Expression of K13/v-FLIP Gene of Human Herpesvirus 8 and Apoptosis in Kaposi's Sarcoma Spindle Cells

J Natl Cancer Inst. 1999 Oct 20;91(20):1725-33. doi: 10.1093/jnci/91.20.1725.

Abstract

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.

Results and 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.

Implications: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigens, Viral / analysis
  • Antigens, Viral / genetics*
  • Apoptosis*
  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • Carrier Proteins / analysis
  • Carrier Proteins / genetics*
  • Down-Regulation
  • Gene Expression*
  • Genes, Viral*
  • Herpesvirus 8, Human / genetics*
  • Humans
  • Immunohistochemistry
  • In Situ Hybridization
  • In Situ Nick-End Labeling
  • Intracellular Signaling Peptides and Proteins*
  • Lymph Nodes / metabolism
  • Lymph Nodes / virology
  • Neoplasm Staging
  • Nuclear Proteins / analysis
  • Nuclear Proteins / genetics*
  • Open Reading Frames
  • RNA Probes
  • RNA, Messenger / analysis
  • RNA, Neoplasm / analysis
  • RNA, Viral / analysis
  • Sarcoma, Kaposi / genetics
  • Sarcoma, Kaposi / pathology
  • Sarcoma, Kaposi / virology*
  • Transcription, Genetic
  • Up-Regulation
  • Viral Proteins / genetics

Substances

  • Antigens, Viral
  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • CFLAR protein, human
  • Carrier Proteins
  • HHV8-Vcyc protein, Human herpesvirus 8
  • Intracellular Signaling Peptides and Proteins
  • Nuclear Proteins
  • RNA Probes
  • RNA, Messenger
  • RNA, Neoplasm
  • RNA, Viral
  • Viral Proteins
  • latency-associated nuclear antigen