title: The peptide derived from the Ig-like domain of human herpesvirus 8 K1 protein induces death in hematological cancer cells.
abstract: BACKGROUND
  Although significant progress has been made in the treatment of lymphomas, many lymphomas exhibit resistance to cell death, suggesting a defective Fas signaling, which remains poorly understood. We previously reported that cells expressing the K1 protein of human herpesvirus 8 (HHV-8) resist death through the complex formation of the Ig-like domain of K1 with Fas. Recently, we investigated whether peptides derived from the Ig-like domain of the K1 protein may affect cell death.
  
  
  METHODS
  K1 positive and negative cell lines were incubated with the K1-derived peptides, and cell death (apoptotic and necrotic) was assessed by flow cytometry and LDH assay. Activation of caspases was assessed by fluorometric assay and flow cytometry. Fas receptor-independent, peptide-mediated cell killing was tested in the Fas-resistant Daudi cell line and Jurkat cell clones deficient in caspase-8 and FADD functionality. Activation of TNF receptors I and II was blocked by pre-incubation with corresponding blocking antibodies. The effect of the K1 peptide in vivo was tested in a mouse xenograft model.
  
  
  RESULTS
  We observed that the peptide S20-3 enhanced cell death in K1-positive BJAB cells and HHV-8 positive primary effusion lymphoma (PEL) cell lines. Similar effects of this peptide were observed in B-cell lymphoma and T-lymphoblastic leukemia cells without K1 expression but not in normal human peripheral blood mononuclear cells. A single intratumoral injection of the S20-3 peptide decreased the growth of Jurkat xenografts in SCID mice. The mechanism of tumor cell death induced by the S20-3 peptide was associated with activation of caspases, but this activity was only partially inhibited by the pan-caspase inhibitor z-VAD. Furthermore, the K1 peptide also killed Fas-resistant Daudi cells, and this killing effect was inhibited by pre-incubation of cells with antibodies blocking TNFRI.
  
  
  CONCLUSIONS
  Taken together, these findings indicate that the S20-3 peptide can selectively induce the death of malignant hematological cell lines by Fas- and/or TNFRI-dependent mechanisms, suggesting the K1-derived peptide or peptidomimetic may have promising therapeutic potential for the treatment of hematological cancers.
authors.affiliation: Department of Lymphoma and Myeloma, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA.
authors.forename: Urszula
authors.initials: U
authors.lastname: Daniluk
authors.forename: Celine
authors.initials: C
authors.lastname: Kerros
authors.forename: Rong-Hua
authors.initials: RH
authors.lastname: Tao
authors.forename: Jillian F
authors.initials: JF
authors.lastname: Wise
authors.forename: Xue
authors.initials: X
authors.lastname: Ao
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Berkova
authors.forename: Felipe
authors.initials: F
authors.lastname: Samaniego
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053181:Caspase 8 / Q000378:metabolism; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D019337:Hematologic Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D019288:Herpesvirus 8, Human / Q000235:genetics / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D016513:Mice, SCID; D010455:Peptides / Q000008:administration & dosage / Q000138:chemical synthesis; D017434:Protein Structure, Tertiary; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D015398:Signal Transduction; D014764:Viral Proteins / Q000008:administration & dosage / Q000138:chemical synthesis; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism
chemical_list: C505533:FADD protein, human; C491901:FAS protein, human; D053200:Fas-Associated Death Domain Protein; C111600:K1 protein, Human herpesvirus 8; D010455:Peptides; D018124:Receptors, Tumor Necrosis Factor; D014764:Viral Proteins; D019014:fas Receptor; D053181:Caspase 8