Abstract
Many proteins and cargoes in eukaryotic cells are secreted through the conventional secretory pathway that brings proteins and membranes from the endoplasmic reticulum to the plasma membrane, passing through various cell compartments, and then the extracellular space. The recent identification of an increasing number of leaderless secreted proteins bypassing the Golgi apparatus unveiled the existence of alternative protein secretion pathways. Moreover, other unconventional routes for secretion of soluble or transmembrane proteins with initial endoplasmic reticulum localization were identified. Furthermore, other proteins normally functioning in conventional membrane traffic or in the biogenesis of unique plant/fungi organelles or in plasmodesmata transport seem to be involved in unconventional secretory pathways. These alternative pathways are functionally related to biotic stress and development, and are becoming more and more important in cell biology studies in yeast, mammalian cells and in plants. The city of Lecce hosted specialists working on mammals, plants and microorganisms for the inaugural meeting on “Unconventional Protein and Membrane Traffic” (UPMT) during 4–7 October 2016. The main aim of the meeting was to include the highest number of topics, summarized in this report, related to the unconventional transport routes of protein and membranes.
Highlights
The definition of the conventional secretory pathway arose from studies realized during the 1960s and 1970s
Autophagy is one possible source for double membrane compartments bypassing the Golgi apparatus in transporting specific cargos directly from endoplasmic reticulum (ER) to the lysosome/vacuole or to the extracellular space/cell wall. It is becoming more and more apparent that autophagy-related endomembrane transport processes are an essential part of basal cellular machinery, but the mode of unconventional secretion that is dependent on autophagy is less clear in mechanistic terms, as well as its intricate interrelations with other processes
Another example of an unconventional role for a conventional trafficking protein was provided by Gian Pietro di Sansebastiano (University of Salento, Lecce, Italy), who at short notice described their work on the syntaxin 5 proteins in A. thaliana
Summary
The definition of the conventional secretory pathway arose from studies realized during the 1960s and 1970s (reviewed in [1]). Such proteins include members of the Annexin family, cytoskeletal proteins, Heat Shock Proteins, members of the interleukin family, fibroblast growth factors, and others (see review [8] for references). The mechanism of membrane permeabilization required for Interleukin-1β release seems to be distinct from the formation of membrane pores required for other types of unconventional protein secretion that do not result in cell death but still needs further characterization. He further discussed this observation in the context of evolution
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