UV IRRADIATION OF A B-CELL HYBRIDOMA INCREASES EXPRESSION OF ALKALINE-PHOSPHATASE - INVOLVEMENT IN APOPTOSIS

Expression of alkaline phosphatase (APase) by 7TD1 B-cell hybridoma wa s amplified by ultraviolet irradiation; cell growth was inhibited and cell death by apoptosis was increased. Irradiation induced high levels of APase activity in cycling as well as in apoptotic cells. In contra st, APase activity faded with time in nonirradiated cells and was no l onger expressed in spontaneous apoptotic cells appearing after several days in culture. This was demonstrated by cell morphology, DNA fragme ntation, and flow cytometry after simultaneous staining of DNA with Ho echst 33342 and APase with naphthol AS-TR phosphate-fast red RC fluore scent reagent. Levamisole, a specific inhibitor of APase activity, alm ost totally abrogated apoptosis induced by ultraviolet irradiation at doses that failed to affect 7TD1 cell survival. These data suggest tha t APase could play a role in the signalling cascade that mediates apop tosis in irradiated cells.