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Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus.
J Bacteriol. 2021 10 12; 203(21):e0030821.JB

Abstract

Salmonella enterica serovar Typhimurium utilizes a type three secretion system (T3SS) carried on the Salmonella pathogenicity island 1 (SPI1) to invade intestinal epithelial cells and induce inflammatory diarrhea. HilA activates expression of the T3SS structural genes. Expression of hyper invasion locus A (hilA) is controlled by the transcription factors HilD, HilC, and RtsA, which act in a complex feed-forward regulatory loop. The nucleoid-associated protein H-NS is a xenogeneic silencer that has a major effect on SPI1 expression. In this work, we use genetic techniques to show that disruptions of the chromosomal region surrounding hilD have a cis effect on H-NS-mediated repression of the hilD promoter; this effect occurs asymmetrically over ∼4 kb spanning the prgH-hilD intergenic region. CAT cassettes inserted at various positions in this region are also silenced in relation to the proximity to the hilD promoter. We identify a putative H-NS nucleation site, and its mutation results in derepression of the locus. Furthermore, we genetically show that HilD abrogates H-NS-mediated silencing to activate the hilD promoter. In contrast, H-NS-mediated repression of the hilA promoter, downstream of hilD, is through its control of HilD, which directly activates hilA transcription. Likewise, activation of the prgH promoter, although in a region silenced by H-NS, is strictly dependent on HilA. In summary, we propose a model in which H-NS nucleates within the hilD promoter region to polymerize and exert its repressive effect. Thus, H-NS-mediated repression of SPI1 is primarily through the control of hilD expression, with HilD capable of overcoming H-NS to autoactivate. IMPORTANCE Members of the foodborne pathogen Salmonella rely on a type III secretion system to invade intestinal epithelial cells and initiate infection. This system was acquired through horizontal gene transfer, essentially creating the Salmonella genus. Expression of this critical virulence factor is controlled by a complex regulatory network. The nucleoid protein H-NS is a global repressor of horizontally acquired genomic loci. Here, we identify the critical site of H-NS regulation in this system and show that alterations to the DNA over a surprisingly large region affect this regulation, providing important information regarding the mechanism of H-NS action.

Authors+Show Affiliations

Department of Microbiology, University of Illinois at Urbana-Champaigngrid.35403.31, Urbana, Illinois, USA.Department of Microbiology, University of Illinois at Urbana-Champaigngrid.35403.31, Urbana, Illinois, USA.

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural

Language

eng

PubMed ID

34424033

Citation

Kalafatis, Marinos, and James M. Slauch. "Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus." Journal of Bacteriology, vol. 203, no. 21, 2021, pp. e0030821.
Kalafatis M, Slauch JM. Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus. J Bacteriol. 2021;203(21):e0030821.
Kalafatis, M., & Slauch, J. M. (2021). Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus. Journal of Bacteriology, 203(21), e0030821. https://doi.org/10.1128/JB.00308-21
Kalafatis M, Slauch JM. Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus. J Bacteriol. 2021 10 12;203(21):e0030821. PubMed PMID: 34424033.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Long-Distance Effects of H-NS Binding in the Control of hilD Expression in the Salmonella SPI1 Locus. AU - Kalafatis,Marinos, AU - Slauch,James M, Y1 - 2021/08/23/ PY - 2021/8/24/pubmed PY - 2021/12/22/medline PY - 2021/8/23/entrez KW - H-NS KW - SPI1 KW - Salmonella SP - e0030821 EP - e0030821 JF - Journal of bacteriology JO - J Bacteriol VL - 203 IS - 21 N2 - Salmonella enterica serovar Typhimurium utilizes a type three secretion system (T3SS) carried on the Salmonella pathogenicity island 1 (SPI1) to invade intestinal epithelial cells and induce inflammatory diarrhea. HilA activates expression of the T3SS structural genes. Expression of hyper invasion locus A (hilA) is controlled by the transcription factors HilD, HilC, and RtsA, which act in a complex feed-forward regulatory loop. The nucleoid-associated protein H-NS is a xenogeneic silencer that has a major effect on SPI1 expression. In this work, we use genetic techniques to show that disruptions of the chromosomal region surrounding hilD have a cis effect on H-NS-mediated repression of the hilD promoter; this effect occurs asymmetrically over ∼4 kb spanning the prgH-hilD intergenic region. CAT cassettes inserted at various positions in this region are also silenced in relation to the proximity to the hilD promoter. We identify a putative H-NS nucleation site, and its mutation results in derepression of the locus. Furthermore, we genetically show that HilD abrogates H-NS-mediated silencing to activate the hilD promoter. In contrast, H-NS-mediated repression of the hilA promoter, downstream of hilD, is through its control of HilD, which directly activates hilA transcription. Likewise, activation of the prgH promoter, although in a region silenced by H-NS, is strictly dependent on HilA. In summary, we propose a model in which H-NS nucleates within the hilD promoter region to polymerize and exert its repressive effect. Thus, H-NS-mediated repression of SPI1 is primarily through the control of hilD expression, with HilD capable of overcoming H-NS to autoactivate. IMPORTANCE Members of the foodborne pathogen Salmonella rely on a type III secretion system to invade intestinal epithelial cells and initiate infection. This system was acquired through horizontal gene transfer, essentially creating the Salmonella genus. Expression of this critical virulence factor is controlled by a complex regulatory network. The nucleoid protein H-NS is a global repressor of horizontally acquired genomic loci. Here, we identify the critical site of H-NS regulation in this system and show that alterations to the DNA over a surprisingly large region affect this regulation, providing important information regarding the mechanism of H-NS action. SN - 1098-5530 UR - https://www.unboundmedicine.com/medline/citation/34424033/Long_Distance_Effects_of_H_NS_Binding_in_the_Control_of_hilD_Expression_in_the_Salmonella_SPI1_Locus_ L2 - https://journals.asm.org/doi/10.1128/JB.00308-21?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -