Division of Cell Signalling and Immunology, School of Life Sciences, Wellcome Trust Building, University of Dundee, Dundee, DD1 5EH, UK.
Department of Cancer Biology, Dana Farber Cancer Institute, Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, USA.
Sci Rep. 2021 May 12;11(1):10093. doi: 10.1038/s41598-021-89356-4.
Janus Kinases (JAKs) have emerged as an important drug target for the treatment of a number of immune disorders due to the central role that they play in cytokine signalling. 4 isoforms of JAKs exist in mammalian cells and the ideal isoform profile of a JAK inhibitor has been the subject of much debate. JAK3 has been proposed as an ideal target due to its expression being largely restricted to the immune system and its requirement for signalling by cytokine receptors using the common γ-chain. Unlike other JAKs, JAK3 possesses a cysteine in its ATP binding pocket and this has allowed the design of isoform selective covalent JAK3 inhibitors targeting this residue. We report here that mutating this cysteine to serine does not prevent JAK3 catalytic activity but does greatly increase the IC50 for covalent JAK3 inhibitors. Mice with a Cys905Ser knockin mutation in the endogenous JAK3 gene are viable and show no apparent welfare issues. Cells from these mice show normal STAT phosphorylation in response to JAK3 dependent cytokines but are resistant to the effects of covalent JAK3 inhibitors. These mice therefore provide a chemical-genetic model to study JAK3 function.
Janus 激酶（JAKs）在细胞因子信号转导中发挥着重要作用，因此成为治疗多种免疫疾病的重要药物靶点。哺乳动物细胞中存在 4 种 JAK 同工型，而 JAK 抑制剂的理想同工型特征一直是争论的焦点。由于 JAK3 的表达主要局限于免疫系统，并且需要使用共同γ链的细胞因子受体进行信号转导，因此它被认为是理想的靶点。与其他 JAK 不同，JAK3 在其 ATP 结合口袋中含有一个半胱氨酸，这使得能够设计针对该残基的同工型选择性共价 JAK3 抑制剂。我们在这里报告，将该半胱氨酸突变为丝氨酸不会阻止 JAK3 的催化活性，但会大大增加共价 JAK3 抑制剂的 IC50。在内源性 JAK3 基因中具有 Cys905Ser 点突变的小鼠是存活的，并且没有表现出明显的福利问题。来自这些小鼠的细胞对 JAK3 依赖性细胞因子的 STAT 磷酸化反应正常，但对共价 JAK3 抑制剂的作用具有抗性。因此，这些小鼠为研究 JAK3 功能提供了一种化学生物学模型。
