Nuclear matrix provides linkage sites for translocated NF-kappa B: morphological evidence

In response to the binding of extracellular ligands to cell surface receptors, multiple transcription factors are activated in the cytoplasm and translocated into the nucleus where they exert positive or negative control over cellular genes. The human transcription factor NF-kappa B family regulates the expression of a large number of genes involved in the host defence mechanism. They are typically present in the cytoplasm bound to the inhibitory I kappa B proteins. The activation of NF-kappa B involves the signal-induced degradation of these proteins, allowing NF-kappa B to translocate to the nucleus. In this study, by multiparametric analysis, we recognise in RPMI-8402 DMSO-activated cells the intracellular movement of transcription factor NF-kappa B providing its definite intranuclear collocation. Intact cells, purified nuclei and nuclear matrix preparations after 4 h of treatment were processed for morphological and biochemical analyses. Light and electron microscope observations show, in untreated cells, the presence of NF-kappa B protein homogeneously retained in the cytoplasm. Treated cells display a massive presence of NF-kappa B at the nuclear level bound to the interchromatin region. Immunoblotting of the same specimens confirms the strong association of NF-kappa B with the nuclear scaffold. Taken together, the data presented in this manuscript support a model where DMSO treatment provokes the cleavage and translocation of NF-kappa B from the cytoplasm to the nucleus and, in particular, in the proteinaceous network of the nuclear matrix sustaining the active role of this subcellular structure on regulation of eukaryotic gene expression.