The activation mechanism of the phosphatase SHP-2 by PD-1: a molecular view on cancer immune-escape

蛋白酪氨酸磷酸酶(PTPs)在许多细胞过程中起着关键作用。PTP胞浆内含Src同源2结构域的磷酸酶2(SHP-2)与多种白血病和实体瘤密切相关，已成为抗癌治疗的重要靶点。SHP-2也是抑制性受体信号的关键媒介，通过与免疫检查点受体如程序性死亡-1(PD-1)的相互作用。PD-1的功能是控制过度的免疫激活；此外，它还提供了一种肿瘤逃避免疫系统的手段。最近的证据支持这样的观点，即抑制SHP-2或PD-1的活性足以恢复T细胞的激活，从而允许免疫系统攻击肿瘤。在这种背景下，研究SHP-2与PD-1的相互作用成为抑制肿瘤免疫逃逸的可能途径。SHP-2由三个结构域和一个无序的C-末端组成。N-SH2和C-SH2两个结构域能够结合磷酸肽；PTP结构域包含催化裂解并负责酶活性，而C-末端无序尾巴具有调节作用。在本项目中，我们研究了PD-1的磷酸化胞质尾巴激活SHP-2的机制，这是通过尾巴与两个SH2结构域的二价相互作用来介导的。我们使用结构生物学、生物物理、生化和细胞分析来回答有关SH2结构域在激活过程中的作用以及伴随着SHP-2活性的刺激和调节而发生的构象变化的结构和机制问题。我们的目的是从原子结构水平上了解Pd-1活化SHP-2的机理。

Protein tyrosine phosphatases (PTPs) play key roles in numerous cellular processes. The PTP cytoplasmic Src homology 2 domain-containing phosphatase 2 (SHP-2) is involved in various kinds of leukemias and solid tumors, and is emerging as an important target for anticancer therapy. SHP-2 is also a key mediator of inhibitory receptor signaling, through its interaction with immune checkpoint receptors like the programmed death-1 (PD-1). PD-1 functions to control excessive immune activation; in addition it provides a means by which tumors evade the immune system. Recent evidence supports the notion that inhibition of either SHP-2 or PD-1 activity is sufficient to restore T cell activation, thereby allowing for the immune system to attack the tumor. In this context, studying the interaction of SHP-2 with PD-1 becomes relevant as a possible pathway to inhibit cancer immune escape. SHP-2 consists of three domains and a disordered C-terminal tail. Two domains, the N-SH2 and C-SH2, are able to bind phosphopeptides; the PTP domain contains the catalytic cleft and is responsible for the enzymatic activity, while the C-terminal disordered tail has a regulatory role. In this project, we study the activation mechanism of SHP-2 by the phosphorylated cytoplasmatic tail of PD-1, which is mediated by the divalent interaction of the tail with the two SH2 domains. We use structure biology, biophysical, biochemical and cellular assays to answer structural and mechanistic questions concerning the role of either of the SH2 domains in the activation process, as well as the conformational changes accompanying stimulation and regulation of SHP-2 activity. Our aim is to provide an understanding of the mechanism of activation of SHP-2 by PD-1 at the atomic structural level.