Targets of v-myc tumorigenesis in the avian embryo depend on time and not on site of retroviral infection

Heregulin selectively upregulates vascular endothelial growth factor secretion in cancer cells and stimulates angiogenesis

The interaction between the erbB tyrosine kinase receptors and their ligands plays an important role in tumor growth via the regulation of autocrine and paracrine loops. We report the effect of heregulin beta1, the ligand for erbB-3 and erbB-4 receptors, on the regulation of vascular endothelial growth factor (VEGF) expression, using a panel of breast and lung cancer cell lines with constitutive erbB-2 overexpression or engineered to stably overexpress the erbB-2 receptor. We demonstrate that heregulin beta1 induces VEGF secretion in most cancer cell lines, while no significant effect was observed in normal human mammary and bronchial primary cells. Overexpression of erbB-2 receptor results in induction of the basal level of VEGF and exposure to heregulin further enhances VEGF secretion. This is associated with increased VEGF mRNA expression. In contrast, VEGF induction is significantly decreased in a T47D cell line where erbB-2 is functionally inactivated. Conditioned media from heregulin-treated cancer cells, but not from normal cells, stimulates endothelial cell proliferation; this paracrine stimulation is inhibited by co-exposure to a specific VEGF neutralizing antibody. Furthermore, heregulin-mediated angiogenesis is observed in the in vivo CAM assay. This study reports the first evidence of VEGF regulation by heregulin in cancer cells. Oncogene (2000) 19, 3460 - 3469

Avian models in developmental biology

The avian embryo is uniquely amenable to experimental manipulation. The most widely used models are chimeras resulting from heterotopic or orthotopic exchanges of rudiments between chick and quail embryos, according to Le Douarin's technique (1969). Cell migrations and fates are traced in these chimeras either through the identification of quail cell nuclei stained for DNA or by means of monoclonal antibodies that recognize a particular lineage in only one of the two species. The ontogeny of the hemopoietic and endothelial lineages, as enlightened through appropriately designed chimeras, is reviewed in the present article. Homologies recently disclosed in mouse and human embryo are emphasized. Finally, the possibilities afforded by retroviral somatic transgenesis in the avian embryo will be envisaged.

Patterns of integration and expression of retroviral, non-replicative vectors in avian embryos: embryo developmental stage and virus subgroup envelope modulate tissue-tropism

We previously demonstrated that Avian Leukemia Viruses (ALV) carrying the v-myc gene specifically induce two types of tumors, cardiomyocytic tumors when the virus is injected before embryonic day 3 (E3), skin tumors when the virus is injected at E3 or E5. Aiming to elucidate the mechanisms which determine this time-dependent change in target, we infected chick and quail embryos at E3 and E5 with replication-deficient, lacZ gene-carrying, ALV-based viruses produced by a packaging cell line. Three constructs driven by 3 different Long Terminal Repeats (LTRs) were tested and yielded similar results. When the constructs were inoculated at E3 and the lacZ gene product revealed 5 days later, around 70% of the embryos carried lacZ+ clones in the heart, around 50% had positive clones in the skin anywhere on the body, while a few embryos displayed clones in internal organs (liver, stomach, lungs). Immunocytological identification of the heart cell type(s) expressing the virus revealed that the only cells infected were cardiomyocytes. When the constructs were inoculated at E5, no lacZ+ clones appeared in the heart but all were located in the cephalic skin. In order to examine the relationship between viral integration and expression, DNA of different organs or tissues from lacZ stained embryos was analyzed by PCR. A tight correlation between integration and expression in the heart and in the skin was revealed in most cases. In contrast, a significant PCR signal was often detected in the liver or the stomach despite weak or absent expression as revealed by lacZ+ clones. We then investigated the influence of envelope glycoprotein subgroups on the tropism of these constructs. The lacZ vector driven by RAV-2 LTRs was packaged as subgroups A, B or E viral particles. The A subgroup, used in the part of the study described above, infects both chick and quail while the B and E subgroups are specific for chick or quail respectively. These B and E subgroups induced lacZ+ clones in the heart (after E3 injection) while no clones or only a few were detected in the skin either after E3 or E5 injection. The following conclusions can be drawn: 1) cardiomyocytes are at E3 the major target for integration and expression of ALV-derived viruses in vivo; 2) targets change rapidly with embryonic age; and 3) tissue-specific infections depend on the envelope subgroup, thus presumably on the presence of the cognate receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

MC29-immortalized clonal avian heart cell lines can partially differentiate in vitro

We established quail clonal heart muscle cell lines from cardiac rhabdomyosarcomas developed in embryos injected in ovo with the MC29 virus containing the v-myc oncogene. These clones were characterized by means of antibodies detecting markers of striated muscle cells. Two clones were selected for further characterization on the basis of a distribution of myogenic markers similar to that in normal early embryonic cardiac muscle cells. However, these muscle markers progressively disappeared with time in culture. Cardiomyocytic differentiation could be reinduced in culture, by associating the avain cardiac cells with 3T3 cells in a defined synthetic medium. Muscle markers were then reexpressed in all cardiac cells as soon as Day 1 after coculture. Multiplication of cardiac cells continued at the same time. This is characteristic of cardiac clones since MC29-infected quail myoblasts and MC29-infected quail fibroblasts exhibited a split response to 3T3 association, i.e., decreased growth and enhanced differentiation. The cardiac clones were maintained in vitro for more than 60 generations (6 months) without morphological changes. To our knowledge, this is the first description of clonal embryonic avian heart cell lines.