Inherited STING-activating mutation underlies a familial inflammatory syndrome with lupus-like manifestations

Abstract

Innate immunity to viral infection involves induction of the type I IFN response; however, dysfunctional regulation of this pathway leads to inappropriate inflammation. Here, we evaluated a nonconsanguineous family of mixed European descent, with 4 members affected by systemic inflammatory and autoimmune conditions, including lupus, with variable clinical expression. We identified a germline dominant gain-of-function mutation in TMEM173, which encodes stimulator of type I IFN gene (STING), in the affected individuals. STING is a key signaling molecule in cytosolic DNA-sensing pathways, and STING activation normally requires dimerization, which is induced by 2'3' cyclic GMP-AMP (cGAMP) produced by the cGAMP synthase in response to cytosolic DNA. Structural modeling supported constitutive activation of the mutant STING protein based on stabilized dimerization. In agreement with the model predictions, we found that the STING mutant spontaneously localizes in the Golgi of patient fibroblasts and is constitutively active in the absence of exogenous 2'3'-cGAMP in vitro. Accordingly, we observed elevated serum IFN activity and a type I IFN signature in peripheral blood from affected family members. These findings highlight the key role of STING in activating both the innate and adaptive immune responses and implicate aberrant STING activation in features of human lupus.

Figure 3. Intracellular localization of p.V155M STING.

STING localization in primary fibroblasts assessed by confocal microscopy. (A) Healthy control and (C) patient fibroblasts (III-2) at steady state. (B) Healthy control and (D) patient fibroblasts (III-2) after 8-hour stimulation with 4 μg/ml 2′3′-cGAMP. Images are representative of 3 independent experiments. Scale bar: 15 μm.

Figure 2. Constitutive activation of the mutant STING in vitro.

(A) Luciferase induction in HEK293FT cells cotransfected with empty vector (EV), wild-type STING, V155M STING, and a luciferase plasmid under the control of the IFNB promoter and stimulated with increasing amounts of synthetic 2′3′-cGAMP complexed to lipofectamine (maximal dose, 4 μg/ml; dose-response dilution factor, 3) (n = 3, mean and SEM; paired t test, *P < 0.05). (B) Immunoblot of STING expression in HEK293FT cells transfected with wild-type and V155M STING (representative of 3 independent experiments).

Figure 1. Familial STING mutation associates with inflammatory and autoimmune condition.

(A) Pedigree of the family carrying the STING V155M heterozygous mutation. Affected individuals are indicated by black boxes and circles; deceased individuals are indicated by diagonal bars; patient III-2 is indicated by an arrow. (B) Familial segregation of the V155M mutation. (C) Lung CT scan from patient III-2, showing interstitial lung disease in a parenchymal view (left) and fibrosis in a mediastinal view (right). (D) Lung biopsy from patient III-2 (Masson’s trichrome; original magnification, ×10) and immunohistochemistry (hematoxylin; original magnification, ×10; left), with anti-CD20 (middle) and anti CD68 (right) antibodies, showing macrophage alveolar infiltration, follicular hyperplasia, and mild interstitial fibrosis.