APRIL Jurg Tschopp* Institute of Biochemistry, University of Lausanne, Ch. des Boveresses 155, Epalinges, CH-1066, Switzerland * corresponding author tel: 41 21 692 5738, fax: 41 21 692 5705, e-mail:
[email protected]. DOI: 10.1006/rcwy.2000.05011.
SUMMARY APRIL is a member of the TNF family. While transcripts of APRIL are of low abundance in normal tissues, high levels of mRNA are detected in transformed cell lines, and in human cancers of the colon, thyroid, and lymphoid tissues in vivo. The addition of recombinant APRIL to various tumor cells stimulates their proliferation. Moreover, APRIL-transfected NIH 3T3 cells show an increased rate of tumor growth in nude mice when compared with the parental cell line. The receptor of APRIL is currently unknown. APRIL may be implicated in the regulation of tumor cell growth.
BACKGROUND
Discovery The discovery of APRIL arose from studies aimed at identifying novel members of the TNF ligand by screening public databases using a profile search (Bucher et al., 1996). Several cDNA clones were identified encoding a novel protein of 250 amino acids with significant sequence homology to known members of this family (Hahne et al., 1998).
Structure The absence of a signal peptide suggests that APRIL is a type II membrane protein that is typical of the members of the TNF ligand family. Based on the known structure of the homologous lymphotoxin (Banner et al., 1993), APRIL is predicted to contain
eight strands in its extracellular domain, which are folded into an antiparallel sandwich structure.
Main activities and pathophysiological roles Recombinant soluble APRIL leads to an increased proliferation of various tumor cell lines, including Raji B cells, Jurkat T cells, and MCF-7 carcinoma cells. NIH 3T3 cells overexpressing full-length APRIL proliferate faster. When injected into nude mice, APRIL-expressing NIH 3T3 cells form tumors significantly faster than do parental NIH 3T3 cells (Hahne et al., 1998). Together with the observation that APRIL mRNA is increased in tumor cell lines and in metastatic tumors, this suggests that increased APRIL expression may be involved in tumorigenesis.
GENE AND GENE REGULATION
Accession numbers GenBank: Human gene: AF046888
Chromosome location The gene has been localized to chromosome 17p13.
Relevant linkages The APRIL gene is found adjacent to that for TWEAK.
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Cells and tissues that express the gene Human APRIL mRNA is found in peripheral blood lymphocytes (PBLs) and prostate gland. Expression is particularly high in tumor tissues (thyroid and colon carcinoma, and lymphoma), and in cell lines (promyelocytic leukemia, HL-60; HeLa cell S3; chronic myelogenous leukemia, K562; lymphoblastic leukemia, MOLT-4; Burkitt's lymphoma, Raji; colorectal adenocarcinoma, SW480; lung carcinoma, A459; melanoma, G361).
Discussion of crystal structure No crystal structure is available. However, the crystal structure of APRIL is expected to be homologous to that of lymphotoxin , CD40L, and TNF , for which structural information is available (being an elongated, antiparallel pleated sheet sandwich with a `jelly-roll' topology, three monomers associating intimately about a 3-fold axis of symmetry to form a compact, bell-shaped trimer) (Eck and Sprang, 1989; Banner et al., 1993; Karpusas et al., 1995).
Important homologies PROTEIN
APRIL is a member of the TNF ligand family (Figure 2).
Sequence The protein sequence of APRIL is shown in Figure 1.
Description of protein APRIL is a type II membrane protein lacking a signal peptide.
Posttranslational modifications There is a putative glycosylation site at asparagine 124. The extracellular region is processed by an unknown protease (possibly furin), which cleaves in a highly basic region of the stalk region (RKRRAVLTQKQKK). The receptor-binding domain of APRIL is thereby released.
Figure 1 Protein sequence of APRIL. The transmembrane domain is underlined. Sequence Transmembrane domain underlined.
1 MPASSPFLLA PKGPPGNMGG PVREPALSVA LWLSWGAALG AVACAMALLT QQTELQSLRR 61 EVSRLQGTGG PSQNGEGYPW QSLPEQSSDA LEAWENGERS RKRRAVLTQK QKKQHSVLHL 121 VPINATSKDD SDVTEVMWQP ALRRGRGLQA QGYGVRIQDA GVYLLYSQVL FQDVTFTMGQ 181 VVSREGQGRQ ETLFRCIRSM PSHPDRAYNS CYSAGVFHLH QGDILSVIIP RARAKLNLSP 241 HGTFLGFVKL
Figure 2 Alignment comparing seven members of the TNF ligand family. APRIL TNFa TXa FASL TRAIL TWEAK TRANCE
117 VLHLVPINATSKDDS..........DVTE VMWQPA.LRRGRGLQA....QGYGVRIQDAGVYLLYSQVLFQDVT..........FTMGQ V LQWLNR..RANALLANGVELRDNQLVVPSEGLYLIYSQVLFKGQGCPS....THVLLTHTI 89 VAHVVANPQAEGQ................ LLWRAN..TDRAFLQDGFSLSNNSLLVPTSGIYFVYSQVVFSGKAYSPKATSSPLYLAHEV 64 AAHLIGDPSKQNS................ LEWEDT..YGIVLLSGVKY.KKGGLVINETGLYFVYSKVYFRGQSCN......NLPLSHKV 146 VAHLTGKSNSRSMP............... WESSR.SGHSFLSNLHL.RNGELVIHEKGFYYIYSQTYFRFQEEIK....ENTKNDKQM 123 AAHITGTRGRSNTLSSPNSKNEKALGRKINS WEKARINSSSPLRYNR..QIGEFIVTRAGLYYLYCQVHFDEGKAVY..LKLDLLVDGVL 143 AAHYEVHPRPGQDGAQAGV......DGTVSG WYHD..RGWGKISNMTF.SNGKLIVNQDGFYYLYANICFRHHETSGDLATEYLQLMVYV 164 FAHLTINATDIPSGSH.........KVSLSS
PRIL TNFa TXa FASL TRAIL TWEAK TRANCE
182 157 136 212 189 223 242
DRAYNSCYSAGVFHLHQGDILSVIIPRARAKLNLSPHGTFLGFVKL VSREGQG...RQETLFRCIRSMP........SHP IYLGGVFQLEKGDRLSAEINRPDYLDFAESGQVYFGIIAL SRIAVSY...QTKVNLLSAIKSPCQRETPEGAEAKPWYEP QLFSSQY...PFHVPLLSSQKMV......YPGLQEPWLHSMYHGAAFQLTQGDQLSTHTDGIPHLVLSP.STVFFGAFAL YMRNSKY...PQDLVMMEGKMMS......YCTTGQMWARSSYLGAVFNLTSADHLYVNVSELSLVNFEE.SQTFFGLYKL VQYIYKYTSYPDPILLMKSARNS.....CWSKDAEYGLYSIYQGGIFELKENDRIFVSVTNEHLIDMDH.EASFFGAFLV VSGLLALRPGSSLRIRTLPWAHLKAAP.FLTYFGLFQV ALRCLEE...FSATAASSLGP...............QLRLCQ TKTSIKI...PSSHTLMKGGSTK.....YWSGNSEFHFYSINVGGFFKLRSGEEISIEVSNPSLLDPDQ.DATYFGAFKV
APRIL
CELLULAR SOURCES AND TISSUE EXPRESSION
Cellular sources that produce Many cell lines express APRIL mRNA. There is no report on protein expression.
IN VITRO ACTIVITIES
In vitro findings APRIL accelerates the growth of many cell lines.
Bioassays used The bioassay used is an increased proliferation rate of Jurkat cells (Hahne et al., 1998).
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References Banner, D. W., D'Arcy, A., Janes, W., Gentz, R., Schoenfeld, H. J., Broger, C., Loetscher, H., and Lesslauer, W. (1993). Crystal structure of the soluble human 55 kd TNF receptor±human TNF beta complex: implications for TNF receptor activation. Cell 73, 431±445. Bucher, P., Karplus, K., Moeri, N., and Hofmann, K. (1996). A flexible search technique based on generalized profiles. Computer Chem. 20, 3±24. Eck, M. J., and Sprang, S. R. (1989). The structure of tumor necrosis factor-alpha at 2.6 A resolution. Implications for receptor binding. J. Biol. Chem. 264, 17595±17605. Hahne, M., Kataoka, T., Schroter, M., Hofmann, K., Irmler, M., Bodmer, J. L., Schneider, P., Bornand, T., Holler, N., French, L. E., Sordat, B., Rimoldi, D., and Tschopp, J. (1998). APRIL, a new ligand of the tumor necrosis factor family, stimulates tumor cell growth. J. Exp. Med. 188, 1185± 1190. Karpusas, M., Hsu, Y. M., Wang, J. H., Thompson, J., Lederman, S., Chess, L., and Thomas, D. (1995). 2 A crystal structure of an extracellular fragment of human CD40 ligand. Structure 3, 1031±1039.
