Gre factors-mediated control of hilD transcription is essential for the invasion of epithelial cells by Salmonella enterica serovar Typhimurium

Abstract

The invasion of epithelial cells by Salmonella enterica serovar Typhimurium is a very tightly regulated process. Signaling cascades triggered by different environmental and physiological signals converge to control HilD, an AraC regulator that coordinates the expression of several virulence factors. The expression of hilD is modulated at several steps of the expression process. Here, we report that the invasion of epithelial cells by S. Typhimurium strains lacking the Gre factors, GreA and GreB, is impaired. By interacting with the RNA polymerase secondary channel, the Gre factors prevent backtracking of paused complexes to avoid arrest during transcriptional elongation. Our results indicate that the Gre factors are required for the expression of the bacterial factors needed for epithelial cell invasion by modulating expression of HilD. This regulation does not occur at transcription initiation and depends on the capacity of the Gre factors to prevent backtracking of the RNA polymerase. Remarkably, genetic analyses indicate that the 3’-untranslated region (UTR) of hilD is required for Gre-mediated regulation of hilD expression. Our data provide new insight into the complex regulation of S. Typhimurium virulence and highlight the role of the hilD 3’-UTR as a regulatory motif.

The Small RNA PinT Contributes to PhoP-Mediated Regulation of the Salmonella Pathogenicity Island 1 Type III Secretion System in Salmonella enterica Serovar Typhimurium

“…2C), suggesting that PinT also directly represses rtsA translation in Salmonella. Lastly, we addressed whether overexpression of PinT affects hilD expression via the 3= UTR, which is known to affect the stability of the hilD mRNA (24,25). It is possible that PinT binding to the 3= UTR could lead to degradation of the mRNA, contributing to decreased expression of hilA.…”

“…1). Several regulatory systems have been implicated in controlling hilD mRNA stability or translation, acting at either the 5= untranslated region (UTR) or 3= UTR of the hilD mRNA (20)(21)(22)(23)(24)(25). Other systems directly control hilA expression or more globally affect the entire system (12,(26)(27)(28).…”

Oxygen‐dependent regulation of SPI1 type three secretion system by small RNAs in Salmonella enterica serovar Typhimurium

“…The hilD mRNA also has an unusually long ~300 nt 3′ UTR, which apparently affects the stability of the message. Several mechanisms of regulation at the 3′ UTR have been characterized (Lopez‐Garrido et al , ; Gaviria‐Cantin et al , ; El Mouali et al , ).…”

Involvement of Transcription Elongation Factor GreA in Mycobacterium Viability, Antibiotic Susceptibility, and Intracellular Fitness

“…Furthermore, our data demonstrated that glgX, a gene involved in starch and sucrose metabolism, regulated by the anti-backtracking activity of GreA is required for the optimal growth of M. smegmatis. Recently, studies in Salmonella enterica serovar Typhimurium demonstrated that GreA-mediated rescue of backtracked paused complexes during transcription is crucial in promoting hilD expression through its 3 -UTR (Gaviria-Cantin et al, 2017). In addition, GreA enhanced expression of several E. coli RNAP promoters in vitro (Erie et al, 1993;Feng et al, 1994;Hsu et al, 1995;Maddalena et al, 2016).…”