Functional analysis of two abnormal antithrombin proteins with different intracellular kinetics

Area of Science:

• Genetics
• Molecular Biology
• Hematology

Background:

• Hereditary antithrombin (AT) deficiency type I is linked to venous thrombosis.
• Decreased AT antigen levels in blood are characteristic of this deficiency.

Purpose of the Study:

• To analyze the mechanism by which novel and known abnormal AT variants cause type I AT deficiency.
• To investigate the cellular processing and secretion of identified AT variants.

Main Methods:

• Constructed and expressed wild-type and variant AT vectors in human embryonic kidney 293 cells.
• Evaluated AT antigen levels and N-glycosylation using western blot analysis.
• Examined subcellular co-localization and degradation pathways via confocal microscopy and chase experiments.

Main Results:

• Identified a novel variant (c.613delC) and a known variant (c.283T>C).
• Both variants showed reduced extracellular secretion with normal N-glycosylation.
• Impaired transport to the Golgi apparatus and differential degradation pathways (proteasomal for c.613delC, ER retention for c.283T>C) were observed.

Conclusions:

• Identified AT variants lead to suppressed secretion and impaired ER-Golgi transport.
• These findings elucidate the mechanism of type I AT deficiency.
• Provides insights for future therapy development for AT deficiency.