Identification of a Novel Single Amino Acid Substitution (V666G) of JAK1 from a Patient with Acute Lymphoblastic Leukemia Impairs JAK3 Mediated Il-2 Signaling
The Janus kinase (JAK) family, notably JAK1, JAK2 and JAK3 are recognized as oncogenic drivers in high risk Acute Lymphoblastic Leukemia (ALL). The bulk of activating JAK mutations are thought to occur within functional hot-spots across Janus Homology (JH) domains. The most frequently mutated regions is the JH2 pseudo-kinase, which provides a negative regulatory role to the adjacent catalytically active JH1 kinase domain. Despite the prevalence of JAK activating mutations and a need for new therapeutic inhibitors, there is a lack of understanding in the allosteric regulation of JAK kinases. Here we sought to identify mutations involved in driving ALL in the El Paso del Norte population, comprised of an 80% Hispanic demographic; an ethnic group associated with high-risk ALL. Using Whole Exome Sequencing, we detected a novel mutation, V666G, localized within the JH2 domain of JAK1. This mutant is proximal to well-known and characterized JAK1 activating mutations. Unexpectedly, the V666G mutation resulted in a JAK1 kinase-dead like phenotype as indicated by a lack of autophosphorylation and cross-phosphorylation by JAK family members. Furthermore, a dominant negative effect of kinase dead JAK1 (K908A) and the JAK1 V666G mutant occurred across JAK family auto and cross activation. JAK3 was autoactivated in the absence of JAK1, however, the presence of inactive JAK1, either K908A or V666G mutations, reduced JAK3 Tyr phosphorylation. In the context of Interleukin-2 (IL-2) signaling, a dominant negative effect by JAK1 V666G was observed on downstream effectors. The presence of JAK1 V666G decreased Tyr phosphorylation on ALL associated JAK3 activating mutants M511I and A573V. These findings reveal a dominant negative role of JAK1 on JAK3 and support a mechanism by which JAK1 may regulate JAK3 autoactivation and IL-2 signaling. Elucidation of the trans-inhibitory interactions between JAK1 and JAK3 may propagate new ways to allosterically inhibit overactive JAK kinases in cancer.
Hernandez Grant, Alice, "Identification of a Novel Single Amino Acid Substitution (V666G) of JAK1 from a Patient with Acute Lymphoblastic Leukemia Impairs JAK3 Mediated Il-2 Signaling" (2020). ETD Collection for University of Texas, El Paso. AAI27961900.