Abstract
BackgroundBacteria engage cell surface receptors and intracellular signaling molecules to enter the cell. Unc119 is an adaptor protein, which interacts with receptors and tyrosine kinases. Its role in bacterial invasion of cells is unknown.Methodology/Principal FindingsWe used biochemical, molecular and cell biology approaches to identify the binding partners of Unc119, and to study the effect of Unc119 on Abl family kinases and Shigella infection. We employed loss-of-function and gain-in-function approaches to study the effect of Unc119 in a mouse model of pulmonary shigellosis. Unc119 interacts with Abl family kinases and inhibits their kinase activity. As a consequence, it inhibits Crk phosphorylation, which is essential for Shigella infection. Unc119 co-localizes with Crk and Shigella in infected cells. Shigella infectivity increases in Unc119-deficient epithelial and macrophage cells. In a mouse model of shigellosis cell-permeable TAT-Unc119 inhibits Shigella infection. Conversely, Unc119 knockdown in vivo results in enhanced bacterial invasion and increased lethality. Unc119 is an inducible protein. Its expression is upregulated by probacteria and bacterial products such as lipopolysacharide and sodium butyrate. The latter inhibits Shigella infection in mouse lungs but is ineffective in Unc119 deficiency.ConclusionsUnc119 inhibits signaling pathways that are used by Shigella to enter the cell. As a consequence it provides partial but significant protection from Shigella infections. Unc119 induction in vivo boosts host defense against infections.
Highlights
During the bacterial infection various proteins from the pathogen and the host participate in bacterial entry and cellular response [1]
We assumed that Unc119 would promote bacterial infection because of its role in Src family kinases (SFKs) activation
To study the effect of Unc119 on bacterial infection, we knocked down Unc119 expression by 70–90% in human epithelial cells (Caco2 and HeLA) and mouse embryonic fibroblasts (NIH 3T3, abbreviated as 3T3) using Small interfering RNA (siRNA) (Figure 1A) and infected them with Shigella flexneri
Summary
During the bacterial infection various proteins from the pathogen and the host participate in bacterial entry and cellular response [1]. Shigella delivers multiple virulence proteins into host cells through the type III secretion system (TSS) [3,4] One of these effector proteins is IpaB, which interacts with the mammalian cell surface receptor CD44 [5,6]. The interaction of Shigella effectors with these host receptors is likely to facilitate the initial contact of the bacterium to the cell membrane, especially in the region of cholesterol-rich lipid rafts At this stage the TSS proteins interact with cellular proteins to reorganize the cytoskeletal structures that results in their engulfment [8,9,10]. Abl kinase phosphorylates N-WASP [16], which is an essential activator of Arp2/3
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