Seminar of Alison Forrester - Unité de Recherche en Biologie Cellulaire (URBC) - University of Namur, Belgium

Alison Forrester  

 Modulation of the early secretory pathway and the effects on interlinked cellular processes 

Abstract:  For 30% of nascent proteins, biosynthesis starts in the Endoplasmic Reticulum (ER). Once properly folded, proteins undergo COPII-dependent transport from the ER exit site (ERES) to the ER-Golgi Intermediate Compartment (ERGIC) then to the Golgi, where they are distributed or secreted. Each step in the secretory pathway is linked to specific post-translational modifications, that regulate protein folding and thus function. Protein trafficking is complex and tightly regulated, however it remains error prone, and errors cause a wide range of common diseases. Therefore, the identification of novel tools that can target the secretory pathway is key to developing therapies against these common diseases of aberrant secretion.

The first specific pharmacological inhibitor of ERES, Retro-2, was discovered in 2020. Retro-2 targets ERES component Sec16A and decreases anterograde trafficking of SNARE protein Syntaxin 5, providing proof of principle that the ERES can be specifically and acutely targeted. Therefore, the research aim of my team is to develop an overarching and integrated understanding of the mechanisms and therapeutic outcomes of ERES modulation, the effects of this modulation on homeostasis, and on the coordination of dynamic cellular processes and the secretory pathway.

To develop tools to modulate the secretory pathway, we have performed high throughput trafficking assays on a diverse set of molecules, from which we have made a shortlist of hit compounds. From this we have identified a pharmacophore to identify traffic-targeting compounds with which we will perform an in silico screen of wider chemical libraries. We have shown that one of our lead compounds specifically slows ER to Golgi trafficking of type I and II procollagen, and we are now testing this in a mouse model of hepatic fibrosis. Although we know that the compound's target is Sec16A, it is not clear how targeting this causes such a specific effect on cargo trafficking. We have shown that the compound interrupts the interaction of key ERES proteins, Sec16A-Sec13. This interaction is responsible for stabilising Sec16A, which is essential for efficient ERES cycling, however the decreased interaction is unexpected and we will characterise the frequency of this during physiological regulation of ERES function.

In addition, Sec13 is not only involved at the ERES, but also at GATOR2 and the Nuclear Pore Complex. All three complexes regulate major catabolic pathways, and we propose that Sec13 acts as the factor that coordinates these processes. Therefore, we are currently studying whether the Sec16A-Sec13 interaction is involved in physiological regulation of the ERES, and thus, through increasing the free pool of Sec13, coordinates the activation of GATOR2 and NPC complexes. This information will begin to describe the interlinked effects of ERES modulation, and whether modulation of trafficking through regulation of the Sec16-Sec13 interaction can be used as a therapeutic approach in diseases of aberrant secretion.