Carcinogenic polycyclic aromatic hydrocarbons increase intracellular Ca2+ and cell proliferation in primary human mammary epithelial cells

Previous studies have shown that polycyclic aromatic hydrocarbons (PAHs)mobilize intracellular Ca2+ in human T cells by inositoltrisphosphate-dependent mechanisms resulting from activation ofphospholipase C-gamma by SRC-related protein tyrosine kinases, therebymimicking antigen-receptor activation. Ca2+ appears to play an importantsecond messenger role in growth factor control of cell proliferation inhuman mammary epithelial cells (HMEC), such as the epidermal growth factorreceptor pathway. The purpose of the present studies was to determine ifPAHs are able to increase intracellular Ca2+ in primary cultures of HMECand increase cell proliferation. Two carcinogenic and two non-carcinogenicPAHs were tested for their ability to increase intracellular Ca2+ in HMEC.The carcinogenic PAHs dimethylbenz[a]anthracene (DMBA) and benzo[a] pyrene(BaP) were able to cause Ca2+ elevation in HMEC at early time points (2 h)and caused sustained alterations in Ca2+ homeostasis (18 h). DMBA showedmaximal effects at early time points (2 h), while BaP showed maximaleffects on sustained Ca2+ (18 h). 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD), a potent dioxin and tumor promoter, produced maximal Ca2+ elevationat 2 h, with a return to near baseline levels by 6 h. The non-carcinogenicPAHs benzo[e]pyrene and anthracene did not significantly alterintracellular Ca2+ at any time point. alpha-Naphthoflavone significantlyreduced the Ca2+ response induced by BaP treatment, but not by DMBA orTCDD, suggesting that P450 1A or 1B metabolism of BaP may be important inthe sustained Ca2+ elevating response. In evaluating the effects of BaP onHMEC proliferation, BaP was found to increase the number of cells recoveredafter 4 days in culture in the absence or presence of variousconcentrations of epidermal growth factor. These studies provide initialevidence that Ca2+ signaling may be associated with mitogenesis in HMEC,which may play a role in tumor promotion and progression produced by PAHs.