Cloning, expression and characterization of a cDNA (6A8) encoding a novel human alpha-mannosidase

Literature and patent analysis of the cloning and identification of human functional genes in China

The Human Genome Project was launched at the end of the 1980s. Since then, the cloning and identification of functional genes has been a major focus of research across the world. In China too, the potentially profound impact of such studies on the life sciences and on human health was realized, and relevant studies were initiated in the 1990s. To advance China's involvement in the Human Genome Project, in the mid-1990s, Committee of Experts in Biology from National High Technology Research and Development Program of China (863 Program) proposed the "two 1%" goal. This goal envisaged China contributing 1% of the total sequencing work, and cloning and identifying 1% of the total human functional genes. Over the past 20 years, tremendous achievement has been accomplished by Chinese scientists. It is well known that scientists in China finished the 1% of sequencing work of the Human Genome Project, whereas, there is no comprehensive report about "whether China had finished cloning and identifying 1% of human functional genes". In the present study, the GenBank database at the National Center of Biotechnology Information, the PubMed search tool, and the patent database of the State Intellectual Property Office, China, were used to retrieve entries based on two screening standards: (i) Were the newly cloned and identified genes first reported by Chinese scientists? (ii) Were the Chinese scientists awarded the gene sequence patent? Entries were retrieved from the databases up to the cut-off date of 30 June 2011 and the obtained data were analyzed further. The results showed that 589 new human functional genes were first reported by Chinese scientists and 159 gene sequences were patented (http://gene.fudan.sh.cn/introduction/database/chinagene/chinagene.html). This study systematically summarizes China's contributions to human functional genomics research and answers the question "has China finished cloning and identifying 1% of human functional genes?" in the affirmative.

α-Mannosidase 2C1 attenuates PTEN function in prostate cancer cells

PTEN dephosphorylates the 3-position phosphate of phosphatidylinositol 3,4,5 triphosphate (PIP(3)), thereby inhibiting AKT activation. Although attenuation of PTEN function has a major role in tumourigenesis, the underlying mechanisms remain unclear. Here we show that α-mannosidase 2C1 (MAN2C1) inhibits PTEN function in prostate cancer (PC) cells and is associated with a reduction in PTEN function in primary PC. MAN2C1 activates AKT and promotes the formation of PTEN-positive DU145 cell-derived xenograft tumours by imparing endogenous PTEN function. In 659 PC patients who were examined, ~60% of tumours were PTEN positive with elevated AKT activation. Of these, 80% display MAN2C1 overexpression that co-localizes with PTEN. Increases in MAN2C1 were detected only in PTEN-positive prostatic intraepithelial neoplasia and carcinomas, and showed a significant association with PC recurrence only in patients with PTEN-positive PCs. Mechanistically, MAN2C1 binds PTEN thereby inhibiting its PIP(3) phosphatase activity. These findings show that MAN2C1 function as a PTEN-negative regulator in PC cells.

hMan2c1 transgene promotes tumor progress in mice

In order to study the biological significance of alpha-mannosidase Man2c1, hMan2c1 transgenic mice were developed. In 113 F0 mice, eight were found to be genomic PCR positive for hMan2c1; 9/20 (45%) F1 mice, 16/21 (76.2%) F2 mice, and 12/14 (85.7%) F3 mice were genomic PCR positive for hMan2c1. RT-PCR demonstrated hMan2c1 mRNA transcription in four of eight transgenic lines. Enzymatic activity on p-nitrophenyl-alpha-D: -mannopyranoside was enhanced in 35# and 54# transgenic mice and real-time RT-PCR showed hMan2c1 mRNA expression in these mice. Reduced Con A binding to splenocytes implied N-glycosylation modification of host proteins by hMan2c1 transgene. hMan2c1 transgene promoted growth, invasion, and metastasis to lung of implanted hepatoma H22 and sarcoma S180. The average weights of H22 and S180 tumors were 3.98 +/- 1.62, 3.29 +/- 0.76, 1.69 +/- 1.09, and 3.19 +/- 0.44, 2.72 +/- 1.38, 0.97 +/- 0.41 g for 35#, 54# transgenic mice and wild type mice (W), respectively, (35# or 54# versus W, paired t-test, P < 0.05). In 35# and 54# mice 5/10 and 3/10 showed lung metastasis of H22 tumor in contrast with 1/10 in W mice. In 35# and 54# mice 1/6 and 2/6 showed lung metastasis of S180 tumor in contrast with 0/6 in W mice. The possible mechanism of the promotion was explored on both humoral and cellular immunity. Reduced antibody response to BSA was observed in transgenic mice, suggesting that specific antibody response to tumor antigens might be suppressed by hMan2c1 transgene. However, NK cytotoxicity in splenocytes was not affected by the transgene.

Resistance of SKW6 cell to apoptosis induction with anti-Fas antibody upon transduction of a reverse fragment to a cDNA encoding human 6A8 alpha-mannosidase

The effect of transduction with a reverse fragment to a cDNA encoding human 6A8 alpha-mannosidase on apoptosis induction of human B cell line SKW6 by anti-Fas antibody was tested. Apoptosis-inducer of anti-Fas monoclonal antibody was used to induce apoptosis in SKW6 cells. Giemsa's staining, Annexin-V-FLUOS staining and DNA ladder test were used to determine the events of apoptosis. Indirect immunofluorescent staining with anti-Fas antibody was performed to detect the surface Fas expression. In a time-course test of 12, 24 and 36 h for apoptosis induction by anti-Fas antibody, DNA ladder was observed in the wild-type SKW6 cells in a time-dependent fashion. Mock transduction had no effect on DNA ladder production. However, no DNA ladder was detected in the rAAV-antisense 6A8 cDNA-transduced SKW6. Results from Annexin-V-FLUOS staining on anti-Fas antibody-treated cells revealed that the staining-positive rate in the rAAV-antisense 6A8 cDNA-transduced SKW6 cells was decreased in comparison to that in the wild-type and the mock-transduced cells. Giemsa's staining observation showed that the number of dying (with apoptotic bodies) and dead cells was reduced in the rAAV-antisense 6A8 cDNA-transduced SKW6 cells in comparison with that in the wild-type and the mock-transduced cells upon anti-Fas antibody induction. The transduction did not affect the expression of Fas molecular on cell surface. 100% cells in all the groups showed Fas expression. The SKW6 cells became resistant to apoptosis induction by anti-Fas antibody upon transduction with a reverse fragment to a cDNA encoding human 6A8 alpha-mannosidase. The transduction did not affect the expression of Fas molecule on cells.

Characterization and subcellular localization of human neutral class IIα-mannosidase cytosolic enzymes/free oligosaccharides/glycosidehydrolase family 38/M2C1/N-glycosylation

A glycosyl hydrolase family 38 enzyme, neutral alpha-mannosidase, has been proposed to be involved in hydrolysis of cytosolic free oligosaccharides originating either from ER-misfolded glycoproteins or the N-glycosylation process. Although this enzyme has been isolated from the cytosol, it has also been linked to the ER by subcellular fractionations. We have studied the subcellular localization of neutral alpha-mannosidase by immunofluorescence microscopy and characterized the human recombinant enzyme with natural substrates to elucidate the biological function of this enzyme. Immunofluorescence microscopy showed neutral alpha-mannosidase to be absent from the ER, lysosomes, and autophagosomes, and being granularly distributed in the cytosol. In experiments with fluorescent recovery after photo bleaching, neutral alpha-mannosidase had slower than expected two-phased diffusion in the cytosol. This result together with the granular appearance in immunostaining suggests that portion of the neutral alpha-mannosidase pool is somehow complexed. The purified recombinant enzyme is a tetramer and has a neutral pH optimum for activity. It hydrolyzed Man(9)GlcNAc to Man(5)GlcNAc in the presence of Fe(2+), Co(2+), and Mn(2+), and uniquely to neutral alpha-mannosidases from other organisms, the human enzyme was more activated by Fe(2+) than Co(2+). Without activating cations the main reaction product was Man(8)GlcNAc, and Cu(2+) completely inhibited neutral alpha-mannosidase. Our findings from enzyme-substrate characterizations and subcellular localization studies support the suggested role for neutral alpha-mannosidase in hydrolysis of soluble cytosolic oligomannosides.

Man2C1, an alpha-mannosidase, is involved in the trimming of free oligosaccharides in the cytosol

The endoplasmic-reticulum-associated degradation of misfolded (glyco)proteins ensures that only functional, correctly folded proteins exit from the endoplasmic reticulum and that misfolded ones are degraded by the ubiquitin-proteasome system. During the degradation of misfolded glycoproteins, they are deglycosylated by the PNGase (peptide:N-glycanase). The free oligosaccharides released by PNGase are known to be further catabolized by a cytosolic alpha-mannosidase, although the gene encoding this enzyme has not been identified unequivocally. The findings in the present study demonstrate that an alpha-mannosidase, Man2C1, is involved in the processing of free oligosaccharides that are formed in the cytosol. When the human Man2C1 orthologue was expressed in HEK-293 cells, most of the enzyme was localized in the cytosol. Its activity was enhanced by Co2+, typical of other known cytosolic alpha-mannosidases so far characterized from animal cells. The down-regulation of Man2C1 activity by a small interfering RNA drastically changed the amount and structure of oligosaccharides accumulating in the cytosol, demonstrating that Man2C1 indeed is involved in free oligosaccharide processing in the cytosol. The oligosaccharide processing in the cytosol by PNGase, endo-beta-N-acetylglucosaminidase and alpha-mannosidase may represent the common 'non-lysosomal' catabolic pathway for N-glycans in animal cells, although the molecular mechanism as well as the functional importance of such processes remains to be determined.

Inhibition of the α-mannosidase Man2c1 gene expression enhances adhesion of Jurkat cells

Protein N-glycosylation plays very important roles in immunity and alpha-mannosidase is one of the key enzymes in N-glycosylation. This paper reports that inhibition of alpha-mannosidase Man2c1 gene expression enhances adhesion of Jurkat T cells. In comparison to the controls with normal expression of the enzyme, Jurkat cells with the inhibition of Man2c1 gene expression (AS cell) formed larger aggregates in culture, indicating an enhancement of adhesion between the cells. mRNA differential display analysis discovered up-regulation of several adhesion molecule genes in the AS cell. Because of the pivotal role played by CD54-LFA-1 interaction in immune cell interaction, this study focused on the contribution of enhanced expression of CD54 and LFA-1 to the enhanced adhesion of AS Jurkat cells. These facts, including increased binding of AS cells to ICAM-1-Fc, Mg(2+) activation of the binding of AS cells to ICAM-1-Fc and enhanced aggregation of AS cells, together with the inhibiting effect of a blocking CD11a mAb on the binding to ICAM-1-Fc and aggregation of the cells demonstrate an important contribution of enhanced CD54-LFA-1 interaction to increased adhesion between AS cells. The enhanced CD54-LFA-1 interaction also resulted in increased adhesion between AS Jurkat T cells and Raji B cells. In addition, AS cells showed cytoskeletal rearrangement. The data imply a biological significance of MAN2C1 in T-cell functioning.

Inhibition of 6A8 alpha-mannosidase gene expression resulted in telomere length shortening in nasopharyngeal carcinoma cell CNE-2L2

Telomere length shortening was observed in the nasopharyngeal carcinoma cell CNE-2L2 when 6A8 alpha-mannosidase expression was inhibited by antisense 6A8 DNA. Transduction with mock or an irrelevant DNA did not affect the telomere length in the carcinoma cells. Telomerase activity and mRNA transcription of TRF 1 and 2 were not changed in the cells treated with antisense 6A8. The Con A binding test showed an enhancement on the proteins isolated from the cells treated with antisense 6A8, but not on those from mock- or irrelevant DNA-treated cells. The data imply an association between glycosylation modification with telomere shortening in antisense 6A8-treated cells.

Unique metal dependency of cytosolic alpha-mannosidase from Thermotoga maritima, a hyperthermophilic bacterium

A putative cytosolic alpha-mannosidase gene from a hyperthermophilic marine bacterium Thermotoga maritima was cloned and expressed in Escherichia coli. The purified recombinant enzyme appeared to be a homodimer of a 110-kDa subunit. The enzyme showed metal-dependent ability to hydrolyze p-nitrophenyl-alpha-D-mannopyranoside. In the absence of a metal, the enzyme was inactive. Cobalt and cadmium supported high activity (60 U/mg at 70 degrees C), while the activity with zinc and chromium was poor. Cobalt (0.8 mol) bound to 1 mol monomer with a K(d) of 70 microM. The optimum pH and temperature were 6.0 and 80 degrees C, respectively. The activity was inhibited by swainsonine, but not by 1-deoxymannojirimycin, which is in agreement with the features of cytosolic alpha-mannosidase.

Suppression of 6A8 ?-mannosidase gene expression reduced the potentiality of growth and metastasis of human nasopharyngeal carcinoma

Suppression of alpha-mannosidases by chemicals has been shown to reduce the potentiality of growth and metastasis of various tumors. In our study, the effect of 6A8 alpha-mannosidase (MAN 6A8), recently discovered in our laboratory, on malignant behaviors of tumor cells was examined. Since the suppressive effect of chemicals on alpha-mannosidase is not specific, antisense technique was used to specifically inhibit expression of the MAN 6A8 in human nasopharyngeal carcinoma cells, CNE-2L2. Two cell clones, AS1 and AS2, with pronounced suppression of MAN 6A8 expression were developed. Wild-type (W), mock-transduced (M) and irrelevant DNA-transduced (IR) CNE-2L2 cells with normal expression of the enzyme were used as controls. Malignant behaviors of the cells were examined. Significant inhibition of growth of AS cells in vitro measured by MTT assay, colony formation and anchorage-independent colony formation was found. Pronounced inhibition of formation of tumors from AS cells inoculated into nude mice and metastasis was also observed. W, M and IR cells cultured in plate wells appeared dispersed with a fibroblastic or epithelial morphology, whereas AS cells were in compact sheets with an epithelioid organization. Since E-cadherin is the key factor in homophilic adhesion of epithelial cells, its expression on the surface of CNE-2L2 cells was determined. E-cadherin expression on AS cells was enhanced, whereas it was markedly diminished on W, M and IR cells. In addition, lamellipodia, which play an important role in cell spreading and mobility, almost disappeared on AS cells. The results demonstrate a significant suppressive effect of reduced expression of MAN 6A8 on malignant behaviors of CNE-2L2 cells.

Long-term expression of a transferred gene in Epstein-Barr virus transformed human B cells

Delivering a gene into the Epstein-Barr virus (EBV)-transformed B cells is useful in studying effects of the gene on B-cell functions. However, although people have been able to efficiently transfer genes into and get them expressed in B-lympho blastoid cells for a time probably long enough to kill the cells using vectors harbouring oriP, the expression time of the delivered gene is not long enough in order to study the gene function in B cells. To solve this problem, we constructed an adeno-associated virus (AAV) plasmid pAGX(+) based on plasmids pSub201 and pRc/CMV. We developed and packaged recombinant AAV (rAAV) expression vectors containing an antisense or a sense DNA fragment of 6A8 cDNA encoding a human alpha-mannosidase, or an antisense fragment of 5D4 cDNA encoding a human cell membrane protein, or EYFP DNA. EBV-transformed B cell SKW6 and 3D5 were transduced with those rAAV or the mock. Transduction with the rAAV-EYFP showed an infection frequency of 64 +/- 3.5% and 58 +/- 6.2% for SKW6 and 3D5 cell, respectively. Genomic polymerase chain reaction (PCR) for neoR gene indicated an integration of the transferred gene into the host DNA. After being cultured and propagated for over 12 months, the cells were detected for the expression of the transferred gene. The RT-PCR, enzymatic assay and Con A binding test demonstrated an inhibition of 6A8 alpha-mannosidase in both SKW6 and 3D5 cells transduced with the antisense 6A8 DNA. Immunofluorescence staining with monoclonal antibodies (MoAb) 5D4 showed a reduction of the 5D4 protein expression on both the cells transduced with the antisense 5D4 DNA. The DNA fragmentation assay showed a resistance of the cells with 6A8 alpha-mannosidase inhibition to apoptosis induction by anti-Fas antibody. The data indicate that the AAV vector pAGX(+) can efficiently introduce genes into EBV-transformed B cells and the delivered gene can be expressed in the cells for more than 12 months which may be long enough for the study of gene functions in B cells.