Burkholderia pseudomallei rpoSmediates iNOS suppression in human hepatocyte (HC04) cells

Abstract

Burkholderia pseudomallei is an intracellular Gram-negative bacterial pathogen and the causative agent of melioidosis, a widespread disease in Southeast Asia. Reactive nitrogen, in an intermediate form of nitric oxide (NO), is one of the first lines of defense used by host cells to eliminate intracellular pathogens, through the stimulation of inducible nitric oxide synthase (iNOS). Studies in phagocytotic cells have shown that the iNOS response is muted in B. pseudomallei infection, and implicated the rpoS sigma factor as a key regulatory factor mediating suppression. The liver is a main visceral organ affected by B. pseudomallei, and there is little knowledge about the interaction of liver cells and B. pseudomallei. This study investigated the induction of iNOS, as well as autophagic flux and light-chain 3 (LC3) localization in human liver (HC04) cells in response to infection with B. pseudomallei and its rpoS deficient mutant. Results showed that the rpoS mutant was unable to suppress iNOS induction and that the mutant showed less induction of autophagy and lower co-localization with LC3, and this was coupled with a lower intracellular growth rate. Combining these results suggest that B. pseudomallei rpoS is an important factor in establishing infection in liver cells.

Investigation of host–pathogen interaction between Burkholderia pseudomallei and autophagy-related protein LC3 using hydrophobic chromatography-based technique

“…Since B. pseudomallei PP844 has been studied about the ability to suppress the expression of iNOS rather than rpoS mutant in both phagocytic and non-phagocytic cells [ 11 , 12 ], the induction of an alternative host killing mechanism as autophagy in elimination of intracellular pathogen, B. pseudomallei has been addressed in murine macrophage [ 36 ]. To investigate the role of autophagy induced by B. pseudomallei infected human macrophage U937cell line, the expression level of microtubule-associated protein light chain 3 (LC3), a key autophagy-related protein was determined.…”

“…On the other hand, B. pseudomallei rpoS mutant seems to lack the ability to trigger autophagy as shown as the expression level of LC3 in U937cells. Recent study, B. pseudomallei rpoS mutant has shown the low level of autophagy induction as well as the lower level of colocalization with LC3 in infected hepatocyte cell line, HC04 [ 12 ]. Interestingly, based on the guideline for the use and interpretation of autophagy [ 44 ], autophagic flux of B. pseudomallei wild type PP844 infected U937 comparing with rpoS mutant at 24 h of post infection time has already determined (Sanongkiet S, personal communication).…”

“…Many virulence factors of B. pseudomallei have been characterized for the governing pathogenesis in host cells. RpoS sigma factor, one bacterial virulence factor has been studied the regulation in MNGCs formation and iNOS expression in both phagocytic and non-phagocytic cells [ 11 , 12 ].…”

The Role of Nitric Oxide in Regulating Intestinal Redox Status and Intestinal Epithelial Cell Functionality

“…Most resting cells do not express iNOS, which is the primary isoform of NOS in intestinal cells, but could be induced by cytokines and some microbial products. The expression of iNOS can be constitutive or induced in vivo, for example by cytokines [9,10,11,12] during large intestinal inflammation or triggered by bacterial infections [13,14,15,16]. In IECs that are polarized, stable end-products of NO, such as nitrite and nitrate, are primarily found on the apical side.…”