Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen induces expression of the helix-loop-helix protein Id-1 in human endothelial cells.
Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) (also known as human herpesvirus 8) is a gamma-2 herpesvirus believed to be the etiologic agent responsible for KS. The pathogenesis of this potentially life-threatening neoplasm is complex and unclear, and it is currently unknown how KSHV causes KS. Id (named for inhibitor of DNA binding or inhibitor of differentiation) proteins were identified in 1990 and found to be naturally occurring dominant-negative inhibitors of basic helix-loop-helix transcription factors. Id-1, the most well-studied member of this family, has since been shown to play a key role in several biological systems including cellular differentiation, cell cycle regulation, and tumorigenesis. In this report, we demonstrate that Id-1 is expressed at high levels in KS tumor cells both in vitro and in vivo but is expressed at relatively modest levels in endothelial cells (ECs), the likely precursor of the KS tumor cell. Infection of precursor cells with KSHV may be responsible for this enhanced expression, as KSHV infection induced Id-1 27-fold in ECs under our experimental conditions. Furthermore, we demonstrate that the KSHV-encoded latency-associated nuclear antigen (LANA) protein appears to be involved. Expression of LANA in ECs resulted in Id-1 induction that was almost identical to the induction seen with KSHV-infected ECs. These results demonstrate the expression of Id-1 in KS tumor cells and indicate the KSHV LANA protein may be, at least in part, responsible. This may be an important mechanism by which KSHV allows KS tumor cells to escape normal cell cycle regulation and enhances their proliferation.
Tang
Jun
J
Department of Pathology and Skin Cancer Research Program, Cardinal Bernardin Cancer Center, Loyola University Medical Center, Maywood, Illinois 60153, USA.
Gordon
Gabriel M
GM
Müller
Maike G
MG
Dahiya
Madhu
M
Foreman
Kimberly E
KE
D000956:Antigens, Viral; D002455:Cell Division; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000821:virology*; D018257:Helix-Loop-Helix Motifs; D019288:Herpesvirus 8, Human / Q000378:metabolism / Q000472:pathogenicity*; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1; D009687:Nuclear Proteins / Q000494:pharmacology*; D012097:Repressor Proteins; D012514:Sarcoma, Kaposi; D012867:Skin / Q000098:blood supply; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D000956:Antigens, Viral; C497453:ID1 protein, human; D051798:Inhibitor of Differentiation Protein 1; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C109540:latency-associated nuclear antigen