Proteomic insight into the effects of the Salmonella ubiquitin ligase SlrP on host cells

Abstract

The virulence of the human and animal pathogen Salmonella enterica serovar Typhimurium is dependent on two type III secretion systems. These systems translocate proteins called effectors into eukaryotic host cells. SlrP is a Salmonella type III secretion effector with ubiquitin ligase activity. Here, we used two complementary proteomic approaches, two-dimensional gel electrophoresis and iTRAQ (isobaric tags for relative and absolute quantification) to study the consequences of the presence of SlrP in human epithelial cells. We identified 37 proteins that were differentially expressed in HeLa cells expressing slrP compared to control cells. Microarray analysis revealed that more than a half of differentially expressed proteins did not show changes in the transcriptome, suggesting post-transcriptional regulation. A gene ontology overrepresentation test carried out on the differentially expressed proteins revealed enrichment of ontology terms related to several types of junctions mediating adhesion in epithelial cells. Consistently, slrP-transfected cells showed defects in migration and adhesion. Our results suggest that the modification of cell-cell interaction ability of the host could be one of the final consequences of the action of SlrP during an infection.

The NEL Family of Bacterial E3 Ubiquitin Ligases

“…In addition, a mouse model (strain 129SvJ) to study the role of single effectors in persistence, the ability of bacteria to survive in the host weeks after infection, revealed that both SspH1 and SspH2 significantly contributed to persistence of S. enterica serovar Typhimurium during systemic infection [ 194 ]. Studies carried out at the cellular level suggested that heterologous expression of SlrP in human epithelial HeLa cells induced defects in migration and adhesion [ 195 ] and increased cell death [ 105 ]. Additionally, using HeLa cells as infection model, SspH1 was shown, together with SptP, to downregulate the NF-κB-dependent expression of the pro-inflammatory cytokine IL-8 [ 137 ].…”

Host Cell Death Responses to Non-typhoidal Salmonella Infection

“…Salmonella effector proteins also induce apoptosis via these signaling pathways. SlrP is an E3 ubiquitin ligase translocated by both SPI-1 and SPI-2 that interacts with thioredoxin-1 (Trx1) and the ER chaperone protein, ERdj3 (43–46). Expression of SlrP increased cytotoxicity in infected HeLa cells, suggesting a role for SlrP in inducing intrinsic apoptosis in infected epithelial cells (43, 44).…”

Revisiting Bacterial Ubiquitin Ligase Effectors: Weapons for Host Exploitation

“…Thus, it is of fundamental importance to gain further understandings of the mechanisms operated by bacterial effectors in order to hijack host ubiquitylation pathways. For instance, among the still so many unanswered questions, identifying whether the mono-ubiquitylation of Salmonella SopB is performed by host or bacterial E3 ligases, or which E3 ligase is responsible for the apposition of K63-linked ubiquitin chains on the Salmonella outer membrane [ 103 ] and which pathogen effector targets remain to be identified [ 104 ], and could help developing novel anti-bacterial therapeutic strategies besides the common and well-established ones based on traditional antibiotics.…”