Constitutively Active NFκB Is Required for the Survival of S-type Neuroblastoma*

Abstract

The NFκB transcription factors can both promote cell survival and induce apoptosis depending on cell type and context. Neuroblastoma (NB) cells display two predominant culture phenotypes identified as N- and S-types. Malignant S-type cells express neither high levels of MYCN nor Bcl-2, suggesting that other survival mechanisms are important. We characterized NFκB activity in S-type cells and determined its role in their survival. S-type lines (SH-EP1 and SK-N-AS) were treated with pyrrolidine dithiocarbamate (PDTC), a NFκB inhibitor, orl-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK), a serine protease inhibitor that blocks IκBα degradation. Both agents induced cell death, suggesting that constitutive NFκB activity is required for survival. The transient expression of a super-repressor IκBα mutant killed S-type cells. The inhibition of NFκB produced an apoptotic response characterized by the collapse of the mitochondrial transmembrane electrochemical gradient, caspase-9 activation, and apoptotic DNA changes. Constitutive NFκB DNA binding activity specifically involving p65 and p50 was demonstrated in S- but not N-type cells by electromobility supershift and gene reporter assays. This study demonstrates a role for NFκB in the survival of S-type NB tumor cells and suggests that NFκB activity and function differ according to NB tumor cell phenotype.