K. Kokame et al., Nonradioactive differential display cloning of genes induced by homocysteine in vascular endothelial cells, METHODS, 16(4), 1998, pp. 434-443
Hyperhomocysteinemia is known to be a risk factor for arteriosclerosis and
thrombosis. To elucidate the mechanisms by which homocysteine may promote v
ascular diseases. we have applied a modified nonradioactive differential di
splay analysis that evaluates changes in gene expression induced by homocys
teine treatment of cultured human umbilical vein endothelial cells (HUVECs)
. We identified six upregulated and one downregulated gene. One upregulated
gene was GRP78/BiP, an endoplasmic reticulum (ER)-resident molecular chape
rone, suggesting that unfolded proteins would accumulate in the ER because
of redox potential changes caused by homocysteine. Another upregulated gene
encoded a bifunctional enzyme with activities of methylenetetrahydrofolate
dehydrogenase and methenyltetrahydrofolate cyclohydrolase, which is involv
ed in homocysteine metabolism. A third upregulated gene encoded activating
transcription factor 4. Homology searches of the remaining four clones fail
ed to retrieve any similar sequences with a known function. We isolated a f
ull-length cDNA of one of the upregulated genes from a HUVEC library. It en
coded a novel protein with 394 amino acids, which was termed RTP (reducing
agent and tunicamycin-responsive protein). Northern blot analysis revealed
that RTP mRNA expression was induced in HUVECs treated with not only homocy
steine but also 2-mercaptoethanol and tunicamycin, both of which are known
to induce ER stress. RTP mRNA was ubiquitously expressed in human adult org
ans, and seemed to be regulated in mouse embryogenesis. Consequently, our d
ifferential display analysis revealed that homocysteine alters the expressi
vity of multiple proteins, especially ER stress-responsive ones. This poten
tial ability of homocysteine may be involved in atherogenesis, (C) 1998 Aca
demic Press.