Changes in PtdIns(4,5)P2 Induced by Etoposide Treatment Modulates Small Intestinal P-Glycoprotein <i>via</i> Radixin

Abstract

Previously, we reported that repeated oral administration of etoposide (ETP) increases P-glycoprotein (P-gp) expression in association with activation of ezrin/radixin/moesin (ERM) via Ras homolog gene family member A (RhoA)/Rho-associated coiled-coil containing protein kinase (ROCK) signaling in the small intestine. However, the detailed mechanisms of this pathway have yet to be fully elucidated. Recently, phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], one of the most abundant phosphoinositides in the plasma membrane, has attracted attention regarding its involvement in the plasma membrane localization of various membrane proteins. PtdIns(4,5)P2 is an essential factor in the dissociation and subsequent membrane translocation (activation) of ERM, and its synthetic pathway is known to be highly regulated by RhoA/ROCK signaling. Here, we examined the involvement of PtdIns(4,5)P2 in the mechanism by which ETP treatment increases small intestinal P-gp levels, and we determined which protein within ERM contributes to this phenomenon. Key words P-glycoprotein; radixin; phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2); Ras homolog gene family member A (RhoA); Rho-associated coiled-coil containing protein kinase (ROCK); small intestine We previously reported that repeated oral treatment with etoposide (ETP), an anticancer drug that is a substrate for Pglycoprotein (P-gp), 1) activates ezrin/radixin/moesin (ERM), which are scaffold proteins for P-gp in the small intestine. 2,3)Activated ERM may in turn increase P-gp expression in the plasma membrane of the small intestine under ETP treatment.2,3) ERM activation is regulated by Ras homolog gene family member A (RhoA) and Rho-associated coiled-coil containing protein kinase (ROCK) signaling, as demonstrated in our previous studies 2,3) and others. 4,5) In our reports we proposed the possibility that of the ERM proteins, radixin may contribute to the above phenomena more than ezrin or moesin 6)

Regulation of breast cancer resistance protein and P-glycoprotein by ezrin, radixin and moesin in lung, intestinal and renal cancer cell lines

“…On the other hand, in the liver, Rdx alone controls P‐gp, while in brain capillary endothelial cells, ezrin (Ezr) and moesin (Msn) are involved in the membrane expression and transport function of P‐gp . We and other researchers have shown that P‐gp membrane localization and function are regulated by Rdx in the intestine . Moreover, we established that there are tissue‐specific differences in the effects of ERM proteins on P‐gp function between intestinal cancer Caco‐2 cells and renal cancer Caki‐1 cells .…”

“…[16,17] We and other researchers have shown that P-gp membrane localization and function are regulated by Rdx in the intestine. [8,[18][19][20] Moreover, we established that there are tissue-specific differences in the effects of ERM proteins on P-gp function between intestinal cancer Caco-2 cells and renal cancer Caki-1 cells. [21] Furthermore, it was suggested that the ERM proteins regulating P-gp activity were similar in normal and cancerous tissues.…”

Subcellular distribution of ezrin/radixin/moesin and their roles in the cell surface localization and transport function of P-glycoprotein in human colon adenocarcinoma LS180 cells

“…On the contrary, siRNAs against radixin and moesin did not cause any alterations in the levels of ABCB1 mRNA or its cell surface localization. Kobori et al has previously shown that repeated oral administration of etoposide, an anticancer drug and a strong substrate of P-gp, to mice increases the expression of P-gp via the activation of radixin, in the plasma membrane of small intestine where the protein-protein interaction between P-gp and radixin was detected by immunoprecipitation analysis [51,[65][66][67]. Of note, not only radixin but also ezrin and moesin interacted with P-gp in the plasma membrane fraction of the small intestine in mice [65,66].…”

Rapid Increase of Gastrointestinal P-Glycoprotein Functional Activity in Response to Etoposide Stimulation

“…We reported that etoposide, a bitter-tasting oral anticancer drug, is a P-gp substrate, 7) and other researchers have shown that exposure to this drug for several days results in an increase in the membrane localization of ERM proteins and P-gp in mouse small intestine. 11,12) Moreover, it was reported that a 9 h PTC exposure in Caco-2 cells and mice intestine increased P-gp mRNA, leading to an increase of P-gp functional activity. 13) Therefore, in this study, we investigated the short-term effect of etoposide on P-gp transport function and its mechanism in order to clarify whether etoposide can rapidly enhance the transport function of P-gp.…”