Identification of CsrC and Characterization of Its Role in Epithelial Cell Invasion in Salmonella enterica Serovar Typhimurium

Abstract

The csr regulatory system of Salmonella regulates the expression of the genes of Salmonella pathogenicity island 1 (SPI1) required for the invasion of epithelial cells. This system consists of the posttranscriptional regulator CsrA and an untranslated regulatory RNA, CsrB, that opposes the action of CsrA. Here we identify and characterize the role of a second regulatory RNA, CsrC, whose ortholog was discovered previously in Escherichia coli. We show that a mutant of csrC has only mild defects in invasion and the expression of SPI1 genes, as does a mutant of csrB, but that a double csrB csrC mutant is markedly deficient in these properties, suggesting that the two regulatory RNAs play redundant roles in the control of invasion. We further show that CsrC, like CsrB, is controlled by the BarA/SirA two-component regulator but that a csrB csrC mutant exhibits a loss of invasion equivalent to that of a barA or sirA mutant, indicating that much of the effect of BarA/SirA on invasion functions through its control of CsrB and CsrC. In addition to their control by BarA/SirA, each regulatory RNA is also controlled by other components of the csr system. The loss of csrB was found to increase the level of CsrC by sevenfold, while the loss of csrC increased CsrB by nearly twofold. Similarly, the overexpression of csrA increased CsrC by nearly 11-fold and CsrB by 3-fold and also significantly increased the stability of both RNAs.

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…UvrY directly binds to the csrB and csrC promoters in vitro (63,73), yet the details of its transcription activation mechanism have not been determined. Though Csr/Rsm-inhibitory sRNAs of various species may bear little sequence identity outside the CsrA/RsmA binding sequences, their expression in most cases is highly dependent on the UvrY ortholog (73)(74)(75)(76)(77)(78)(79). Whether UvrY and its various orthologs have additional regulatory roles remains to be determined, although the GacA protein of P. aeruginosa was proposed only to regulate Rsm sRNA transcription (80).…”

“…Another study identified barA and csrB as regulators of SPI1, which led to further studies on the effects of csrA (271,272). CsrC was identified by its homology with E. coli csrC (77,273). Mutations in barA, sirA, csrB, and csrC all cause decreases in SPI1 gene expression.…”

Comprehensive Alanine-scanning Mutagenesis ofEscherichia coliCsrA Defines Two Subdomains of Critical Functional Importance

“…Regulation of gene expression by CsrAregulated in other species (i.e. Pseudomonas, Erwinia, Salmonella, and Vibrio) is believed to occur in a similar manner as in E. coli (15)(16)(17)(18)(19). The affinity of CsrA for a particular RNA target depends on both the RNA sequence and secondary structure (10,20,21).…”

Regulation ofSalmonella entericaPathogenicity Island 1 by DNA Adenine Methylation

“…The ferric uptake regulatory protein, Fur, and the BarA/SirA two-component system are SPI-1 activators (Fortune et al 2006;Ellermeier and Slauch 2008). In turn, HilE (Fahlen et al 2000) and Lon (Takaya et al 2003;Boddicker and Jones 2004) are negative regulators of SPI-1.…”