Phorbol myristate acetate stimulates phagosome-lysosome fusion in mouse macrophages.

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Abstract
The effect of the tumor promoter phorbol myristate acetate (PMA) on phagosome-lysosome (P-L) fusion in mouse macrophages was studied using fluorescence. Treatment with 0.1-1.0 .mu.g PMA/ml caused a striking increase in the rate and extent of P-L fusion. Exposure of cells to phorbol, free myristate, or the monoesters of PMA did not reproduce this effect. Macrophages required from 2-3 h of pretreatment to express maximal P-L fusion, and this was maintained for at least 20 h when cells were returned to PMA-free medium. Catalase, superoxide dismutase, indomethacin and hydrocortisone, agents that block the effect of PMA on H2O2, O2- [superoxide anion], prostaglandins or plasminogen activator, respectively, did not affect the stimulation of P-L fusion by PMA. The protein synthesis inhibitors puromycin and cycloheximide blocked PMA effects under conditions in which the high fusion rate of 4 d [day] cells was not affected. Labeled PMA was rapidly taken up by macrophages, with a plateau of uptake at .apprx. 3 h. When cells were returned to PMA-free medium, cell-associated label was rapidly released, returning to background levels within 1 h. The released label was a metabolite of PMA by TLC. This product migrated between the monoester phorbol-12-myristate and free phorbol. Rapid metabolism of PMA was also observed by a macrophage cell line, J774, and, to a lesser extent, by primary rat embryo fibroblasts.