Control of the HLA antigen processing pathways by the HLA class III-encoded BAT3

主要组织相容性基因复合体（MHC）的生物合成编码的I类和II类分子是肽受体，它们将抗原肽呈递给T淋巴细胞。MHC I类和II类分子的生物合成对于抗原呈递至关重要。因此，MHC基因的调节对于免疫应答的控制是重要的。我们发现，MHC III类编码的BAT 3调节MHC I类和II类加工途径的组分。MHC I类和II类基因在转录水平上受到调控。对II类基因调控的研究表明，II类反式激活因子CIITA通过BAT 3的表达而稳定。CIITA和BAT 3基因均被IFN γ处理的细胞诱导/增强。新合成的CIITA与BAT 3结合。该复合物获得了一个尚未鉴定的翻译后修饰。此外，用γ干扰素治疗使BAT 3和CIITA从胞质溶胶易位到细胞核，在细胞核中调节II类基因。最近，我们发现，除了II类基因，I类基因的调节BAT 3的表达。通过选择性BAT 3 RNA剪接实现MHC I类和II类基因的差异调节。BAT 3基因包含3个差异剪接的外显子。基于剪接事件，可能存在多达8种BAT 3剪接变体。我们从细胞cDNA中分离出六个BAT 3的剪接变体。鉴定了一种BAT 3变体，其专门调节II类表达，而第二种变体调节I类表达。本项目将研究单个BAT 3变体对MHC I类和/或II类表达的作用。通过BAT 3表达调节MHC I类分子的机制尚未阐明。我们希望确定影响I类表达的BAT 3调节因子。此外，我们还想探讨BAT 3如何从胞质转移到细胞核，并随后调节MHC基因的机制。几种细胞因子对于抗原呈递细胞的分化是重要的。这些细胞因子中的一些刺激BAT 3表达并影响BAT 3的细胞内定位。我们确定了诱导树突状细胞分化的细胞因子对BAT 3水平和BAT 3变体的组成的影响。将探索细胞因子对BAT 3基因的刺激，并检查细胞因子对BAT 3 RNA剪接的可能影响。基于我们用细胞系获得的结果，我们想研究BAT 3在原代细胞中的作用。我们的目的是研究BAT 3和BAT 3变体在树突状细胞发育中的作用，并揭示一种控制抗原呈递细胞中MHC I类和II类表达的新机制。

The biosynthesis of major histocompatibility gene complex (MHC) encoded class I and class II molecules are peptide receptors, which present antigenic peptides to T lymphocytes. The biosynthesis of MHC class I and class II molecules is critical for antigen presentation. Therefore, regulation of MHC genes is important for the control of immune responses. We discovered that MHC class III encoded BAT3 regulates components of the MHC class I and class II processing pathways. MHC class I and class II genes are regulated on the transcriptional level. Investigation of class II gene regulation revealed that the class II transactivator CIITA is stabilized by expression of BAT3. Both, CIITA and BAT3 genes are induced/enhanced by IFN gammatreatment of cells. Newly synthesized CIITA binds to BAT3. This complex acquires a not yet identified posttranslational modification. In addition, treatment with gamma interferon translocates BAT3 and CIITA from the cytosol to the nucleus, where class II genes are regulated. Recently, we discovered that in addition to class II, class I genes are regulated by BAT3 expression. Differential regulation of MHC classes I and II genes is achieved by alternative BAT3 RNA splicing. The BAT3 gene contains 3 exons which are differentially spliced. Based on the splicing events up to 8 splice variants of BAT3 may exist. We isolated six splice variants of BAT3 from cellular cDNA. One BAT3 variant was identified, which exclusively regulates class II expression, whereas a second variant regulates class I expression. The role of the individual BAT3 variants for MHC class I and/or class II expression will be investigated in this project. The mechanism of MHC class I regulation by BAT3 expression is not yet unravelled. We want to identiy BAT3-regulated factors which impact on class I expression. In addition, we want to explore the mechanism how BAT3 translocates from the cytosol to the nucleus with subsequent regulation of MHC genes. Several cytokines are important for differentiation of antigen presenting cells. Some of these cytokines stimulate BAT3 expression and influence intracellular localization of BAT3. We determined that cytokines which induce differentiation of dendritic cells impact on the BAT3 level and on the composition of BAT3 variants. Stimulation of the BAT3 gene by cytokines will be explored and a possible impact of cytokines on BAT3 RNA splicing will be inspected. Based on the results which we obtained with cell lines, we want to study the role of BAT3 in primary cells. Our aim is to investigate the role of BAT3 and of BAT3 variants for developing dendritic cells and to unravel a novel mechanism for the control of MHC class I and class II expression in antigen presenting cells.