Association Between Ptp22 1858 Single-nucleotide Polymorphism And The Susceptibility Of Autoimmune Diseases In Chinese Population

Ever since the completion of "Human Genome Project" in 2003, scientists from many countries have already begun the exploration in the post-genome era. They have opened new chapters in various areas of life sciences, but also ushered in a number of unprecedented challenges. One of the most difficult tasks is how to utilize the massive information and data decoded by the HGP to investigate the relationship between gene abnormality and human disease.After more than two centuries exploration, scientists have gradually understood the basic nature of genetic diseases, and divided them into three categories: single-gene disorders (also known as Mendelian disease), chromosome abnormalities, and multifactorial disorders. Among them, those caused by multi-genes and multiple factors are the most complex diseases, because they involve a variety of gene abnormalities adding up together to form a certain disease. In this circumstance, no single gene could lead to the disease alone; instead, each abnormal gene will increase the risk of a certain illness, thus adding many difficulties in disease prevention, diagnosis and treatment. There are many chronic diseases proven to result from multiple genetic factors, such as heart disease, hypertension, diabetes, arthritis, Alzheimer's disease, cancers, obesity, and autoimmune diseases.Autoimmune disease refers to the body's own immune system attacks self-antigens, leading to the tissue damage. Usually the immune system is under tight regulation and control, giving no response to its own antigens, that is immune tolerance; and the malfunction of immune tolerance will lead to autoimmune diseases. Recently researchers have found that the lymphoid-specific tyrosine phosphatase LYP is closely linked to various autoimmune diseases. LYP is a kind of protein tyrosine phosphatase encoded by Ptpn22. As is known, protein phosphorylation is the most important process of cell signal transduction. The protein kinase and protein phosphatase together control the substrate protein to turn between the phosphorylated form and dephosphorylated form, thus mediating its activity and controlling the whole signal transduction pathway. Therefore, protein phosphorylation plays the key role in all kind of body activities, including metabolism, gene transcription and translation, cell cycle progression, protein-protein interactions, immune response, apoptosis and cell movement, and so on.LYP plays a very important negative role in T cell signal transduction pathway. It consists of 807 amino acids with 110kDa molecular weight, and is predominately expressed in lymphoid tissues and cells. LYP contains a catalytic domain in the N terminal, and four proline-rich regulatory domains (P1~P4) in the C terminal. In vivo, the P1 domain of LYP can bind to the SH3 domain of Csk, and together dephosphorylate the downstream Src family kinase (such as Lck, Fyn and Zap-70, etc.), thus reducing T cell signaling. It is reported that a single-nucleotide polymorphism present in the gene Ptpn22 encoding LYP maybe connected with the occurrence of autoimmune diseases.Single-nucleotide polymorphism (SNP) refers to the DNA sequence polymorphism in the level of genome brought by a single nucleotide variation. SNPs are the most common genetic variations (about 90%) of human being, and widely distribute in the human genome. But not all of this kind of variation could be called as SNPs: only those stably exist in at least 1% of the population can be called as single-nucleotide polymorphisms. Different ethnic groups more or less have their unique SNPs, but for human beings as a whole, 85% of the SNPs are the same. SNPs are closely related to human diseases. Though it cannot determine the occurrence of a certain diseases, it can affect human susceptibility to disease, especially those present in the genome coding region. Therefore, as the most common type of human genetic variation, SNPs have a very high value in the field of biomedicine, medical diagnostics, and drug development. Recent studies show that the C1858T SNP present in Ptpn22 is connected with the occurrence of autoimmune diseases. In European and the American populations, people carrying 1858T allele are more prone to suffer from autoimmune diseases than those carrying 1858C allele, including rheumatoid arthritis, systemic lupus erythematosus, and type 1 diabetes. This SNP can lead to the substitution from an arginine (R) into a tryptophan (W) in the 620 amino acid of the P1 domain of LYP, where LYP interact with Csk, therefore undermining their binding interaction, and finally affects the activity of LYP. Researches have found that 1858T allele will increase the activity of LYP, that is to say this is a gain-of-function variation. It may result in the abnormal T cells development in the thymus and the lack of immune tolerance.Although Ptpn22 C1858T SNP has been reported to have connections with autoimmune diseases, the distribution and contribution of this SNP are different in various countries and populations. So scientists speculated that this SNP might occur in the late stage of human evolution. Scientists have already found the increased susceptibility brought by the 1858T allele in American and European Populations; however, this conclusion is not convincible when applied to other populations, such as Chinese population, even Asian populations. Therefore, on this basis, this subject detected the occurrence of Ptpn22 1858T allele in Chinese autoimmune diseases patients as well as healthy controls with an improved method, to find whether there is any association between this SNP and the susceptibility of autoimmune diseases in Chinese population. Since China's population takes almost 1/5 of the world's population and its ancestors are different with European and American populations, this research may help the prevention, diagnosis, and treatment of autoimmune disease among Chinese patients. Finally, we drew a conclusion that is different with past research: the 1858T allele dose not increase the susceptibility for autoimmune diseases in Chinese population.As the pathogenic 1858T allele can cause the increased activity of LYP, the specific inhibitors and anti-antibodies of LYP may help the treatment of autoimmune diseases. Based on this, we cloned the LYP catalytic domain Lyp-Cat, and expressed and purified two fusion proteins GST-LYP-Cat and MBP-LYP-Cat, in order to study the biological function of LYP in the level of protein and screen its specific inhibitors. In addition, we used LYP-Cat as immunogen in the immunization of mice to prepare and purify polyclonal anti-LYP-Cat antibodies, hoping to provide some help for future research in this area, as well as facilitating the prevention, diagnosis, and treatment of autoimmune diseases.