Aggressive acute myeloid leukemia in PU.1/p53 double-mutant mice.

PU.1 downregulation within hematopoietic stem and progenitor cells (HSPCs) is the primary mechanism for the development of acute myeloid leukemia (AML) in mice with homozygous deletion of the upstream regulatory element (URE) of PU.1 gene. p53 is a well-known tumor suppressor that is often mutated in human hematologic malignancies including AML and adds to their aggressiveness; however, its genetic deletion does not cause AML in mouse. Deletion of p53 in the PU.1(ure/ure) mice (PU.1(ure/ure)p53(-/-)) results in more aggressive AML with shortened overall survival. PU.1(ure/ure)p53(-/-) progenitors express significantly lower PU.1 levels. In addition to URE deletion we searched for other mechanisms that in the absence of p53 contribute to decreased PU.1 levels in PU.1(ure/ure)p53(-/-) mice. We found involvement of Myb and miR-155 in downregulation of PU.1 in aggressive murine AML. Upon inhibition of either Myb or miR-155 in vitro the AML progenitors restore PU.1 levels and lose leukemic cell growth similarly to PU.1 rescue. The MYB/miR-155/PU.1 axis is a target of p53 and is activated early after p53 loss as indicated by transient p53 knockdown. Furthermore, deregulation of both MYB and miR-155 coupled with PU.1 downregulation was observed in human AML, suggesting that MYB/miR-155/PU.1 mechanism may be involved in the pathogenesis of AML and its aggressiveness characterized by p53 mutation.

5-azacitidine in aggressive myelodysplastic syndromes regulates chromatin structure at PU.1 gene and cell differentiation capacity.

Epigenetic 5-azacitidine (AZA) therapy of high-risk myelodysplastic syndromes (MDS) and acute myelogenous leukemia (AML) represents a promising, albeit not fully understood, approach. Hematopoietic transcription factor PU.1 is dynamically regulated by upstream regulatory element (URE), whose deletion causes downregulation of PU.1 leading to AML in mouse. In this study a significant group of the high-risk MDS patients, as well as MDS cell lines, displayed downregulation of PU.1 expression within CD34+ cells, which was associated with DNA methylation of the URE. AZA treatment in vitro significantly demethylated URE, leading to upregulation of PU.1 followed by derepression of its transcriptional targets and onset of myeloid differentiation. Addition of colony-stimulating factors (CSFs; granulocyte-CSF, granulocyte-macrophage-CSF and macrophage-CSF) modulated AZA-mediated effects on reprogramming of histone modifications at the URE and cell differentiation outcome. Our data collectively support the importance of modifying the URE chromatin structure as a regulatory mechanism of AZA-mediated activation of PU.1 and induction of the myeloid program in MDS.

The role of PU.1 and GATA-1 transcription factors during normal and leukemogenic hematopoiesis.

Hematopoiesis is coordinated by a complex regulatory network of transcription factors and among them PU.1 (Spi1, Sfpi1) represents a key molecule. This review summarizes the indispensable requirement of PU.1 during hematopoietic cell fate decisions and how the function of PU.1 can be modulated by protein-protein interactions with additional factors. The mutual negative regulation between PU.1 and GATA-1 is detailed within the context of normal and leukemogenic hematopoiesis and the concept of 'differentiation therapy' to restore normal cellular differentiation of leukemic cells is discussed.

The STT3 protein is a component of the yeast oligosaccharyltransferase complex.

N-linked protein glycosylation is an essential process in eukaryotic cells. In the central reaction, the oligosaccharyltransferase (OTase) catalyzes the transfer of the oligosaccharide Glc3Man9GlcNac2 from dolicholpyrophosphate onto asparagine residues of nascent polypeptide chains in the lumen of the endoplasmic reticulum. The product of the essential gene STT3 is required for OTase activity in vivo, but is not present in highly purified OTase preparations. Using affinity purification of a tagged Stt3 protein, we now demonstrate that other components of the OTase complex, namely Ost1p, Wbp1p and Swp1p, specifically co-purify with the Stt3 protein. In addition, different conditional stt3 alleles can be suppressed by overexpression of either OST3 and OST4, which encode small components of the OTase complex. These genetic and biochemical data show that the highly conserved Stt3p is a component of the oligosaccharyltransferase complex.

Stepwise assembly of the lipid-linked oligosaccharide in the endoplasmic reticulum of Saccharomyces cerevisiae: identification of the ALG9 gene encoding a putative mannosyl transferase.

The core oligosaccharide Glc3Man9GlcNAc2 is assembled at the membrane of the endoplasmic reticulum on the lipid carrier dolichyl pyrophosphate and transferred to selected asparagine residues of nascent polypeptide chains. This transfer is catalyzed by the oligosaccharyl transferase complex. Based on the synthetic phenotype of the oligosaccharyl transferase mutation wbp1 in combination with a deficiency in the assembly pathway of the oligosaccharide in Saccharomyces cerevisiae, we have identified the novel ALG9 gene. We conclude that this locus encodes a putative mannosyl transferase because deletion of the gene led to accumulation of lipid-linked Man6GlcNAc2 in vivo and to hypoglycosylation of secreted proteins. Using an approach combining genetic and biochemical techniques, we show that the assembly of the lipid-linked core oligosaccharide in the lumen of the endoplasmic reticulum occurs in a stepwise fashion.

STT3, a highly conserved protein required for yeast oligosaccharyl transferase activity in vivo.

N-linked glycosylation is a ubiquitous protein modification, and is essential for viability in eukaryotic cells. A lipid-linked core-oligosaccharide is assembled at the membrane of the endoplasmic reticulum and transferred to selected asparagine residues of nascent polypeptide chains by the oligosaccharyl transferase (OTase) complex. Based on the synthetic lethal phenotype of double mutations affecting the assembly of the lipid-linked core-oligosaccharide and the OTase activity, we have performed a novel screen for mutants in Saccharomyces cerevisiae with altered N-linked glycosylation. Besides novel mutants deficient in the assembly of the lipid-linked oligosaccharide (alg mutants), we identified the STT3 locus as being required for OTase activity in vivo. The essential STT3 protein is approximately 60% identical in amino acid sequence to its human homologue. A mutation in the STT3 locus affects substrate specificity of the OTase complex in vivo and in vitro. In stt3-3 cells very little glycosyl transfer occurs from incomplete lipid-linked oligosaccharide, whereas the transfer of full-length Glc3Man9GlcNAc2 is hardly affected as compared with wild-type cells. Depletion of the STT3 protein results in loss of transferase activity in vivo and a deficiency in the assembly of OTase complex.

Angiomyofibroblastoma of the vulva.

Angiomyofibroblastoma is a rare, myxoid tumor of the vulva. To date only 12 cases have been reported in the world literature. Patients are usually premenopausal and present with a vulval mass initially diagnosed as a Bartholin's cyst. The lesions are well circumscribed and range from 0.5 to 12 cm in size. Microscopically the tumors are characterized by high cellularity, numerous blood vessels, and plump stromal cells. Treatment is by surgical excision. There are currently no published reports of local recurrence or metastatic disease. Angiomyofibroblastoma should be differentiated from other neoplasms of the vulva where radical surgical treatment is indicated. A Case Report of angiomyofibroblastoma of the periclitoral region diagnosed in a postmenopausal woman is presented.

Thiols, gold-thiols, zinc-thiols and the redox state of hemoglobin.

The beta subunit of human hemoglobin can be oxidized site-specifically through beta-Cys-93 by Cu(II)(His)2. A series of thiol ligands, gold thiols and zinc(II) inhibit this oxidation. The thiol inhibitors formed a transient ternary intermediate involving Cu(I) with consequent inhibition of electron transfer from the Fe(II)-heme. The intermediate led to the formation of a disulfide at the beta-Cys-93 site. The most effective thiols achieved maximum inhibition at one equivalent per beta heme. Gold thiols and zinc complexes inhibited heme oxidation by competing with the Cu(II)(His)2 for the beta-Cys-93 site.