Abstract
Pathogenic intestinal bacteria lead to significant disease in humans. Here we investigated the role of the multifunctional protein, Apurinic/apyrimidinic endonuclease 1 (APE1), in regulating the internalization of bacteria into the intestinal epithelium. Intestinal tumor-cell lines and primary human epithelial cells were infected with Salmonella enterica serovar Typhimurium or adherent-invasive Escherichia coli. The effects of APE1 inhibition on bacterial internalization, the regulation of Rho GTPase Rac1 as well as the epithelial cell barrier function were assessed. Increased numbers of bacteria were present in APE1-deficient colonic tumor cell lines and primary epithelial cells. Activation of Rac1 was augmented following infection but negatively regulated by APE1. Pharmacological inhibition of Rac1 reversed the increase in intracellular bacteria in APE1-deficient cells whereas overexpression of constitutively active Rac1 augmented the numbers in APE1-competent cells. Enhanced numbers of intracellular bacteria resulted in the loss of barrier function and a delay in its recovery. Our data demonstrate that APE1 inhibits the internalization of invasive bacteria into human intestinal epithelial cells through its ability to negatively regulate Rac1. This activity also protects epithelial cell barrier function.
Highlights
Food-borne bacterial infections are a major cause of disease that negatively impacts both quality and quantity of life [1]
To select the most suitable bacteria for the studies, we first determined the ability of different bacteria to become internalized into T84 by comparing Salmonella enterica serovar Typhimurium (SL1344) (MOI 10), adherent-invasive Escherichia coli strain LF82 (AIEC/LF82), enteropathogenic E. coli (EPEC), E. coli (K12) and C. jejuni
Rac1 mRNA expression was increased in APE1deficient epithelial cells (Figure S1B, C) so our evaluation focused on how apyrimidinic endonuclease 1 (APE1) regulated Rac1 function in the process of bacterial internalization
Summary
Food-borne bacterial infections are a major cause of disease that negatively impacts both quality and quantity of life [1]. Occurring acute intestinal infections include Shigella flexneri, Salmonella enterica serovar Typhimurium and Campylobacter jejuni. The incidence of these infections has not changed in recent decades and the Centers for Disease Control and Frontiers in Immunology | www.frontiersin.org den Hartog et al. Prevention estimate that 48 million people are infected annually resulting in 128,000 hospitalizations and 3,000 deaths in the US alone [2, 3]. Invasion of epithelial cells by bacteria is facilitated by the activation Rho GTPases, including Rac, subsequent to the translocation of effector molecules mediated by the secretion system [14,15,16]. Activation of Rac leads to cytoskeleton rearrangements and internalization of the bacteria
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