In the HAART era Kaposi’s sarcoma (KS) remains the second
most frequent tumor in HIV-infected patients worldwide,
and it is the most common cancer in Sub-Saharan Africa. KS
is a multicentric angioproliferative disorder characterized by
pathognomic spindle cells of endothelial origin, and is casually
associated to human herpesvirus 8, known also as KS
associated herpesvirus (KSHV).
KSHV infects endothelial cells, induces the formation
of spindle morphology and promotes angiogenesis. We are
studying the molecular mechanisms associated to KSHV
angiogenesis. We have determined that KSHV induces angiogenesis
with two distinct mechanisms. The first is through
NF-kappaB activation, via stimulation of the IkappaB kinase
(IKK). KSHV selectively triggers the production of high
levels of MCP-1, whereas it does not affect the expression
of other NF-kappaB-dependent proinflammatory proteins.
Interestingly, inhibition of MCP-1 abrogates KSHV angiogenesis.
When NFkB is inhibited, infection still results in a
residual angiogenic activity, approximately 30-40% of the
maximal level. Our experiments have shown that this second
mechanism is dependant upon the transcription factor ATF-4.
Infact, KSHV infection of endothelial cells results in a significant
upregulation of ATF-4. In addition, transfection of
ATF-4 in uninfected endothelial cells induces in vitro angiogenic
behaviour. Furthermore, ATF-4 has a direct effect on
the activation of MCP-1 promoter.
The results show that KSHV promotes angiogenesis by
stimulation of two different cellular mechanisms, NFkB and
ATF-4, that converge on activating MCP-1. The strict dependance
of KSHV angiogenesis on MCP-1 and the elucidation
of molecular mechanism involved in this process could result
in a better understanding of the angiogenetic process, its
involvement in cancer and will help in designing novel therapies
to reduce KS growth and vascularizatio
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