1575. Proteostasis modulation improves signal transducer and activator of transcription (STAT3) activity in autosomal dominant hyper-IgE syndrome (AD HIES)
Session: Poster Abstract Session: Microbial and Host Genetic Factors in Disease
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
Background: AD HIES is a primary immunodeficiency caused by mutations of STAT3. The molecular basis for defective STAT3 function, however, is unclear, and treatment is supportive. We hypothesize that AD HIES mutations decrease STAT3 stability. Also, since STAT3 depends on chaperones, such as tailless-complex polypeptide-1 ring complex (TRiC) and heat shock proteins (HSP) 70 and 90, for biogenesis and optimal function, we further hypothesize that AD HIES STAT3 function can be improved through enhanced STAT3 proteostasis.

Methods: Mutations were characterized using computer modeling (Evolutionary Trace, PoPMuSiC, I-mutant, MUpro, SDM, DFIRE). STAT3 protein half-life (t1/2), a surrogate marker of stability, was measured in EBV-transformed B cell lines (EBLs) from AD HIES and control patients. EBLs were treated with proteostasis modulators HSF1A, a small molecule that upregulates TRiC (3uM x 48h), and geranylgeranylacetone (GGA), an anti-ulcer drug that upregulates HSP70 and 90 (3uM x 48h). After IL-21 stimulation, total and phosphotyrosylated (pY) STAT3 were measured using Luminex bead-based assays, and expression of the STAT3 target gene SOCS3 was measured using Q-RT-PCR. 

Results: Seventy-three mutations were characterized using computer modeling; 78% were predicted to impair structure and destabilize STAT3. Consistent with this, STAT3 t1/2 in EBLs containing mutations predicted to impair stability (R423Q, V463del, S611N, T622I, N647D, Y657S, V637M) was significantly reduced (24-80%, p<0.01) compared with STAT3 t1/2 in EBLs with mutations predicted not to affect stability (R382W) or controls. Treatment of EBLs containing mutations predicted to impair stability with HSF1A and GGA each normalized STAT3 protein t1/2 (p<0.01), increased pY-STAT3 levels from 10-80% to 40-150% of wild type (WT; p<0.01), and increased SOCS3 mRNA levels from 10-20% to 40-80% of WT (p<0.01). HSF1A, but not GGA, increased total STAT3 levels from 40-90% to 110-200% of WT (p<0.05).

Conclusion: Thus, most STAT3 mutations identified in AD HIES patients are destabilizing and their function can be improved dramatically with the use of proteostasis modulators, which provide a novel treatment approach to improve STAT3 function and prevent infection in AD HIES patients.

Claire E. Bocchini, MD, Pediatrics, Section of Infectious Disease, Baylor College of Medicine, Houston, TX and David J. Tweardy, MD, Medicine, Baylor College of Medicine, Houston, TX

Disclosures:

C. E. Bocchini, None

D. J. Tweardy, None

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