Different regulation of P-glycoprotein function between Caco-2 and Caki-1 cells by ezrin, radixin and moesin proteins.

OBJECTIVES: P-glycoprotein (P-gp) mediates efflux of many xenobiotics, including therapeutic drugs, from normal and tumour tissues, and its functional localization on the plasma membrane of cells is regulated by scaffold proteins, such as ezrin, radixin and moesin (ERM proteins). We previously reported that radixin is involved in post-translational regulation of P-gp in hepatocellular carcinoma HepG2 cells and mouse small intestine, but not in mouse kidney. METHODS: Here, we investigated whether the role of ERM proteins in regulation of P-gp transport activity in cancers is the same as that in the corresponding normal tissues, using human colon adenocarcinoma (Caco-2) cells and renal carcinoma (Caki-1) cells. KEY FINDINGS: In Caco-2 cells, radixin silencing alone reduced the P-gp-mediated intracellular accumulation of rhodamine123 (Rho123), while the mRNA level of P-gp was unchanged. Thus, it appears that only radixin among the ERMs regulates P-gp activity in Caco-2 cells. On the other hand, none of the ERM proteins influenced P-gp activity in Caki-1 cells. CONCLUSIONS: The regulation of P-gp by ERM proteins is different between Caco-2 and Caki-1 cells. Moreover, these regulatory properties are the same as those of the corresponding normal tissues, and suggest that tissue-specific differences in the regulation of P-gp by ERM proteins are retained in cancerous tissues.

Recommended Daily Dose of Sesame Lignans Has No Influence on Oral Absorption of P-Glycoprotein Substrates in Rats.

Sesamin (SM) and episesamin (ESM) are constituents of sesame seeds, which are used in health foods and considered to have various beneficial effects in the prevention of lifestyle-related diseases. P-Glycoprotein (P-gp) is an ATP-binding cassette transporter involved in drug absorption in the human gastrointestinal tract. A recent report indicated that SM influences P-gp-mediated drug transport. In the present study, we investigated whether SM and ESM inhibit P-gp in vitro, using Caco-2 cells and the typical P-gp substrates rhodamine123 (Rho123) and fexofenadine. SM and ESM showed no effect on accumulation of these compounds, indicating that SM and ESM do not influence P-gp function. In addition, an in vivo study using Rho123 indicated that SM and ESM do not affect absorption of P-gp substrates. Overall, these results suggest that health foods containing SM and ESM are unlikely to interact with P-gp substrates.