Biology subjects

Shum, A. K.

Publications and source records attributed to Shum, A. K..

5 recordsLinked to original sources

bioRxiv2026

The COPI coatomer influences LDL receptor activity, hepatic lipid storage, and apoB secretion

BackgroundDecreased hepatic removal of low density lipoproteins (LDL) and increased apolipoprotein B (apoB) production cause hypercholesterolemia, a major causal risk factor of atherosclerotic cardiovascular disease (ASCVD). By a genome-wide siRNA screen, we previously identified subunits of the Coat protein I (COPI) complex to limit LDL uptake into Huh-7 hepatocarcinoma cells. MethodsThese findings were validated by targeted in vitro experiments as well as genetic association studies in humans and three mouse models with mutated or disrupted COPI genes. ResultsSilencing of COPA, COPB1, COPB2, ARCN1, COPG1, and COPZ1 in Huh-7 cells resulted in decreased uptake of LDL and aberrant glycosylation and altered cell surface abundance of the LDL receptor (LDLR) as well as increased apoB secretion and cellular lipid storage. Single nucleotide polymorphisms of ARCN1 were associated with lower ARCN1 expression and higher levels of LDL-cholesterol (LDL-C). Rare variants of COPA and COPG1 were enriched among patients with LDL-C > 5 mmol/L. Patients and mice carrying other rare immunopathogenic missense variants of COPA and COPG1 did not present with elevated plasma levels of LDL-C, while hepatic knockdown of murine Copg1 increased the concentrations of non-HDL-cholesterol in plasma and triglycerides in the liver. ConclusionsThe COPI coatomer regulates LDLR activity and apoB secretion as well as lipid content of liver cells. Loss of function of some variants of COPI genes are associated with higher LDL-C levels.

cell biology↗

bioRxiv2024

Activated STING in the thymus alters T cell development and selection leading to autoimmunity

Classifying systemic inflammatory disorders as autoinflammatory or autoimmune provides insight into disease pathogenesis and whether treatment should target innate molecules and their signaling pathways or the adaptive immune response. COPA syndrome is a monogenic disorder of immune dysregulation that leads to interstitial lung disease and high-titer autoantibodies. Studies show constitutive activation of the innate immune molecule STING is centrally involved in disease. However, the mechanisms by which STING results in loss of T cell tolerance and autoimmunity in COPA syndrome or more common autoimmune diseases is not understood. Using CopaE241K/+ mice, we uncovered a functional role for STING in the thymus. Single cell data of human thymus demonstrates STING is highly expressed in medullary thymic epithelial cells (mTECs) involved in processing and presenting self-antigens to thymocytes. In CopaE241K/+ mice, activated STING in mTECs triggered interferon signaling, impaired macroautophagy and caused a defect in negative selection of T cells. Wild-type mice given a systemic STING agonist phenocopied the selection defect and showed enhanced thymic escape of a T cell clone targeting a self-antigen also expressed in melanoma. Our work demonstrates STING activation in TECs shapes the T cell repertoire and contributes to autoimmunity, findings important for settings that activate thymic STING. SummaryActivation of STING in thymic epithelial cells shifts the T cell repertoire to promote autoimmunity providing a new mechanistic link between innate and adaptive immunity.

immunology↗

bioRxiv2023

PhIP-Seq uncovers novel autoantibodies and unique endotypes in interstitial lung disease

Interstitial lung diseases (ILDs) are a heterogeneous group of disorders that can develop in patients with connective tissue diseases (CTD). Establishing autoimmunity in ILD impacts prognosis and treatment. ILD patients are screened for autoimmunity by assaying for anti-nuclear autoantibodies, rheumatoid factors and other non-specific tests. However, this approach has not been rigorously validated and may miss autoimmunity that manifests as autoantibodies to tissue antigens not previously defined in ILD. Here, we use Phage Immunoprecipitation-Sequencing (PhIP-Seq) to conduct a large, multi-center unbiased autoantibody discovery screen of ILD patients and controls. PhIP-Seq identified 17 novel autoreactive targets, and machine learning classifiers derived from these targets discriminated ILD serum from controls. Among these 17 candidates, we validated Cadherin Related Family Member 5 (CDHR5) as an autoantigen and found CDHR5 autoantibodies in patients with rheumatologic disorders and importantly, subjects not previously diagnosed with autoimmunity. Lung tissue of CDHR5 autoreactive patients showed transcriptional profiles consistent with activation of NF{kappa}B signaling and upregulation of chitotriosidase (CHIT1), a molecular pathway linked to fibrosis. Our study shows PhIP-Seq uncovers novel autoantibodies in ILD patients not revealed by standard clinical tests. Furthermore, CDHR5 autoantibodies may define a novel molecular endotype of ILD characterized by inflammation and fibrosis.

molecular biology↗

bioRxiv2020

Homeostatic regulation of STING by Golgi-to-ER membrane traffic

Coat protein complex I (COP-I) mediates the retrograde transport from the Golgi to the ER1,2. Mutation of the COPA gene, encoding one of the COP-I subunits (-COP), causes an immune dysregulatory disease (COPA syndrome)3. The molecular mechanism by which the impaired retrograde transport results in autoinflammation is not understood. Here we report that STING4, an innate immunity protein, is a cargo of the Golgi-to-ER membrane transport. In the presence of the disease-causative -COP variants, STING cannot be retrieved back to the ER from the Golgi. The forced Golgi residency of STING results in the cGAS-independent and palmitoylation-dependent activation of the STING downstream signalling pathway. Surf45, a protein that circulates between the ER and the Golgi, binds STING and -COP, and mediates retrograde transport of STING to the ER. STING/Surf4/-COP complex is disrupted in the presence of the disease-causative -COP variant. Intriguingly, the STING ligand cGAMP also impairs the formation of STING/Surf4/-COP complex. Our results suggest a homeostatic regulation of STING at the resting state by the Golgi-to-ER membrane traffic and provide insights into the pathogenesis of COPA syndrome.

cell biology↗

bioRxiv2020

A defect in COPI-mediated transport of STING causes immune dysregulation in COPA syndrome

Pathogenic COPA variants cause a Mendelian syndrome of immune dysregulation with elevated type I interferon signaling1,2. COPA is a subunit of coat protein complex I (COPI) that mediates Golgi to ER transport3. Missense mutations that disrupt the COPA WD40 domain impair binding and sorting of proteins targeted for retrieval to the ER but how this causes disease remains unknown1,4. Given the importance of COPA in Golgi-ER transport, we speculated that type I interferon signaling in COPA syndrome involves missorting of STING. Here we show that a defect in COPI transport due to mutant COPA causes ligand-independent activation of STING. Furthermore, SURF4 is an adapter molecule that facilitates COPA-mediated retrieval of STING at the Golgi. Activated STING stimulates type I interferon driven inflammation in CopaE241K/+ mice that is rescued in STING-deficient animals. Our results demonstrate that COPA maintains immune homeostasis by regulating STING transport at the Golgi. In addtion, activated STING contributes to immune dysregulation in COPA syndrome and may be a new molecular target in treating the disease.

immunology↗