Modulation of Apo‐1/Fas (CD95)‐induced programmed cell death in myeloma cells by interferon‐α₂

Abstract

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. Several cytokines have been reported to interfere with spontaneous and even Apo-1/Fas-induced apoptosis, but no attempt has been made yet to investigate these interactions and the possible underlying mechanisms in myeloma cells. Since in myeloma patients Interferon (IFN)-alpha2 displays a profound therapeutic effect in vivo, which is usually attributed to its growth inhibitory and/or immunomodulatory capacity, we set out to study the potential interference of IFN-alpha2 with Apo-1/Fas-induced apoptosis. Contrary to expectations, IFN-alpha2 reduced the degree of apoptosis caused by the treatment of five Apo-1/Fas-sensitive myeloma cell lines with a Fas monoclonal antibody (mAb). Simultaneous application of IFN-alpha2 and Fas mAb was superior to the prolonged (i.e. >8 h) preincubation with the cytokine as far as inhibition of Apo-1/Fas-induced apoptosis was concerned. This effect of IFN-alpha2 was neither explained by a down-regulation of the Apo-1/Fas receptor nor caused by modulation of the expression levels of c-myc, bcl-2-, bcl-xL, bax- or p53 genes. IFN-alpha2 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-ribosyltransferase, a substrate of Interleukin-beta1 converting enzyme (ICE) and homologues. However, activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) mimicked the effects of IFN-alpha2. Furthermore, the bis-indolylmaleimide GF 109203X, a specific inhibitor of PKC, inhibited the effect of PMA as well as that of IFN-alpha2 on Apo-1/Fas-induced apoptosis. These results point to a PKC-dependent mechanism of transient interaction between the intracellular signaling along the IFN-alpha2 and the Apo-1/Fas pathway (downstream of MAPK signaling as well as of ICE homologues), which becomes exhausted by prolonged stimulation with the cytokine. According to our data IFN-alpha2, applied continuously and in high doses resembling the therapeutic situation in vivo, inhibits myeloma growth. However, based on the observed inhibitory effect of IFN-alpha2 on Apo-1/Fas-induced apoptosis, a partial inhibition of the natural immune surveillance on myeloma cells by endogenous IFN-alpha2 present in the bone marrow microenvironment of this malignancy should be investigated.

Antiviral Treatment with Alpha Interferon Up-Regulates CD14 on Liver Macrophages and Its Soluble Form in Patients with Chronic Hepatitis B

“…In contrast to the uptake of apoptotic cells by DCs, which results in the processing and presentation of Ag to T cells (1), the CD14-mediated uptake of apoptotic cells by macrophages diverts the phagocytosed antigenic material from T-cell recognition (17). This mechanism could be enhanced by the known effect of IFN-␣ on the CD95-mediated pathway of apoptosis: increased levels of expression of CD95 on infected cells (12,28,45) and the concomitant up-regulation of the Fas ligand on NK effector cells (20) may result in the accelerated apoptosis of infected cells, which in turn are removed by CD14-expressing Kupffer cells without further activation of the infiltrating lymphocytes. In line with this interpretation, we found no evidence of a significant involvement of DCs in the liver.…”

Response of hairy cells to IFN-α involves induction of apoptosis through autocrine TNF-α and protection by adhesion

“…Several previous studies examining the killing of other cell types by IFN have implicated CD95/CD95L. 22,24,28,30,42 We therefore examined the role of these proteins in the IFN-␣-induced killing of HCs. Our demonstration that CD95/CD95L is not involved suggests that HCs may belong to the category of type II cells, which express CD95 but fail to form the death-inducing signaling complex.…”

Interferon-α protects myeloma cell lines from dexamethasone-induced apoptosis

“…9 Moreover, Milner et al 8 also demonstrated that IFN-␣ can protect Burkitt's lymphoma lines from Ca 2+ ionophore ionomycin induced apoptosis. In a recent study Egle et al 36 reported that IFN-␣ can block Fasinduced apoptosis in autonomously growing lymphoblastoid…”