Targeted Delivery of an Antigenic Peptide to the Endoplasmic Reticulum: Application for Development of a Peptide Therapy for Ankylosing Spondylitis

The development of suitable methods to deliver peptides specifically to the endoplasmic reticulum (ER) can provide some potential therapeutic applications of such peptides. Ankylosing spondylitis (AS) is strongly associated with the expression of human leukocytic antigen-B27 (HLA-B27). HLA-B27 heavy chain (HC) has a propensity to fold slowly resulting in the accumulation of misfolded HLA-B27 HC in the ER, triggering the unfolded protein response, and forming a homodimer, (B27-HC)2. Natural killer cells and T-helper 17 cells are then activated, contributing to the major pathogenic potentials of AS. The HLA-B27 HC is thus an important target, and delivery of an HLA-B27-binding peptide to the ER capable of promoting HLA-B27 HC folding is a potential mechanism for AS therapy. Here, we demonstrate that a His6-ubiquitin-tagged Tat-derived peptide (THU) can deliver an HLA-B27-binding peptide to the ER promoting HLA-B27 HC folding. The THU-HLA-B27-binding peptide fusion protein crossed the cell membrane to the cytosol through the Tat-derived peptide. The HLA-B27-binding peptide was specifically cleaved from THU by cytosolic ubiquitin C-terminal hydrolases and subsequently transported into the ER by the transporter associated with antigen processing. This approach has potential application in the development of peptide therapy for AS.

开发能够将肽类特异性递送至内质网（endoplasmic reticulum, ER）的合适方法，可为此类肽类带来潜在治疗应用。强直性脊柱炎（Ankylosing spondylitis, AS）与人类白细胞抗原-B27（human leukocytic antigen-B27, HLA-B27）的表达密切相关。HLA-B27重链（HLA-B27 heavy chain, HC）易于缓慢折叠，导致错误折叠的HLA-B27 HC在内质网中蓄积，触发未折叠蛋白反应（unfolded protein response），并形成同源二聚体(B27-HC)₂。随后自然杀伤细胞（natural killer cells）与辅助性T细胞17（T-helper 17 cells）被激活，参与强直性脊柱炎的主要致病过程。因此，HLA-B27 HC是重要的治疗靶点，将可促进HLA-B27 HC折叠的HLA-B27结合肽递送至内质网，是强直性脊柱炎治疗的潜在策略。本研究证实，6×组氨酸-泛素标记的Tat衍生肽（His6-ubiquitin-tagged Tat-derived peptide, THU）可将HLA-B27结合肽递送至内质网，以促进HLA-B27 HC折叠。该THU-HLA-B27结合肽融合蛋白可通过Tat衍生肽穿过细胞膜进入胞质溶胶。胞质溶胶中的泛素C端水解酶（ubiquitin C-terminal hydrolases）可特异性切割THU与HLA-B27结合肽，随后切割释放的肽段可通过抗原加工相关转运体（transporter associated with antigen processing）转运至内质网。该方法在强直性脊柱炎肽类治疗的研发中具有潜在应用价值。