An atopy-associated polymorphism in the ectodomain of the IL-4R(alpha) chain (V50) regulates the persistence of STAT6 phosphorylation.
Several commonly occurring polymorphisms in the IL-4R(alpha) have been associated with atopy in humans; the Q576R and the S503P polymorphisms reside in the cytoplasmic domain, whereas the I50 to V50 polymorphism resides in the extracellular domain of the IL-4R(alpha). The effects of these polymorphisms on signaling remain controversial. To determine the effect of the polymorphisms on IL-4 signaling in human cells, we stably transfected the human monocytic cell line U937 with murine IL-4R(alpha) cDNA bearing the I or V at position 50 and the P503/R576 double mutant. Each form of the murine IL-4R(alpha) mediated tyrosine phosphorylation of STAT6 in response to murine IL-4 treatment similar to the induction of tyrosine phosphorylation by human IL-4 signaling through the endogenous human IL-4R(alpha). After IL-4 removal, tyrosine-phosphorylated STAT6 rapidly decayed in cells expressing I50 or P503R576 murine IL-4Ralpha. In contrast, STAT6 remained significantly phosphorylated for several hours after murine IL-4 withdrawal in cells expressing the V50 polymorphism. This persistence in tyrosine-phosphorylated STAT6 was associated with persistence in CIS mRNA expression. Blocking IL-4 signaling during the decay phase using the JAK inhibitor AG490 or the anti-IL-4R(alpha) Ab M1 abrogated the persistence of phosphorylated STAT6 observed in the V50-IL-4R(alpha)-expressing cells. These results indicate that the V50 polymorphism promotes sustained STAT6 phosphorylation and that this process is mediated by continued engagement of IL-4R(alpha), suggesting enhanced responses of V50 IL-4R when IL-4 is limiting.
Ford
Andrew Q
AQ
Center for Vascular and Inflammatory Disease, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Heller
Nicola M
NM
Stephenson
Linda
L
Boothby
Mark R
MR
Keegan
Achsah D
AD
D002460:Cell Line; D006801:Humans; D006967:Hypersensitivity; D020125:Mutation, Missense; D010766:Phosphorylation; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000235:genetics; D019948:Receptors, Interleukin-4 / Q000235:genetics*; D050800:STAT6 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics
D012333:RNA, Messenger; D019948:Receptors, Interleukin-4; D050800:STAT6 Transcription Factor; C494101:STAT6 protein, human