RESUMO
The proto-oncogene product c-Myc can induce cell growth and proliferation. It regulates a large number of RNA polymerase II-transcribed genes, many of which encode ribosomal proteins, translation factors and other components of the biosynthetic apparatus. We have found that c-Myc can also activate transcription by RNA polymerases I and III, thereby stimulating production of rRNA and tRNA. As such, c-Myc may possess the unprecedented capacity to induce expression of all ribosomal components. This may explain its potent ability to drive cell growth, which depends on the accumulation of ribosomes. The activation of RNA polymerase II transcription by c-Myc is often inefficient, but its induction of rRNA and tRNA genes can be very strong in comparison. We will describe what is known about the mechanisms used by c-Myc to activate transcription by RNA polymerases I and II.
Assuntos
RNA Polimerases Dirigidas por DNA/metabolismo , Proteínas Proto-Oncogênicas c-myc/metabolismo , Ativação Transcricional , Animais , RNA Polimerases Dirigidas por DNA/genética , Humanos , Camundongos , Modelos Biológicos , Proto-Oncogene Mas , RNA Polimerase I/genética , RNA Polimerase I/metabolismo , RNA Polimerase II/genética , RNA Polimerase II/metabolismo , RNA Polimerase III/genética , RNA Polimerase III/metabolismo , RNA Ribossômico/genética , RNA de Transferência/genéticaRESUMO
The androgen receptor (AR) is a ligand-activated transcription factor that recognises and binds to specific DNA response elements upon activation by the steroids testosterone or dihydrotestosterone. In vitro, two types of response element have been characterised - non-selective elements that bind the androgen, glucocorticoid and progesterone receptors, and androgen receptor-selective sequences. In the present study, the allosteric effects of DNA binding on the receptor amino-terminal domain (NTD) were studied. Binding to both types of DNA response element resulted in changes in the intrinsic fluorescence emission spectrum for four tryptophan residues within the AR-NTD and resulted in a more protease-resistant conformation. In binding experiments, it was observed that the presence of the AR-NTD reduced the affinity of receptor polypeptides for binding to both selective and non-selective DNA elements derived from the probasin, PEM and prostatin C3 genes respectively, without significantly altering the protein-base pair contacts. Taken together, these results highlight the role of intra-domain communications between the AR-NTD and the DNA binding domain in receptor structure and function.