Characterization of missense mutations in the signal peptide and propeptide of FIX in hemophilia B by a cell-based assay

Author:

Gao Wenwen1ORCID,Xu Yaqi1ORCID,Liu Hongli1ORCID,Gao Meng1ORCID,Cao Qing1ORCID,Wang Yiyi1ORCID,Cui Longteng1ORCID,Huang Rong1ORCID,Shen Yan1,Li Sanqiang1ORCID,Yang Haiping12,Chen Yixiang1ORCID,Li Chaokun3ORCID,Yu Haichuan4ORCID,Li Weikai5ORCID,Shen Guomin1ORCID

Affiliation:

1. Department of Medical Genetics, Institute of Hemostasis and Thrombosis, School of Basic Medical Sciences, and

2. First Affiliated Hospital, Henan University of Science and Technology, Luoyang, People’s Republic of China;

3. Sino-UK Joint Laboratory for Brain Function and Injury, School of Basic Medical Sciences, and

4. Department of Biochemistry and Molecular Biology, School of Medical Laboratory, Xinxiang Medical University, Xinxiang, People’s Republic of China; and

5. Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO

Abstract

AbstractMany mutations in the signal peptide and propeptide of factor IX (FIX) cause hemophilia B. A FIX variants database reports 28 unique missense mutations in these regions that lead to FIX deficiency, but the underlying mechanism is known only for the mutations on R43 that interfere with propeptide cleavage. It remains unclear how other mutations result in FIX deficiency and why patients carrying the same mutation have different bleeding tendencies. Here, we modify a cell-based reporter assay to characterize the missense mutations in the signal peptide and propeptide of FIX. The results show that the level of secreted conformation-specific reporter (SCSR), which has a functional γ-carboxyglutamate (Gla) domain of FIX, decreases significantly in most mutations. The decreased SCSR level is consistent with FIX deficiency in hemophilia B patients. Moreover, we find that the decrease in the SCSR level is caused by several distinct mechanisms, including interfering with cotranslational translocation into the endoplasmic reticulum, protein secretion, γ-carboxylation of the Gla domain, and cleavage of the signal peptide or propeptide. Importantly, our results also show that the SCSR levels of most signal peptide and propeptide mutations increase with vitamin K concentration, suggesting that the heterogeneity of bleeding tendencies may be related to vitamin K levels in the body. Thus, oral administration of vitamin K may alleviate the severity of bleeding tendencies in patients with missense mutations in the FIX signal peptide and propeptide regions.

Publisher

American Society of Hematology

Subject

Hematology

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