Expression of K13/v-FLIP gene of human herpesvirus 8 and apoptosis in Kaposi's sarcoma spindle cells.
BACKGROUND
Human herpesvirus 8 (HHV8) infection is associated with all forms of Kaposi's sarcoma (KS). The HHV8 genome locus ORFK13-72-73 (ORF = open reading frame) encodes proteins that may be important in HHV8-mediated pathogenesis, i.e., the latency-associated nuclear antigen (encoded by ORF73), viral-cyc-D (v-cyc-D), a viral homologue of cellular cyclin D (encoded by ORF72), and viral-FLIP (v-FLIP), a homologue of the cellular FLICE (Fas-associated death domain-like interleukin 1 beta-converting enzyme) inhibitory protein (encoded by ORFK13; is an inhibitor of apoptosis [programmed cell death]). Through differential splicing events, this locus expresses individual RNA transcripts that encode all three proteins (tricistronic transcripts) or just two of them (v-FLIP and v-cyc-D; bicistronic transcripts). We examined expression of these transcripts in KS tissues.


METHODS
We collected tissues from patients with KS of different stages. By use of an optimized in situ hybridization procedure, we examined different ORFK13-72-73 locus transcripts in HHV8-infected cells in skin lesions and in one adjacent lymph node. Apoptosis in KS lesions was determined by use of an in situ assay.


CONCLUSIONS
Our results indicate the following: 1) Transcripts from the ORFK13-72-73 locus appear to be spliced differentially in latently infected KS cells in skin lesions and in HHV8-infected cells in lymph nodes; specifically, ORFK13-ORF72 bicistronic transcripts were expressed abundantly in KS cells, whereas ORFK13-ORF72-ORF73 tricistronic transcripts were detected only in lymph node cells. 2) Sequences encoding the antiapoptotic protein v-FLIP are expressed at very low levels in early KS lesions, but expression increases dramatically in late-stage lesions. 3) The increase in expression of v-FLIP-encoding transcripts is associated with a reduction in apoptosis in KS lesions.


CONCLUSIONS
These data suggest that functional v-FLIP is produced in vivo and that antiapoptotic mechanisms may be involved in the rapid growth of KS lesions, where only a few cells undergoing mitosis are generally observed.
Stürzl
M
M
Institute of Molecular Virology, GSF-National Research Center for Environment and Health, Neuherberg, Germany. Stuerzl@gsf.de
Hohenadl
C
C
Zietz
C
C
Castanos-Velez
E
E
Wunderlich
A
A
Ascherl
G
G
Biberfeld
P
P
Monini
P
P
Browning
P J
PJ
Ensoli
B
B
D000956:Antigens, Viral / Q000032:analysis / Q000235:genetics*; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics*; D015536:Down-Regulation; D015870:Gene Expression; D005814:Genes, Viral; D019288:Herpesvirus 8, Human / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D047908:Intracellular Signaling Peptides and Proteins; D008198:Lymph Nodes / Q000378:metabolism / Q000821:virology; D009367:Neoplasm Staging; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics*; D016366:Open Reading Frames; D015347:RNA Probes; D012333:RNA, Messenger / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D012367:RNA, Viral / Q000032:analysis; D012514:Sarcoma, Kaposi / Q000235:genetics / Q000473:pathology / Q000821:virology*; D014158:Transcription, Genetic; D015854:Up-Regulation; D014764:Viral Proteins / Q000235:genetics
D000956:Antigens, Viral; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; C118264:HHV8-Vcyc protein, Human herpesvirus 8; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D015347:RNA Probes; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D012367:RNA, Viral; D014764:Viral Proteins; C109540:latency-associated nuclear antigen