Abstract
BackgroundSaquinavir, a protease inhibitor utilized in HIV infection, shows antitumor activity in various experimental models. In previous studies performed in our laboratory the drug was found to induce a substantial increase of telomerase activity in normal peripheral blood mononuclear cells. Aim of the present investigation was to test whether saquinavir was able to increase telomerase activity and the expression of the catalytic subunit of telomerase, hTERT, in human malignant hematopoietic cells.MethodsHuman Jurkat CD4+ T cell leukaemia cell line was used throughout the present study. The antiproliferative effect of saquinavir was tested by the MTT assay. Telomerase activity was determined according to the telomeric repeat amplification protocol. The expression of hTERT mRNA was semi-quantitative evaluated by RT-PCR amplification and quantitative Real Time PCR. The binding of the transcription factor c-Myc to its specific E-Box DNA binding-site of hTERT promoter was analyzed by Electophoretic Mobility Shift Assay (EMSA). The amount of c-Myc in cytoplasm and nucleus of leukemia cells was determined by Western Blot analysis, and c-Myc down-regulation was obtained by siRNA transfection.ResultsSaquinavir produced a substantial increase of telomerase activity in Jurkat cells in vitro without increasing but rather reducing target cell proliferation rate. Telomerase up-regulation appeared to be the result of enhanced expression of hTERT. Saquinavir-mediated up-regulation of hTERT gene was the result of the increased binding of proteins to the E-Box sequence of the promoter. Moreover, saquinavir amplified the expression of c-Myc especially in the nuclear cell fraction. The direct influence of saquinavir on this transcription factor was also demonstrated by the antagonistic effect of the drug on siRNA induced c-Myc suppression. Since c-Myc is the main responsible for hTERT transcription, these findings suggest that the main mechanism underlying saquinavir-induced telomerase activation is mediated by c-Myc up-regulation.ConclusionsSaquinavir augments hTERT expression while inhibiting leukemic cell growth. Experimental evidences show that this effect is mediated by saquinavir-influenced increase of c-Myc levels. This could have relevance in terms of enhanced hTERT-dependent tumor cell immunogenicity and suggests new paharmacological approaches interfering with c-Myc dependent pathways.
Highlights
Saquinavir, a protease inhibitor utilized in HIV infection, shows antitumor activity in various experimental models
Influence of saquinavir on telomerase activity of Jurkat cell line Telomerase is a specialized RNA template-containing reverse transcriptase able to compensate for telomeric loss occurring at each cell replication, which is reactivated in tumor cells [13]
We analyzed the effect of saquinavir on telomerase activity of Jurkat cells after 24, 48 and 72 h of treatment
Summary
Saquinavir, a protease inhibitor utilized in HIV infection, shows antitumor activity in various experimental models. Several protease inhibitors (PI) have been long term FDAapproved agents for the treatment of human immunodeficiency virus (HIV-1) infection [1] These compounds [2,3,4] including the NO derivative of saquinavir [5,6], have shown noticeable antitumor activity, that is distinct from their antiviral properties. This finding has been originated by the observation that patients taking antiretroviral protease inhibitors showed a lower incidence of infection-associated malignancies leading to the hypothesis that these drugs could have antineoplastic properties [7]. The direct antitumor effects of saquinavir was confirmed by McLean et al [7] who demonstrated how the drug is able to induce endoplasmic reticulum stress, autophagy, and apoptosis in human ovarian cancer cells in vitro
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