title: Alterations in human B cell calcium homeostasis by polycyclic aromatic hydrocarbons: possible associations with cytochrome P450 metabolism and increased protein tyrosine phosphorylation.
abstract: Previous studies performed in this laboratory have shown that certain benzo(a)pyrene (BaP) metabolites, such as benzo(a)pyrene-7,8-dihydrodiol (BaP-7,8-diol) and benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), were more effective in elevating intracellular Ca2+ in normal human peripheral blood mononuclear cell (HPBMC) T and B cells than was BaP. Additionally, it has been shown that the suppression of human T cell mitogenesis produced by polycyclic aromatic hydrocarbons (PAHs) and certain BaP metabolites is reversed by treatment with alpha-naphthoflavone (ANF), a cytochrome P450 1A and 1B inhibitor. ANF also diminishes the elevation in intracellular calcium (Ca2+) produced by BaP in HPBMC. In the present studies, we further defined the relationships between intracellular Ca2+ elevation produced by BaP and two immunotoxic P450-derived metabolites, BaP-7,8-diol and BPDE in the Daudi human B cell line. At 1, 4, and 18 h, both BaP-7,8-diol and BPDE produced a significant rise in intracellular Ca2+. This effect, however, was not observed with BaP or benzo(e)pyrene (BeP), a nonimmunotoxic PAH. To evaluate the potential role of cytochrome P450 metabolism in PAH-induced Ca2+ elevation, Daudi cells were pretreated with ANF for 4 h, followed by treatment with BaP metabolites for 18 h. ANF completely reversed the rise in Ca2+ produced by BaP-7,8-diol, but had no effect on the Ca2+ elevation produced by BPDE. These results suggest that BPDE may be the ultimate P450 metabolite responsible for Ca2+ elevation in human B cells. BaP-7,8-diol and BPDE were found to increase tyrosine phosphorylation in Daudi whole cell lysates and to increase tyrosine phosphorylation of two important Src-related protein tyrosine kinases (PTKs), Lyn and Syk. Inhibition of tyrosine phosphorylation by herbimycin A was found to largely prevent the increase in intracellular Ca2+ produced by BaP-7,8-diol and BPDE, suggesting that Ca2+ elevation is coupled to increased tyrosine phosphorylation in Daudi. BPDE was found to produce a statistically significant increase in tyrosine phosphorylation of Lyn and Syk within 10 min of exposure. Collectively, these data demonstrate that certain P450-derived metabolites of BaP may be responsible for PTK activation and an increase intracellular Ca2+, which may alter antigen receptor signaling in human B cells.
authors.affiliation: University of New Mexico College of Pharmacy, Toxicology Program, Albuquerque 87131-1066, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Mounho
authors.forename: S W
authors.initials: SW
authors.lastname: Burchiel
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000633:toxicity; D001402:B-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000633:toxicity*; D001571:Benzoflavones / Q000494:pharmacology; D016227:Benzoquinones; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004101:Dihydroxydihydrobenzopyrenes / Q000633:toxicity; D006801:Humans; D047029:Lactams, Macrocyclic; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives
chemical_list: D001571:Benzoflavones; D016227:Benzoquinones; D065607:Cytochrome P-450 Enzyme Inhibitors; D004101:Dihydroxydihydrobenzopyrenes; D047029:Lactams, Macrocyclic; D011809:Quinones; C017228:benzo(a)pyrene 7,8-dihydrodiol; D017828:Rifabutin; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; C011512:alpha-naphthoflavone; C020754:herbimycin; D003577:Cytochrome P-450 Enzyme System; D011505:Protein-Tyrosine Kinases; D002118:Calcium