Two novel multidrug resistance associated protein (MRP/ABCC) from the Mediterranean mussel (Mytilus galloprovincialis): characterization and expression patterns in detoxifying tissues

Abstract

Multidrug resistance associated proteins (MRP) belong to the ABCC branch of the ABC transporters. The MRP together with P-gp (P-glycoprotein; MDR1; ABCB1) and BCRP (breast cancer resistance protein; ABCG2) confer multixenobiotic resistance (MXR) in marine vertebrates. In aquatic invertebrates, little is known about the presence and role of these ABC transporters. The ABC transporters play an important role in the absorption, distribution, and excretion of drugs, xenobiotics, and endogenous compounds and are predominantly expressed in excretory organs. In the present study, we identified and characterized two MRP/ABCC transporters (mrp1 and mrp2) from the Mediterranean mussel (Mytilus galloprovincialis Lamarck, 1819). The two cDNAs finally obtained were 4648 bp for mrp1 and 5065 bp for mrp2 with open reading frames of 1500 and 1524 residues, respectively. Analysis of the amino acid sequences revealed the structural organization of ABC transporters with the typical and highly conserved motifs. The expression levels of these genes revealed that the highest expression of mrp1 and mrp2 genes was found in the digestive gland followed by gills, and the lowest expression of the three tissues was detected in the mantle. The expression of these genes was also studied in mussels naturally contaminated with okadaic acid (from a bloom of Dinophysis acuminata Claparède and Lachmann, 1859). The overexpression of mrp2 in the digestive gland suggests that this gene is involved in the process of detoxification of okadaic acid in M. galloprovincilais. These expression patterns agree with the suggested role of these genes in the protection against endogenous or exogenous compounds in aquatic organisms.