Genetics of COPA syndrome

Abstract

Inborn errors of immunity usually not only result in immunodeficiency but may also manifest as immune dysregulation in the form of autoinflammation, autoimmunity, or sometimes malignancy. One of the most recently discovered monogenic disorder of immune dysregulation is COPA syndrome. COPA syndrome is an inherited autoimmune disorder caused by mutations in COPA gene. COPA gene encodes for α subunit of the COP1 protein, which is involved in the reverse vesicular protein transport from Golgi apparatus to the endoplasmic reticulum (ER). The inheritance pattern of COPA syndrome is autosomal dominant, and the patients typically present with interstitial lung disease with pulmonary hemorrhage and subsequently develop arthritis. Immunological features involve autoantibody formation, elevated expression of IL-1β and IL-6, and increase in the number of Th17 cells. Molecular pathophysiology of COPA syndrome is not clearly understood. However, it is known that accumulation of unfolded proteins in ER leads to ER stress, which is an indirect result of aberrant vesicular transport of proteins from Golgi apparatus to ER and defective cellular autophagy. ER stress induces inflammation and is responsible for pathogenesis of a large number of chronic inflammatory diseases. Unfolded protein response process responds to improperly folded proteins and defends against stress in ER to ensure the fidelity of the protein folding. It maintains the expression of stress-response genes and causes initiation of inflammatory signaling pathways essential for the innate immunity. Mutation in COPA gene associated with defective protein sorting to ER has unearthed a new primary immunodeficiency disease with a unique clinical phenotype. This review highlights the clinical and molecular aspects of COPA syndrome.

Keywords: COPA syndrome; Golgi apparatus; arthritis; autoimmunity; autoinflammation; endoplasmic reticulum stress; interleukins; interstitial lung disease; protein transport.

Figure 1

Schematic representation of COPA gene with annotated exons and protein structure describing the respective domains with most reported mutations.

Figure 2

Cartoon depicting ER stress and Inflammation. Abbreviations: BiP, binding immunoglobulin protein; eIF2α, eukaryotic translation-initiation factor 2α; ER, endoplasmic reticulum; IRE1α, inositol-requiring 1α; Iκβ, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor; NF-kB, nuclear factor-kB; PERK, protein kinase (PKR)-like ER kinase; TRAF2, TNF receptor-associated factor 2.