Background and objective: As a new cryptolepine derivative containing indole and quinoline structures, SYUIQ-5 has been reported to induce and stabilize G-quadruplex, inhibit c-myc promoter and telomerase activity. This study was to investigate autophagy induced by a G-quadruplex ligand SYUIQ-5 and its mechanisms in nasopharyngeal cancer cells.
Methods: The protein levels of microtubule-associated protein 1 light chain 3 (LC3), Akt, p-Akt, autophagy-related genes BNIP3 (adenocarcinoma E1B19KD interacting protein 3) and Beclin1 were determined by Western blot in nasopharyngeal cancer cell lines CNE1, CNE2 and HONE1. The mRNA levels of LC3 and BNIP3 was detected using reverse transcription polymerase chain reaction (RT-PCR). RNA interference was used to block the expression of BNIP3 and the effect of BNIP3 was evaluated in SYUIQ-5-induced autophagy. The localization of FOXO3a was observed using confocal immunofluorescence.
Results: The protein and mRNA levels of LC3 in CNE1, CNE2 and HONE1 were up-regulated in a dose-dependent manner after being treated with 0.25-2 microg/mL SYUIQ-5 for 48 h. Incubation of CNE2 cells with SYUIQ-5 markedly inhibited the phosphorylation of Akt, but did not statistically change the total Akt level. After incubation with 3 microg/mL SYUIQ-5 for 24 h, nuclear translocation of FOXO3a was observed under confocal immunofluorescence in CNE2 cells. Autophagy-related gene BNIP3 was significantly elevated in nasopharyngeal cancer cells, whereas Beclin1 was not significantly changed. Knockdown of BNIP3 expression using small interfering RNA caused LC3-II down-regulation.
Conclusion: SYUIQ-5 induces autophagy in cancer cells. This may be related to SYUIQ-5-mediated p-Akt down-regulation and FOXO3a nuclear translocation, which promot LC3 transcription. BNIP3 is involved in SYUIQ-5 induced autophagy.