Housekeeping promoter 5'pcmah-2 of pig CMP-N-acetylneuraminic acid hydroxylase gene for NeuGc expression

Human ST3Gal II and ST6GalNAc IV genes increase human serum-mediated cytotoxicity to xenogeneic cells

Carbohydrate-antigens widely existed on glycoproteins and glycosphingolipids of all mammalian cells play a crucial role in self-defense and immunity. Xeno-reactive antibodies included in natural human sera play a protecting role in an acute phase-rejection of xenotransplantation. In this study, we investigated the effect of an alteration of glycosylation-pattern, caused by human sialyltransferases such as hST3Gal II or hST6GalNAc IV, on human serum mediated cytotoxicity in pig kidney PK15 cells. From LDH cytotoxicity assay, cytotoxicity to human serum was significantly increased in hST3Gal II and hST6GalNAc IV-transfected PK15 cells, as compared to the control. In the hST6Gal I-carrying cells, the cytotoxicity to human serum was rather decreased. Moreover, flow cytometry analysis revealed that an alteration of pig glycosylation-pattern by hST3Gal II or hST6GalNAc IV influences on a binding of human IgM or IgG, respectively, in pig kidney cells, regardless of Gal antigen alteration. Finally, we found that hST6GalNAc IV contributed to increase of terminal disialylated tetrasaccharide structure, disialyl T antigen, as evidenced by increase of the MAL II lectin binding capacity in the hST6GalNAc IV-transfected PK15 cells, compared with control. Therefore, our results suggest that carbohydrate antigens, such as disialyl T antigen, newly synthesized by the ST3Gal II- and ST6GalNAc IV are potentially believed to be new xeno-reactive elements.

Gram-Negative Bacterial Endotoxin LPS Induces NeuGc Loss through Ets1-Dependent Downregulation of Intestine-Specific pcmah Transcript in Porcine Intestinal Cells

N-glycolylneuraminic acid (NeuGc), a non-human sialic acid derivative synthesized by cytidine-5′-monophospho-N-acetylneuraminic acid hydroxylase (CMAH), plays a crucial role in mediating infections by certain pathogens. Although it has been postulated that NeuGc biosynthesis and CMAH expression are downregulated during microbial infection, the underlying mechanisms remain unclear. The present study showed that exposure to lipopolysaccharide (LPS), a Gram-negative bacterial endotoxin, leads to loss of NeuGc biosynthesis in pig small intestinal I2I-2I cells. This LPS-induced NeuGc loss was accompanied by decreased CMAH transcript levels, especially intestine-specific 5′pcmah-1. Furthermore, LPS suppressed the activity of the Pi promoter responsible for 5′pcmah-1 by inhibiting DNA binding of Est1. These findings provide insight into the regulatory mechanisms of Neu5Gc biosynthesis during pathogenic infectious events, which may represent a host defense mechanism that protects the self against pathogenic bacterial infections even in non-sanitary environments.

Molecular characterization of cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) associated with the erythrocyte antigens in dogs

Background

N-glycolylneuraminic acid (Neu5Gc) is synthesized from its precursor N-acetylneuraminic acid (Neu5Ac) by cytidine-5′-monophospho-N acetylneuraminic acid hydroxylase (CMAH), which is encoded by the CMAH gene. Most mammals have both Neu5Gc and Neu5Ac, but humans and ferrets have only Neu5Ac because of loss-of-function mutations. Dogs and cats are polymorphic for Neu5Gc and Neu5Ac expression like cats, in which the CMAH gene is responsible for the AB Blood group system. Although the CMAH gene has been characterized in many species, not much is known about it in dogs. In this study, we cloned the dog CMAH cDNA, and performed mRNA expression analysis of this gene in several organs. We also identified single nucleotide polymorphisms (SNPs) in the CMAH gene.

Results

We cloned the 1737-bp open reading frame of the dog CMAH gene. This gene consists of at least 14 coding exons and codes for a polypeptide of 578 amino acids and is located on chromosome 35. The amino acid identities of dog CMAH with the corresponding sequences from cat, pig, chimpanzee, mouse, and rat were high (89 to 93%). RT-PCR analysis showed that the dog CMAH cDNA was expressed in various tissues. We identified four exonic SNPs (three synonymous and one non-synonymous), 11 intronic SNPs, and an indel in 11 dog breeds by analyzing the nucleotide sequences of the 14 exons, including the coding region of CMAH. In the genotype of the non-synonymous SNP, c.554 A > G (p.Lys185Arg), in a total of 285 dogs of seven different breeds, the allele G was widely distributed, and the allele A was the most frequent in the Shiba dogs. The dogs expressing Neu5Ac did not carry the loss-of-function deletion of CMAH found in humans and ferrets, and it remains unclear whether the point mutations influence the expression of Neu5Ac.

Conclusions

We characterized the canine CMAH gene at the molecular level for the first time. The results obtained in this study provide essential information that will help in understanding the molecular roles of the CMAH gene in canine erythrocyte antigens.

Intestine specific regulation of pig cytidine-5'-monophospho-N-acetylneuraminic acid hydroxylase gene for N-glycolylneuraminic acid biosynthesis

N-glycolylneuraminic acid (Neu5Gc), a generic form of sialic acid, is enzymatically synthesized by cytidine-5′-monophospho-N-acetylneuraminic acid hydroxylase (CMAH). Although expression of pig CMAH gene pcmah encoding CMAH has been reported to be regulated by pathogenic infection and developmental processes, little is known about the mechanisms underlying the regulation of pcmah gene expression. The objective of this study was to determine mechanism(s) involved in intestine specific regulation of pcmah gene by identifying several cis-acting elements and nuclear transcription factors that could directly interact with these cis-acting elements. We identified intestine specific promoter region (Pi) of pcmah gene located at upstream regions of the 5′flanking region of exon 1a and found that the promoter region is responsible for the transcriptional regulation of 5′pcmah-1. Based on reporter assays using serially constructed luciferase genes with each deleted promoter, we demonstrated that the Pi promoter activity was more active in intestinal IPI-2I cells than that in kidney PK15 cells, corresponding to both mRNA expression patterns in the two cell lines. In addition, we found that Sp1 transcription factor was necessary for basal activity of Pi promoter and that Ets-1 contributed to intestine-specific activity of Pi promoter. This study helps us understand transcriptional regulation of pcmah in the intestine of pig tissues. It also allows us to consider potential roles of Neu5Gc in interaction with environmental factors present in the intestinal tissue during pathogenic infection and developmental process.