Evidence for and against the presence of polynuclear aromatic hydrocarbon and 2,3,7,8-tetrachloro- p-dioxin binding proteins in the marine mussels, Bathymodiolus and Modiolus modiolus

Chemosynthetic mussels were collected in the vicinity of gas and petroleum seeps in the Gulf of Mexico. Aryl hydrocarbon hydroxylase (AHH) and glutathione S-transferase (GST) activities in the hepatopancreas and gill, respectively, were elevated in mussels collected at the site more highly contaminated with polynuclear aromatic hydrocarbons (PAHs). The aryl hydrocarbon receptor (AhR) and the 4S PAH binding protein (PBP) are ligand activated transcription factors which regulate expression of various genes including cytochrome P450 1A. The presence of these proteins was investigated in PAH-exposed mussels. RT-PCR analysis revealed only a 45.2% nucleotide similarity between the AhR2 from Fundulus heteroclitus and from mussel mRNA transcripts containing a putative member of the PAS gene family. Furthermore, in gel electrophoretic mobility shift and protein cross-linking assays utilizing mussel cytosol which was incubated with 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), no specifically-bound retarded band with a [ 32P]dioxin responsive element was clearly indicated. Likewise, sucrose density gradient analysis of cytosol incubated with [ 3H]TCDD did not give a specifically-bound 8-10S peak associated with the AhR complex. In contrast, incubation of mussel cytosol with [ 3H]benzo(a)pyrene (BaP) gave a 4S peak which was not displaced by TCDD but was nonspecifically decreased by excess BaP or benzo(ghi)perylene. The potential role of the 4S PAH binding protein in the induction of CYP1A-dependent activity in these species is currently unclear. Mussels collected from the North Sea were treated with BaP (5 mg/kg) or TCDD (20 μg/kg) for 48 h to investigate induction of enzyme activities in mussels from a pristine location. Western blot analysis indicated the presence of a 33 kDa protein when a PAH binding protein antibody was used, but no detectable induction of AHH or GST activity was observed in the treated mussels.