Expression of p53 and human herpesvirus‐8 (HHV‐8)–encoded latency‐associated nuclear antigen with inhibition of apoptosis in HHV‐8–associated malignancies

BACKGROUND Kaposi sarcoma (KS) and primary effusion lymphoma (PEL) cells express human herpesvirus‐8 (HHV‐8)–encoded latency‐associated nuclear antigen (LANA) (open reading frame [ORF] 73 protein), suggesting that LANA plays an important role in the pathogenesis of HHV‐8–associated malignancies. Recently, the binding of LANA to p53 was demonstrated in vitro. In the current study, the authors investigated the association between p53 and LANA expression with apoptosis in HHV‐8–associated malignancies in vivo. METHODS Twenty‐six cases of KS, 1 case of HHV‐8–associated solid lymphoma, 2 PEL cell lines, and an HHV‐8–associated lymphoma engrafted in severe combined immunodeficiency (SCID) mice were examined. Immunohistochemistry using the catalyzed signal amplification system was employed to detect LANA and p53 on paraffin embedded tissues and the immunofluorescence technique was used on cell lines. To detect apoptosis, the TdT‐mediated dUTP nick end labeling (TUNEL) method was used. For mutation analysis of p53, exons 5–9 of the p53 gene were amplified by polymerase chain reaction and examined by direct sequencing. RESULTS Immunohistochemistry revealed that LANA and p53 were expressed in the tumor cells of all these specimens, and apoptotic cells were rarely detected in them using the TUNEL method. Immunofluorescence assay revealed that LANA colocalized with p53 in the nuclei of PEL cells. Sequencing analysis indicated that there was no mutation in the deduced amino acid sequences of p53 in KS tissues. CONCLUSIONS These data suggest colocalization of p53 and LANA and the inhibition of apoptosis in HHV‐8–associated malignancies in vivo, supporting the results found in vitro that p53 inhibition by LANA suppresses cell death, as reported previously. These results also suggest that the p53 pathway is crucial in the pathogenesis of HHV‐8–associated malignancies. Cancer 2001;92:3076–84. © 2001 American Cancer Society. In Kaposi sarcoma and primary effusion lymphoma, herpesvirus‐8–encoded latency‐associated nuclear antigen (LANA) and p53 were expressed, but very rarely was apoptosis identified. In addition, no mutation was detected in the sequences of p53, suggesting that LANA inhibits p53‐dependent apoptosis.