A spontaneous internal deletion of the c-myb protooncogene enhances transcriptional activation in bovine T lymphoma cells

Modification of mRNA expression after treatment with anabolic agents and the usefulness for gene expression-biomarkers

With this feasibility study a first step towards a new monitoring system for hormonal treatments was done. Screening of regulation and function of anabolic sex steroids via modified gene expression of mRNA in various tissues could be a new approach to trace treatments with unknown drugs or newly combined cocktails. In the study, uterus, liver and muscle tissue from 24 cycling heifers were taken after the animals were treated either with Melengestrol Acetate (MGA), Finaplix-H (200 mg Trenbolone Acetate) or Ralgro (36 mg Zeranol) for 56 days. In every treatment group always two heifers were given 1-fold, 3-fold and 10-fold doses of the standard preparation, the control group without any treatment consisted of two animals. The different tissue gene expression profiles were investigated via the candidate gene approach. Totally 57 candidate genes were selected according to their functionality by screening the actual literature and composed to functional groups: angiogenesis, apoptosis, cell cycle, endocrine factors, energy metabolism, inflammatory factors, muscle function, oncogenes, protein metabolism and transcription factors. Gene expression was measured using quantitative real-time RT-PCR (qRT-PCR) technology. From 24 tested candidate genes in the liver, 17 showed a significant regulation. Eight genes were influenced by MGA, 9 by Finaplix-H, and 4 by Ralgro. For the muscle tissue 19 genes were tested with the result that in the neck muscle 11 genes were regulated and in the hind limb muscle 8 genes. In the neck 5 genes were affected by MGA, 6 by Finaplix-H and 3 by Ralgro. Only 2 genes were influenced by MGA in the hind limb muscle. Finaplix-H affected 6 and Ralgro 4 genes. In the uterus 29 target genes were tested and 13 were significantly influenced by the anabolic sex steroids. Under Finaplix-H treatment eight target genes were regulated and Ralgro and MGA showed a significant regulation in four target genes. The highest gene expression changes under anabolic treatment were observed in the uterus. The analyzed genes showed significant regulations but further studies, testing different animal husbandry conditions will be needed to identify meaningful expression patterns for the different tissues. With the investigation of the regulation and possible function of anabolic sex steroids via gene expression, a preparatory work for the development of an expression pattern for drug screening was made.

Identification of protein instability determinants in the carboxy-terminal region of c-Myb removed as a result of retroviral integration in murine monocytic leukemias

The c-myb oncogene has been a target of retroviral insertional mutagenesis in murine monocytic leukemias. One mechanism by which c-myb can be activated is through the integration of a retroviral provirus into the central portion of the locus, causing premature termination of c-myb transcription and translation. We had previously shown that a leukemia-specific c-Myb protein, truncated at the site of proviral integration by 248 amino acids, had approximately a fourfold-increased half-life compared to the normal c-Myb protein, due to its ability to escape rapid degradation by the ubiquitin-26S proteasome pathway. Here we provide evidence for the existence of more than one instability determinant in the carboxy-terminal region of the wild-type protein, which appear to act independently of each other. The data were derived from examination of premature termination mutants and deletion mutants of the normal protein, as well as analysis of another carboxy-terminally truncated protein expressed in leukemia. Evidence is provided that one instability determinant is located in the terminal 87 amino acids of the protein and another is located in the vicinity of the internal region that has leucine zipper homology. In leukemias, different degrees of protein stability are attained following proviral integration depending upon how many determinants are removed. Interestingly, although PEST sequences (rich in proline, glutamine, serine, and threonine), often associated with degradation, are found in c-Myb, deletion of PEST-containing regions had no effect on protein turnover. This study provides further insight into how inappropriate expression of c-Myb may contribute to leukemogenesis. In addition, it will facilitate further studies aimed at characterizing the specific role of individual regions of the normal protein in targeting to the 26S proteasome.

Characterization of differentially expressed genes in the bovine T lymphoma cell line

A differential display (D.D.) analysis was made to detect differentially expressed genes in a bovine T lymphoma cell line, BTL-26, derived from the calf type of sporadic bovine lymphosarcoma. A D.D. analysis comparing BTL-26 with the bovine epithelial cell line CKT-1 and healthy bovine thymocytes yielded 24 cDNA clones. The DNA sequencing analysis followed by a homology search showed that 20 of the 24 cDNA clones had no significant homology to any sequences in DNA data base. The remaining four genes were homologous to known sequences. Northern blot hybridization among BTL-26, CKT-1 and healthy bovine thymocytes showed that a cDNA clone, BC8, was differentially expressed in BTL-26. The cloning of full-length cDNA for the BC8 clone and its DNA sequences showed that the BC8 clone is a bovine nuclear domain protein homologous to the human NDP52 gene. Northern blot analysis showed that the BC8 clone bovine NDP52 was predominantly expressed in tumor cell line BTL-26, compared with the transcripts from several bovine tissues.

Instability of the 12-nucleotide repeat in c-myb gene of bovine T-lymphoma cells

Insertion of a 12-nucleotide repeat in c-myb gene exon 9 was observed in about 15% of sporadic bovine T-lymphomas. The 12-nucleotide repeat in the T-lymphoma cells showed deletion and insertion of the repeat units during cultivation of the cells. To know whether deficiency in DNA loop repair is involved in the instability of the repeat, abilities to bind and correct the loop structure in nuclear extracts were examined. The nuclear extracts of all examined cells had ability to bind and correct the loop structure. These data suggest that instability of the 12-nucleotide repeat in bovine T-lymphoma cells might be independent of deficiency of DNA loop repair function.