Frequent nuclear localization of ICAD and cytoplasmic co-expression of caspase-8 and caspase-3 in human lymphomas

Lymphoma cells often display in vitro resistance to FAS-induced apoptosis, in which capases act as crucial cell death effecters. Following FAS stimula tion, caspase-8 activates caspase-3, which in turn activates the caspase-ac tivated DNAse (CAD) by proteolysis of its inhibitor (ICAD). To investigate the mechanism of FAS resistance, the expression of caspase-8 was analysed b y immunohistochemistry, together with that of the substrates caspase-3 and ICAD, in 52 representative samples from non Hodgkin's lymphoma (NHL), 12 fr om Hodgkin's disease (HD), and eight benign lymphoid tissues, In benign tis sues, caspase-8 was co-expressed with caspase-3 in the cytoplasm in germina l centre (GC) cells and was co-expressed,vith ICAD in the nuclei of the man tle and marginal zone cells, ICAD expression was weak or absent in GC cells . Cytoplasmic staining for both caspase-8 and caspase-3 was present in 11/1 2 cases of diffuse large cell B-NHL, Caspase-8 positivity was nuclear and c ytoplasmic in 9/9 follicular NHLs, in 5/5 mantle cell NHLs and in 6/6 margi nal zone NHLs. Five out of six: peripheral T-cell NHLs expressed cytoplasmi c caspase-8, Ten out of the 12 HD cases lacked significant cytoplasmic stai ning for caspase-3 and caspase-8 in the majority of Reed-Stenberg cells. Al l lymphoma cases exhibited predominant nuclear ICAD positivity. Subcellular fractionation analysis of three lymphoma samples and normal mantle zone ce lls confirmed that ICAD and caspase-8 were at least partly localized in the nucleus. These results show that the profile of caspase-8 expression is co rrelated with histological lymphoma subtypes; that caspase-8 is co-expresse d,vith caspase-3 in GC cells and their neoplastic counterparts; that ICAD h as an immunohistochemical nuclear localization irt vivo; and that caspase-8 and ICAD can be co-expressed in the nuclei of mantle zone and marginal zon e cells; their unexpected nuclear localization allows a reappraisal of the biochemical cascade of caspase activation, Copyright (C) 2000 John Wiley & Sons, Ltd.