A Salmonella-encoded microRNA-like RNA facilitates bacterial invasion and intracellular replication via suppressing host cell inducible nitric oxide synthase

As the leading cause of food-borne illness in the world, Salmonella have evolved a sophisticated machinery to alter host cell function to promote virulence and survival.In this study, we compare production of non-coding RNAs between Salmonella-infected cells and mock infection cells. Using Solexa deep sequencing, we detected a panel of 19-24nt Salmonella-derived non-coding RNA fragments with considerable large copy numbers in human colonic epithelial HT-29 cells following Salmonella infection.The fragment with the highest copy number, Sal-1, was further validated by both quantitative reverse transcription polymerase chain reaction (qRT-PCR) and northern blot. The generation of Sal-1 requires the infection of host cells by Salmonella, and the processing of the Sal-1 “primary” or “precursor” to the mature Sal-1 in Salmonella-infected cells is Dicer-independent but Argonaute 2 (Ago2)-dependent. Functionally, Sal-1 suppresses the expression of colonic epithelial cell endogenous inducible nitric oxide synthase (iNOS) via targeting its open reading frame and thus reduces the bacterial resistance of host cells. Overall design: Screening and identification of Salmonella-encoded microRNA-like RNA fragments