MODULATION OF APO-1 FAS (CD95)-INDUCED PROGRAMMED CELL-DEATH IN MYELOMA CELLS BY INTERFERON-ALPHA(2)/

The Apo-1/Fas (CD95) antigen is known to be involved in the process of T cell-mediated target cell killing and has recently been shown to be expressed on myeloma cell lines and native malignant plasma cells. Se veral cytokines have been reported to interfere with spontaneous and e ven Apo-1/Fas-induced apoptosis, but no attempt has been made yet to i nvestigate these interactions and the possible underlying mechanisms i n myeloma cells. Since in myeloma patients Interferon (IFN)-alpha(2) d isplays a profound therapeutic effect in vivo, which is usually attrib uted to its growth inhibitory and/or immunomodulatory capacity, we set out to study the potential interference of IFN-alpha(2) with Apo-1/Fa s-induced apoptosis. Contrary to expectations, IFN-alpha(2) reduced th e degree of apoptosis caused by the treatment of five Apo-1/Fas-sensit ive myeloma cell lines with a Fas monoclonal antibody (mAb). Simultane ous application of IFN-alpha(2) and Fas mAb was superior to the prolon ged (i.e. > 8 h) preincubation with the cytokine as far as inhibition of Apo-1/Fas-induced apoptosis was concerned. This effect of IFN-alpha (2) was neither explained by a down-regulation of the Apo-1/Fas recept or nor caused by modulation of the expression levels of c-myc, bcl-2-, bcl-x(L), bax- or p53 genes. IFN-alpha(2) did not alter the Apo-1/Fas -induced activity of Mitogen-activated protein kinase (MAPK) 1 and did not inhibit the Apo-1/Fas-mediated proteolytic cleavage of ADP-ribosy ltransferase, a substrate of Interleukin-beta 1 converting enzyme (ICE ) and homologues. However, activation of protein kinase C (PKC) by pho rbol 12-myristate 13-acetate (PMA) mimicked the effects of IFN-alpha(2 ). Furthermore, the bis-indolylmaleimide GF 109203X, a specific inhibi tor of PKC, inhibited the effect of PMA as well as that of IFN-alpha(2 ) on Apo-1/Fas-induced apoptosis. These results point to a PKC-depende nt mechanism of transient interaction between the intracellular signal ing along the IFN-alpha(2) and the Apo-1/Fas pathway (downstream of MA PK signaling as well as of ICE homologues), which becomes exhausted by prolonged stimulation with the cytokine. According to our data IFN-al pha(2), applied continuously and in high doses resembling the therapeu tic situation in vivo, inhibits myeloma growth. However, based on the observed inhibitory effect of IFN-alpha(2) on Apo-1/Fas-induced apopto sis, a partial inhibition of the natural immune surveillance on myelom a cells by endoggenous IFN-alpha(2) present in the bone marrow microen vironment of this malignancy should be investigated.