15 kDa granulysin causes differentiation of monocytes to dendritic cells but lacks cytotoxic activity.

Granulysin is expressed as two isoforms by human cytotoxic cells: a single mRNA gives rise to 15 kDa granulysin, a portion of which is cleaved to a 9 kDa protein. Studies with recombinant 9 kDa granulysin have demonstrated its cytolytic and proinflammatory properties, but much less is known about the biologic function of the 15 kDa isoform. In this study, we show that the subcellular localization and functions of 9 and 15 kDa granulysin are largely distinct. Nine kilodalton granulysin is confined to cytolytic granules that are directionally released following target cell recognition. In contrast, 15 kDa granulysin is located in distinct granules that lack perforin and granzyme B and that are released by activated cytolytic cells. Although recombinant 9 kDa granulysin is cytolytic against a variety of tumors and microbes, recombinant 15 kDa granulysin is not. The 15 kDa isoform is a potent inducer of monocytic differentiation to dendritic cells, but the 9 kDa isoform is not. In vivo, mice expressing granulysin show markedly improved antitumor responses, with increased numbers of activated dendritic cells and cytokine-producing T cells. Thus, the distinct functions of granulysin isoforms have major implications for diagnosis and potential new therapies for human disease.

15 kDa Granulysin versus GM-CSF for monocytes differentiation: analogies and differences at the transcriptome level.

BACKGROUND: Granulysin is an antimicrobial and proinflammatory protein with several isoforms. While the 9 kDa isoform is a well described cytolytic molecule with pro-inflammatory activity, the functions of the 15 kDa isoform is less well understood. Recently it was shown that 15 kDa Granulysin can act as an alarmin that is able to activate monocytes and immature dendritic cells. Granulocyte Macrophage Colony Stimulating Factor (GM-CSF) is a growth factor widely used in immunotherapy both for in vivo and ex vivo applications, especially for its proliferative effects. METHODS: We analyzed gene expression profiles of monocytes cultured with 15 kDa Granulysin or GM-CSF for 4, 12, 24 and 48 hours to unravel both similarities and differences between the effects of these stimulators. RESULTS: The analysis revealed a common signature induced by both factors at each time point, but over time, a more specific signature for each factor became evident. At all time points, 15 kDa Granulysin induced immune response, chemotaxis and cell adhesion genes. In addition, only 15 kDa Granulsyin induced the activation of pathways related to fundamental dendritic cell functions, such as co-stimulation of T-cell activation and Th1 development. GM-CSF specifically down-regulated genes related to cell cycle arrest and the immune response. More specifically, cytokine production, lymphocyte mediated immunity and humoral immune response were down-regulated at late time points. CONCLUSION: This study provides important insights on the effects of a novel agent, 15 kDa granulysin, that holds promise for therapeutic applications aimed at the activation of the immune response.

Granulysin delivered by cytotoxic cells damages endoplasmic reticulum and activates caspase-7 in target cells.

Granulysin is a human cytolytic molecule present in cytotoxic granules with perforin and granzymes. Recombinant 9-kDa granulysin kills a variety of microbes, including bacteria, yeast, fungi, and parasites, and induces apoptosis in tumor cells by causing intracellular calcium overload, mitochondrial damage, and activation of downstream caspases. Reasoning that granulysin delivered by cytotoxic cells may work in concert with other molecules, we crossed granulysin transgenic (GNLY(+/-)) mice onto perforin (perf)- or granzyme B (gzmb)-deficient mice to examine granulysin-mediated killing in a more physiologic whole-cell system. Splenocytes from these animals were activated in vitro with IL-15 to generate cytolytic T cells and NK cells. Cytotoxic cells expressing granulysin require perforin, but not granzyme B, to cause apoptosis of targets. Whereas granzyme B induces mitochondrial damage and activates caspases-3 and -9 in targets, cytotoxic cell-delivered granulysin induces endoplasmic reticulum stress and activates caspase-7 with no effect on mitochondria or caspases-3 and -9. In addition, recombinant granulysin and cell-delivered granulysin activate distinct apoptotic pathways in target cells. These findings suggest that cytotoxic cells have evolved multiple nonredundant cell death pathways, enabling host defense to counteract escape mechanisms employed by pathogens or tumor cells.

Expression and purification of 15 kDa granulysin utilizing an insect cell secretion system.

Granulysin is an antimicrobial and proinflammatory protein expressed in activated human T cells and natural killer cells. A single mRNA produces the 15 kDa isoform which is then cleaved at the amino and carboxy termini to produce the 9 kDa isoform. Recombinant 9 kDa granulysin has been studied in detail but little is known about the function of the 15 kDa isoform, and no protocol has been published describing expression and purification of this form. Two commercially available preparations of the recombinant 15 kDa granulysin contain tags that may affect function. Here we describe for the first time a method to produce 15 kDa granulysin as a secreted protein from insect cells. The 15 kDa granulysin is purified using a HiTrap Heparin column and a Resource S column. A typical a yield of purified 15 kDa granulysin is 0.6 mg/L of insect cell supernatant.

Granulysin activates antigen-presenting cells through TLR4 and acts as an immune alarmin.

Granulysin (GNLY), an antimicrobial protein present in the granules of human cytotoxic T lymphocytes and natural killer (NK) cells, is produced as an intact 15-kDa form that is cleaved to yield a 9-kDa form. Alarmins are endogenous mediators that can induce recruitment and activation of antigen-presenting cells (APCs) and consequently promote the generation of immune response. We hypothesized that GNLY might function as an alarmin. Here, we report that both 9- and 15-kDa forms of recombinant GNLY-induced in vitro chemotaxis and activation of both human and mouse dendritic cells (DCs), recruited inflammatory leucocytes, including APCs in mice, and promoted antigen-specific immune responses upon coadministration with an antigen. GNLY-induced APC recruitment and activation required the presence of Toll-like receptor 4. The observed activity of recombinant GNLY was not due to endotoxin contamination. The capability of the supernatant of GNLY-expressing HuT78 cells to activate DC was blocked by anti-GNLY antibodies. Finally we present evidence that supernatants of degranulated human NK92 or primary NK cells also activated DCs in a GNLY- and Toll-like receptor 4-dependent manner, indicating the physiologic relevance of our findings. Thus, GNLY is the first identified lymphocyte-derived alarmin capable of promoting APC recruitment, activation, and antigen-specific immune response.

Modified pathway to synthesize ribulose 1,5-bisphosphate in methanogenic archaea.

Several sequencing projects unexpectedly uncovered the presence of genes that encode ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RubisCO) in anaerobic archaea. RubisCO is the key enzyme of the Calvin-Benson-Bassham (CBB) reductive pentose phosphate pathway, a scheme that does not appear to contribute greatly, if at all, to net CO2 assimilation in these organisms. Recombinant forms of the archaeal enzymes do, however, catalyze a bona fide RuBP-dependent CO2 fixation reaction, and it was recently shown that Methanocaldococcus (Methanococcus) jannaschii and other anaerobic archaea synthesize catalytically active RubisCO in vivo. To complete the CBB pathway, there is a need for an enzyme, i.e., phosphoribulokinase (PRK), to catalyze the formation of RuBP, the substrate for the RubisCO reaction. Homology searches, as well as direct enzymatic assays with M. jannaschii, failed to reveal the presence of PRK. The apparent lack of PRK raised the possibility that either there is an alternative pathway to generate RuBP or RubisCO might use an alternative substrate in vivo. In the present study, direct enzymatic assays performed with alternative substrates and extracts of M. jannsachii provided evidence for a previously uncharacterized pathway for RuBP synthesis from 5-phospho-D-ribose-1-pyrophosphate (PRPP) in M. jannaschii and other methanogenic archaea. Proteins and genes involved in the catalytic conversion of PRPP to RuBP were identified in M. jannaschii (Mj0601) and Methanosarcina acetivorans (Ma2851), and recombinant Ma2851 was active in extracts of Escherichia coli. Thus, in this work we identified a novel means to synthesize the CO2 acceptor and substrate for RubisCO in the absence of a detectable kinase, such as PRK. We suggest that the conversion of PRPP to RuBP might be an evolutional link between purine recycling pathways and the CBB scheme.

Synthesis of catalytically active form III ribulose 1,5-bisphosphate carboxylase/oxygenase in archaea.

Ribulose 1,5 bisphosphate carboxylase/oxygenase (RubisCO) catalyzes the biological reduction and assimilation of carbon dioxide gas to organic carbon; it is the key enzyme responsible for the bulk of organic matter found on earth. Until recently it was believed that there are only two forms of RubisCO, form I and form II. However, the recent completion of several genome-sequencing projects uncovered open reading frames resembling RubisCO in the third domain of life, the archaea. Previous work and homology comparisons suggest that these enzymes represent a third form of RubisCO, form III. While earlier work indicated that two structurally distinct recombinant archaeal RubisCO proteins catalyzed bona fide RubisCO reactions, it was not established that the rbcL genes of anaerobic archaea can be transcribed and translated to an active enzyme in the native organisms. In this report, it is shown not only that Methanococcus jannaschii, Archaeoglobus fulgidus, Methanosarcina acetivorans, and Methanosarcina barkeri possess open reading frames with the residues required for catalysis but also that the RubisCO protein from these archaea accumulates in an active form under normal growth conditions. In addition, the form III RubisCO gene (rbcL) from M. acetivorans was shown to complement RubisCO deletion strains of Rhodobacter capsulatus and Rhodobacter sphaeroides under both photoheterotrophic and photoautotrophic growth conditions. These studies thus indicate for the first time that archaeal form III RubisCO functions in a physiologically significant fashion to fix CO(2). Furthermore, recombinant M. jannaschii, M. acetivorans, and A. fulgidus RubisCO possess unique properties with respect to quaternary structure, temperature optima, and activity in the presence of molecular oxygen compared to the previously described Thermococcus kodakaraensis and halophile proteins.