Summary
The metalloproteinase ADAMTS13 cleaves VWF multimers instantaneously when they are
released from endothelial cells. Absent or manifestly diminished proteolytic activity
of ADAMTS13 results in the appearance and accumulation of ultralarge VWF multimers
(ULVWFM) in plasma, characterised by the manifestation of Thrombotic Thrombocytopenic
Purpura (TTP). Despite congenital defects, infections and the actions of drugs such
as cyclosporine A, doxycycline and corticosteroids apparently are involved in its
development. To examine the possibility of transcriptional regulation of ADAMTS13
activity, we analyzed RNA levels in various cell culture systems and the response
to known and assumed modulators of gene expression. We demonstrate the expression
of ADAMTS13 in liver homogenates and a parenchyma liver cell culture system Hep3B,
supporting the hypothesis that liver is an important source of plasma ADAMTS13, whereas
there was no alteration in gene expression after stimulation of liver cells with proinflammatory
stimuli such as endotoxin, TNF-α, IL-6, IL-1β as well as immuno-suppressive agents,
such as cyclosporine A, a variety of steroids as well as doxycycline. Therefore, we
analysed the ADAMTS13 gene for binding sites of transcription factors in silico and compared the data with those found in two sets of 24 genes considered either
as differentially regulated by prototypic inflammatory regulation or as unvaried under
various conditions. On the basis of these data, the promotor of ADAMTS13 features
the characteristics of a gene, which remains unvaried under a variety of conditions.
To our knowledge, the current data demonstrate for the first time, that an alteration
in transcriptional activity is negligible in accounting for diminished proteolytic
activity as observed under various experimental and, in particular, clinical conditions.
Keywords
ADAMTS13 - von Willebrand factor - gene expression