Identification and characterization of human herpesvirus 8 open reading frame K9 viral interferon regulatory factor by a monoclonal antibody.

Objective: To identify and characterize an open reading frame (ORF) in association with its mRNA and a coding protein recognized by anti-human herpesvirus 8 (HHV-8) monoclonal antibody B291.

Study design/methods: The antigen detected by B291 was characterized by immunofluorescence method, Western blot analysis, laser confocal microscopy, and immunohistology cDNA of the protein was identified by immunoscreening the HHV-8 cDNA library with B291 and sequenced. Structure and kinetics of the mRNA expression was investigated by 5',3' rapid amplification of cDNA ends (RACE) and Northern blot analysis.

Results: Viral interferon regulatory factor (vIRF; approximately 50 kd) was a protein recognized by B291. It was detected in 12-O-tetradecanoyl phorbol-13 acetate (TPA)-induced, but not uninduced, HHV-8-infected cell lines (BCBL-1 and BCP-1) and the tumor cells obtained from a SCID mouse injected with uninduced BCBL-1. The expression of vIRF was predominantly in the nucleus and was partially diminished by phosphonoformic acid (PFA) treatment, whereas the mRNA (approximately 2.4 kb) was accumulated.

Conclusions: vIRF is an early protein expressed in the nucleus and may be involved in Kaposi's sarcoma tumor formation.