Cloning and expression analysis of P-glycoprotein gene in Crassostrea ariakensis

P-glycoprotein (P-gp), as an ATP-binding cassette transporter, can transport a variety of substrates across the cell membrane in human and animals, even in aquatic animals. Multixenobiotic resistance phenomenon (MXR) related to the P-gp has been identified and characterized in several aquatic organisms, however, the nature of this transporter and the structural basis for the resistance are still poorly understood. In this study, to provide an insight into the roles of P-gp in resistance of bivalve against environmental pollution and toxins, complete cDNA of P-gp gene in Crassostrea ariakensis was cloned and analyzed. The accumulation of okadaic acid (OA), a main component of diarrhetic shellfish poisoning (DSP) toxins, and expression of P-gp in gills, digestive glands and mantle of C. ariakensis, were detected upon exposure to Prorocentrum lima, a known producer of DSP toxins. The complete sequence of oyster P-gp showed a high identity to MDR/P-gp/ABCB proteins from other species and contained some classical features of ABCB transport proteins. Upon exposure to P. lima for 72 h, the OA level increased 2.5-fold in gills and 6.4-fold in digestive glands of C. ariakensis. Meanwhile, the expression of P-gp mRNA increased 2.4-fold in gills and decreased slightly in digestive glands. No significant difference in P-gp protein expression was found by western blot in all of the tissues analyzed in P. lima-exposed oysters. Taking all of our results into account, we speculate that P-gp likely plays a role in the response to DSP toxins in C. ariakensis.