Study on the molecular mechanism of two new mutations causing haemophilia B / 中华检验医学杂志

ABSTRACT

Objective To study two new factor Ⅸ mutations Cys82Ser and Ile288Ser in vitro and research the molecular mechanism of haemophilia B. Methods PcDNA3. 1 ( - ) FⅨwt expression plasmid was prepared. The mutated FⅨcDNA expression plasmids, PcDNA3.1 ( - ) FⅨM1 (Cys82Ser) and PcDNA3. 1 ( - ) F Ⅸ M2 (Ile288Ser) were constructed by megaprimer method respectively. Transient expression experiments were performed using HEK293 cells transfected with the expression vectors containing the wild-type or the mutation recombinant cDNA. PcDNA3. 1 ( - ) was used as a blank control. The expression proteins were detected by ELISA, factor activity assay and flourescence stain. Results The results suggested that the two FⅨ gene mutations did not induce the reduction of the mutant FⅨ mRNA compared with the wild-type FⅨ mRNA. The FⅨAg in culture media and cell lysate of wild type conduct were assigned as 100. 0%. The results of PcDNA3.1 ( - ) FⅨ M1 mutation protein were (27. 1 ± 5. 2)% and (99.4 ±4. 1)% respectively. For PcDNA3. 1( - )FⅨM2, the results were (5.3 ± 1.8)% and (31.7 ±2. 5)% respectively. The FⅨ C in culture media of wild type conduct was also assigned as 100. 0%. Then the two types of mutant protein were ( 8. 5 ± 3.2 ) % and ＜ 1%, respectively. Immunofluorescence microscopy result suggested that the intensity of perinuclear spot was reduced in cells transfected with PcDNA3.1 ( - ) FⅨM2 while staining for PcDNA3. 1 ( - ) FⅨM1 was predominantely diffuse without perinnclear enhancement. Conclusions These results strongly suggest that the FⅨ Cys82Ser mutation protein is not been correctly folded, by any possibility. The mutation protein has secretion defect. The secretion dysfunction and the protein degradation intracellular are possiblely the molecular pathology of Ile288Ser mutant protein.