The Latency-associated Nuclear Antigen of Kaposi's Sarcoma-associated Herpesvirus Transactivates the Telomerase Reverse Transcriptase Promoter

Abstract

Telomerase is a multi-subunit ribonucleoprotein holoenzyme that stabilizes telomere length through the addition of new repeat sequence to the ends of chromosomes. Telomerase reverse transcriptase is the subunit of this complex responsible for the enzymatic activity of telomerase. Expression of the reverse transcriptase is regulated at the level of transcription through the action of transcription factors that target its promoter. Most Kaposi's sarcoma tumor cells are latently infected with the Kaposi's sarcoma-associated herpesvirus, and the constitutive expression of a viralencoded latency-associated nuclear antigen has been shown to be important for the maintenance of the viral episome. The proliferative nature of Kaposi's sarcoma suggests that this antigen may also play a critical role in viral-mediated oncogenesis. In this study telomerase reverse transcriptase promoter elements cloned into a luciferase reporter plasmid were analyzed to determine the ability of the latency-associated nuclear antigen to regulate transcription. The latency-associated nuclear antigen transactivated the full-length promoter in 293T, 293, and BJAB cell lines. Furthermore, truncation promoter studies implicated sequence from ؊130 to ؉5 in viral-mediated activation. This region contains five Sp1 transcription factor-binding sites. Electrophoretic mobility shift assays indicated that the latency-associated nuclear antigen targets and affects the Sp1-DNA complex in the context of BJAB nuclear extracts.

Regulation of the human telomerase reverse transcriptase gene

“…All reporter constructs were more strongly expressed in either line than in normal ®broblasts, and there were no signi®cant di erences between the activity of any of the reporters in the telomerase positive and the ALT line. Knight et al (2001) have also reported hTERT promoter activity in an ALT cell line SUSM-1 when using another reporter containing 1.7 kb of the hTERT¯anking region. Even more strikingly, we observed no di erences in the expression of the same hTERT reporters when we compared them in a breast carcinoma line and its derivatives in which transfer of a single normal chromosome 3 has reduced hTERT mRNA by at least 30-fold, to undetectable levels (Ducrest et al, 2001).…”

Regulation and Autoregulation of the Promoter for the Latency-associated Nuclear Antigen of Kaposi's Sarcoma-associated Herpesvirus

“…In addition to its role in viral episome maintenance, LANA modulates host cell behavior to create a suitable environment for latent KSHV persistence. LANA can cooperate with activated ras in fibroblast transformation assays (38) and activates the human telomerase promoter (39). Biochemical studies show that LANA binds to p53, Rb (38,40), and a growing number of cellular transcription factors: Ring3, mSin3, ATF/CREB2, and CREB-binding protein (41)(42)(43)(44).…”

Epstein‐Barr virus latent membrane 2A (LMP2A) down‐regulates telomerase reverse transcriptase (hTERT) in epithelial cell lines

“…Interestingly, a number of viral oncogenic proteins such as human papillomavirus (HPV) E6 and the latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus have been shown capable of inducing telomerase activity through a direct transactivation of the hTERT gene and in turn contributing to the transformation process. 38,39 Given a potential role for LMP2A in EBVmediated tumorigenesis, we hypothesized a link between LMP2A and telomerase or hTERT regulation. To our surprise, LMP2A showed a significant inhibition of telomerase and hTERT expression, pointing to the diverse influence of tumor-viral proteins on telomerase/hTERT regulation.…”