Caspase-7 cleavage of Kaposi sarcoma-associated herpesvirus ORF57 confers a cellular function against viral lytic gene expression.
Kaposi sarcoma-associated herpesvirus (KSHV) ORF57 is a viral early protein essential for KSHV multiplication. We found that B cells derived from cavity-based B cell lymphoma with lytic KSHV infection display activation of caspase-8 and cleavage of ORF57 in the cytoplasm by caspase-7 at the aspartate residue at position 33 from the N terminus. Caspase-7 cleavage of ORF57 is prevented by pan-caspase inhibitor z-VAD, caspase-3 and caspase-7 inhibitor z-DEVD, and caspase-7 small interfering RNAs. The caspase-7 cleavage site (30)DETD(33) in ORF57 is not cleavable by caspase-3, although both enzymes use DEXD as a common cleavage site. B cells with lytic KSHV infection and caspase-7 activation exhibited a greatly reduced level of ORF57. A majority of the cells expressing active caspase-7 appeared to have no detectable ORF57 and vice versa. Upon cleavage with caspase-7, ORF57 was deficient in promoting the expression of viral lytic genes. Inhibiting caspase-7 cleavage of ORF57 in KSHV(+) BCBL-1 cells by z-VAD, z-DEVD, or caspase-7 small interfering RNA led to increased expression of viral lytic genes and production of cell-free virus particles. Collectively, our data provide the first compelling evidence that caspase cleavage of ORF57 may represent a cellular function against lytic KSHV infection.
HIV and AIDS Malignancy Branch, National Institutes of Health, Bethesda, Maryland 20892, USA.
Vladimir
V
Majerciak
Michael
M
Kruhlak
Pradeep K
PK
Dagur
J Philip
JP
McCoy
Zhi-Ming
ZM
Zheng
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D015967:Gene Expression Regulation, Viral; D019288:Herpesvirus 8, Human / Q000378:metabolism*; D006801:Humans; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D014779:Virus Replication
D000590:Amino Acid Chloromethyl Ketones; D034741:RNA, Small Interfering; D012367:RNA, Viral; D014764:Viral Proteins; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D053148:Caspase 3; D053179:Caspase 7