Interestingly, EPZ-6438 cost siRNA-mediated inhibition of c-Myc was followed by a marked decline of hTERT expression, which was restored by concomitant exposure to saquinavir (Figure 3E). Pooled results relative to 2 separate siRNA experiments are shown in Figure 3F. Discussion The present report shows for the first time that an antiretroviral molecule belonging to PIs such as saquinavir, is able to induce a rapid

increase of telomerase activity in malignant cells of haematopoietic origin, while inhibiting their proliferative potential. In a number of different biological systems, telomerase activation is linked to increased cell proliferation and malignant cell aggressiveness [24]. However, in the case of saquinavir, our results did not show increased target cell proliferation, but rather cell inhibition. This in accordance CB-839 with previous findings of other laboratories that demonstrated antitumor effects of this drug in different experimental models [3, 4, 12, 25]. The inhibition of tumor cell growth and the pro-apoptotic effects of saquinavir have been linked to its suppressive activity on proteosoma [26], metalloproteases and neoangiogenesis [4]. All these AR-13324 cost effects appear to be mainly the consequence

of saquinavir-induced impairment of Akt activation based on molecule phosphorylation [27]. In previous studies, we have shown that saquinavir is able to increase telomerase activity of normal peripheral blood mononuclear cells [8, 9]. The present study extends this observation to ifenprodil Jurkat cells, a T leukaemia cell line. In the case of MNC, the results indicated that saquinavir increased telomerase activity either non-stimulated, or stimulated with PHA or with anti-CD3 plus anti-CD28 monoclonal antibodies. In our leukaemia model we revealed that drug-induced telomerase up-regulation was essentially due to increased expression

and activation of the reverse transcriptase component (i.e. hTERT) of the enzyme complex. This has been found in terms of either increased hTERT mRNA and protein level. The mechanism underlying this effect appears to be related to the activation of hTERT gene promoter revealed by the increased binding of nuclear extracts of Jurkat cells to the E-Box sequence of the promoter, 24 h after exposure to saquinavir, as shown by EMSA analysis illustrated in Figure 3A. Previous studies performed by Furuya et al. [28], showed that survivin up-regulates hTERT expression through a cascade of intracellular signals starting from activation of Aurora B kinase that phosphorylates c-Myc which, in turn, in association with phosphorylated SP1, binds and activates hTERT promoter. In our hands, saquinavir was found to increase the expression of c-Myc, especially in the nuclear fraction of drug-treated Jurkat cells, thus suggesting that this could be at least one of the biochemical events responsible of telomerase activation. No data are presently available to ascertain whether saquinavir is involved in survivin circuit with activating function.