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Invertebrate Cytokines: Tunicate Cell Proliferation Stimulated by an Interleukin 1-Like Molecule (Urochrdata/Lymo Ne/Lm Mundoog/Mitogenes) DAVID A

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Invertebrate Cytokines: Tunicate Cell Proliferation Stimulated by an Interleukin 1-Like Molecule (Urochrdata/Lymo Ne/Lm Mundoog/Mitogenes) DAVID A Proc. Natl. Acad. Sci. USA Vol. 88, pp. 9518-9522, November 1991 Cell Biology Invertebrate cytokines: Tunicate cell proliferation stimulated by an interleukin 1-like molecule (Urochrdata/lymo ne/lm munDoog/mitogeneS) DAVID A. RAFTOS*t, EDWIN L. COOPER**, GAIL S. HABICHT§, AND GREGORY BECK§ *Department of Anatomy and Cell Biology, University of California, Los Angeles, CA 90024; and §Department of Pathology, State University of New York, Stony Brook, NY 11794 Communicated by Charles H. Sawyer, July 1, 1991 (receivedfor review April 16, 1991) ABSTRACT Tunicte pharyngeal cells include lympho- cate hemolymph and the 20-kDa tunicate IL-i-like proteins cyte-like cells and granular amoebocytes. They are Involved in are inhibited by preincubation with anti-mammalian IL-1 the specific lgeneic and phagocytic reactions of tunites. antibodies (2). Little is known about their regulation or control. A tunicate These data suggest that cytokine-like molecules have been Interleukin 1 (IL-1)-Hlke fraction is shown to snulate the conserved during evolution to the degree that functional prliferation of these cels in vitro. This fraction, designated cross-reactivity occurs over large phylogenetic distances (1, tunicate IL-f1, was isolated from tunicate hemolymph by gel 3, 6). In addition to the action of invertebrate cytokine-like fltration and chromatofociusing chromatography. Mitogenic molecules on mammalian cells, we have shown that human responses to tuncte L1 were dose dependent and could be recombinant IL-2 can stimulate the proliferation of tunicate eliminated rapidly by removing tunicate IL-1L from culture cells in vitro (14). Perhaps such cross-reactivities reflect the medium. A second tun hte molymph fraction had no effect existence of invertebrate cytokine-based regulatory systems on tunicate cell proliferation even though it exhibited IL-1-like for host defense that are homologous to those of mammals. activity in a mouse thymocyte proliferation assay. Phytohe- In this study, we investigate the function of invertebrate mawglutinin did not act synergistically with either fraction. IL-1-like molecules in their native species. An IL-i-like These data are diused in terms ofthe function and evolution fraction from tunicates, tunicate IL-1p3, is shown to stimulate Of IL-i-like molecules in invertebrates. the proliferation of tunicate cells in vitro. Interleukin 1 (IL-1)-like activities have been identified in a number of invertebrate species (1-3). Beck and Habicht (1) MATERIALS AND METHODS have shown that fractionated coelomic fluid and cell extracts Reagents, Culture Plates, and Filters. Unless stated other- from the echinoderm (starfish) Asteriasforbesi stimulate the wise, all reagents were purchased from Sigma. [methyl- proliferation of murine thymocytes in a lymphocyte prolif- 3H]Thymidine (6.7 or 20 Ci/mmol; 1 Ci = 37 GBq) and eration assay for IL-1. Stimulatory activity resides in an Ecolite scintillation cocktail were supplied by ICN. Tissue -20-kDa fraction of the coelomic fluid (3). In addition to its culture plasticware was purchased from Costar. Filter ster- thymocyte stimulatory activity, this fraction induces mam- ilization units (0.22 ,um) were purchased from either Millipore malian fibroblast proliferation, enhances fibroblast protein or Costar. synthesis, increases the production ofprostaglandin E2, and Tunicates. Solitary tunicates (Styela clava) were purchased is cytotoxic for the human cell line A375 (1, 3). All of these from Marinus (Long Beach, CA). They were maintained in an functions are characteristic of mammalian IL-1 (4-7). The aerated aquarium filled with 180 liters of artificial seawater 20-kDa coelomic fluid fraction comprises three protein spe- [ASW; 3.4% (wt/vol), Instant Ocean, Aquarium Systems, cies with isoelectric points (pI values 7.5, 5.4, and 4.8) that Mentor, OH] at 15'C. are similar to predominant forms of mammalian IL-1 (pI Harvesting of Tunicate Hemolymph. Hemolymph was har- values 7.2 and 5.0) (1, 8, 9). Moreover, polyclonal antibodies the specific to human IL-1 inhibit the stimulatory effects of the vested by severing the stolons oftunicates and collecting 20-kDa echinoderm proteins on mouse thymocytes (1). exuding fluid in chilled polyethylene centrifuge tubes. Hemo- Similar IL-i-like activities have been identified in annelids cytes were then removed by centrifugation (1000 x g for 15 and tunicates (G.B., G.S.H., and E.L.C., unpublished data; min at 40C). The resulting cell-free hemolymph was filter see also refs. 2 and 4). The detection of tunicate IL-i-like sterilized (0.22-pum filters; Costar) and stored at -20°C for up molecules is ofparticular interest. Tunicates are invertebrate to 6 months before use. members ofthe phylum Chordata and so are likely to exhibit Gel-Filtration Chromatography. Tunicate IL-1 molecules significant molecular and functional homologies with verte- were purified from 100 ml of tunicate cell-free hemolymph. brates (10). Hemolymph or cell extracts from eight species of The hemolymph was cleared by centrifugation (10,000 x g for tunicates can stimulate mouse thymocyte proliferation (2). 30 min at 40C) and concentrated =10:1 by ultrafiltration using Stimulation has been attributed to two molecular mass frac- a PM 10 membrane (Amicon). The concentrate was applied tions (:20 and >50 kDa), the smaller of which is within the to an Ultrogel AcA 54 gel-filtration column (2.6 x 85 cm; molecular mass range ofechinoderm IL-i-like molecules and Pharmacia). This column was calibrated with bovine serum mammalian IL-is (2, 5, 11, 12). The smaller tunicate IL-i-like albumin (67 kDa), ovalbumin (43 kDa), chymotrypsinogen A fraction segregates into neutral and acidic species with pI (25 kDa), and RNase A (13.7 kDa) (Pharmacia) as size values that correspond closely to those of echinoderm IL-1- standards. The column was eluted (1 ml/min; 40C) with like molecules and mammalian IL-is (2, 7, 13). As with echinoderms, the stimulatory effects of concentrated tuni- Abbreviations: IL-1, interleukin 1; tunicate IL-1, tunicate IL-1-like fraction; ASW, artificial seawater; PHA, phytohemagglutinin. tPresent address: c/o Prof. R. L. Raison, School of Biological and The publication costs of this article were defrayed in part by page charge Biomedical Sciences, University of Technology, P.O. Box 123, payment. This article must therefore be hereby marked "advertisement" Broadway, Sydney, N.S.W., 2007, Australia. in accordance with 18 U.S.C. §1734 solely to indicate this fact. *To whom reprint requests should be addressed. 9518 Downloaded by guest on September 30, 2021 Cell Biology: Raftos et al. Proc. Natl. Acad. Sci. USA 88 (1991) 9519 phosphate-buffered saline containing gentamicin (10 j.g/ml). Incubation of Tunicate Explants with IL-i-like Fractions. Three-milliliter fractions were collected and the effluent was Explants were equilibrated to culture conditions for 3 days monitored at 280 nm. Fractions were diluted 1:1 with RPMI before hemolymph fractions that contained IL-1-like activity 1640 medium and sterilized by filtration. Aliquots of the were added. After the equilibration period, explants were diluted fractions were tested for IL-1-like activity in a murine transferred to either fresh T-RPMI or to T-RPMI containing thymocyte proliferation assay using thymocytes from 4- to 20% (vol/vol) tunicate hemolymph, concentrated tunicate 8-week-old BALB/c mice or by cytotoxicity ofA375 cells as hemolymph, IL-1-like fractions, phytohemagglutinin (PHA), described (1, 3). Recombinant human IL-la (a kind gift from or combinations of the above. Subsequently, tissues were Dainippon Pharmaceutical, Osaka) was used to construct transferred to fresh medium every 3 days. standard curves to determine the number of units of IL-1 in Quantification of [3H]Thymidine Uptake. To quantify each experimental sample as described (1, 3). Specific activ- [3H]thymidine uptake by cultured tissue, explants were re- ities of highly purified tunicate IL-1 fractions were deter- moved from tissue culture plates and pooled in 2 ml of the mined as units per mg of protein. same medium in which they had been cultured. Tissues were Chromatofocusing. Gel-filtration fractions that incorpo- then incubated at 150C with 2.5 ,Ci of [3H]thymidine per ml. rated peaks of IL-1-like activity were pooled and concen- After 18 hr, excess [3H]thymidine was removed by washing trated to =5 ml (PM 10 ultrafiltration). These samples were explants four times (1 hr per wash) in 4 ml of ASW on a dialyzed against 25 mM imidazole hydrochloride (pH 8.4) hematology mixer. Washed explants were transferred to before being applied to a PBE 94 chromatofocusing column scintillation vials (1 explant per vial) containing 200 pl of (Pharmacia), which was equilibrated in 25 mM imidazole trypsin [2% (wt/vol) in ASW] and digested overnight at 3TC. hydrochloride (pH 8.4) at 40C. The chromatofocusing column Two milliliters of scintillation cocktail were then added to was eluted with Polybuffer 74 HCl (pH 4.0) (Pharmacia) to each vial so that the incorporated radioactivity could be give a linear pH gradient from pH 8.4 to pH 4.0 as per the quantified in a Beckman LS 3150P scintillation counter. manufacturer's instructions. After elution, fractions were Statistical Analysis. The significance of differences be- brought to a pH of -7.2 by adding 4 M Tris base (pH 11). The tween treatments was determined by two-tailed Student's t effluent was monitored at 280 nm, and the column eluates tests (16). Differences were deemed to be significant if P were sterilized by filtration before being assayed for IL-1 values were <0.05. activity as described above. Tunicate Tissue Culture Medium. Tunicate tissue culture medium (T-RPMI) was prepared in sterile-filtered ASW and RESULTS contained, per liter, 454 mg of RPMI 1640 powder (with Effect of T-RPMI and Unfractionated Hemolymph on L-glutamine, without sodium bicarbonate), 105 units of pen- pHlThymidine Uptake.
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