Benzo[a]pyrene up-regulates the expression of the proliferating cell nuclear antigen (PCNA) and multixenobiotic resistance polyglycoprotein (P-gp) in Baltic Sea blue mussels (Mytilus edulis L.)

The expression of protein biomarkers in Baltic Sea blue mussels was analyzed after three days exposure to low (2.8 μg/animal/day), intermediate (28 μg/animal/day), or high (280 μg/animal/day) nominal doses of benzo[a]pyrene (BaP). Significant expression changes were found in the animals exposed to the low dose, the lowest reported dose for DNA adduct formation in the gills of Baltic Sea blue mussels. Up-regulated expression of the proliferating cell nuclear antigen (PCNA), quantified from Western blots, and no change in the 5-bromo-deoxyuridine (BrdU) staining pattern, determined by immunocytochemistry, indicated that the observed PCNA response was mainly non-proliferative, and thus possibly due to DNA damage. The expression of the multixenobiotic resistance polyglycoprotein (P-gp) was also up-regulated, proving its usefulness as an exposure marker to planar organic compounds. No effect of the BaP treatment with respect to the retinoblastoma 110 protein or heat shock proteins 60 and 70 was found. The variance in the medium and high dose data was too large to allow for the detection of significant expression changes. We suggest PCNA to be a marker for genotoxic stress derived from the polycyclic aromatic hydrocarbon BaP, irrespective of whether the stress leads to DNA repair or to cell proliferation.