Increased transcription of the c-myc oncogene in two methylcholanthrene-induced quail fibroblastic cell lines

Role of Marek's disease herpesvirus in the induction of tumours in Japanese quail (Coturnix coturnix japonica) by methylcholanthrene

The QT35 cell line, established from 20-methylcholanthrene (MCA)-induced tumours in Japanese quail, is positive for Marek's disease virus (MDV), and therefore we examined whether MDV is important for the development of MCA-induced tumours. Japanese quail were inoculated with the JM16 strain of MDV at 1 or 3 days of age or left uninoculated. At 3 weeks of age, quail were injected in the breast muscle with 4 mg MCA in corn oil or corn oil alone. Quail were observed for tumours three times/week and at post mortem at 11 to 12 weeks of age. MDV DNA was detected by polymerase chain reaction (PCR) in spleens of 14/20 birds inoculated with JM16+corn oil and of 53/71 birds inoculated with JM16+MCA. Interestingly, 1/74 quail was positive in the MCA group alone for MDV DNA. Tumours were collected for histopathology, cell line development, and PCR and reverse transcriptase-PCR for the presence of MDV. Tumours developed in 38/83 MCA-treated and 32/85 JM16+MCA-treated quail. Fibrosarcomas without metastasis were the only tumours observed in the MCA-treated quail, while quail treated with JM16 and MCA developed undifferentiated tumours, fibrosarcomas, lymphosarcomas or combinations with or without metastasis. One out of 20 quail receiving JM16 alone developed a lymphosarcoma. Cell line development was not influenced by JM16. Tumours from MCA-treated quail were negative for MDV, while 19/29 were positive in the JM16+MCA group. MDV transcripts were present in 13/18 tumours examined in the JM16+MCA group. In conclusion, MDV did not affect tumour development but did influence tumour aggression and histological type.

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

The present study extends our previous data, showing that the v-myc oncogene induces heart tumors and skin anomalies in young avian embryos [Saule et al., Proc. Natl. Acad. Sci. USA 84, 7982-7986 (1987)]. We now report that the target cells which become transformed are the same, whether the MC29 retrovirus is injected at E3 in various sites of the embryo (coelom, heart, brain, lateral plate mesoderm) or deposited on the embryo. Furthermore we confirm, in the quail, the time-specific pattern previously observed in the chick. In the quail, the incidence of heart tumors falls from 100% to 28% when injection is delayed from E3 to E4. By contrast, the incidence of skin anomalies rises from 30% to 64% when injection is delayed from E3 to E4. The skin defect, which consists of the presence of bell-shaped cornified feathers, could be assigned to hyperkeratinization of the epidermis. Both the dermis and the epidermis displayed hyperproliferation, whereas skin muscle hypertrophy during the embryonic period could not be confirmed. The presence of myc gene products was investigated using an antibody that recognizes both the c- and v-myc proteins. In the skin of control embryos, nuclei were well stained at E12-E13. At E14 the signal had disappeared. In abnormal skin patches from infected embryos, the antibody still marked heavily epidermal and dermal nuclei at E18. Finally we injected MC29 through the chorioallantoic vein in E10 chickens. No tumors were found during embryonic life, but 81% of the chickens developed tumors of hemopoietic or endothelial origin from the 14th posthatching day onwards. Studies of MC29 integration sites demonstrated that these tumors were derived from only a few transformed cells. Thus, contrasting with in vitro experiments, in vivo this virus has a restricted number of targets varying with the time of injection.

Characterization of a MH2 mutant lacking the v-myc oncogene

We have previously reported that a virus, MH2-PA200, lacking the ability to transform quail embryo cells, could be isolated from wild type (wt) MH2 stocks passaged on chicken neuroretina cells. We report here the molecular cloning and extensive characterization of this MH2-PA200 provirus. Molecularly cloned MH2-PA200 DNA was found to stimulate the growth of neuroretina cells by transfection assays and our results indicate that this recombinant virus was derived from the RAV-1 helper virus, in which v-mil and a small part of v-myc of MH2 were acquired at the expense of helper (delta gag-pol-delta env) sequences. In order to assess the precise boundary between the myc and env genes we determined the nucleotide sequence of the junction fragment and showed that 11 of 13 nucleotides of the env gene were identical to the myc sequence at the recombination point. The nucleotide sequence of the myc-env junction fragment of another similar and independently generated MH2 mutant showed similarly 9 nucleotides of homology between the env and myc sequences at the recombination point that took place at another site, suggesting that a homologous recombination occurred between MH2 and RAV-1 viruses to generate MH2-PA200 and similar mutants.

Expression of protooncogenes in murine osteosarcomas

The expression of 7 protooncogenes (c-sis, c-abl, c-mos, c-bas, c-Ki-ras, c-fos, c-myc) was examined in transplants and established cell lines from spontaneous and radiation-induced murine osteosarcomas. The transplant tumors were compared with different tissues, particularly skeletal tissue (sternum), and the osteosarcoma cell lines with fibroblast lines from the same mouse strains. C-sis was expressed above the level of controls in 2 osteosarcomas (TV, Os5). Three osteosarcomas showed over-expression of c-abl (TVK, DOS, Os5), c-bas (DOS, Os5 and V893) and c-fos (TVK, DOS, Os5), and 4 osteosarcomas showed over-expression of c-Ki-ras (TVK, DOS, Os5, Os16) and c-myc (TVK, DOS, TV, Os5). C-mos expression was not observed under the conditions used. One cell line (Os5) showed an altered transcript (1 kb transcript of c-fos). Apart from the relatively frequent increase in expression of the c-myc and c-ras-family, there was no indication that any particular protooncogene or combination of protooncogenes was associated with murine osteosarcomas.

Characterization of a myc-containing retrovirus generated by propagation of an MH2 viral subgenomic RNA

We have previously isolated, from wild-type MH2 virus that contains the two oncogenes mil and myc, mutants defective in one or the other oncogene product. We report here the molecular cloning and extensive characterization of MH2 CL25 provirus lacking the v-mil oncogene. Our results indicate that this virus corresponds to the propagation of the 2.8-kilobase subgenomic RNA of MH21.