Conformational disruption of PI3Kδ regulation by immunodeficiency mutations inPIK3CDandPIK3R1.
Activated PI3K Delta Syndrome (APDS) is a primary immunodeficiency disease caused by activating mutations in either the leukocyte-restricted p110δ catalytic (PIK3CD) subunit or the ubiquitously expressed p85α regulatory (PIK3R1) subunit of class IA phosphoinositide 3-kinases (PI3Ks). There are two classes of APDS: APDS1 that arises from p110δ mutations that are analogous to oncogenic mutations found in the broadly expressed p110α subunit and APDS2 that occurs from a splice mutation resulting in p85α with a central deletion (Δ434-475). As p85 regulatory subunits associate with and inhibit all class IA catalytic subunits, APDS2 mutations are expected to similarly activate p110α, β, and δ, yet APDS2 largely phenocopies APDS1 without dramatic effects outside the immune system. We have examined the molecular mechanism of activation of both classes of APDS mutations using a combination of biochemical assays and hydrogen-deuterium exchange mass spectrometry. Intriguingly, we find that an APDS2 mutation in p85α leads to substantial basal activation of p110δ (>300-fold) and disrupts inhibitory interactions from the nSH2, iSH2, and cSH2 domains of p85, whereas p110α is only minimally basally activated (∼2-fold) when associated with mutated p85α. APDS1 mutations in p110δ (N334K, E525K, E1021K) mimic the activation mechanisms previously discovered for oncogenic mutations in p110α. All APDS mutations were potently inhibited by the Food and Drug Administration-approved p110δ inhibitor idelalisib. Our results define the molecular basis of howPIK3CDandPIK3R1mutations result in APDS and reveal a potential path to treatment for all APDS patients.
Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 2Y2.
Gillian L
GL
Dornan
Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 2Y2.
Braden D
BD
Siempelkamp
Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 2Y2.
Meredith L
ML
Jenkins
Department of Pharmaceutical Chemistry, University of Geneva, CH-1211 Geneva 4, Switzerland.
Oscar
O
Vadas
Department of Immunobiology, Yale University, New Haven, CT 06511.
Carrie L
CL
Lucas
Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 2Y2; jeburke@uvic.ca.
John E
0000-0001-7904-9859
JE
Burke
D020134:Catalytic Domain / Q000235:genetics*; D002462:Cell Membrane / Q000378:metabolism; D058534:Class I Phosphatidylinositol 3-Kinases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D058543:Class Ia Phosphatidylinositol 3-Kinase; D057075:Enzyme Assays; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D000073659:Gain of Function Mutation; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000188:drug therapy / Q000235:genetics*; D013058:Mass Spectrometry / Q000379:methods; D008958:Models, Molecular; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics* / Q000378:metabolism; D000081207:Primary Immunodeficiency Diseases; D011487:Protein Conformation; D011687:Purines / Q000494:pharmacology* / Q000627:therapeutic use; D052999:Quinazolinones / Q000494:pharmacology* / Q000627:therapeutic use; D016032:Randomized Controlled Trials as Topic; D017384:Sequence Deletion
D058534:Class I Phosphatidylinositol 3-Kinases; D058543:Class Ia Phosphatidylinositol 3-Kinase; D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D011687:Purines; D052999:Quinazolinones; C588001:PIK3R1 protein, human; C486018:PIK3CD protein, human; C552946:idelalisib
HDX-MS; PI3K/AKT; PIK3CD; PIK3R1; phosphoinositides