HIV-Tat–Mediated Delivery of an LPTS Functional Fragment Inhibits Telomerase Activity and Tumorigenicity of Hepatoma Cells

Background & AimsHuman liver-related putative tumor suppressor (LPTS) is a gene that encodes a telomerase inhibitory protein that is similar to human Pin2/TRF1-interacting protein. The LPTS protein binds directly to the telomerase catalytic subunit (human telomerase reverse transcriptase) and suppresses telomerase activity. Telomere maintenance and telomerase activity are required for long-term proliferation of cancer cells, so LPTS might be used in anticancer strategies.MethodsThe carboxy-terminal (functional) fragment of LPTS was fused to the transactivator of transcription of human immunodeficiency virus (Tat)—an 11–amino acid peptide that translocates across the cell membrane; the TAT-fused C-terminal of LPTS (TAT–LPTS-LC) was purified and transduced into cells. Telomerase activity was identified by using the telomeric repeat amplification protocol. The effects of the TAT–LPTS-LC protein on cell proliferation and death were evaluated by colorimetric tetrazolium salt and flow cytometry analyses. Tumor growth was analyzed in nude mice.ResultsThe purified TAT–LPTS-LC protein was efficiently delivered into the cells, where it suppressed telomerase activity and shortened telomere length. TAT–LPTS-LC inhibited proliferation of telomerase-positive hepatocellular carcinoma BEL-7404 and hepatoblastoma HepG2cells and induced their death; however, it had no effect on telomerase-negative liver cell line L02 and osteosarcoma cell line Saos-2. In mice, tumor formations by BEL-7404 cells were suppressed by TAT-LPTS-LC treatments.ConclusionsTransduction of hepatoma cells with a fusion protein that contains the C-terminal, functional fragment of LPTS and human immunodeficiency virus Tat (TAT–LPTS-LC) causes telomere shortening, limits proliferation, and inhibits growth of tumors from these cells in mice. TAT–LPTS-LC inhibits telomerase activity and might be developed as an anticancer agent.