Egg yolk phospholipids enriched with 1-O-octadecyl-2-oleoyl-sn-glycero-3-phospho-(N-palmitoyl) ethanolamine inhibit development of experimentally induced tumours

Dietary phospholipids (PLs) and their derivatives have proved active in suppression of various health problems and conditions including cancer. In this work we compared the effect of dietary phospholipids from hen egg yolk enriched with N-acyl ether-phosphatidyl ethanolamine (NAEPE) termed bioactive phospholipids (BAP+ preparation) with PLs lacking NAEPE (BAP- preparation) on the growth of transformed cells in vitro and on the promotion and progression of experimental tumours in vivo. For the in vivo experiments we used the chicken model in which liver, lung, and kidney tumours arose via natural selection from single cells initiated by experimentally introduced somatic mutations caused by insertional mutagenesis. Mutagenized animals were fed BAP+ or BAP- diet in various regimens. We observed that BAP+ at low concentrations killed cells of various tumour cell lines in culture but did not compromise viability of non-transformed cells. Oral administration of the BAP+ preparation efficiently reduced progression of all tumour types. However, it did not significantly reduce the number of already initiated tumours and their growth when BAP+ was discontinued. Our data suggest that NAEPE combined with hen egg PLs significantly interferes with tumour progression, possibly through the inhibition of tumour cell viability.

DNA released by leukemic cells contributes to the disruption of the bone marrow microenvironment

Reciprocal interactions between a tumor and its microenvironment control expansion of tumor cells. Here we show a specific type of interaction in which blasts of experimental leukemia destroy the bone marrow (BM) structures and kill stromal cells. The in vitro experiments showed that the cytotoxic agent released by leukemic cells is the fragmented DNA derived from their genome and occurring in nucleosome-like complexes. This DNA entered nuclei of BM or other cells and induced H2A.X phosphorylation at serine 139, similar to double-strand break-inducing agents. There was a correlation between large amounts of acquired DNA and death of recipient cells. Moreover, the DNA integrated into chromosomal DNA of recipient cells. Primary human acute myeloid leukemia cells also released fragmented DNA that penetrated the nuclei of other cells both in vitro and in vivo. We suggest that DNA fragments released from leukemic and also perhaps other types of tumor cells can activate DNA repair mechanisms or death in recipient cells of a tumor microenvironment, depending on the amount of the acquired DNA. This can impair DNA stability and viability of tumor stromal cells, undermine homeostatic capacity of tumor microenvironment and facilitate tumor progression.

The leucine zipper region of Myb oncoprotein regulates the commitment of hematopoietic progenitors

The development of blood cells proceeds from pluripotent stem cells through multipotent progenitors into mature elements belonging to at least 8 different lineages. The lineage choice process during which stem cells and progenitors commit to a particular lineage is regulated by a coordinated action of extracellular signals and transcription factors. Molecular mechanisms controlling commitment are largely unknown. Here, the transcription factor v-Myb and its leucine zipper region (LZR) are identified as regulators of the commitment of a common myeloid progenitor and progenitors restricted to the myeloid lineage. It is demonstrated that wild-type v-Myb with the intact LZR directs development of progenitors into the macrophage lineage. Mutations in this region compromise commitment toward myeloid cells and cause v-Myb to also support the development of erythroid cells, thrombocytes, and granulocytes, similar to the c-Myb protein. In agreement with that, the wild-type v-Myb induces high expression of myeloid factors C/EBP beta, PU.1, and Egr-1 in its target cells, whereas SCL, GATA-1, and c-Myb are more abundant in cells expressing the v-Myb LZR mutant. It is proposed that Myb LZR can function as a molecular switch, affecting expression of lineage-specifying transcription factors and directing the development of hematopoietic progenitors into either myeloid or erythroid lineages.

Ultrastructural analysis of v-myb oncogene product cooperation with components of avian cell nuclear matrix

The cooperation of the v-Myb oncoprotein with extracted nuclear matrix of avian haematopoietic cells expressing the v-myb oncogene was studied by means of immunoelectron microscopy. The nuclear matrix was extracted by a gentle method of detergent treatment at moderate ionic strength and visualized either in ultrathin LR White sections, in unembedded resin-free sections, and in addition by the aqueous spreading technique. Using anti-Myb polyclonal antibody we have shown interaction of the v-Myb protein product with extracted nuclear matrix. This oncoprotein, however, was easily released from the structure by a detergent as well as by DNAase treatment and ammonium sulphate extraction. Prefixation of structures before detergent treatment prevented this extraction. The v-Myb protein marker was distributed in clusters or associated with fibrillar structures in most cases. Single markers decorating these fibrillar or less dense structures were also detected.

Interaction of V-Myb oncoprotein with spread chromatin of avian haematopoietic cells

Interactions of v-Myb oncoprotein with spread chromatin of avian LSCC-BM2 cells expressing v-myb oncogene were studied by means of immunoelectron microscopy. The application of this technique using anti-Myb polyclonal antibody combined with the Miller type spreading for visualisation of chromatin revealed the presence of Myb protein on stretched chromatin fibres. Intense labelling was apparent on the chromatin dispersed by hypotonic treatment, where the label was present frequently in clusters, although individual marks along the fibrillar molecules were also found. The combination of hypotonic and detergent treatment resulted in better dispersal of chromatin, more frequent detection of active transcription units, but also in removal of some proteins from chromatin fibres. The labelling of chromatin with anti-Myb antibody was substantially reduced in this case and was dependent on detergent concentration used. The marker was found less frequently on chromatin fibres usually present in clusters on remaining protein structures. Our findings confirmed direct interaction of v-Myb protein with chromatin structure. This interaction is apparently affected by detergent treatment.

The Myb leucine zipper is essential for leukemogenicity of the v-Myb protein

The AMV v-Myb oncoprotein causes oncogenic transformation of myelomonocytic cells in vivo and in vitro. Its transforming capacity is strictly dependent upon the N-terminal DNA binding domain, the central transactivation region, and on the C-terminal domain containing a putative leucine zipper motif. Here we show that the v-MybL3,4A mutant, in which Leu325 and Leu332 of the leucine zipper have been replaced by alanines, failed to induce leukemia in virus infected chicken. This demonstrates that the leucine zipper domain is indispensable for v-myb induced leukemogenesis in vivo. v-MybL3,4A was, however, still able to transform myelomonocytic cells from chicken bone marrow in vitro. Yet, while v-mybL3,4A transformed cells were impaired in growth at 37 degrees C, they failed to grow at 42 degrees C, the physiological body temperature of avian species. This might explain the loss of v-MybL3,4A leukemogenic potential in vivo. We also demonstrate that the v-Myb leucine zipper domain interacts in vitro with two host cell proteins, p26 and p28. This interaction is compromised in v-MybL3,4A indicating that binding of v-Myb to p26 and p28 might be important for the leukemogenic potential of v-Myb.

V-myb oncogene and c-myb proto-oncogene expression in avian cells: morphological changes of the cells and topographic localization of myb proteins

Morphological changes of avian cells expressing the v-myb oncogene or c-myb proto-oncogene were studied by means of electron microscopy. Expression of both genes lead to distinct morphological changes of these cells. The nucleus of LSCC-BM2 cells espressing v-myb gene was of normal size but usually of irregular shape. It contained large unravelled nucleoli with typical interstices in some cells. Small nucleolar structures were also localized in the periphery of nuclear membrane. Nuclear envelope revealed reduced perinuclear space between two membranes. LSCC-BK3 cells expressing the c-myb gene were characterized by distinctly enlarged nucleus, in most cases of irregular shape. It contained only one nucleolus markedly enlarged, often unravelled, with apparent interstitial area. Nucleoli with nucleolonemas were observed in some cells. Nuclear envelope formed by two obscure membranes showed reduced perinuclear space. Topographic localization of v-Myb and c-Myb protein products was not basically different, both being detected in the nucleus of avian cells. v-Myb and c-Myb markers were distributed mostly in clusters, usually associated with interchromatin granules, but some marker was associated also with the nuclear membrane. Both Myb products were never detected in nucleolar structures of avian cells. Morphological changes of avian cells expressing myb genes and topographic localization of Myb proteins in these cells were different from those found in the insect cells expressing myb genes. The observed differences are discussed.

Okazaki fragments, a constant component of avian myeloblastosis virus core-bound 7 S DNA

We have shown that the unusual CsCl-buoyant density and velocity sedimentation properties of the isolated host 7 S DNA species associated with the core fraction of avian myeloblastosis virus (AMV) are made mainly by tight association of RNA pieces prevalently joined to the single-stranded portion of this material. It was shown indirectly on sedimentation patterns of [methyl-3H]thymidine and [14C]uridine double-labelled and glyoxylated total AMV DNA, and directly in phosphorylation experiments with T4 polynucleotide kinase performed on the single-stranded portion of AMV DNA that the RNA-DNA link in AMV DNA is of a covalent nature and that the 5'-terminal end of DNA at the RNA-DNA junction is occupied by all four common deoxyribonucleotides. This first evidence of the presence of Okazaki fragments in 7 S AMV DNA clearly indicates that this DNA does not represent a randomly fragmented host DNA included by chance into virions but special fragments of host DNA having the properties of DNA replicative structures with possible consequences for some viral function(s) including those involved in virus-cell interactions.