PERSISTENCE OF CALCIUM ELEVATION IN THE HPB-ALL HUMAN T-CELL LINE CORRELATES WITH IMMUNOSUPPRESSIVE PROPERTIES OF POLYCYCLIC AROMATIC-HYDROCARBONS

The immunosuppressive synthetic methylated polycyclic aromatic hydroca rbon (PAH), 7,12-dimethylbenz[a]anthracene (DMBA), has been shown to c ause both an immediate and a sustained elevation of free intracellular calcium (Ca2+) in human T cells. In the present studies, a series of anthracene- and pyrene-based PAHs were tested for rapid (3 min) and su stained (4 hr) Ca2+ mobilization in the HPB-ALL human T cell line meas ured by flow cytometry using Fluo-3 as a Ca2+ indicator. Immunosuppres sive PAHs produced a sustained Ca2+ elevation for at least 4 hr, while weakly immunosuppressive PAHs caused only a transient increase in Ca2 +. The immunosuppressive PAHs, DMBA, benzo[a]pyrene, dibenz[a,h]anthra cene, and 9,10-dimethylanthracene, produced a sustained increase in in tracellular Ca2+ in HPB-ALL cells. Those PAHs with moderate to minimal immunosuppressive properties (i.e., dibenz[a,c]anthracene, benz[a]ant hracene, benzo[e]pyrene, and anthracene) produced small and transient Ca2+ mobilization responses in HPB-ALL cells. It appeared that methyla tion of anthracene at the 9,10-positions increased the duration of Ca2 + mobilization, whereas the addition of a benzene group in the ''a'' p osition was associated with a transient increase in Ca2+ levels. Genis tein, a protein tyrosine kinase (PTK) inhibitor, partially inhibited t he rapid and sustained PAH-induced Ca2+ mobilization responses, while the protein kinase C (PKC) inhibitors, staurosporine and calphostin C, had essentially no effect on PAH-induced Ca2+ elevation. It appears t hat the action of PAHs on PTKs is important in the rapid Ca2+ response of human T cells. However, additional biochemical mechanisms appear t o be responsible for the sustained elevation of Ca2+ produced by PAHs in T cells. The results of these studies demonstrate that persistent e levation of intracellular Ca2+ by PAHs correlates with their known imm unosuppressive properties. (C) 1994 Academic Press, Inc.