Publications by authors named "Lauren M Sheehan"

12 Publications

  • Page 1 of 1

The Small Molecule H89 Inhibits Inclusion Growth and Production of Infectious Progeny.

Infect Immun 2021 06 16;89(7):e0072920. Epub 2021 Jun 16.

Department of Developmental and Cell Biology, University of California, Irvine, California, USA.

is an obligate intracellular bacterium and the most common reportable cause of human infection in the United States. This pathogen proliferates inside a eukaryotic host cell, where it resides within a membrane-bound compartment called the chlamydial inclusion. It has an unusual developmental cycle, marked by conversion between a replicating form, the reticulate body (RB), and an infectious form, the elementary body (EB). We found that the small molecule H89 slowed inclusion growth and decreased overall RB replication by 2-fold but caused a 25-fold reduction in infectious EBs. This disproportionate effect on EB production was mainly due to a defect in RB-to-EB conversion and not to the induction of chlamydial persistence, which is an altered growth state. Although H89 is a known inhibitor of specific protein kinases and vesicular transport to and from the Golgi apparatus, it did not cause these anti-chlamydial effects by blocking protein kinase A or C or by inhibiting protein or lipid transport. Thus, H89 is a novel anti-chlamydial compound that has a unique combination of effects on an intracellular infection.
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http://dx.doi.org/10.1128/IAI.00729-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8373235PMC
June 2021

A central role for the transcriptional regulator VtlR in small RNA-mediated gene regulation in Agrobacterium tumefaciens.

Sci Rep 2020 09 11;10(1):14968. Epub 2020 Sep 11.

Center for One Health Research, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24060, USA.

LysR-type transcriptional regulators (LTTRs) are the most common type of transcriptional regulators in prokaryotes and function by altering gene expression in response to environmental stimuli. In the class Alphaproteobacteria, a conserved LTTR named VtlR is critical to the establishment of host-microbe interactions. In the mammalian pathogen Brucella abortus, VtlR is required for full virulence in a mouse model of infection, and VtlR activates the expression of abcR2, which encodes a small regulatory RNA (sRNA). In the plant symbiont Sinorhizobium meliloti, the ortholog of VtlR, named LsrB, is involved in the symbiosis of the bacterium with alfalfa. Agrobacterium tumefaciens is a close relative of both B. abortus and S. meliloti, and this bacterium is the causative agent of crown gall disease in plants. In the present study, we demonstrate that VtlR is involved in the ability of A. tumefaciens to grow appropriately in artificial medium, and an A. tumefaciens vtlR deletion strain is defective in motility, biofilm formation, and tumorigenesis of potato discs. RNA-sequencing analyses revealed that more than 250 genes are dysregulated in the ∆vtlR strain, and importantly, VtlR directly controls the expression of three sRNAs in A. tumefaciens. Taken together, these data support a model in which VtlR indirectly regulates hundreds of genes via manipulation of sRNA pathways in A. tumefaciens, and moreover, while the VtlR/LsrB protein is present and structurally conserved in many members of the Alphaproteobacteria, the VtlR/LsrB regulatory circuitry has diverged in order to accommodate the unique environmental niche of each organism.
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http://dx.doi.org/10.1038/s41598-020-72117-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7486931PMC
September 2020

Characterizing the transport and utilization of the neurotransmitter GABA in the bacterial pathogen Brucella abortus.

PLoS One 2020 26;15(8):e0237371. Epub 2020 Aug 26.

Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Blacksburg, Virginia, United States of America.

The neurotransmitter gamma-aminobutyric acid (GABA) is the most abundant inhibitory neurotransmitter in the human brain; however, it is becoming more evident that this non-proteinogenic amino acid plays multiple physiological roles in biology. In the present study, the transport and function of GABA is studied in the highly infectious intracellular bacterium Brucella abortus. The data show that 3H-GABA is imported by B. abortus under nutrient limiting conditions and that the small RNAs AbcR1 and AbcR2 negatively regulate this transport. A specific transport system, gts, is responsible for the transport of GABA as determined by measuring 3H-GABA transport in isogenic deletion strains of known AbcR1/2 regulatory targets; however, this locus is unnecessary for Brucella infection in BALB/c mice. Similar assays revealed that 3H-GABA transport is uninhibited by the 20 standard proteinogenic amino acids, representing preference for the transport of 3H-GABA. Metabolic studies did not show any potential metabolic utilization of GABA by B. abortus as a carbon or nitrogen source, and RNA sequencing analysis revealed limited transcriptional differences between B. abortus 2308 with or without exposure to GABA. While this study provides evidence for GABA transport by B. abortus, questions remain as to why and when this transport is utilized during Brucella pathogenesis.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237371PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7449393PMC
October 2020

The Endoribonuclease RNase E Coordinates Expression of mRNAs and Small Regulatory RNAs and Is Critical for the Virulence of Brucella abortus.

J Bacteriol 2020 09 23;202(20). Epub 2020 Sep 23.

Center for One Health Research, Virginia-Maryland College of Veterinary Medicine, Blacksburg, Virginia, USA

RNases are key regulatory components in prokaryotes, responsible for the degradation and maturation of specific RNA molecules at precise times. Specifically, RNases allow cells to cope with changes in their environment through rapid alteration of gene expression. To date, few RNases have been characterized in the mammalian pathogen In the present work, we sought to investigate several RNases in and determine what role, if any, they have in pathogenesis. Of the 4 RNases reported in this study, the highly conserved endoribonuclease, RNase E, was found to play an integral role in the virulence of Although , which encodes RNase E, is essential in , we were able to generate a strain encoding a defective version of RNase E lacking the C-terminal portion of the protein, and this strain (-tnc) was attenuated in a mouse model of infection. RNA-sequencing analysis revealed massive RNA dysregulation in -tnc, with 122 upregulated and 161 downregulated transcripts compared to the parental strain. Interestingly, several mRNAs related to metal homeostasis were significantly decreased in the -tnc strain. We also identified a small regulatory RNA (sRNA), called Bsr4, that exhibited significantly elevated levels in -tnc, demonstrating an important role for RNase E in sRNA-mediated regulatory pathways in Overall, these data highlight the importance of RNase E in , including the role of RNase E in properly controlling mRNA levels and contributing to virulence in an animal model of infection. Brucellosis is a debilitating disease of humans and animals globally, and there is currently no vaccine to combat human infection by spp. Moreover, effective antibiotic treatment in humans is extremely difficult and can lead to disease relapse. Therefore, it is imperative that systems and pathways be identified and characterized in the brucellae so new vaccines and therapies can be generated. In this study, we describe the impact of the endoribonuclease RNase E on the control of mRNA and small regulatory RNA (sRNA) levels in , as well as the importance of RNase E for the full virulence of This work greatly enhances our understanding of ribonucleases in the biology and pathogenesis of spp.
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http://dx.doi.org/10.1128/JB.00240-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515240PMC
September 2020

The Repressor Function of the Late Regulator EUO Is Enhanced by the Plasmid-Encoded Protein Pgp4.

J Bacteriol 2020 03 26;202(8). Epub 2020 Mar 26.

Department of Microbiology and Molecular Genetics, University of California, Irvine, California, USA

A critical step in intracellular infection is the production of infectious progeny through the expression of late genes. This differentiation step involves conversion from a reticulate body (RB), which is the replicating form of the bacterium, into an elementary body (EB), which is the developmental form that spreads the infection to a new host cell. EUO is an important chlamydial transcription factor that controls the expression of late genes, but the mechanisms that regulate EUO are not known. We report that a plasmid-encoded protein, Pgp4, enhanced the repressor activity of EUO. Pgp4 did not function as a transcription factor because it did not bind or directly modulate transcription of its target promoters. Instead, Pgp4 increased the ability of EUO to bind and repress EUO-regulated promoters and physically interacted with EUO in pulldown assays with recombinant proteins. We detected earlier onset of EUO-dependent late gene expression by immunofluorescence microscopy in Pgp4-deficient and strains. In addition, the absence of Pgp4 led to earlier onset of RB-to-EB conversion in These data support a role for Pgp4 as a negative regulator of chlamydial transcription that delays late gene expression. Our studies revealed that Pgp4 also has an EUO-independent function as a positive regulator of chlamydial transcription. is an important human pathogen that causes more than 150 million active cases of genital and eye infection in the world. This obligate intracellular bacterium produces infectious progeny within an infected human cell through the expression of late chlamydial genes. We showed that the ability of a key chlamydial transcription factor, EUO, to repress late genes was enhanced by a plasmid-encoded protein, Pgp4. In addition, studies with Pgp4-deficient strains provide evidence that Pgp4 delays late gene expression in infected cells. Thus, Pgp4 is a novel regulator of late gene expression in through its ability to enhance the repressor function of EUO.
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http://dx.doi.org/10.1128/JB.00793-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7099128PMC
March 2020

Characterization of Three Small Proteins in Brucella abortus Linked to Fucose Utilization.

J Bacteriol 2018 09 24;200(18). Epub 2018 Aug 24.

Department of Biomedical Sciences and Pathobiology, Center for One Health Research, VA-MD College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA

Elucidating the function of proteins <50 amino acids in length is no small task. Nevertheless, small proteins can play vital roles in the lifestyle of bacteria and influence the virulence of pathogens; thus, the investigation of the small proteome is warranted. Recently, our group identified the protein VtlR as a transcriptional activator of four genes, one of which is the well-studied small regulatory RNA AbcR2, while the other three genes encode hypothetical small proteins, two of which are highly conserved among the order This study provides evidence that all three genes encode authentic small proteins and that all three are highly expressed under oxidative stress, low-pH, and stationary-phase growth conditions. Fractionation of the cells revealed that the proteins are localized to the membranes of We demonstrate that the small proteins under the transcriptional control of VtlR are not accountable for attenuation observed with the deletion strain. However, there is an association between VtlR-regulated genes and growth inhibition in the presence of the sugar l-fucose. Subsequent transcriptomic analyses revealed that initiates the transcription of a locus encoding a putative sugar transport and utilization system when the bacteria are cultured in the presence of l-fucose. Altogether, our observations characterize the role of the VtlR-controlled small proteins BAB1_0914, BAB2_0512, and BAB2_0574 in the biology of , particularly in the capacity of the bacteria to utilize l-fucose. Despite being one of the most common zoonoses worldwide, there is currently no human vaccine to combat brucellosis. Therefore, a better understanding of the pathogenesis and biology of spp., the causative agent of brucellosis, is essential for the discovery of novel therapeutics against these highly infectious bacteria. In this study, we further characterize the virulence-associated transcriptional regulator VtlR in Our findings not only shed light on our current understanding of a virulence related genetic system in spp. but also increase our knowledge of small proteins in the field of bacteriology.
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http://dx.doi.org/10.1128/JB.00127-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6112010PMC
September 2018

Endoribonuclease YbeY Is Linked to Proper Cellular Morphology and Virulence in Brucella abortus.

J Bacteriol 2018 06 24;200(12). Epub 2018 May 24.

Department of Biomedical Sciences and Pathobiology, VA-MD College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA

The YbeY endoribonuclease is one of the best-conserved proteins across the kingdoms of life. In the present study, we demonstrated that YbeY in is linked to a variety of important activities, including proper cellular morphology, mRNA transcript levels, and virulence. Deletion of in led to a small-colony phenotype when the bacteria were grown on agar medium, as well as to significant aberrations in the morphology of the bacterial cell as evidenced by electron microscopy. Additionally, compared to the parental strain, the Δ strain was significantly attenuated in both macrophage and mouse models of infection. The Δ strain also showed increased sensitivities to several -applied stressors, including bile acid, hydrogen peroxide, SDS, and paraquat. Transcriptomic analysis revealed that a multitude of mRNA transcripts are dysregulated in the Δ strain, and many of the identified mRNAs encode proteins involved in metabolism, nutrient transport, transcriptional regulation, and flagellum synthesis. We subsequently constructed gene deletion strains of the most highly dysregulated systems, and several of the YbeY-linked gene deletion strains exhibited defects in the ability of the bacteria to survive and replicate in primary murine macrophages. Taken together, these data establish a clear role for YbeY in the biology and virulence of ; moreover, this work further illuminates the highly varied roles of this widely conserved endoribonuclease in bacteria. spp. are highly efficient bacterial pathogens of animals and humans, causing significant morbidity and economic loss worldwide, and relapse of disease often occurs following antibiotic treatment of human brucellosis. As such, novel therapeutic strategies to combat infections are needed. Ribonucleases in the brucellae are understudied, and these enzymes represent elements that may be potential targets for future treatment approaches. The present work demonstrates the importance of the YbeY endoribonuclease for cellular morphology, efficient control of mRNA levels, and virulence in Overall, the results of this study advance our understanding of the critical roles of YbeY in the pathogenesis of the intracellular brucellae and expand our understanding of this highly conserved RNase.
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http://dx.doi.org/10.1128/JB.00105-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5971472PMC
June 2018

An account of evolutionary specialization: the AbcR small RNAs in the Rhizobiales.

Mol Microbiol 2018 Jan 17;107(1):24-33. Epub 2017 Nov 17.

Department of Biomedical Sciences and Pathobiology, VA-MD College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA.

The AbcR small RNAs (sRNAs) are a fascinating example of two highly conserved sRNAs that differ tremendously at the functional level among organisms. From their transcriptional activation to their regulatory capabilities, the AbcR sRNAs exhibit varying characteristics in three well-studied bacteria belonging to the Rhizobiales order: the plant symbiont Sinorhizobium meliloti, the plant pathogen Agrobacterium tumefaciens, and the animal pathogen Brucella abortus. This review outlines the similarities and differences of the AbcR sRNAs between each of these organisms, and discusses reasons as to why this group of sRNAs has diverged in their genetic organization and regulatory functions across species. In the end, this review will shed light on how regulatory systems, although seemingly conserved among bacteria, can vary based on the environmental niche and lifestyle of an organism.
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http://dx.doi.org/10.1111/mmi.13869DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5752129PMC
January 2018

Proline utilization system is required for infection by the pathogenic α-proteobacterium Brucella abortus.

Microbiology (Reading) 2017 07 21;163(7):970-979. Epub 2017 Jul 21.

Department of Biomedical Sciences and Pathobiology, Center for Molecular Medicine and Infectious Diseases, VA-MD College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24060, USA.

Proline utilization (Put) systems have been described in a number of bacteria; however, the importance and functionality of the Put system in the intracellular pathogen Brucellaabortus has not been explored. Generally, bacterial Put systems are composed of the bifunctional enzyme proline dehydrogenase PutA and its transcriptional activator PutR. Here, we demonstrate that the genes putA (bab2_0518) and putR (bab2_0517) are critical for the chronic infection of mice by B. abortus, but putA and putR are not required for the survival and replication of the bacteria in naive macrophages. Additionally, in vitro experiments revealed that putR is necessary for the ability of the bacteria to withstand oxidative stress, as a ΔputR deletion strain is hypersensitive to hydrogen peroxide exposure. Quantitative reverse transcription-PCR and putA-lacZ transcriptional reporter studies revealed that PutR acts as a transcriptional activator of putA in Brucella, and electrophoretic mobility shift assays confirmed that PutR binds directly to the putA promoter region. Biochemical analyses demonstrated that a purified recombinant B. abortus PutA protein possesses quintessential proline dehydrogenase activity, as PutA is capable of catalysing the conversion of proline to glutamate. Altogether, these data are the first to reveal that the Put system plays a significant role in the ability of B. abortus to replicate and survive within its host, as well as to describe the genetic regulation and biochemical activity of the Put system in Brucella.
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http://dx.doi.org/10.1099/mic.0.000490DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5737144PMC
July 2017

A 6-Nucleotide Regulatory Motif within the AbcR Small RNAs of Mediates Host-Pathogen Interactions.

mBio 2017 06 6;8(3). Epub 2017 Jun 6.

Department of Biomedical Sciences and Pathobiology, Center for Molecular Medicine and Infectious Diseases, VA-MD College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA

In , two small RNAs (sRNAs), AbcR1 and AbcR2, are responsible for regulating transcripts encoding ABC-type transport systems. AbcR1 and AbcR2 are required for virulence, as a double chromosomal deletion of both sRNAs results in attenuation in mice. Although these sRNAs are responsible for targeting transcripts for degradation, the mechanism utilized by the AbcR sRNAs to regulate mRNA in has not been described. Here, two motifs (M1 and M2) were identified in AbcR1 and AbcR2, and complementary motif sequences were defined in AbcR-regulated transcripts. Site-directed mutagenesis of M1 or M2 or of both M1 and M2 in the sRNAs revealed transcripts to be targeted by one or both motifs. Electrophoretic mobility shift assays revealed direct, concentration-dependent binding of both AbcR sRNAs to a target mRNA sequence. These experiments genetically and biochemically characterized two indispensable motifs within the AbcR sRNAs that bind to and regulate transcripts. Additionally, cellular and animal models of infection demonstrated that only M2 in the AbcR sRNAs is required for virulence. Furthermore, one of the M2-regulated targets, BAB2_0612, was found to be critical for the virulence of in a mouse model of infection. Although these sRNAs are highly conserved among , the present report displays how gene regulation mediated by the AbcR sRNAs has diverged to meet the intricate regulatory requirements of each particular organism and its unique biological niche. Small RNAs (sRNAs) are important components of bacterial regulation, allowing organisms to quickly adapt to changes in their environments. The AbcR sRNAs are highly conserved throughout the and negatively regulate myriad transcripts, many encoding ABC-type transport systems. In , AbcR1 and AbcR2 are functionally redundant, as only a double (/) deletion results in attenuation and In the present study, we confirmed that the AbcR sRNAs have redundant regulatory functions and defined two six-nucleotide motifs, M1 and M2, that the AbcR sRNAs utilize to control gene expression. Importantly, only M2 was linked to virulence. Further investigation of M2-regulated targets identified BAB2_0612 as critical for colonization of in mice, highlighting the significance of AbcR M2-regulated transcripts for infection. Overall, our findings define the molecular mechanism of the virulence-associated AbcR system in the pathogenic bacterium .
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http://dx.doi.org/10.1128/mBio.00473-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5461406PMC
June 2017

A LysR-family transcriptional regulator required for virulence in Brucella abortus is highly conserved among the α-proteobacteria.

Mol Microbiol 2015 Oct 14;98(2):318-28. Epub 2015 Aug 14.

Department of Biomedical Sciences and Pathobiology, Center for Molecular Medicine and Infectious Diseases, VA-MD College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24060, USA.

Small RNAs are principal elements of bacterial gene regulation and physiology. Two small RNAs in Brucella abortus, AbcR1 and AbcR2, are required for wild-type virulence. Examination of the abcR loci revealed the presence of a gene encoding a LysR-type transcriptional regulator flanking abcR2 on chromosome 1. Deletion of this lysR gene (bab1_1517) resulted in the complete loss of abcR2 expression while no difference in abcR1 expression was observed. The B. abortus bab1_1517 mutant strain was significantly attenuated in macrophages and mice, and bab1_1517 was subsequently named vtlR for virulence-associated transcriptional LysR-family regulator. Microarray analysis revealed three additional genes encoding small hypothetical proteins also under the control of VtlR. Electrophoretic mobility shift assays demonstrated that VtlR binds directly to the promoter regions of abcR2 and the three hypothetical protein-encoding genes, and DNase I footprint analysis identified the specific nucleotide sequence in these promoters that VtlR binds to and drives gene expression. Strikingly, orthologs of VtlR are encoded in a wide range of host-associated α-proteobacteria, and it is likely that the VtlR genetic system represents a common regulatory circuit critical for host-bacterium interactions.
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http://dx.doi.org/10.1111/mmi.13123DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5846693PMC
October 2015

Coordinated zinc homeostasis is essential for the wild-type virulence of Brucella abortus.

J Bacteriol 2015 May 17;197(9):1582-91. Epub 2015 Feb 17.

Department of Biomedical Sciences and Pathobiology, Center for Molecular Medicine and Infectious Diseases, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA

Unlabelled: Metal homeostasis in bacterial cells is a highly regulated process requiring intricately coordinated import and export, as well as precise sensing of intracellular metal concentrations. The uptake of zinc (Zn) has been linked to the virulence of Brucella abortus; however, the capacity of Brucella strains to sense Zn levels and subsequently coordinate Zn homeostasis has not been described. Here, we show that expression of the genes encoding the zinc uptake system ZnuABC is negatively regulated by the Zn-sensing Fur family transcriptional regulator, Zur, by direct interactions between Zur and the promoter region of znuABC. Moreover, the MerR-type regulator, ZntR, controls the expression of the gene encoding the Zn exporter ZntA by binding directly to its promoter. Deletion of zur or zntR alone did not result in increased zinc toxicity in the corresponding mutants; however, deletion of zntA led to increased sensitivity to Zn but not to other metals, such as Cu and Ni, suggesting that ZntA is a Zn-specific exporter. Strikingly, deletion of zntR resulted in significant attenuation of B. abortus in a mouse model of chronic infection, and subsequent experiments revealed that overexpression of zntA in the zntR mutant is the molecular basis for its decreased virulence.

Importance: The importance of zinc uptake for Brucella pathogenesis has been demonstrated previously, but to date, there has been no description of how overall zinc homeostasis is maintained and genetically controlled in the brucellae. The present work defines the predominant zinc export system, as well as the key genetic regulators of both zinc uptake and export in Brucella abortus. Moreover, the data show the importance of precise coordination of the zinc homeostasis systems as disregulation of some elements of these systems leads to the attenuation of Brucella virulence in a mouse model. Overall, this study advances our understanding of the essential role of zinc in the pathogenesis of intracellular bacteria.
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http://dx.doi.org/10.1128/JB.02543-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4403653PMC
May 2015
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