Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is associated with the angioproliferative KS lesions characterized by spindle-shaped endothelial cells, inflammatory cells,
cytokines,
growth factors, and angiogenic factors. De novo KSHV
infection of human microvascular dermal endothelial cells results in increased secretion of several
growth factors,
cytokines,
chemokines, and angiogenic factors, and the multifunctional
angiogenic protein angiogenin is one of them. KS tissue sections were positive for
angiogenin, highlighting the importance of
angiogenin in KS pathogenesis. Examination of KSHV-mediated
angiogenin upregulation and secretion and potential outcomes revealed that during
infection of primary endothelial cells, KSHV induced a time- and dose-dependent increase in
angiogenin gene expression and
protein secretion beginning as early
as 8 h postinfection and lasting until the fifth day of our observation period. TIVE latently transformed cells (TIVE-LTC) latently infected with KSHV secreted high levels of
angiogenin.
Angiogenin was also detected in BCBL-1 cells (human B cells) carrying KSHV in a latent state. Significant induction of
angiogenin was observed in cells expressing KSHV ORF73 (LANA-1; latent) and ORF74 (lytic) genes alone, and moderate induction was seen with the lytic KSHV ORF50 gene.
Angiogenin bound to surface actin, internalized in a microtubule-independent manner, and translocated into the nucleus and nucleolus of infected cells. In addition, it increased
45S rRNA gene transcription, antiapoptosis, and proliferation of infected cells, thus demonstrating the multifunctional nature of KSHV-induced
angiogenin. These activities were dependent on
angiogenin nuclear translocation, which was inhibited by
neomycin. Upregulation of
angiogenin led to increased activation of
urokinase plasminogen activator and generation of active
plasmin, which facilitated the migration of endothelial cells toward
chemoattractants, including
angiogenin, and chemotaxis was prevented by the inhibition of
angiogenin nuclear translocation. Treatment of KSHV-infected cell supernatants with antiangiogenin
antibodies significantly inhibited endothelial tube formation, and inhibition of nuclear translocation of
angiogenin also blocked the expression of KSHV-induced
vascular endothelial growth factor C. Collectively, these results strongly suggest that by increasing infected endothelial cell
45S rRNA synthesis, proliferation, migration, and angiogenesis, KSHV-induced
angiogenin could be playing a pivotal role in the pathogenesis of KSHV
infection, including a contribution to the angioproliferative nature of KS lesions. Our studies suggested that LANA-1 and vGPCR play roles in KSHV-induced angiogenesis and that the angiogenic potential of vGPCR might also be due to its ability to induce
angiogenin.