Kaposi's sarcoma herpesvirus K15 protein contributes to virus-induced angiogenesis by recruiting PLCγ1 and activating NFAT1-dependent RCAN1 expression

PLoS Pathog. 2012 Sep;8(9):e1002927. doi: 10.1371/journal.ppat.1002927. Epub 2012 Sep 27.


Kaposi's Sarcoma (KS), caused by Kaposi's Sarcoma Herpesvirus (KSHV), is a highly vascularised angiogenic tumor of endothelial cells, characterized by latently KSHV-infected spindle cells and a pronounced inflammatory infiltrate. Several KSHV proteins, including LANA-1 (ORF73), vCyclin (ORF72), vGPCR (ORF74), vIL6 (ORF-K2), vCCL-1 (ORF-K6), vCCL-2 (ORF-K4) and K1 have been shown to exert effects that can lead to the proliferation and atypical differentiation of endothelial cells and/or the secretion of cytokines with angiogenic and inflammatory properties (VEGF, bFGF, IL6, IL8, GROα, and TNFβ). To investigate a role of the KSHV K15 protein in KSHV-mediated angiogenesis, we carried out a genome wide gene expression analysis on primary endothelial cells infected with KSHV wildtype (KSHVwt) and a KSHV K15 deletion mutant (KSHVΔK15). We found RCAN1/DSCR1 (Regulator of Calcineurin 1/Down Syndrome critical region 1), a cellular gene involved in angiogenesis, to be differentially expressed in KSHVwt- vs KSHVΔK15-infected cells. During physiological angiogenesis, expression of RCAN1 in endothelial cells is regulated by VEGF (vascular endothelial growth factor) through a pathway involving the activation of PLCγ1, Calcineurin and NFAT1. We found that K15 directly recruits PLCγ1, and thereby activates Calcineurin/NFAT1-dependent RCAN1 expression which results in the formation of angiogenic tubes. Primary endothelial cells infected with KSHVwt form angiogenic tubes upon activation of the lytic replication cycle. This effect is abrogated when K15 is deleted (KSHVΔK15) or silenced by an siRNA targeting the K15 expression. Our study establishes K15 as one of the KSHV proteins that contribute to KSHV-induced angiogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiogenesis Inducing Agents
  • Animals
  • Calcineurin / metabolism
  • Cell Line
  • Chlorocebus aethiops
  • DNA-Binding Proteins
  • HEK293 Cells
  • Herpesvirus 8, Human / genetics
  • Herpesvirus 8, Human / growth & development
  • Herpesvirus 8, Human / metabolism*
  • Human Umbilical Vein Endothelial Cells / virology*
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Molecular Sequence Data
  • Muscle Proteins / genetics
  • Muscle Proteins / metabolism*
  • NFATC Transcription Factors / metabolism
  • Neovascularization, Pathologic / virology*
  • Phospholipase C gamma / metabolism*
  • RNA Interference
  • RNA, Small Interfering
  • Sarcoma, Kaposi / virology
  • Sequence Deletion
  • Vero Cells
  • Viral Proteins / genetics
  • Viral Proteins / metabolism*


  • Angiogenesis Inducing Agents
  • DNA-Binding Proteins
  • Intracellular Signaling Peptides and Proteins
  • K15 protein, Human herpesvirus 8
  • Muscle Proteins
  • NFATC Transcription Factors
  • NFATC2 protein, human
  • RCAN1 protein, human
  • RNA, Small Interfering
  • Viral Proteins
  • Calcineurin
  • Phospholipase C gamma

Associated data

  • GENBANK/JX228174

Grant support

This work was supported by Collaborative Research Centre (CRC 566 of the Deutsche Forschungsgemeinschaft), the European Union Integrated Project INCA (The role of chronic infections in the development of cancer; LSHC-CT-2005-018704) and the Molecular Medicine PhD Program of Hannover Medical School. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.