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

Abstract

Objectives Ezrin (Ezr), radixin (Rdx) and moesin (Msn) (ERM) proteins anchor other proteins to the cell membrane, serving to regulate their localization and function. Here, we examined whether ERM proteins functionally regulate breast cancer resistance protein (BCRP) and P‐glycoprotein in cell lines derived from lung, intestinal and renal cancers. Methods ERM proteins were each silenced with appropriate siRNA. BCRP and P‐gp functions were evaluated by means of efflux and uptake assays using 7‐ethyl‐10‐hydroxycamptothecin (SN‐38) and rhodamine123 (Rho123) as specific substrates, respectively, in non‐small cell lung cancer HCC827 cells, intestinal cancer Caco‐2 cells and renal cancer Caki‐1 cells. Key findings In HCC827 cells, the efflux rates of SN‐38 and Rho123 were significantly decreased by knockdown of Ezr or Msn, but not Rdx. However, BCRP function was unaffected by Ezr or Rdx knockdown in Caco‐2 cells, which do not express Msn. In Caki‐1 cells, Rdx knockdown increased the intracellular SN‐38 concentration, while knockdown of Ezr or Msn had no effect. Conclusions Our findings indicate that regulation of BCRP and P‐gp functions by ERM proteins is organ‐specific. Thus, if the appropriate ERM protein(s) are functionally suppressed, accumulation of BCRP or P‐gp substrates in lung, intestine or kidney cancer tissue might be specifically increased.

Physiological Roles of ERM Proteins and Transcriptional Regulators in Supporting Membrane Expression of Efflux Transporters as Factors of Drug Resistance in Cancer

“…ERM proteins bind to integral membrane proteins, scaffold proteins, and Rho-related proteins (Table 1) [57]. It was recently established that ERM proteins act as scaffolds to anchor efflux transporters to the cell membrane, thereby regulating the functional activity [36]. Luciani et al found that treatment of macrophages with interferon γ increased the expression of P-gp on the cell membrane and its co-localization with Ezr among ERM proteins.…”

“…We also investigated whether ERM proteins functionally regulate P-gp in non-small cell lung cancer HCC827 cells [36]. In HCC827 cells, Ezr or Msn knockdown significantly reduced the Rho123 efflux rate.…”

“…However, the mRNA expression levels of transporters do not necessarily correlate with protein expression level or functional activity [32], as exemplified by P-gp [33,34]. Transporters exhibit functional activity only when expressed on the cell membrane [33,35,36], and therefore scaffold proteins that anchor the transporter to the cell membrane play a critical role. Recently, several research groups including our own have reported that ezrin (Ezr), radixin (Rdx), and moesin (Msn), which are generically known as ERM proteins, serve as anchors to immobilize a variety of proteins, including transporters, at the cell membrane.…”

“…EMT has also been suggested to be involved in drug resistance, since drug excretion from cancer cells is promoted during EMT, though the mechanisms involved have not yet been fully clarified. We recently showed that Snail induces ERM proteins [36]. In the second part of this article, we will review recent research, including clinical findings, on the relationship between the ERM scaffold proteins and the transcriptional regulatory factors that induce their expression.…”

KD025, an anti‑adipocyte differentiation drug, enhances the efficacy of conventional chemotherapeutic drugs in ABCG2‑overexpressing leukemia cells

“…A number of studies reported that the most common cause of MDR is the abnormally high expression of ATP-binding cassette (ABC) transporters in leukemia cells (6,7). In fact, it was shown that the overexpression of ABCB1, ABCC1 and ABCG2 was involved in the efflux of various antitumor agents out of the cells (8). These proteins have the ability to transport a plethora of chemotherapeutics with diverse structures and functions outside of the cells.…”