Arrivals and departures at the plasma membrane: direct and indirect transport routes

Abstract

Studies carried out during the last 2 decades have dramatically increased our knowledge of the pathways and mechanisms of intracellular membrane traffic, most recently due to the developments in light microscopy and in vivo imaging of fluorescent fusion proteins. These studies have also revealed that certain molecules do not behave according to the classical transportation rules first documented in cell biology textbooks in the 1980s and 1990s. Initially, unconventional mechanisms of secretion that do not involve passage of cargo through the stacked Golgi cisternae were thought to confer on cells the ability to discard excess amounts of protein products. With time, however, more physiological mechanisms and roles have been proposed for an increasing number of secretory processes that bypass the Golgi apparatus.

Heat Shock Protein HSP27 Secretion by Ovarian Cancer Cells Is Linked to Intracellular Expression Levels, Occurs Independently of the Endoplasmic Reticulum Pathway and HSP27’s Phosphorylation Status, and Is Mediated by Exosome Liberation

“…Protein secretion may also occur by direct translocation through the cytoplasmic membrane or by uptake into different types of export vesicles including exosomes [41]. In prostate cancer cells, HSP27 protein is unspecifically incorporated into exosomes [22], and in OC cells, Dolo et al identified a protein release by cellular vesicle shedding [42].…”

Secretion of fatty acid binding protein aP2 from adipocytes through a nonclassical pathway in response to adipocyte lipase activity

“…However, upon induction of lipolysis, GFP signal became less diffuse and assumed a more peripheral and punctate pattern, suggesting that aP2 may be compartmentalized into structures that mediate its secretion. Nonclassical secretion can occur through several pathways, many of which include intracellular membranous structures and vesicles ( 46 ). Therefore, we asked whether aP2 localizes to a membranous compartment during lipolysis by conducting subcellular fractionation experiments.…”

The secretory pathway at 50: a golden anniversary for some momentous grains of silver

“…Recent research, for example, reveals fascinating mechanisms that are deployed to transport very large cargoes, such as polymers of newly synthesized collagen, which could not be physically accommodated within the confines of the carrier vesicles that transport standard cargoes between the secretory pathway’s stations (Venditti et al , 2012; Lavieu et al , 2014; Malhotra et al , 2015). Furthermore, at least some proteins, including a subset of those that populate the membrane of the primary cilium, appear to pursue a variant version of the secretory pathway via which they bypass some or all of the structures of the Golgi complex (Hoffmeister et al , 2011; Prydz et al , 2013; Tian et al , 2014). These are but a few of the additional functions and specialized adaptations of the secretory pathway that Jamieson and Palade could not have predicted when they interpreted the tracks of the autoradiographic silver grains that traveled across their electron micrographs half a century ago.…”