Ac. Garber et al., DNA binding and modulation of gene expression by the latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus, J VIROLOGY, 75(17), 2001, pp. 7882-7892
Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with Kaposi's
sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. T
he latency-associated nuclear antigen (LANA) is highly expressed in these m
alignancies and has been shown to play an important role in episomal mainte
nance, presumably by binding to a putative oriP. In addition, LANA modulate
s cellular and viral gene expression and interacts with the cellular tumor
suppressors p53 and retinoblastoma suppressor protein. Many of these featur
es are reminiscent of Epstein-Barr virus nuclear antigens (EBNAs), a family
of six proteins expressed during latency. EBNA-1 is required for episome m
aintenance, binds to oriP, and strongly activates transcription from two pr
omoters, including its own. We have previously shown that LANA can transact
ivate its own promoter and therefore asked whether LANA, like EBNA-1, activ
ates transcription by direct binding to DNA. By using recombinant LANA expr
essed from vaccinia virus vectors for electrophoretic mobility shift assays
, we found that LANA does not bind to its own promoter. In contrast, LANA b
inds specifically to sequences containing an imperfect 20-by palindrome in
the terminal repeat (TR) of KSHV. We further show that the C-terminal domai
n of LANA is sufficient for site-specific DNA binding. Unlike EBNA-1, which
activates transcription through binding of oriP, we found that LANA inhibi
ts transcription from a single TR binding site. A multimerized TR as found
in the viral genome results in strong transcriptional suppression when link
ed to a heterologous promoter. These data suggest that LANA, although fulfi
lling functions similar to those of EBNA-1, does so by very different mecha
nisms.