Role of the COP9 signalosome in transcription modulation of genes involved in lipid metabolism and ergosterol biosynthesis in S.cerevisiae

Several components of the ubiquitin/proteasome system (UPS) have been shown to be necessary for the tight regulation of gene expression with possible important implications for cellular homeostasis. Recent evidence shows that part of this regulatory action is at transcriptional level. A key component of the UPS is the COP9 signalosome (CSN), a protein complex conserved in all eukaryotes which removes the small peptide NEDD8 (an ubiqu- itin like modifier) from the cullin-RING family of E3 ubiquitin ligases. The reaction catalyzed by CSN is necessary for the regu- lation of the assembly/disassembly cycles of these ligases and is essential in all higher eukaryotes. At the cellular level, CSN mutants from different organisms display de-repression and, more in general, mis-regulation of several sets of genes. The CSN from budding yeast S.cerevisiae has been recently character- ized. In contrast to other eukaryotes, all the CSN subunits from S.cerevisiae are non-essential. The non essentiality of CSN com- ponents and the availability of powerful genetic tools make S.cerevisiae a very promising model system to elucidate some aspects of the regulatory role of this complex. We performed a transcriptomic analysis of a S.cerevisiae strain deleted in CSN5 (the de- neddylating subunit of the yeast Cop9 complex), as com- pared with its isogenic wild type strain. Data suggest that Csn5 is involved in the modulation of several genes controlling lipid metabolism and ergosterol biosynthesis. In order to support a real involvement of Cop9 signalosome in the regulation of lipid metabolism and ergosterol biosynthesis, we performed real time RT-PCR on 11 genes to test their modulation in all deletion mutants of the Cop9 components. All the modulations were con- firmed for delta csn5 and most of them were observed in most of the other mutants. We also tested the various deletion strains for phenotypic features related to defects in ergosterol biosynthesis. The results are discussed.