Characterization of missense variants in the signal peptide of C1 esterase inhibitor.

Abstract

Hereditary angioedema with C1 esterase inhibitor (C1INH) deficiency is caused by variants in the SERPING1 gene. A decrease in C1INH function results in overproduction of bradykinin, causing enhanced vascular permeability and swelling. Signal peptide (SP) is essential for C1INH secretion. While SP variants in the SERPING1 gene have been reported, their genotype-phenotype correlations have not been well characterized. To investigate the impact of SP variants, we systematically evaluated 33 SP variants of C1INH by examining their expression, function, and intracellular location. The SP variants were transiently transfected into 293T cells. Their concentration was compared to wild-type C1INH. Functional analyses were performed by assessing their binding with activated C1s, kallikrein, and factor XIIa. Transfected HeLa cells were used to assess the intracellular localization of C1INH variants. Of 33 SP variants, 6 were poorly synthesized. Among these, 3 are in the H region (L10R, L12R, L13-L15del) and 3 are in the C-terminal region (G17R, A20D, S22L). Compared to wild type, the remaining variants demonstrated normal recombinant protein expression and intact binding activity to their substrates. Protein aggregates were observed in the endoplasmic reticulum of L10R-, G17R-, and S22L-transfected cells. The H- and C-terminal regions of SP are critical for C1INH production. Shortening or introducing positive charges into the hydrophobic core of the H-terminal region can lead to pathogenic consequences. Disrupting the SP cleavage site in the C-terminal region impairs protein production. This study provides new insights into the impact of SP variants on C1INH expression leading to hereditary angioedema.