Interactions of pleiotrophin with receptor type protein tyrosine phosphatase

多效素 (PTN) 是一种重要的细胞因子，负责刺激细胞分化、神经发育、 血管生成和造血干细胞维持。尽管 PTN 对术后组织再生至关重要 损伤、细胞因子的错误表达常常导致致病条件。具体来说，PTN是 在大量癌症中过度表达，PTN 活性的降低会降低生长速度和 这些癌症的转移潜力。这表明 PTN 信号传导可能是治疗 疾病的数量。然而，人们对PTN信号传导的结构机制知之甚少。我们想要 研究调节 PTN 与受体型蛋白酪氨酸相互作用的结构决定因素 Zeta 磷酸酶 (PTPRZ)、硫酸软骨素 (CS) 蛋白聚糖和与 PTN 相关的受体 有丝分裂和血管生成活性。我们的假设是 PTN 的两个独立域可以交叉链接 PTPRZ 通过与其糖胺聚糖链或核心蛋白结合，导致 PTPRZ 自身抑制。我们 想要确认我们的模型并研究 GAG 诱导的 PTN 寡聚体在 PTN 信号传导中是否是必需的。 在我们的初步研究中，我们已经确定了 PTN 的结构并显示了 PTN 对 糖胺聚糖取决于聚糖的硫酸化密度和艾杜糖醛酸含量。我们还展示了 由于无法解释的原因，PTN 的 C 末端尾部对于 PTPRZ 信号转导至关重要，对于 与 PTPRZ 中发现的 CS 类型保持稳定的相互作用，并且 PTN 与 PTPRZ 蛋白的亲和力比 CS 更高，从而为 PTPRZ 提供了额外的机制 交联。我们还表明，PTN 寡聚化仅在糖胺聚糖存在的情况下发生 PTN 寡聚界面很可能涉及 PTN 中的两个结构域。建立在 我们的初步研究取得了成功，我们希望进一步研究 PTN 信号传导的结构机制。 具体来说，我们建议：1）确定 PTN-GAG 复合物的结构，重点关注过硫酸盐 硫酸皮肤素，可能是一种有效的 PTN 抑制剂。 2) 确定PTN的低聚物结构 并设计 PTN 的必需单体，以检查 PTN 寡聚物在与 PTPRZ 相互作用中的作用。 3) 确定 PTN 与 PTPRZ 蛋白质成分相互作用的功能影响并找到其他 PTPRZ 核心蛋白中的 PTN 结合位点。这些相互作用可能是 PTN-PTPRZ 的重要组成部分 因此，如果不考虑这种相互作用，PTN 活性的调节就不完整。 4） 使用新模型研究 PTN 的活性是否与其交联蛋白聚糖的能力相关 蛋白多糖系统。该系统将使我们能够测试交联是否依赖于核心蛋白 PTPRZ 并研究聚糖硫酸化密度和长度对 PTN 交联和活性的影响。

Pleiotrophin (PTN) is a vital cytokine responsible for stimulating cell differentiation, neural development, angiogenesis and hematopoietic stem cell maintenance. Although PTN is crucial to tissue regeneration after injury, errant expression of the cytokine often leads to pathogenic conditions. Specifically, PTN is overexpressed in a large number of cancers and reduction of PTN activity decreases the growth rates and metastatic potentials of those cancers. This indicates PTN signaling maybe a valuable target for treating a number of ailments. However, little is known about the structural mechanism of PTN signaling. We want to investigate structural determinants that regulate PTN’s interactions with receptor-type protein tyrosine phosphatase zeta (PTPRZ), a chondroitin sulfate (CS) proteoglycan and the receptor associated with PTN’s mitogenic and angiogenic activities. Our hypothesis is that PTN’s two independent domains can cross link PTPRZ by binding to their glycosaminoglycan chains or core proteins, resulting in PTPRZ auto-inhibition. We want to confirm our model and investigate whether GAG-induced PTN oligomer is necessary in PTN signaling. In our preliminary studies, we have determined PTN’s structure and showed PTN’s affinity for glycosaminoglycan is dependent on the sulfation density and iduronate content of the glycan. We also showed that the C-terminal tail of PTN, known to be crucial for PTPRZ signaling for unexplained reasons, is essential to maintaining stable interactions with the type of CS found in PTPRZ, and that PTN binds to a segment of the PTPRZ protein with even higher affinity than CS, thereby providing additional mechanisms for PTPRZ crosslinking. We also showed that PTN oligomerization only happens in the presence of glycosaminoglycans and the PTN oligomerization interface most likely involve both structural domains in PTN. Building on the success of our preliminary studies, we want to further investigate structural mechanisms of PTN signaling. Specifically, we propose to: 1) Determine structures of PTN-GAG complexes with a focus on oversulfated dermatan sulfate, which can potentially be a potent PTN inhibitor. 2) Determine the oligomer structure of PTN and engineer obligatory monomers of PTN to examine the role of PTN oligomers in its interactions with PTPRZ. 3) Determine the functional impact of PTN’s interactions with the protein component of PTPRZ and find other PTN-binding sites in the PTPRZ core protein. These interactions could be a crucial part of PTN-PTPRZ signaling, therefore modulation of PTN activity is not complete without considering such interactions. 4) Investigate whether PTN’s activity is associated with its ability to crosslink proteoglycans using a novel model proteoglycan system. This system will allow us to test whether crosslinking is dependent on the core protein of PTPRZ and investigate the influence of glycan sulfation density and length on crosslinking and activity of PTN.