MYB induces the expression of the oncogenic corepressor SKI in acute myeloid leukemia

Acute myeloid leukemia (AML) arises through clonal expansion of transformed myeloid progenitor cells. The SKI proto-oncogene is highly upregulated in different solid tumors and leukemic cells, but little is known about its transcriptional regulation during leukemogenesis. MYB is an important hematopoietic transcription factor involved in proliferation as well as differentiation and upregulated in most human acute leukemias. Here, we find that MYB protein binds within the regulatory region of the SKI gene in AML cells. Reporter gene assays using MYB binding sites present in the SKI gene locus show MYB-dependent transcriptional activation. SiRNA-mediated depletion of MYB in leukemic cell lines reveals that MYB is crucial for SKI gene expression. Consistently, we observed a positive correlation of MYB and SKI expression in leukemic cell lines and in samples of AML patients. Moreover, MYB and SKI both were downregulated by treatment with histone deacetylase inhibitors. Strikingly, differentiation of AML cells induced by depletion of MYB is attenuated by overexpression of SKI. Our findings identify SKI as a novel MYB target gene, relevant for the MYB-induced differentiation block in leukemic cells.

Identification and in silico structural analysis of Gallus gallus protein arginine methyltransferase 4 (PRMT4)

Protein arginine methyltransferase 4 (PRMT4) is an essential epigenetic regulator of fundamental and conserved processes during vertebrate development, such as pluripotency and differentiation. Surprisingly, PRMT4 homologs have been identified in nearly all vertebrate classes except the avian genome. This raises the possibility that in birds PRMT4 functions are taken over by other PRMT family members. Here, we reveal the existence of a bona fidePRMT4 homolog in the chicken, Gallus gallus. Using a biochemical approach, we initially purified a putative chicken PRMT4 protein and thus provided the first evidence for the presence of an endogenous PRMT4‐specific enzymatic activity toward histone H3 arginine 17 (H3R17) in avian cells. We then isolated a G. gallus PRMT4 (ggPRMT4) transcript encompassing the complete open reading frame. Recombinant ggPRMT4 possesses intrinsic methyltransferase activity toward H3R17. CRISPR/Cas9‐mediated deletion of ggPRMT4 demonstrated that the transcript identified here encodes avian PRMT4. Combining protein–protein docking and homology modeling based on published crystal structures of murine PRMT4, we found a strong structural similarity of the catalytic core domain between chicken and mammalian PRMT4. Strikingly, in silico structural comparison of the N‐terminal Pleckstrin homology (PH) domain of avian and murine PRMT4 identified strictly conserved amino acids that are involved in an interaction interface toward the catalytic core domain, facilitating for the first time a prediction of the relative spatial arrangement of these two domains. Our novel findings are particularly exciting in light of the essential function of the PH domain in substrate recognition and methylation by PRMT4.

Homo-oligomerization of the activating natural killer cell receptor NKp30 ectodomain increases its binding affinity for cellular ligands

The natural cytotoxicity receptors, comprised of three type I membrane proteins NKp30, NKp44, and NKp46, are a unique set of activating proteins expressed mainly on the surface of natural killer (NK) cells. Among these, NKp30 is a major receptor targeting virus-infected cells, malignantly transformed cells, and immature dendritic cells. To date, only few cellular ligands of NKp30 have been discovered, and the molecular details of ligand recognition by NKp30 are poorly understood. Within the current study, we found that the ectodomain of NKp30 forms functional homo-oligomers that mediate high affinity binding to its corresponding cellular ligand B7-H6. Notably, this homo-oligomerization is strongly promoted by the stalk domain of NKp30. Based on these data, we suggest that homo-oligomerization of NKp30 in the plasma membrane of NK cells, which might be favored by IL-2-dependent up-regulation of NKp30 expression, provides a way to improve recognition and lysis of target cells by NK cells.

PRMT4 is a novel coactivator of c-Myb-dependent transcription in haematopoietic cell lines

Protein arginine methyltransferase 4 (PRMT4)–dependent methylation of arginine residues in histones and other chromatin-associated proteins plays an important role in the regulation of gene expression. However, the exact mechanism of how PRMT4 activates transcription remains elusive. Here, we identify the chromatin remodeller Mi2α as a novel interaction partner of PRMT4. PRMT4 binds Mi2α and its close relative Mi2β, but not the other components of the repressive Mi2-containing NuRD complex. In the search for the biological role of this interaction, we find that PRMT4 and Mi2α/β interact with the transcription factor c-Myb and cooperatively coactivate c-Myb target gene expression in haematopoietic cell lines. This coactivation requires the methyltransferase and ATPase activity of PRMT4 and Mi2, respectively. Chromatin immunoprecipitation analysis shows that c-Myb target genes are direct transcriptional targets of PRMT4 and Mi2. Knockdown of PRMT4 or Mi2α/β in haematopoietic cells of the erythroid lineage results in diminished transcriptional induction of c-Myb target genes, attenuated cell growth and survival, and deregulated differentiation resembling the effects caused by c-Myb depletion. These findings reveal an important and so far unknown connection between PRMT4 and the chromatin remodeller Mi2 in c-Myb signalling.

Our manuscript deals with the Protein arginine methyltransferase 4 (PRMT4), which modifies arginine residues in histones and other chromatin-associated proteins and plays an important role in the regulation of gene expression. We addressed the question of how the transcriptional function of PRMT4 might contribute to cell lineage specification despite its ubiquitious expression pattern and how this could explain its involvement in tumorigenesis. As protein associations are likely to provide an answer to this question, we attempted to identify novel interaction partners of PRMT4 using a biochemical approach. By this means, we found that PRMT4 binds Mi2α and its close relative Mi2β. In the search for the biological role of this interaction, we found that PRMT4 and Mi2α/β interact with the transcription factor c-Myb and cooperatively coactivate c-Myb target gene expression in haematopoietic cell lines. Depletion of PRMT4 or Mi2α/β in human erythroleukemia cells resulted in deregulated cell proliferation and differentiation resembling the effects caused by c-Myb depletion. Our findings unravel an important and so far unknown connection between PRMT4 and the chromatin remodeller Mi2 in c-Myb signalling and gene activation and identify both coregulators as attractive targets for leukaemia research and therapy in the future.

Homoleptic lanthanide amides as homogeneous catalysts for alkyne hydroamination and the Tishchenko reaction

The homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides of the general type [Ln[N(SiMe3)2]3] (1) (Ln=Y, lanthanide) represent a new class of Tishchenko precatalysts and, to a limited extent, precatalysts for the hydroamination/cyclization of aminoalkynes. It is shown that 1 is the most active catalyst for the Tishchenko reaction. This contribution presents investigations on the scope of the reaction, substrate selectivity, lanthanide-ion size-effect, and kinetic/mechanistic aspects of the Tishchenko reaction catalyzed by 1. The turnover frequency is increased by the use of large-center metals and electron-withdrawing substrates. The reaction rate is second order with respect to the substrate. While donor atoms, such as nitrogen, oxygen, or sulfur, on the substrate decrease the turnover frequency, 1 shows a tolerance for a large number of functional groups. For the hydroamination/cyclization of aminoalkynes, 1 is less active than the well-known metallocene catalysts. On the other hand, 1 is much more readily accessible (one-step synthesis or commercially available), than the metallocenes and might therefore be an attractive alternative catalyst.

Immunization with rough mutants of Salmonella minnesota: initial studies in human subjects

Vaccines prepared from unheated and boiled, acetone-precipitated Salmonella minnesota R595 (Re chemotype mutant) were administered subcutaneously to 122 healthy volunteers. Titers of antibody to Re lipopolysaccharide, the basal core structure of endotoxin, as measured by indirect hemagglutination, rose in a dose-responsive fashion after immunization. Febrile reactions, usually mild, occurred after 7% of injections with the highest doses (2.0 and 3.0 x 10(10) organisms), and mild local soreness and tenderness were noted after approximately one-third of injections. Passive immunization of mice with sera from immunized subjects demonstrated that protective activity against challenge with both heterologous, viable gram-negative bacilli and endotoxin developed. Although measuring serum protective activity, developing a serological assay that correlates with protective activity, and potential vaccine toxicity remain problems, immunization of humans with the Re mutant results in serum protective activity against endotoxin and viable bacilli and has the potential for clinical usefulness.

Immunization with rough mutants of Salmonella minnesota: protective activity of IgM and IgG antibody to the R595 (Re chemotype) mutant

We evaluated the immunoglobulin class responsible for the protective activity in serum obtained from humans and rabbits after immunization with the R595 (Re chemotype) mutant of Salmonella minnesota. Whole serum obtained before immunization and the IgG and IgM fractions failed to protect mice against lethal challenge with viable Klebsiella pneumoniae or Morganella morganii or with Salmonella typhi lipopolysaccharide (LPS). The protective activity of postimmunization serum resided solely in IgM antibody, whereas IgG antibody exhibited no protective activity. IgM antibody to the Re mutant was protective against bacterial challenge with both test strains of bacteria and S. typhi LPS. IgM antibody, at approximately the same concentration present in postimmunization serum, increased the LD50 of K. pneumoniae from less than 8.0 x 10(2) to greater than 2.0 x 10(4). These findings indicate that commercially prepared human IgG with high titers of antibody to antigens of the core portion of LPS would have little clinical utility.

Long-term development of a primary lung sarcoma, probably lymphangiosarcoma--a case report

A small primary lung lesion had remained unchanged in size over a period of 8 years. Within the ensuing 2 years rapid tumor growth occurred. On operation the surgical specimen revealed a tumor mass of 87.2 cm3. Within 6 months after resection, the tumor occurred on the same side. Extensive tumor infiltration of the chest wall prevented any further surgery. The histo-morphologic picture of both lesions was consistent with a lymphangiosarcoma without evidence of high grade malignancy. The patient died of cardio-respiratory insufficiency due to extension of the tumor mass. Unfortunately no autopsy was performed. Tumor growth rates, macroscopic reconstruction and electron microscopic evaluations are presented. This case report again points out that size and long-time stability of solitary lung nodules are not necessarily reliable criteria for assessing prognosis.