The Golgi as a potential membrane source for autophagy

Abstract

In macroautophagy (hereafter autophagy), a morphological hallmark is the formation of double-membrane vesicles called autophagosomes that sequester and deliver cytoplasmic components to the lysosome/vacuole for degradation. This process begins with an initial sequestering compartment, the phagophore, which expands into the mature autophagosome. A tremendous amount of work has been carried out to elucidate the mechanism of how the autophagosome is formed. However, an important missing piece in this puzzle is where the membrane comes from. Independent lines of evidence have shown that preexisting organelles may continuously supply lipids to support autophagosome formation. In our analysis, we identified several components of the late stage secretory pathway that may redirect Golgi-derived membrane to autophagosome formation in response to starvation conditions.

Figure 1

Schematic representation of membrane flow in the secretory pathway and autophagy. In nutrient-rich conditions, secretory vesicles are sorted from the Golgi to the plasma membrane for secretion. Upon starvation conditions, the Golgi-derived membrane flow may be redirected to the phagophore assembly site. Besides the Golgi, other organelles, such as the ER and possibly the mitochondria, are also involved in this process.