Structure of a Janus kinase cytokine receptor complex reveals the basis for dimeric activation

Abstract

Cytokines signal through cell surface receptor dimers to initiate activation of intracellular Janus Kinases (JAKs). We report the 3.6-Å resolution cryo-EM structure of full-length JAK1 complexed with a cytokine receptor intracellular Box1/Box2 domain, captured as an activated homodimer bearing the Val→Phe (VF) mutation prevalent in myeloproliferative neoplasms. The seven domains of JAK1 form an extended structural unit whose dimerization is mediated by close-packed pseudokinase (PK) domains. The oncogenic VF mutation lies within the core of the JAK1 PK dimer interface, enhancing packing complementarity to facilitate ligand-independent activation. The C-terminal tyrosine kinase domains are poised to phosphorylate the receptor STAT-recruiting motifs projecting from the overhanging FERM-SH2 domains. Mapping of constitutively active JAK mutants supports a two-step allosteric activation mechanism and reveals new opportunities for selective therapeutic targeting of oncogenic JAK signaling.

Structural insights into the assembly of gp130 family cytokine signaling complexes

“…S7), including the Epo-EpoR complex ( 29 ), insulin-insulin receptor complex ( 30 ), and IGF1-IGF1R complex ( 31 ). Moreover, the ~30 Å distance is also comparable to the distance between the two membrane-proximal FERM-SH2 domains of dimeric JAK1 bound to Box1/Box2 motifs of a cytokine receptor on the intracellular side ( 32 ). These consistent observations suggest that bringing the two signaling receptor juxtamembrane domains to ~30 Å apart might be a prerequisite for activating the JAK/STAT pathway.…”

JAK2 Alterations in Acute Lymphoblastic Leukemia: Molecular Insights for Superior Precision Medicine Strategies

“…In particular, it has been postulated that JAK2 p. R683 mutations disrupt the pseudokinase domain-mediated autoinhibitory interaction, therefore inhibitors that can stabilize this interaction may be able to overcome the effects of these mutations. The recent discovery that apposing JAK1 monomers dimerize via their pseudokinase domains also positions this dimerisation interface as a potentially novel targetable site ( Glassman et al, 2022 ). JAK2 dimerisation may also be mediated via the pseudokinase domains however the full-length structure of JAK2 is yet to be determined.…”

“…Mutagenesis studies have demonstrated that JAK2 p. V617F confers cytokine-independent signaling activation ( Baxter et al, 2005 ; James et al, 2005 ; Kralovics et al, 2005 ; Senkevitch and Durum, 2017 ). Activating JAK2 mutations, including JAK2 p. V617F, were initially predicted to confer cytokine-independent signaling through disruption of the JH2-mediated autoinhibitory interaction, facilitating mutant-JAK2 dimerization ( Gnanasambandan and Sayeski, 2011 ; Ungureanu et al, 2011 ; Hubbard, 2018 ; Glassman et al, 2022 ). In addition, a recent report using single-molecule microscopy demonstrated that the JAK2 p. V617F mutation confers cytokine-independent dimerization of receptor subunits (50% of the maximum level for TPOR, 25% for EPOR and 10% for hGHR), with a stable time-dependent dimer formation similar to cytokine binding ( Wilmes et al, 2020 ).…”

“…This suggested that disruption of the JH2-mediated autoinhibitory interaction alone is not sufficient to constitutively activate signaling through JAK2 ( Hammaren et al, 2019a ; Hammaren et al, 2019b ). Leroy et al (2016) and Glassman et al (2022) have proposed two molecular mechanisms for JAK2 constitutive activation by JAK2 p. V617F ( Leroy et al, 2016 ; Glassman et al ). The first mechanism destabilizes the JH2-JH1 autoinhibitory interaction through the formation of a π stacking interaction between JAK2 p. V617F and JAK2 p. F595, which stabilizes the JAK2 pseudokinase domain αC helix in a straightened conformation ( Bandaranayake et al, 2012 ; Leroy et al, 2016 ; Hubbard, 2018 ).…”

Deciphering signal transduction networks in the liver by mechanistic mathematical modelling

“…Cytokine receptor chains comprise an extracellular domain that interacts with the cytokine, a single transmembrane domain and a signal-transducing cytoplasmic domain. Upon ligand binding, the cytokine receptor chains on the cell surface associate or are stabilized as dimers or oligomers [ 8 ]. The cytoplasmic domain lacks intrinsic kinase activity and associates with a protein tyrosine kinase of the Janus kinase (JAK) family [ 9 ].…”