Human glycosyltransferase gene

Abstract: A human GnT-III gene having a specific restriction map represented by Fig. 1 of the attached Drawings and a length of approximately 1.6 kb is disclosed, together with a human GnT-III gene which is hybridizable with said gene. A process for producing human GnT-III is provided, which comprises incubating a transformant wherein one of the above-mentioned genes is used and harvesting. The sequencing listing shows a part of the base sequence.

Description: This invention relates to a human glycosyltransferase gene and a process for producing the transferase which is useful in the field of sugar engineering. UDP-N-acetylglucosamine:β-D-mannoside β1-4N-acetylglucosaminyltransferase III (EC 2.4.1.144: hereinafter referred to simply as GnT-III), which is an enzyme transferring a GlcNAc residue in UDP-N-acetylglucosamine (UDP-GlcNAc) to a mannose (Man) residue forming a β1-4 bond in an asparagine binding type sugar chain, was reported for the first time by Narasimhan [see Journal of Biological Chemistry , 257 , 10235-10242 (1982)]. The GlcNAc transferred by GnT-III, which is called a bisecting GlcNAc, has been found out in the sugar chains of various glycoproteins. It has been further reported by Narasimhan et al. [see J. Biol. Chem. , 263 , 1273-1282 (1988)] and Pascale et al. [see Carcinogenesis , 10 , 961-964 (1989)] that the activity of GnT-III increases in rat liver accompanying its canceration. In addition, Ishibashi et al. have reported an increase in the activity of GnT-III in the serum of a human patient with hepatic cancer [see Clinica Chimica Acta , 185 , 325-332 (1989]. Regarding genes, furthermore, a gene coding for GnT-III originating in rat (rat GnT-III) has been isolated by one of the present inventors [see Japanese Patent Application No. 69345/1992]. As described above, GnT-III plays an important role in vivo and is a highly useful enzyme in the diagnosis of cancer because its activity increases accompanying canceration. However reports on human GnT-III have been limited to the determination of its activity and there has been no report of isolation of a human GnT-III gene so far. The present invention aims at specifying a human GnT-III gene and providing a genetic engineering process for producing human GnT-III. The present invention provides an isolated gene as claimed in claim 1, a gene hybridizable therewith, a vector containing either gene, a transformed cell containing the vector and a method of producing human GnT III using the transformed cell. The present invention can be summarized as follows. The present invention relates to a human glycosyltransferase gene. The present invention also relates to a process for producing a human glycosyltransferase. The present inventors have prepared a probe from a rat GnT-III gene, screened a human cDNA library for clones containing a gene coding for human GnT-III by using this probe, and succeeded in the isolation of the gene coding for human GnT-III and the expression of human GnT-III with the use of this gene, thus completing the present invention. Now the present invention will be described in detail. Examples of the probe which can be used in the detection of a gene coding for human GnT-III include a DNA fragment of approximately 1.4 kb which is obtained by cleaving a plasmid SV3 containing the rat GnT-III gene described in the Japanese Patent Application No. 69345/1992 with a restriction enzyme Hin dIII. The plasmid SV3 can be prepared from Escherichia coli XL1-Blue SV3 (FERM BP-4325) which has been deposited with Fermentation Research Institute, Agency of Industrial Science and Technology. By using this DNA fragment as a probe, for example, a commercially available human cDNA library can be screened for a gene coding for human GnT-III by plaque hybridization. As the result of the screening, two positive clones are obtained from 3 x 10⁶ plaques and respectively named H2 and H3. These clones are digested with Eco RI and then subcloned into, for example, the Eco RI site of Bluescript IISK⁺ (Stratagene). These subcloned plasmids are named respectively pBluescript II (H2) and pBluescript II (H3). Figure 2 shows a relationship between H2 and H3 revealed by analyzing with restriction enzymes. Examination of the base sequences of these H2 and H3 reveals that no initiator codon ATG is involved therein. In order to obtain a full-length gene coding for human GnT-III, therefore, screening of the human cDNA library is effected again with the use of H2 and H3 as a probe. As the result, four positive clones are obtained from 7 x 10⁵ plaques. These clones are digested with Eco RI and then subcloned into, for example, the Eco RI site of Bluescript IISK⁺. From among the subcloned DNAs, two DNAs containing an initiator codon are named respectively H15 and H20. The plasmids having H15 and H20 subcloned therein are named respectively pBluescript II (H15) and pBluescript II (H20). Figure 2 shows a relationship between H15 and H20 revealed by analyzing with restriction enzymes. Next, an expression plasmid containing a full-length human GnT-III gene can be constructed by, for example, excising H20 from pBluescirpt II (H20) with Eco RI and integrating it into pSVK3 (Pharmacia) to prepare pSVK(H20). Further, a fragment excised from pBluescript II (H3) having H3 integrated thereinto with Not I and Xho I is integrated into the pSVK(H20) in such a manner as to replace the Not I- Xho I fragment of the pSVK(H20) therewith, thus constructing an expression plasmid EX20F (see Fig. 3). The base sequence of the DNA fragment integrated into EX20F can be determined by the dideoxy method. SEQ ID NO. 1 in the sequence listing shows a part of the base sequence thus determined. As the result of screening of an open reading frame (ORF), an ORF is found out in bases Nos. 169 to 1761. Figure 1 shows a restriction map of this ORF region. SEQ ID NO. 2 in the sequence listing shows the base sequence and the deduced amino acid sequence of the ORF region. Human GnT-III producing cells can be obtained by transforming expression cells by an expression plasmid and examining the capability of the transformant to express human GnT-III. Examples of usable expression cells include COS-1 cells (ATCC CRL 1650). For example, the COS-1 cells can be transformed by the above expression plasmid EX20F. Then the transformant is incubated and the activity of GnT-III expressed in the transformant is determined to specify a gene coding for human GnT-III. This gene is integrated into EX20F and a part of its base sequence is located on a DNA fragment represented by SEQ ID NO. 1. Human GnT-III can be produced by genetic engineering technique by incubating the above transformant. By effecting hybridization with the use of the gene thus obtained as a probe under strict conditions, it is anticipated that genes for enzymes analogous to that of the present invention, which are different therefrom in sequence but expected to have a similar activity, may be obtained. The term "under stringent conditions" as used herein means that the hybridization of a nylon membrane having DNAs immobilized thereon with the probe is conducted in a solution containing 6 x SSC (1 x SSC means a solution prepared by dissolving 8.76 g of sodium chloride and 4.41 g of sodium citrate in 1 liter of water), 1% of sodium lauryl sulfate, 100 µg/ml of salmon sperm DNA, and 5 x Denhardt's (containing bovine serum albumin, polyvinylpyrrolidone and Ficoll each at a concentration of 0.1%) at 65°C for 20 hours. As described above in detail, the present invention enables a gene coding for human GnT-III to be isolated and provides a process for producing human GnT-III by using the gene. This gene and its decomposition products are usable in the determination of human GnT-III during the expression process in vivo and, therefore, useful in the genetic diagnosis of cancer, and so forth. In addition, various antibodies can be immunologically prepared by using polypeptides coded for by the gene of the present invention. These antibodies are also useful in the field of diagnosis and for the purification of human GnT-III. Brief Description of the Drawings Figure 1 is a drawing showing a restriction map of a gene coding for human GnT-III. Figure 2 is a drawing showing relationships among four DNAs H2, H3, H15 and H20. Figure 3 is a drawing showing the construction of a plasmid EX20F. Example To further illistrates the present invention in greater detail, and not by way of limitation, the following Examples will be given. Example 1 (1) Screening of cDNA library SV3 was prepared from Escherichia coli XL1-Blue SV3 (FERM BP-4325) transformed by a plasmid SV3 and the plasmid was digested with Hin dIII to give a DNA fragment of approximately 1.4 kb. This DNA fragment was radiolabeled with [α-³²P] dCTP (3000 Ci/mmol, Amersham) by using a Multiprime DNA Labeling System (Amersham) to thereby give a probe. By using the obtained probe, a human cDNA library [Human Fetal Liver 〈λgt10〉, Clonetech] was screened for the target clone by plaque hybridization. As a result, two positive clones were obtained from 3 x 10⁶ plaques. From these clones, DNAs were extracted and digested with Eco RI. The digestion products thus obtained were subcloned into Bluescript IISK⁺ and the DNAs thus subcloned (approximately 1.3 kb and approximately 1.5 kb) were respectively named H2 and H3, while the plasmids were respectively named pBluescript II (H2) and pBluescript II (H3). Figure 2 shows the restriction maps of these DNAs and a relationship between them. (2) Cloning of upstream region containing initiator codon H2 and H3 were radiolabeled in the same manner as the one described in the above Example 1-(1) to thereby give probes. By using these probes, screening of a human cDNA library was carried out in the same manner as the one described in the above Example 1-(1) to obtain four positive clones from 7 x 10⁵ plaques. The Eco RI-digestion products thereof were subcloned into Bluescript IISK⁺. The base sequences of the DNAs thus subcloned were identified and two DNAs containing an initiator codon (approximately 1.6 kb and approximately 1.5 kb) were named respectively H15 and H20, while the plasmids corresponding thereto were named respectively pBluescript II (H15) and pBluescript II (H20). Figure 2 shows the restriction maps of these DNAs and a relationship between thereof with H2 and H3. Example 2 (1) Construction of expression plasmid The pBluescript II (H20) prepared in the above Example 1-(2) was digested with Eco RI to excise H20, which was integrated into the Eco RI site of an expression vector pSVK3 (Pharmacia) for eukaryotic cells to thereby give pSVK(H20). Separately, the pBluescript II (H3) prepared in the above Example 1-(1) was digested with Not I and Xho I to obtain an Not I- Xho I fragment (approximately 0.9 kb) containing the downstream region of the human GnT-III gene. Next, an expression plasmid EX20F for eukaryotic cells was constructed by digesting pSVK(H20) with Not I and Xho I, excising the Not I- Xho I fragment away, and integrating the Not I- Xho I fragment (approximately 0.9 kb) of pBLuescript II (H3) in its place (see Fig. 3). The base sequence of the DNA fragment integrated into EX20F was determined by the dideoxy method. A part of this base sequence is represented by SEQ ID NO. 1 in the sequence listing. As the result of the screening for an ORF, an ORF was found in the bases Nos. 169 to 1761. Figure 1 shows a restriction map of this ORF region. SEQ ID NO. 2 in the sequence listing shows the base sequence and the deduced amino acid sequence of the ORF region. (2) Transformation and expression of human GnT-III gene The COS-1 cells to be used for expressing human GnT-III were incubated in Dulbecco's modified Eagle medium containing 10% of FCS in the presence of 5% of CO₂ at 37°C under moist conditions. Subsequently, the EX20F prepared in the above Example 2-(1) was introduced into the COS-1 cells by electropolation with the use of a Gene Pulser (Bio-Rad). More specifically, approximately 5 x 10⁶ cells and a recombinant plasmid or a control vector were suspended in 0.8 ml of 20 mM Hepes buffer (pH 7.05) containing 137 mM of NaCl, 5 mM of KCl, 0.7 mM of Na₂HPO₄ and 6 mM of dextrose, and treated at a voltage of 250 V/0.4 cm and at a capacitance of 960 µFD. After the completion of the transformation, the incubation was carried out for 2 days and then the cells were harvested and sonicated in PBS to determine the GnT-III activity in the sonicated cell suspension. It was found that the cells which had not been treated with the plasmid and those which had been treated with the control plasmid pSVK3 had no GnT-III activity, whereas the cells transformed by the plasmid EX20F had a GnT-III activity, suggesting that the human GnT-III gene had been expressed therein. Thus it has been proved that a gene coding for human GnT-III exists on the DNA fragment which have been integrated into EX20F and a part of the base sequence of which is represented by SEQ ID NO. 1 in the sequence listing. (3) Determination of GnT-III activity The GnT-III activity was determined in accordance with the description given in Biochimica et Biophysica Acta , 1035 , 313-318 (1990). More precisely, by using 80 µM of pyridylamino (PA) Gn, Gn-bi [GlcNAc β1-2Man α1-6 (GlcNAc β1-2Man α1-3)Man β1-4 GlcNAc β1-4 GlcNAc-PA] as a receptor, UDP-GlcNAc serving as a sugar donor was added in such a manner as to give a final concentration of 80 µM to a 125 mM solution of 2-(N-morpholino)ethanesulfonic acid buffer (MES buffer, pH 6.25) containing 10 mM of MnCl₂, 200 mM of GlcNAc and 0.5% (v/v) of Triton X-100. After reacting the mixture at 37°C for 1 hour, the GnT-III activity was determined by analyzing by HPLC. Effects of the Invention According to the present invention, a gene for human GnT-III having an important role in vivo and an industrial process for producing this enzyme are provided. The gene and enzyme are useful in the fields of, for example, biochemistry and diagnosis.

Claims: Isolated gene encoding human glycosyltransferase III (GnT-III), wherein the nucleotide sequence is as shown by SEQ ID NO. 2 in the sequence listing, or a derivative thereof by way of nucleic acid deletion, substitution, insertion, inversion, addition or replacement. Isolated gene encoding human GnT-III which is hybridizable with the gene of claim 1 under stringent conditions. A vector which contains the isolated gene of claim 1 or 2. A transformed cell which contains the vector of claim 3. A method of producing human GnT-III which comprises cultivating transformed cells of claim 4 and isolating human GnT-III from the culture medium in which the transformed cells have been cultivated.

Inventors: NISHIKAWA ATSUSHI, TANIGUCHI NAOYUKI, NISHIKAWA, ATSUSHI, TANIGUCHI, NAOYUKI
Applicants: TAKARA SHUZO CO, TAKARA SHUZO CO. LTD.
Application year: 1993
Main classification: C12N15
IPC codes: C12N15, C12N5, C12N9, C12R1