Differential Effects of CSF-1R D802V and KIT D816V Homologous Mutations on Receptor Tertiary Structure and Allosteric Communication

The colony stimulating factor-1 receptor (CSF-1R) and the stem cell factor receptor KIT, type III receptor tyrosine kinases (RTKs), are important mediators of signal transduction. The normal functions of these receptors can be compromised by gain-of-function mutations associated with different physiopatological impacts. Whereas KIT D816V/H mutation is a well-characterized oncogenic event and principal cause of systemic mastocytosis, the homologous CSF-1R D802V has not been identified in human cancers. The KIT D816V oncogenic mutation triggers resistance to the RTK inhibitor Imatinib used as first line treatment against chronic myeloid leukemia and gastrointestinal tumors. CSF-1R is also sensitive to Imatinib and this sensitivity is altered by mutation D802V. Previous in silico characterization of the D816V mutation in KIT evidenced that the mutation caused a structure reorganization of the juxtamembrane region (JMR) and facilitated its departure from the kinase domain (KD). In this study, we showed that the equivalent CSF-1R D802V mutation does not promote such structural effects on the JMR despite of a reduction on some key H-bonds interactions controlling the JMR binding to the KD. In addition, this mutation disrupts the allosteric communication between two essential regulatory fragments of the receptors, the JMR and the A-loop. Nevertheless, the mutation-induced shift towards an active conformation observed in KIT D816V is not observed in CSF-1R D802V. The distinct impact of equivalent mutation in two homologous RTKs could be associated with the sequence difference between both receptors in the native form, particularly in the JMR region. A local mutation-induced perturbation on the A-loop structure observed in both receptors indicates the stabilization of an inactive non-inhibited form, which Imatinib cannot bind.集落刺激因子1受体（colony stimulating factor-1 receptor, CSF-1R）与干细胞因子受体KIT同属Ⅲ型受体酪氨酸激酶（receptor tyrosine kinases, RTKs），是信号转导的重要介导分子。此类受体的正常功能可因功能获得性突变受损，这类突变伴随不同的病理生理效应。尽管KIT D816V/H突变是特征明确的致癌事件，也是系统性肥大细胞增多症的主要诱因，但同源的CSF-1R D802V突变尚未在人类癌症中被检出。KIT D816V致癌突变会诱发对伊马替尼（Imatinib）的耐药性，而伊马替尼正是慢性髓系白血病与胃肠道肿瘤的一线治疗药物。CSF-1R同样对伊马替尼敏感，而D802V突变会改变这一敏感性。此前针对KIT中D816V突变的计算机模拟表征（in silico characterization）研究表明，该突变会引发近膜区（juxtamembrane region, JMR）的结构重排，并促进其脱离激酶结构域（kinase domain, KD）。本研究证实，等效的CSF-1R D802V突变虽会削弱部分调控JMR与KD结合的关键氢键相互作用，但并不会对JMR产生类似的结构影响。此外，该突变会破坏受体两个关键调节片段——JMR与A环（A-loop）之间的别构通讯。然而，KIT D816V突变所引发的向活性构象的转变，并未在CSF-1R D802V突变中出现。这两种同源RTKs中等效突变所产生的不同影响，可能与二者天然状态下的序列差异相关，尤其是在JMR区域。在两种受体中均观察到的、由突变引发的A-loop结构局部扰动，表明其稳定形成了一种伊马替尼无法结合的非抑制性失活构象。