System-wide responses to heterologous protein production in the fungus Trichoderma reesei

Trichoderma reesei is an industrial protein production host famous for its exceptional protein secretion capability. Protein production can cause stress to cells by compromised protein folding or transport in the secretory pathway. T. reesei is known to respond to secretion stress by unfolded protein response (UPR) and repression through secretion stress (RESS). We have studied the effects of heterologous protein production in bioreactor cultivations on the transcriptome and proteome of T. reesei. As an example of secreted and UPR causing protein, a transformant producing human tissue plasminogen activator (tPA), was studied with semi-genomic transcription profiling methods, cDNA subtraction libraries and cDNA-AFLP and 2D proteomics. In addition effect of chemical dithiothreitol (DTT) and a transformant over-expressing IREI protein (UPR pathway sensor protein) were analysed. Data from various secretion stress transcription profiling experiments in S. cerevisiae were combined from literature and compared to results from T. reesei. The transcriptional responses of T. reesei and S. cerevisiae show clear overlap, especially with UPR related genes involved in protein translocation, folding and glycosylation in the ER, but also some interesting differences. As an example of a protein causing no UPR, a transformant producing Melanocarpus albomyces laccase was studied with oligonucleotide microarrays. Moderate downregulation of secreted proteins was detected.