Received for publication June 3, 2008.
Revised August 1, 2008.
Accepted for publication August 1, 2008.

Lipopolysaccharide Increases Cell Surface P-glycoprotein that Exhibits Diminished Activity in Intestinal Epithelial Cells

Abstract

Increasingly, it is recognized that commensal microflora regulate epithelial cell processes through the dynamic interaction of pathogen-associated molecular patterns and host pattern recognition receptors such as Toll-like receptor 4 (TLR4). We therefore investigated the effects of bacterial lipopolysaccharide (LPS) on intestinal P-glycoprotein (P-gp) expression and function. Human SW480 (P-gp+/TLR4+) and Caco-2 (P-gp+/TLR4-) cells were treated with media control or LPS (100 ng/ml) for 24 hours prior to study. P-gp function was assessed by measuring the intracellular concentration of Rhodamine 123 (Rh123). To confirm P-gp specific effects, breast cancer resistance protein (BCRP/ABCG2) and multidrug resistance-associated protein 2 (MRP-2/ABCC2) were also analyzed. Treatment of SW480 cells with LPS led to diminished P-gp activity which could be prevented with polymyxin B (control: 207 ± 16 vs. LPS: 402 ± 22 vs LPS ± polymyxin B: 238 ± 26 pmoles Rh123/mg protein, p<0.05 control vs. LPS). These effects could be blocked by using polymyxin B and were not seen in the P-gp+/TLR4- Caco-2 cell line (control: 771 ± 28 vs. LPS: 775 ± 59 pmoles Rh123/mg protein). Total cellular levels of P-gp did not change in LPS treated SW480 cells however a significant increase in cell surface P-gp was detected. No change in activity, total protein, or apically located MRP-2 was detected following LPS treatment. Sequence analysis confirmed wildtype status of SW480 cells. These data suggest that activation of TLR4 in intestinal epithelial cells leads to an increase in plasma membrane P-gp that demonstrates a diminished capacity to transport substrate.

Key words: ABC transporters, p-glycoprotein