Hormonal regulation of protein synthesis in cultured kidney cells

From Rous sarcoma virus to plasminogen activator, src oncogene and cancer management

Plasminogen activator (PLAU) is a serine protease that converts plasminogen to plasmin, a general protease, which promotes fibrinolysis and degradation of extracellular matrix. PLAU was reported in 1970s as one of the robustly induced enzymatic activities in Rous sarcoma virus (RSV)-transformed chicken cells. More than three decades later, with the completion of the sequencing of the chicken genome and the subsequent availability of Affymetrix GeneChip genome arrays, several laboratories have surveyed the transcriptional program affected by the RSV transformation. Interestingly, the PLAU gene was shown to be the most highly upregulated transcript. The induction of PLAU was a transformation-dependent process because viruses with deleted Src gene did not induce the transcription of the PLAU gene. Both Src and PLAU genes are associated with and contribute to the complex phenotype of human cancer. Although the activity and structures of these two enzymes are well characterized, the precise molecular function of these gene products in signaling networks is still not fully understood. Yet, the knowledge of their association with cancer is already translated into the clinical setting. Src kinase inhibitors are being tested in clinical trials of cancer therapy, and PLAU gene and its inhibitor have been included as biomarkers with strong prognostic and therapeutic predictive values. This vignette reviews the history of PLAU and Src discovery, and illuminates the complexity of their relationship, but also points to their emerging impact on public health.

Transcriptional profile of Rous Sarcoma Virus transformed chicken embryo fibroblasts reveals new signaling targets of viral-src

Transformation of chicken fibroblasts in vitro by Rous Sarcoma Virus represents a model of cancer in which a single oncogene, viral src, uniformly and rapidly transforms primary cells in culture. We experimentally surveyed the transcriptional program affected by Rous Sarcoma Virus (RSV) in primary culture of chicken embryo fibroblasts. As a control, we used cells infected with non-transforming RSV mutant td106, in which the src gene was deleted. Using Affymetrix GeneChip Chicken Genome Arrays, we report 811 genes that were modulated more than 2.5 fold in the virus transformed cells. Among these, 409 genes were induced and 402 genes were repressed by viral src. From the repertoire of modulated genes, we selected 20 genes that were robustly changed. We then validated and quantified the transcriptional changes of most of the 20 selected genes by real-time PCR. The set of strongly induced genes contains vasoactive intestinal polypeptide, MAP kinase phosphatase 2 and follistatin, among others. The set of strongly repressed genes contains TGF beta 3, TGF beta-induced gene, and deiodinase. The function of several robustly modulated genes sheds new light on the molecular mechanism of oncogenic transformation.

Expression of the yes proto-oncogene in cerebellar Purkinje cells

To identify the kinds of cells in the brain that express the yes proto-oncogene, we examined chicken brains by using immunofluorescent staining and in situ hybridization. Both approaches showed that the highest level of the yes gene product was in cerebellar Purkinje cells. In addition, we analyzed Purkinje cell degeneration (pcd) mutant mice. The level of yes mRNA in cerebella of pcd mutants was four times lower than that found in cerebella of normal littermates. Our studies point to Purkinje cells as an attractive model for functional studies of the yes protein.

Expression of the yes proto-oncogene in cerebellar Purkinje cells

To identify the kinds of cells in the brain that express the yes proto-oncogene, we examined chicken brains by using immunofluorescent staining and in situ hybridization. Both approaches showed that the highest level of the yes gene product was in cerebellar Purkinje cells. In addition, we analyzed Purkinje cell degeneration (pcd) mutant mice. The level of yes mRNA in cerebella of pcd mutants was four times lower than that found in cerebella of normal littermates. Our studies point to Purkinje cells as an attractive model for functional studies of the yes protein.

Hormonal regulation of extracellular plasminogen activators and Mr approximately 54,000 plasminogen activator inhibitor in human neoplastic cell lines, studied with monoclonal antibodies

We have studied the regulation by glucocorticoids and dibutyryl cAMP of the amounts of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA) and a Mr approximately 54000 plasminogen activator inhibitor accumulated in serum-free conditioned culture fluid by a human fibrosarcoma, a human glioblastoma and a human melanoma cell line (HT-1080, UCT/gl-1 and Bowes). For the quantitation of u-PA and t-PA, we used sandwich-type ELISA with a combination of polyclonal and monoclonal antibodies. For an estimation of variations in the amount of the inhibitor, we used sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by Coomassie blue staining of conditioned culture fluid proteins, the inhibitor protein band being identified by its selective removal by passage of the conditioned culture fluids through a column with monoclonal antibodies against the inhibitor. The modulation of the 3 proteins by the hormonal agents varied greatly between the cell lines. The proteins were independently regulated, in the sense that the hormonal agents did not concomitantly change their levels in the direction expected either to increase or decrease total extracellular plasminogen activator activity. In conditioned culture fluids containing both t-PA and inhibitor, the two were present in the medium as a Mr approximately 120 000 complex. In contrast, no u-PA inhibitor complexes were found in conditioned culture fluid from any of the cell lines; this is likely to be due to the occurrence of u-PA in the culture fluid in the one-chain proenzyme form, which, unlike active u-PA, does not react with the inhibitor. These findings illustrate the complexity of the regulation of extracellular plasminogen activator activity, and imply that the presumed functional diversity of u-PA and t-PA may be related to their independent regulation.