ABSTRACT
Proteasomes and lysosomes constitute the major cellular systems that catabolize proteins to recycle free amino acids for energy and new protein synthesis. Tripeptidyl peptidase II (TPPII) is a large cytosolic proteolytic complex that functions in tandem with the proteasome-ubiquitin protein degradation pathway. We found that autosomal recessive TPP2 mutations cause recurrent infections, autoimmunity, and neurodevelopmental delay in humans. We show that a major function of TPPII in mammalian cells is to maintain amino acid levels and that TPPII-deficient cells compensate by increasing lysosome number and proteolytic activity. However, the overabundant lysosomes derange cellular metabolism by consuming the key glycolytic enzyme hexokinase-2 through chaperone-mediated autophagy. This reduces glycolysis and impairs the production of effector cytokines, including IFN-γ and IL-1ß. Thus, TPPII controls the balance between intracellular amino acid availability, lysosome number, and glycolysis, which is vital for adaptive and innate immunity and neurodevelopmental health.
Subject(s)
Adaptive Immunity , Aminopeptidases/metabolism , Dipeptidyl-Peptidases and Tripeptidyl-Peptidases/metabolism , Glycolysis , Immunity, Innate , Immunologic Deficiency Syndromes/genetics , Immunologic Deficiency Syndromes/metabolism , Proteolysis , Serine Endopeptidases/metabolism , Amino Acid Sequence , Aminopeptidases/chemistry , Animals , Dipeptidyl-Peptidases and Tripeptidyl-Peptidases/chemistry , Female , Humans , Immunologic Deficiency Syndromes/immunology , Lysosomes/metabolism , Male , Models, Molecular , Molecular Sequence Data , Pedigree , Sequence Alignment , Serine Endopeptidases/chemistryABSTRACT
Thyroid peroxidase (TPO) is the key enzyme in thyroid hormone production and a universal autoantigen in Graves' and other autoimmune thyroid diseases. We wished to explore the expression of TPO and whether it was affected by thionamide antithyroid drugs. We studied recombinant TPO, stably expressed by a Chinese hamster ovary cell line (CHO-TPO) and transiently expressed TPO-enhanced green fluorescent protein (eGFP) and -FLAG fusion proteins. Immunoblotting of CHO-TPO cell extracts showed high-molecular weight (HMW) TPO isoforms that were resistant to reduction, as well as 110 kDa monomeric TPO. Co-immunoprecipitation and enzyme-linked-immunosorbent assay (ELISA) binding studies of FLAG- and eGFP-tagged TPO demonstrated TPO dimerisation. CHO-TPO cells cultured in methimazole (MMI) for 10 days showed a significant reduction in HMW-TPO isoforms at MMI concentrations of 1 microM and above (p < 0.01), whereas monomeric TPO expression was unchanged. We observed a similar reduction in HMW-TPO in CHO-TPO cells cultured in propylthiouracil (10 microM and above). Binding of Graves' disease patient sera and TPO-Fabs to enzymatically active TPO that was captured onto solid phase was not abrogated by MMI. The cellular localisation of TPO in CHO-TPO cells was unchanged by MMI treatment. Our demonstration of homodimeric TPO and the reduction in HMW-TPO isoforms during thionamide treatment of CHO-TPO cells shows, for the first time, an effect of thionamides on TPO structure. This suggests a structural correlate to the effect of thionamides on TPO enzymatic activity and opens up a novel potential mechanism for thionamide immunomodulation of autoimmune thyroid disease.
Subject(s)
Autoimmunity/immunology , Immunomodulation/immunology , Iodide Peroxidase/chemistry , Iodide Peroxidase/metabolism , Protein Structure, Quaternary , Thiazoles , Thyroid Gland/immunology , Animals , Antithyroid Agents/metabolism , CHO Cells , Cricetinae , Cricetulus , Humans , Iodide Peroxidase/genetics , Methimazole/metabolism , Molecular Weight , Propylthiouracil/metabolism , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/metabolism , Protein Multimerization , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Thiazoles/metabolismABSTRACT
CONTEXT/OBJECTIVES: It is known that different autoimmune diseases often share the same susceptibility genes. In this study we aimed to investigate if loci found associated with common autoimmune diseases in recent genome-wide association studies also could be susceptibility loci for autoimmune Addison's disease (primary adrenal insufficiency). DESIGN/PATIENTS: A total of 139 tagging single nucleotide polymorphisms (SNPs) in 11 candidate genes (IL2, IL21, IL2RA, CLEC2D, CD69, ERBB3, PTPN11, SH2B3, CLEC16A, CIITA, and PTPN2) were genotyped in a case/control study design consisting of Norwegian Addison's disease patients (n = 332) and Norwegian healthy control individuals (n = 1029). Five SNPs were subsequently selected for analysis in a United Kingdom sample set consisting of Addison's disease patients (n = 210) and controls (n = 191). RESULTS: Polymorphisms in CLEC16A and CIITA remained significantly associated with Addison's disease in the Norwegian sample set at the 0.05 level, even after correction for multiple testing. CLEC16A and CIITA are both located at 16p13, but linkage disequilibrium patterns and logistical regression analyses suggest that SNPs in these two genes are independently associated with Addison's disease. We were not able to confirm these associations in the United Kingdom material, however, this may well be due to the limited sample size and lack of statistical power. CONCLUSION: Two alleles at 16p13 are independently associated with the risk of Addison's disease in the Norwegian population, suggesting this chromosomal region to harbor common autoimmunity gene(s), CLEC16A and CIITA being possible independent candidates.
