Trafficking from the Endoplasmic Reticulum to the Golgi complex and gene expression profiling during the cell stress

The elucidation of the molecular mechanisms regulating the export from the Endoplasmic Reticulum (ER) and the transport to post-ER compartments of secretory proteins represents the basic aim of the present PhD project. To ensure that only properly folded proteins exit the ER and locate to their final destination, a quality control system inspects protein folding within the ER. However, several physiological and pathological conditions generate the accumulation of unfolded proteins within the organelle. The ER reacts to this condition, known as ER stress, by turning on the Unfolded Protein Response (UPR), an integrated signal transduction pathway that transforms the unfolding signals into the expression of molecules required to restore protein homeostasis. Notably, the response to the ER stress affects many functions of the secretory pathway and, in particular, the ER-export. Therefore, an essential aim of the present experimental work was to describe the effect of the ER stress on the molecular events that regulate the exit from ER and the trafficking to the Golgi complex. Experimental results suggest that the ER stress response attenuates the ER-to-Golgi trafficking by affecting COPII function. This control occurs by targeting Sec16 protein expression and by modifying Sec23a recycling properties on the ER membrane. The results concerning this part are analyzed and discussed in the chapter III. Since the UPR carries out its function through the regulation of gene expression, we decided to identify new molecular actors of the UPR control by analyzing gene expression profiles in ER stressed cells. In particular, given the increasing importance of microRNAs in the regulation of several signaling transduction pathways, we analyzed the microRNome changes induced by the UPR activation. In parallel, we characterized the proteome signature in the same stress conditions. The results obtained by the study of microRNome and proteome profiles are described in the chapter IV. [edited by author]