RtsA Coordinately Regulates DsbA and theSalmonellaPathogenicity Island 1 Type III Secretion System

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Abstract
Salmonellaserovars cause a wide variety of diseases ranging from mild gastroenteritis to life-threatening systemic infections. An important step inSalmonella entericaserovar Typhimurium infection is the invasion of nonphagocytic epithelial cells, mediated by a type III secretion system (TTSS) encoded onSalmonellapathogenicity island 1 (SPI1). The SPI1 TTSS forms a needle complex through which effector proteins are injected into the cytosol of host cells, where they promote actin rearrangement and engulfment of the bacteria. We previously identified theSalmonella-specific regulatory protein RtsA, which induces expression ofhilAand, thus, the SPI1 genes. Here we show that thehilAregulators RtsA, HilD, and HilC can each induce transcription ofdsbA, which encodes a periplasmic disulfide bond isomerase. RtsA induces expression ofdsbAindependent of either the SPI1 TTSS or the only known regulator ofdsbA, the CpxRA two-component system. We show that DsbA is required for both the SPI1 and SPI2 TTSS to translocate effector proteins into the cytosol of host cells. DsbA is also required for survival during the systemic stages of infection. We also present evidence that production of SPI1 effector proteins is coupled to assembly of the TTSS. This feedback regulation is mediated at either the transcriptional or posttranscriptional level, depending on the particular effector. Loss of DsbA leads to feedback inhibition, which is consistent with the hypothesis that disulfide bond formation plays a role in TTSS assembly or function.