lymphocyte serine proteases (granzymes) 1, 2, and 3 mediated DNA fragmentation in susceptible target cells.

We reported the characterization of three serine proteases (granzymes 1, 2, and 3) from human cytotoxic T lymphocytes. In this study, human granzymes 1, 2, and 3 were purified from the cytoplasmic granules of lymphokine activated killer (LAK) cells by gel filtration and cation exchange chromatography. Human perforin was purified by phenyl superose and heparin-agarose chromatography. Each purified granzyme was used with purified perforin to study DNA fragmentation in target cells of both human and murine origin. As measured by agarose gel electrophoresis and [125I]dUrd assay, the granzymes induced oligonucleosomal DNA fragmentation and [125I]dUrd release respectively from various target cells. Murine target cells were generally more susceptible to nuclear DNA release than were human targets. Both enzyme activity and nuclear DNA breakdown were significantly inhibited by 3,4-dichloroisocoumarin (DCI) or by heat inactivation of each granzyme. Perforin alone or granzyme alone failed to fragment nuclear DNA in various target cells. We conclude that human granzymes are an important family of effector molecules that with perforin induce DNA fragmentation in susceptible target cells.

Expression of human recombinant granzyme A zymogen and its activation by the cysteine proteinase cathepsin C.

Human granzyme A is one of the serine proteinases present in the granules of cytotoxic T lymphocytes and natural killer cells. Granzymes are synthesized as inactive proenzymes with an amino-terminal prodipeptide, which is processed during transport of granzymes to the cytotoxic granules, where they are stored as active proteinases. In this study, we explored the possibility of producing recombinant granzymes. Recombinant human granzyme A zymogen was expressed in several eukaryotic cell lines (HepG2, Jurkat, and COS-1) after infection with a recombinant vaccinia virus containing full-length granzyme A cDNA. Immunoblot analysis of cell lysates showed that all infected cells produced a disulfide-linked homodimer of identical molecular weight as natural granzyme A. Infected HepG2 cells produced the largest amount of this protease (approximately 160 times more than lymphokine activated killer (LAK) cells). The recombinant protein only had high mannose type oligosaccharides as did the natural protein. Although infected HepG2 and COS cells contained high granzyme A antigen levels, lysates from these cells did not show any granzyme A proteolytic activity. However, the inactive proenzyme could be converted into active granzyme A by incubation with the thiol proteinase cathepsin C (dipeptidyl peptidase I). This study is the first to demonstrate expression of an active recombinant human cytotoxic lymphocyte proteinase and conversion of inactive progranzyme A into an active enzyme by cathepsin C. We suggest that a similar approach can be used for the production of other granzymes and related proteinases.