Department of Pathology, School of Medicine, Keio University, Shinjuku-ku, Tokyo, Japan.
PLoS One. 2013 Apr 29;8(4):e62304. doi: 10.1371/journal.pone.0062304. Print 2013.
CD26 is a type II glycoprotein known as dipeptidyl peptidase IV and has been identified as one of the cell surface markers associated with various types of cancers and a subset of cancer stem cells. Recent studies have suggested that CD26 expression is involved in tumor growth, tumor invasion, and metastasis. The CD26 is shown in an extensive intracellular distribution, ranging from the cell surface to the nucleus. We have previously showed that the humanized anti-CD26 monoclonal antibody (mAb), YS110, exhibits inhibitory effects on various cancers. However, functions of CD26 on cancer cells and molecular mechanisms of impaired tumor growth by YS110 treatment are not well understood. In this study, we demonstrated that the treatment with YS110 induced nuclear translocation of both cell-surface CD26 and YS110 in cancer cells and xenografted tumor. It was shown that the CD26 and YS110 were co-localized in nucleus by immunoelectron microscopic analysis. In response to YS110 treatment, CD26 was translocated into the nucleus via caveolin-dependent endocytosis. It was revealed that the nuclear CD26 interacted with a genomic flanking region of the gene for POLR2A, a subunit of RNA polymerase II, using a chromatin immunoprecipitation assay. This interaction with nuclear CD26 and POLR2A gene consequently led to transcriptional repression of the POLR2A gene, resulting in retarded cell proliferation of cancer cells. Furthermore, the impaired nuclear transport of CD26 by treatment with an endocytosis inhibitor or expressions of deletion mutants of CD26 reversed the POLR2A repression induced by YS110 treatment. These findings reveal that the nuclear CD26 functions in the regulation of gene expression and tumor growth, and provide a novel mechanism of mAb-therapy related to inducible translocation of cell-surface target molecule into the nucleus.
CD26 是一种 II 型糖蛋白，也被称为二肽基肽酶 IV，已被确定为与各种类型的癌症和癌症干细胞亚群相关的细胞表面标志物之一。最近的研究表明，CD26 的表达与肿瘤生长、肿瘤侵袭和转移有关。CD26 表现出广泛的细胞内分布，从细胞膜到细胞核。我们之前已经表明，人源化抗 CD26 单克隆抗体 (mAb)YS110 对各种癌症具有抑制作用。然而，CD26 在癌细胞上的功能以及 YS110 治疗导致肿瘤生长受损的分子机制尚不清楚。在这项研究中，我们证明了 YS110 的治疗诱导了癌细胞和异种移植瘤中细胞表面 CD26 和 YS110 的核转位。免疫电子显微镜分析显示，CD26 和 YS110 在核内共定位。响应 YS110 治疗，CD26 通过 caveolin 依赖性内吞作用转位到核内。通过染色质免疫沉淀分析揭示，核 CD26 与 RNA 聚合酶 II 的亚基 POLR2A 基因的基因侧翼区相互作用。这种与核 CD26 和 POLR2A 基因的相互作用导致 POLR2A 基因的转录抑制，从而导致癌细胞增殖受阻。此外，用内吞作用抑制剂处理或表达 CD26 的缺失突变体可逆转 YS110 治疗诱导的 POLR2A 抑制，从而阻止 CD26 的核内转运。这些发现揭示了核 CD26 在基因表达和肿瘤生长调节中的作用，并提供了一种与 mAb 治疗相关的细胞表面靶分子可诱导转位到核内的新机制。
