We identify the helicase-SANT-associated (HSA) domain as the primary binding platform for nuclear actin-related proteins (ARPs) and actin. Individual HSA domains from chromatin remodelers (RSC, yeast SWI-SNF, human SWI-SNF, SWR1 and INO80) or modifiers (NuA4) reconstitute their respective ARP-ARP or ARP-actin modules. In RSC, the HSA domain resides on the catalytic ATPase subunit Sth1. The Sth1 HSA is essential in vivo, and its omission causes the specific loss of ARPs and a moderate reduction in ATPase activity. Genetic selections for arp suppressors yielded specific gain-of-function mutations in two new domains in Sth1, the post-HSA domain and protrusion 1, which are essential for RSC function in vivo but not ARP association. Taken together, we define the role of the HSA domain and provide evidence for a regulatory relationship involving the ARP-HSA module and two new functional domains conserved in remodeler ATPases that contain ARPs.Transcriptional regulation involves the concerted action of chromatin regulators, transcription factors and the basal transcription machinery. The two general types of chromatin regulators are chromatin remodelers, which reposition and restructure nucleosomes 1 , and chromatin modifiers, which add or remove covalent marks from the histone proteins 2 . These chromatin regulatory complexes work together to mark and move nucleosomes, which can either help silence or activate transcription, depending on the context. Remodelers bear a catalytic ATPase subunit required for ATP-dependent nucleosome repositioning 1,3,4 , whereas modifier complexes bear one or more subunits with histone-modification potential 2,5,6 . However, in both cases, most of the subunits of chromatin regulatory complexes are nonenzymatic. These attendant subunits are specialized for diverse tasks: targeting the complex to particular nucleosomes, enabling complex association with particular DNA binding proteins or other complexes, or helping to regulate enzymatic activity.Intriguingly, actin and ARPs are among the associated subunits of certain chromatinremodeling and chromatin-modifying complexes 7-9 . ARPs have been studied extensively in the budding yeast Saccharomyces cerevisiae, which contains ten ARPs 10 . Four ARPs (ARPs

NF-kappa B regulates normal and pathological processes, including neoplasia, in a tissue-context-dependent manner. In skin, NF-kappa B is implicated in epidermal homeostasis as well as in the pathogenesis of squamous cell carcinoma; however, its function in the underlying mesenchymal dermis has been unclear. To gain insight into NF-kappa B roles in these two adjacent cutaneous tissue compartments, NF-kappa B effects on expression of 12 435 genes were determined in epidermal keratinocytes and dermal fibroblasts. Although NF-kappa B induced proinflammatory and antiapoptotic genes in both settings, it exhibited divergent effects on growth regulatory genes. In keratinocytes, but not in fibroblasts, NF-kappa B induced p21(CIP1), which was sufficient to inhibit growth of both cell types. Levels of growth inhibitory factor (GIF), in contrast, were increased by NF-kappa B in both settings but inhibited growth only in keratinocytes. These findings indicate that transcription factors such as NF-kappa B can program tissue-selective effects via both differential target gene induction as well as by inducing common targets that exert differing effects depending on cellular lineage.

Figure 1Generation of epithelial cells with altered NF-κB function. Normal keratinocytes were transduced with retroviral expression vector for (a) lacZ normal control, (b) constitutively active p50, and (c) the trans-dominant IκBαM super-repressor, then subjected to immunofluorescence staining with antibody to p50 (bars = 5 µm). Note marked nuclear expression in p50-transduced cells and blockade of nuclear-localized p50 in IκBαM.NF-κB subunit transcription activation domains in that these changes are not observed with transcriptionally inactive mutants; the basis for this effect is unclear. This approach, however, has been shown previously to produce the predicted respective induction or blockade of NF-κB-driven gene expression in epithelial cells, both in the case of p50 and p65 alone as well as both subunits together (21) and provides a basis for determining the effects altering NF-κB function on apoptosis in this setting.Fas is expressed in epithelial cells and is implicated as a potentially important mediator of epithelial cell death in settings of inflammation (33-35) and ultraviolet injury (5,36). Cotransduction with vectors altering NF-κB function and a retroviral vector for human Fas/CD95 was used to study NF-κB effects on Fas-triggered apoptosis in epithelial cells. Fas activation in normal control and in IκBαM[+] cells leads to rapid cellular rounding, shrinkage, and detachment in the majority of cells; however, these changes are not seen in NF-κB subunit-expressing cells (Figure 2, a-c and f). These morphologic changes are consistent with apoptosis, a possibility supported by detection of DNA strand breakage using TUNEL assay and characteristic nuclear morphologic condensation and collapse in these cells (Figure 2, d and e).TNFα is another known trigger of apoptosis in many tissues that also impacts NF-κB function. TNFα activation of NF-κB through the TNF receptor TNFR1 opposes TNFα-induced apoptosis in a number of cell types in a process dependent on TRAF2 (8, 37). Whereas TNFα failed to alter normal keratinocytes or those expressing active NF-κB subunits, NF-κB blockade renders these cells very susceptible to TNFα-induced apoptosis (Figure 3, a-d), suggesting an analogous role for NF-κB in preventing apoptosis in epithelial cells.Blockade of NF-κB function leads to premature epidermal cell apoptosis in vivo. Normal stratified epithelium maintains a balance between cellular proliferation and a specialized form of programmed cell death confined to the outer differentiated cell layer at the stratum granulosum-stratum corneum interface (4). This terminal differentiation-associated cell death is not accompanied by classic cell morphologic features of apoptosis such as cell shrinkage and collapse, membrane blebbing, and nuclear condensation seen in other cell death settings in epithelium such as infection and ultraviolet injury (38). NF-κB translocates into nuclei of cells within outer layers of stratified epithelium (21), and this translocation is accompanied by NF-κB target gene activation (K. Hinata et...