UP-REGULATED EXPRESSION OF BCL-2 IN MULTIPLE-MYELOMA CELLS INDUCED BYEXPOSURE TO DOXORUBICIN, ETOPOSIDE, AND HYDROGEN-PEROXIDE

Enhanced expression of the antiapoptotic gene BCL-2 may participate in chemoresistance. To ascertain if multiple myeloma cells surviving exp osure to chemotherapy alter their BCL-2 expression, we treated the mye loma cell lines 8226, IM-9, and U266 as well as a primary myeloma cell culture with various injurious agents. Doxorubicin, etoposide, and hy drogen peroxide consistently induced a concentration- and time-depende nt upregulation of BCL-2 expression in all myeloma target cell types a ssayed by flow cytometry and Western blot analysis. In contrast, serum starvation, dexamethasone, and anti-fas antibodies had no effect on e xpression. Enhanced expression of BCL-2 was relatively selective as tr eatments had no effect on expression of ig light chains, BCL-X, or act in. An reverse transcriptase-polymerase chain reaction assay showed in creased levels of BCL-2 RNA in 8226 cells as early as 4 hours after tr eatment with doxorubicin at a time when cell recoveries were not decre ased, Thus, doxorubicin stimulates BCL-2 expression in individual 8226 cells rather than simply allowing a selected survival of high BCL-2-e xpressing cells in culture, Doxorubicin-treated 8226 cells with upregu lated BCL-2 expression were relatively resistant to a second exposure of doxorubicin. In addition, BCL-2-transfected IM-9 cells, with enhanc ed expression of BCL-2 which was comparable to that achieved by initia l exposure to doxorubicin, were resistant to doxorubicin and etoposide cytotoxicity. These data suggest that exposure to chemotherapeutic ag ents may enhance BCL-2 expression in surviving myeloma cells and contr ibute to acquired chemoresistance. (C) 1996 by The American Society of Hematology.