Potential role of brachyury in HLA class I antigen processing machinery component downregulation in chordoma cells

摘要 脊索瘤是一种以转录因子过度表达为特征的脊髓肿瘤 短尾畸形除了作为生物标志物的作用外，短尾畸形对疾病的发病机制至关重要，因此似乎 成为一个有吸引力的治疗目标。然而，针对短尾畸形的策略的开发进展缓慢。 完全手术切除，目前的黄金标准治疗，并不总是可行的。放射治疗是主要的 辅助治疗，但不幸的是，已知短尾畸形介导放射抗性，以及化疗， 阻力因此，人们对基于T细胞的新型免疫疗法产生了兴趣，但它们的结果也很差。我们 假设后者是由于缺陷的HLA I类抗原加工机制（APM）组件 在脉络膜细胞中表达。事实上，基于T细胞的免疫疗法依赖于肿瘤细胞的呈递。 抗原肽对宿主的免疫系统的作用，要求HLA I类APM是完全功能性的。我们的分析 少数手术切除的脉络膜肿瘤显示HLA I类APM表达缺陷， 常见于脉络膜细胞。这些缺陷背后的潜在分子机制一直很差 表征了因此，我们的目标是研究HLA I类APM组件的机制 在脉络膜细胞中表达缺陷。我们关注短尾畸形和蛋白酪氨酸磷酸酶SHP 2， 我们先前已经显示在其它癌症类型中在HLA-I类APM组分下调中起作用。 我们已经发现，高的SHP 2表达与低的HLA I类APM组分表达相关。 SHP 2表达与Brachyury表达呈正相关。此外，委员会认为， 与HLA I类APM成分相关的脉络膜短尾畸形的直接靶点YAP 1 在其他肿瘤类型中下调，发现与SHP 2相互作用。这一点表现在 SHP 2启动子保守区域上的YAP 1结合位点。反过来，SHP 2已被证明可以抑制 通过抑制STAT 1磷酸化表达HLA I类APM组分，STAT 1是一种转录因子， 用于HLA I类APM组分表达。总的来说，这些数据支持Brachyury YAP 1模型。 SHP 2-pSTAT 1-HLA I类APM，证明了短尾在HLA I类APM中的潜在作用 在脉络膜细胞中，通过SHP 2的上调下调组分。因此，我们的目标是：i）描述 短尾畸形在脉络膜细胞中HLA-I类APM组分下调中的潜在作用; ii）评估短尾畸形在HLA-I类APM组分下调中的作用。 小分子SHP 2抑制剂SHP 099恢复HLA I类APM组分表达的体内能力， 在脉络膜细胞中的功能活性;和iii）通过以下步骤评估所述假设模型的临床意义： 确定HLA I类APM成分表达与Brachyury、YAP 1表达的相关性 和SHP 2在手术切除的肿瘤中。所得结果将有助于策略的合理设计 以恢复脉络膜细胞中的HLA I类APM组分表达，这将可能提高 针对这种疾病的T细胞免疫疗法。

ABSTRACT Chordomas are spinal neoplasms uniquely characterized by their overexpression of the transcription factor brachyury. Beyond its role as a biomarker, brachyury is critical for disease pathogenesis and therefore appears to be an attractive target for therapy. However, development of strategies targeting brachyury has had slow progress. Complete surgical resection, the current gold standard treatment, is not always feasible. Radiotherapy is the main adjuvant treatment, but unfortunately brachyury is known to mediate radio-resistance, as well as chemo- resistance. Thus, interest in novel T cell-based immunotherapies arose, but they too yielded poor results. We hypothesize that the latter is due to defective HLA class I antigen processing machinery (APM) component expression in chordoma cells. Indeed, T cell-based immunotherapies are dependent on the presentation of tumor antigen peptides to the host’s immune system, requiring that HLA class I APM is fully functional. Our analysis of a small number of surgically removed chordoma tumors has shown that HLA class I APM expression defects are frequent in chordoma cells. The underlying molecular mechanisms behind these defects have been poorly characterized. Our goal is therefore to investigate the mechanisms underlying HLA class I APM component expression defects in chordoma cells. We focus on brachyury and the protein tyrosine phosphatase SHP2 which we have previously shown to play a role in HLA class I APM component downregulation in other cancer types. We have found that higher SHP2 expression is associated with lower HLA class I APM component expression in chordoma cell lines, and that SHP2 expression is positively correlated with brachyury expression. Furthermore, YAP1, a direct target of brachyury in chordoma which is associated with HLA class I APM component downregulation in other tumor types, was found to interact with SHP2. This was demonstrated by the presence of a YAP1 binding site on conserved regions of the SHP2 promoter. In turn, SHP2 has been shown to suppress HLA class I APM component expression by inhibiting phosphorylation of STAT1, a transcription factor required for HLA class I APM component expression. Overall, these data support the model Brachyury YAP1 SHP2 pSTAT1 HLA class I APM, demonstrating a potential role of brachyury in HLA class I APM component downregulation in chordoma cells, via upregulation of SHP2. Therefore, we aim to: i) delineate the potential role of brachyury in HLA class I APM component downregulation in chordoma cells; ii) assess the in vivo ability of small molecule SHP2 inhibitor SHP099 to restore HLA class I APM component expression and functional activity in chordoma cells; and iii) assess the clinical significance of the hypothesized model by determining the association of HLA class I APM component expression with the expression of brachyury, YAP1 and SHP2 in surgically removed tumors. The results obtained will contribute to the rational design of strategies to restore HLA class I APM component expression in chordoma cells which will likely improve the efficacy of T cell-based immunotherapies for this disease.