人巨细胞病毒(CMV)UL40蛋白及其恒河猴(RhCMV)对应物的信号序列,Rh67,含有一个肽(VMAPRT[L/V][F/I/L/V]L,VL9)由主要组织相容性复合物(MHC)抗原E(MHC-E)呈递。CMVVL9肽取代了来自经典MHC(Ia)信号序列的VL9肽。当CMV破坏抗原加工和呈递以及MHCIa表达时,它们就会丢失。这允许受感染的细胞维持MHC-E表面表达并逃避自然杀伤细胞的杀伤。我们证明了Rh67VL9肽的加工反映了UL40的加工,尽管这两种蛋白质之间缺乏序列保守性。两种VL9肽的加工依赖于宿主蛋白酶信号肽肽酶对其信号序列的切割。如先前针对UL40所示,通过Rh67上调MHC-E表达仅需要其信号序列,VL9上游的序列对于赋予TAP独立性至关重要,与抗原加工相关的转运蛋白。我们的结果还表明,成熟的UL40和Rh67蛋白通过降低MHCIa的表面表达来促进CMV免疫逃避。出乎意料的是,尽管Rh67VL9肽对Rh67的作用具有抗性,但UL40可以部分抵消其自身VL9肽介导的MHC-E表达的上调。这表明两种VL9肽上调MHC-E的机制存在差异,并且将需要进一步的工作来确定是否有任何此类差异对使用人CMV作为载体将RhCMV载体的猿猴免疫缺陷病毒(SIV)疫苗翻译为HIV-1具有影响。
目的:恒河猴巨细胞病毒(RhCMV)介导的猿猴免疫缺陷病毒(SIV)疫苗在恒河猴中诱导的保护性免疫应答取决于疫苗中病毒Rh67基因的存在。Rh67蛋白含有一种肽,该肽允许RhCMV感染的细胞在细胞表面维持主要组织相容性复合物(MHC)抗原E的表达。我们证明了这种肽的生产,称为“VL9”,反映了人巨细胞病毒(CMV)蛋白UL40中存在的等效肽,尽管两种CMV蛋白之间的序列相似性很小。我们还表明,成熟的UL40和Rh67蛋白,没有前面描述的功能,还通过减少对免疫系统检测感染细胞重要的MHC蛋白的细胞表面表达来促进CMV免疫逃避。尽管有这些相似之处,我们的工作还揭示了Rh67和UL40之间的可能差异,这些差异可能对使用人类CMV作为潜在HIV-1疫苗的载体有影响.
The signal sequences of the human cytomegalovirus (CMV) UL40 protein and its rhesus CMV (RhCMV) counterpart, Rh67, contain a peptide (VMAPRT[L/V][F/I/L/V]L, VL9) that is presented by major histocompatibility complex (MHC) antigen E (MHC-E). The CMV VL9 peptides replace VL9 peptides derived from classical MHC (Ia) signal sequences, which are lost when CMV disrupts antigen processing and presentation and MHC Ia expression. This allows infected cells to maintain MHC-E surface expression and escape killing by Natural Killer cells. We demonstrate that processing of the Rh67 VL9 peptide mirrors that of UL40, despite the lack of sequence conservation between the two proteins. Processing of both VL9 peptides is dependent on cleavage of their signal sequences by the host protease signal peptide peptidase. As previously shown for UL40, up-regulation of MHC-E expression by Rh67 requires only its signal sequence, with sequences upstream of VL9 critical for conferring independence from TAP, the transporter associated with antigen processing. Our results also suggest that the mature UL40 and Rh67 proteins contribute to CMV immune evasion by decreasing surface expression of MHC Ia. Unexpectedly, while the Rh67 VL9 peptide is resistant to the effects of Rh67, UL40 can partially counteract the up-regulation of MHC-E expression mediated by its own VL9 peptide. This suggests differences in the mechanisms by which the two VL9 peptides up-regulate MHC-E, and further work will be required to determine if any such differences have implications for translating a RhCMV-vectored simian immunodeficiency virus (SIV) vaccine to HIV-1 using human CMV as a vector.
OBJECTIVE: The protective immune response induced by a rhesus cytomegalovirus (RhCMV)-vectored simian immunodeficiency virus (SIV) vaccine in rhesus macaques depends on the presence of the viral Rh67 gene in the vaccine. The Rh67 protein contains a peptide that allows the RhCMV-infected cells to maintain expression of major histocompatibility complex (MHC) antigen E at the cell surface. We show that production of this peptide, referred to as \"VL9,\" mirrors that of the equivalent peptide present in the human cytomegalovirus (CMV) protein UL40, despite the little sequence similarity between the two CMV proteins. We also show that the mature UL40 and Rh67 proteins, which have no previously described function, also contribute to CMV immune evasion by reducing cell surface expression of MHC proteins important for the immune system to detect infected cells. Despite these similarities, our work also reveals possible differences between Rh67 and UL40, and these may have implications for the use of human CMV as the vector for a potential HIV-1 vaccine.