There are numerous forkhead transcription factors in mammalian cells but we know little about the molecular functions of the majority of these. FOXK2 is a ubiquitously expressed family member suggesting an important function across multiple cell types. Here, we show that FOXK2 binds to the SIN3A and PR-DUB complexes. The PR-DUB complex contains the important tumour suppressor protein, the deubiquitinase BAP1. FOXK2 recruits BAP1 to DNA, promotes local histone deubiquitination and causes changes in target gene activity. Our results therefore provide an important link between BAP1 and the transcription factor FOXK2 and demonstrate how BAP1 can be recruited to specific regulatory loci.

Mature chicken erythrocyte polynucleosomes which are soluble at physiological ionic strength are enriched in beta-globin DNA sequences. Vitellogenin chromatin, which is not expressed in this tissue, is found in aggregation prone, salt insoluble chromatin. There is a direct correlation between the size of soluble fragments and the degree of globin gene enrichment, with the largest fragments being most highly enriched. The highly globin enriched (about 50 fold) polynucleosomes contain significantly elevated levels of acetylated histones H4, H2A.Z, and H2B, and ubiquitinated (prefix "u") histones H2A and H2B (with a significant relative increase of uH2B over uH2A). These polynucleosomes were complexed with histones H1 and H5 but at a lower level than that found in unfractionated chromatin.

Abstract. This study extends the observations on the defects in pseudopod formation of ABP-120 + and ABP-120-cells by a detailed morphological and biochemical analysis of the actin based cytoskeleton. Both ABP-120 + and ABP-120-cells polymerize the same amount of F-actin in response to stimulation with cAMP. However, unlike ABP-120 ÷ cells, ABP-120-cells do not incorporate actin into the Triton X-100-insoluble cytoskeleton at 30-50 s, the time when ABP-120 is incorporated into the cytoskeleton and when pseudopods are extended after cAMP stimulation in wild-type cells. By confocal and electron microscopy, pseudopods extended by ABP-120-cells are not as large or thick as those produced by ABP-120 + cells and in the electron microscope, an altered filament network is found in pseudopods of ABP-120-cells when compared to pseudopods of ABP-120 ÷ cells. The actin filaments found in areas of pseudopods in ABP-120 ÷ cells either before or after stimulation were long, straight, and arranged into space filling orthogonal networks. Protrusions of ABP-120-cells are less three-dimensional, denser, and filled with multiple foci of aggregated filaments consistent with collapse of the filament network due to the absence of ABP-120-mediated cross-linking activity. The different organization of actin filaments may account for the diminished size of protrusions observed in living and fixed ABP-120-cells compared to ABP-120 ÷ cells and is consistent with the role of ABP-120 in regulating pseudopod extension through its crosslinking of actin filaments. p SEUDOPOD extension is an essential feature of many types of cell locomotion. Amoeboid cells in particular are well known for their reliance on pseudopod extension for locomotion. In chemotactic amoebae such as Dictyostelium discoideum, pseudopod extension appears to be a primary event in the reorganization of cytoskeletal polarity that is required for chemotaxis. Despite the demonstrated or suspected importance of the pseudopod in many cell types and after extensive study, modern cell biology has had difficulty in distinguishing definitively among the three general actin based models for how pseudopods are extended (Cooper, 1991;Egelhoff and Spudich, 1991;Condeelis, 1992;Fukui 1993;Lee et al., 1993;Oster and Perelson, 1995;Zigmond, 1993).Part of the problem arises from the complexity of the actin cytoskeleton which contains a multitude of actin binding proteins potentially involved in the temporal and spatial conThe data in this paper are from a thesis to be submitted in partial fulfillment of the requirements for the Degree trol of actin polymerization, filament cross-linking, and sliding (Hartwig and Kwiatkowski, 1991;Luna and Hitt, 1992;Condeelis, 1993a). Taking advantage of model cell populations that exhibit protrusive activity and extend pseudopods synchronously in response to defined stimulation, such as platelets (Hartwig, 1992), neutrophils (Omann, 1987), and Dictyostelium (Condeelis, 1993b), a subset of actin binding proteins specifically involved in pseudopod extension ha...

The canonical Wnt signaling pathway has been the focus of intensive research because of its frequent dysregulation in human cancers. Much of this has been directed towards the aberrant expression and/or activity of the central mediator of this pathway, β-catenin. In particular, the nuclear localization of β-catenin and subsequent inappropriate activation of TCF/LEF-mediated transcription appears to be an important process in both the establishment and maintenance of cancer stem cells. Despite this, the exact mechanisms controlling β-catenin nuclear localization in both normal and malignant cells are poorly understood. This prospect article brings together the many mechanisms previously reported to regulate the nuclear localization of β-catenin and how they are relevant to cancer.

Canonical Wnt/β-catenin signaling is frequently dysregulated in myeloid leukemias and is implicated in leukemogenesis. Nuclear-localized β-catenin is indicative of active Wnt signaling and is frequently observed in acute myeloid leukemia (AML) patients; however, some patients exhibit little or no nuclear β-catenin even where cytosolic β-catenin is abundant. Control of the subcellular localization of β-catenin therefore represents an additional mechanism regulating Wnt signaling in hematopoietic cells. To investigate the factors mediating the nuclear-localization of β-catenin, we carried out the first nuclear/cytoplasmic proteomic analysis of the β-catenin interactome in myeloid leukemia cells and identified putative novel β-catenin interactors. Comparison of interacting factors between Wnt-responsive cells (high nuclear β-catenin) versus Wnt-unresponsive cells (low nuclear β-catenin) suggested the transcriptional partner, LEF-1, could direct the nuclear-localization of β-catenin. The relative levels of nuclear LEF-1 and β-catenin were tightly correlated in both cell lines and in primary AML blasts. Furthermore, LEF-1 knockdown perturbed β-catenin nuclear-localization and transcriptional activation in Wnt-responsive cells. Conversely, LEF-1 overexpression was able to promote both nuclear-localization and β-catenin-dependent transcriptional responses in previously Wnt-unresponsive cells. This is the first β-catenin interactome study in hematopoietic cells and reveals LEF-1 as a mediator of nuclear β- catenin level in human myeloid leukemia.