Efflux Protein Expression in Human Retinal Pigment Epithelium Cell Lines

The objective of this study was to characterize efflux proteins (P-glycoprotein (P-gp), multidrug resistance proteins (MRP1-6) and breast cancer resistance protein (BCRP)) of retinal pigment epithelium (RPE) cell lines. Expression of efflux proteins in two secondary (ARPE-19, D407) and two primary (HRPEpiC and bovine) RPE cell lines was measured by quantitative RT-PCR and western blotting. Furthermore, activity of MRP1 and MRP5 of ARPE-19 cell line was assessed with calcein-AM and carboxydichlorofluorescein (CDCF) probes. Similar efflux protein profile was shared between ARPE-19 and primary RPE cells, whereas D407 cell line was notably different. D407 cells expressed MRP2 and BCRP, which were absent in other cell lines and furthermore higher MRP3 transcript expression was found. MRP1, MRP4 and MRP5 were identified from all human RPE cell lines and MRP6 was not expressed in any cell lines. The pattern of efflux protein expression did not change when ARPE-19 cells were differentiated on filters. The calcein-AM and CDCF efflux tests provided evidence supporting MRP1 and MRP5 activity in ARPE-19 cells. MRP1, MRP4 and MRP5 are the main efflux transporters in RPE cell lines. There are differences in efflux protein expression between RPE cell lines.