Ferritin is a ubiquitously distributed iron-binding protein that plays a key role in cellular iron homeostasis. It is composed of two subunits, termed H (heavy or heart) and L (light or liver). In fibroblasts and other cells, the cytokine tumor necrosis factor-alpha (TNF) specifically induces synthesis of the ferritin H subunit. Using nuclear run-off assays, we demonstrate that this TNF-dependent increase in ferritin H is mediated by a selective increase in ferritin H transcription. Transfection of murine fibroblasts with chimeric genes containing the 5'-flanking region of murine ferritin H fused to the human growth hormone reporter gene reveals that the cis-acting element that mediates this response is located approximately 4.8 kilobases distal to the start site of transcription. Deletion analyses delimit the TNF-responsive region to a 40-nucleotide sequence located between nucleotides -4776 and -4736, which we term FER-2. Electrophoretic mobility shift assays and site-specific mutations indicate that this region contains two independent elements: one contains a sequence that binds a member of the NF-kappa B family of transcription factors, and a second contains a novel sequence that partially conforms to the NF-kappa B consensus sequence and may bind a different member of the NF-kappa B/Rel transcription factor family. Thus, effects of an inflammatory cytokine on ferritin are mediated by a family of transcription factors responsive to oxidative stress.

Abstract. Several members of the rho/rac family of small GTP-binding proteins are known to regulate the distribution of the actin cytoskeleton in various subcellular processes. We describe here a novel rac protein, racE, which is specifically required for cytokinesis, an actomyosin-mediated process. The racE gene was isolated in a molecular genetic screen devised to isolate genes required for cytokinesis in Dictyostelium. Phenotypic characterization of racE mutants revealed that racE is not essential for any other cell motility event, including phagocytosis, chemotaxis, capping, or development. Our data provide the first genetic evidence for the essential requirement of a rho-like protein, specifically in cytokinesis, and suggest a role for these proteins in coordinating cytokinesis with the mitotic events of the cell cycle.T HE intimate association between mitosis and cytokinesis requires a means of coordination between these two processes to insure that the newly duplicated nuclei segregate properly with half of the cytoplasm into the daughter cells. Although much is known about these processes, the mechanism(s) by which they are coordinated remains unknown. The regulation of the mitotic cell cycle has been intensively studied over the last several years. Biochemical and genetic approaches have combined to identify many of the key proteins that control different aspects of the cell cycle. In addition, many of the structural proteins that compose the mitotic apparatus have been characterized. Similarly, much is understood about how cells achieve proper cytoplasmic division. In animal cells, this involves the formation of an equatorial contractile ring that consists largely of actin and myosin and constricts to divide the cell into two . However, it is not understood how these proteins localize to the equator of the cell at the appropriate time and in the correct orientation. From the work of Rappaport (1990), it is clear that the astral microtubules of the mitotic apparatus are intimately involved in determining the placement of the contractile ring. What is not clear is what kind of signals may be involved or how they may be transmitted by the mitotic apparatus to the cell cortex.The rho family of ras-related small GTP-binding proteins (including rho, cdc42, and rac proteins) are known to have profound effects on the actin cytoskeleton (Hall, 1994). Rho proteins have been implicated in the regulation of cytokinesis in both sand dollar (Mabuchi et al., 1993)

The centrosome-nucleus attachment is a prerequisite for faithful chromosome segregation during mitosis. We addressed the function of the nuclear envelope (NE) protein Sun-1 in centrosome-nucleus connection and the maintenance of genome stability in Dictyostelium discoideum. We provide evidence that Sun-1 requires direct chromatin binding for its inner nuclear membrane targeting. Truncation of the cryptic N-terminal chromatinbinding domain of Sun-1 induces dramatic separation of the inner from the outer nuclear membrane and deformations in nuclear morphology, which are also observed using a Sun-1 RNAi construct. Thus, chromatin binding of Sun-1 defines the integrity of the nuclear architecture. In addition to its role as a NE scaffold, we find that abrogation of the chromatin binding of Sun-1 dissociates the centrosome-nucleus connection, demonstrating that Sun-1 provides an essential link between the chromatin and the centrosome. Moreover, loss of the centrosomenucleus connection causes severe centrosome hyperamplification and defective spindle formation, which enhances aneuploidy and cell death significantly. We highlight an important new aspect for Sun-1 in coupling the centrosome and nuclear division during mitosis to ensure faithful chromosome segregation.Key words: aneuploidy, centrosome hyperamplification, nuclear envelope architecture, spindle formation defects, Unc-84 The nuclear envelope (NE) separates the nuclear compartment from the cytoplasm. It is composed of two membranes: the outer nuclear membrane (ONM) and the inner nuclear membrane (INM). The lumen between the two membranes is the perinuclear space (PNS). The ONM is continuous with the endoplasmic reticulum (ER), whereas the INM harbors a unique set of proteins. INM and ONM proteins can interact within the PNS. Underneath the INM, the nuclear lamina is located, which is formed by intermediate filament (IF) proteins and associated proteins. The lamina forms the nucleoskeleton and associates with the INM, chromatin and nuclear pore complexes. Proteins of the NE have important roles. They are involved in nuclear migration and positioning and are essential for many processes such as mitosis, meiosis, differentiation and cell migration. Furthermore, several of the NE proteins have been associated with inherited diseases (1,2). Research in mammalian cells and in Caenorhabditis eleganshas identified conserved components of the NE that link the nucleoskeleton to the cytoskeleton. In C. elegans, two putative INM proteins, matefin/SUN-1 and UNC-84, bind to the nuclear lamina and extend their C-terminus into the PNS where they interact with the C-termini of KASH domain proteins (Klarsicht/Anc-1/Syne homology, designated KASH domain). Matefin/SUN-1 and UNC-84 belong to the SUN family of proteins based on the presence of the conserved SUN (Sad1/UNC-84 homology) domain at their C-terminus. KASH domain proteins are type II transmembrane proteins of the NE and have been identified as molecular linkers connecting the nucleus to actin filaments [filamentous acti...