| BackgroundSystemic lupus erythematosus (SLE) is a multisystem autoimmune diseasecharacterized by immune dysfunction resulting in the production of autoantibodies against many ubiquitous self-antigens. Hallmarks of the disease include the production of antibodies to three nuclear constituents involved in transcription and RNA processing: spliceosome, nucleosome, and small ribonucleoprotein complex (sn-RNP). The etiology of SLE is complex, and evidence has steadily accumulated supporting a multifactorial origin for SLE, which includes genetic predisposition, sex hormones, various retroviral factors and environmental influences. However, the exact pathogenesis of SLE remains unclear up to now, which makes it difficult to diagnose and treat the disease promptly. So it is important to elucidate the etiology and pathogenesis of SLE as soon as possible so as to establish more effective therapy strategies.Recently, there is substantial circumstantial evidence that the development of SLE is involved in retroviruses, particularly Human endogenous retroviruses (HERVs). First, SLE patients produce high titer antibodies to various retroviralproteins, including Gag, Env, and Nef of HIV and HTLV, in the absence of overt retroviral infection. Secondary, new human retroviruses or novel retroviral sequences were isolated from patients with SLE and other related rheumatic autoimmune diseases. Shih et al reported a differential transcription pattern of pol fragments in PBMCs from SLE patients and increased transcription of retroviral products in SLE patients were discovered when compared with healthy donors, indicating that endogenous retrovirus may play an important role in SLE. The exact mechanisms of SLE are unknown, but several candidate mechanisms have been proposed. Endogenous retroviral integration may lead to the development of autoimmunity by integrating at sites involved in immune regulation. Some superantigens encoded by HERVs may lead to specific deletion or expansion of T cell subsets. Moreover, some endogenous retroviruses have regions in sequence that mimic common nuclear protein sequences. Through the process of molecular mimicry, endogenous retroviral sequences stimulate the production of antiretroviral antibodies that are cross-reactive with common nuclear antigens. Therefore molecular mimicry and immunomodulation by HERVs may contribute to the etiopathogenesis of SLE, resulting from dysimmunity of autoreactivity T and B cell.The novel NP9 gene within the human endogenous retrovirus K (HERV-K) env-reading frame is expressed in various tumor tissues and transformed cell lines. NP9 transcript results from a novel, HERV-K type 1-specific splice donor site. A 9-kDa protein coded by NP9 gene localizes predominantly in the cellnucleus. As we know, the autoantibodies in the patients with SLE is related withcell nucleus components. Thus it prompted us to investigate the correlations between SLE and retroviral NP9 gene and potential mechanisms used by endogenous retroviruses in the etiopathogenesis of SLE through prediction of NP9 protein function.Materials and methodsThe peripheral blood from patients with SLE and from healthy donors matched for age and sex was provided by Second Affiliated Hospital, MedicalCollege of Zhejiang University. The peripheral blood mononuclear cells (PBMCs) were separated by Lymphocyte separating medium (Ficoll), and total RNA was isolated according to the Trizol one-step procedure (GIBCO). The endogenous retroviral NP9 gene was isolated and cloned using reverse transcription polymerase chain reaction (RT-PCR) and T-A cloning techniques, and its sequence was determined with Perkin-Elmer ABI 377 DNA Sequencer.High efficient prokaryotic expression system with intact NP9 open reading frame (ORF) was constructed with pQE30 vector using subcloning way. The prokaryotic expression vector pQE30-NP9 was transformed into E.Coli Ml5 and induced by IPTG to express NP9 recombination protein. The protein was analyzed by SDS-PAGE and reclaimed using electroeluting to prepar...
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