Functional characterization of twelve natural PROS1 mutations associated with anticoagulant protein S deficiency.
BACKGROUND
The molecular mechanisms by which PROS1 mutations result in protein S deficiency are still unknown for many of the mutations, particularly for those that result in a premature termination codon. The aim of this study was to analyze the functional relevance on mRNA and protein expression of 12 natural PROS1 mutations associated with protein S deficiency.


METHODS
Five mutations were nonsense, three were small frameshift deletions, one was c.258,259AG>GT at the 3' end of exon 3, one was p.M640T and the last two were c.-7C>G and p.L15H, found in double heterozygosis as [c.-7C>G;44T>A]. The apparently neutral variant p.R233K was also analyzed. PROS1 cDNA was assessed by reverse transcriptase polymerase chain reaction of platelet mRNA. Expression of mutant proteins was determined by site-directed mutagenesis and analyses of transiently transfected PROS1 mutants in COS-7 cells.


RESULTS
Only cDNA from the normal allele was observed from the five nonsense mutations, the frameshift deletion c.1731delT and from c.258,259AG>GT. Both the normal and the mutated alleles were observed from [c.-7C>G;44T>A], c.187,188delTG and p.M640T. Transient expression analyses of PROS1 mutants whose mRNA was normally expressed revealed greatly reduced secretion of p.L15H and c.1272delA, mild secretion values of p.M640T and normal secretion levels of c.-7C>G and, as expected, p.R233K.


CONCLUSIONS
Whereas the main cause of quantitative protein S deficiency associated with missense mutations is defective synthesis, stability or secretion of the mutated protein, the main mechanism for the deficiency associated with mutations that generate a premature termination codon is not the synthesis of a truncated protein, but the exclusion of the mutated allele, probably by nonsense-mediated mRNA decay.
Hurtado
Begoña
B
Center de Genètica Mèdica i Molecular, IDIBELL, L'Hospitalet de Llobregat, Barcelona.
Muñoz
Xavier
X
Mulero
Maria Carme
MC
Navarro
Gemma
G
Domènech
Pere
P
García de Frutos
Pablo
P
Pérez-Riba
Mercè
M
Sala
Núria
N
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D018389:Codon, Nonsense; D016368:Frameshift Mutation; D005838:Genotype; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D020125:Mutation, Missense; D017293:Protein S / Q000096:biosynthesis / Q000235:genetics*; D018455:Protein S Deficiency / Q000235:genetics*; D020871:RNA Stability / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D017384:Sequence Deletion; D014162:Transfection
D018389:Codon, Nonsense; D017293:Protein S; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins