MicA sRNA links the PhoP regulon to cell envelope stress

Abstract

In addition, we found that Hfq strongly affects the expression of phoP independently of MicA, raising the possibility that even more sRNAs, which remain to be identified, could regulate PhoPQ synthesis.

Regulation of bacterial virulence gene expression by cell envelope stress responses

“…In support of a fine-tuning role, production of MicA only modestly downregulates the PhoP regulon. 84 ompT expression was reduced 30-fold by a phoP null mutation but only 3-fold when MicA RNA was overproduced from a plasmid, and only 1.2-fold when MicA was produced from the chromosome of an rseA (RpoE anti sigma factor) null mutant. 84 These effects are indeed modest, although it remains possible that some conditions might drive higher MicA production and a larger effect on the PhoP regulon.…”

“…1). 84 This discovery provides a regulatory connection between an ECF sigma factor and a 2-component system and significantly extends the mechanisms by which the RpoE response can remodel the cell envelope and control virulence gene expression.…”

“…This led to the discovery that MicA base pairs with phoPQ mRNA to inhibit phoP translation, which then reduces ompT gene expression from its PhoP-induced promoter. 84,87 Therefore, the RpoE response can downregulate the PhoPQ regulon via MicA-dependent inhibition of PhoP synthesis. Importantly, the predicted base pairing between MicA and phoPQ mRNA is conserved in several enterobacteria, including Salmonella, Shigella and Enterobacter.…”

The crucial role of PNPase in the degradation of small RNAs that are not associated with Hfq

“…MicA (previously SraD) is an antisense RNA that down-regulates the expression level of outer membrane proteins OmpA (Rasmussen et al 2005;Udekwu et al 2005) and LamB (Bossi and Figueroa-Bossi 2007), as well as the members of the PhoPQ regulon (Coornaert et al 2010).…”

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“…This is very different than the type of regulation seen in the commensal E. coli (Tu et al, 2006), indicating that while there is some similarity in the genes expressed between the two, the regulation of the alternative sigma pathways is not the same. Interestingly, RpoE seems to be involved in the regulation of PhoP/PhoQ activity through Hfq, the same RNA chaperone through which it mediates RpoS expression (Coornaert et al, 2010).…”