Summary
We found a 66-year-old Japanese patient with type I congenital heparin cofactor (HC)
II deficiency manifesting multiple atherosclerotic lesions. To investigate the molecular
pathogenesis of our patient, we performed sequencing analysis and expressed recombinant
human wild-type and mutant HC II molecules in COS-1 and CHO-K1 cells. Sequencing analysis
following amplification of each of all 5 exons and its flanking region showed a single
C to T transition at nucleotide position 12,854 in exon 5, which changed a Pro443 codon (CCG) to Leu codon (CTG). Because this mutation generates a new Bbv I site, the Bbv I digestion pattern of the PCR-amplified exon 5 fragments from each family member
was analyzed. In all cases, the patterns were consistent with the activities and antigen
levels of plasma HC II in those members. Transient transfection, metabolic labeling
and pulse-chase experiments followed by immunoprecipitation analysis showed that the
recombinant mutant HC II molecules were secreted from COS-1 cells in reduced amounts
compared with the wild-type, and that an enhanced intracellular association of the
mutant molecules with a chaperone, GRP78/BiP, was observed in CHO-K1 cells. Northern
blot analysis indicated that the mutant HC II mRNA was transcribed at a similar level
as that of wild-type.
Immunohistochemical staining of the transfected cells revealed that COS-1 cells expressing
the mutant HC II molecules were stained mainly in the perinuclear area. We conclude
that the impaired secretion of the mutant HC II molecules, due to intracellular degradation,
is the molecular pathogenesis of type I congenital HC II deficiency caused by a Pro443 to Leu mutation at reactive P2 site.
Keywords
Heparin cofactor II - thrombosis - thrombin - transfection - chaperone