The objective is to demonstrate that, using different viral and plant genes encoding RNA silencing suppressors, it is possible to modulate the levels of cancer-specific miRNAs (upregulate tumor-suppressor miRNAs and downregulate oncogenic miRNAs). In addition, the transcriptome-wide characterization of such changes of small RNA levels will be provided. Nine different RNA silencing suppressors (viral suppressors HC-Pro, P19, 2b, AC2, P25, P1 of CfMV and of RYMV as well as cellular suppressor RLI from Arabidopsis and from human) will be transiently expressed in HeLa cells. The expression will be verified by Western blotting. After that, total small RNA fraction will be isolated from transfected cells, the corresponding cDNAs will be cloned and deep sequenced using 454 sequencer (in collaboration with Univ. of Helsinki). The subsequent bioinformatic analysis will be carried out in collaboration with Univ. of East Anglia. We expect that different suppressors affect the expression levels of many cancer-associated miRNAs. If this is true, the same suppressors’ cDNAs will be cloned into lentivirus vectors and expressed stably in PC3 prostata carcinoma cell line. Total small RNA will be isolated from these lines to be deep sequenced in the beginning of the next year of the project.