Actin cytoskeleton participates in the early events of autophagosome formation upon starvation induced autophagy.

AGUILERA, M.O.; BERÓN, W.; COLOMBO M.I.

AUTOPHAGY

LANDES BIOSCIENCE

Lugar: Austin, Texas; Año: 2012

1554-8627

Autophagy is a process by which cytoplasmic material is sequestered in a double membrane vesicle destined for degradation. Nutrient deprivation stimulates the pathway and the number of autophagosomes in the cell increases in response to such stimulus. In the current report we have demonstrated that actin is necessary for starvation-mediated autophagy. When the actin cytoskeleton is depolymerized, the increase in autophagic vacuoles in response to the starvation stimulus was abolished without affecting maturation of remaining autophagosomes. In addition, actin filaments colocalized with Atg14L, Beclin 1 and PI3P-rich structures, and some of them have a typical omegasome shape stained with the double FYVE domain or DFCP1. In contrast, no major colocalization between actin and ULK1, ULK2, Atg5 or LC3 was observed. Taking together our data indicate that actin has a role at very early stages of autophagosome formation linked to the PI3P generation step. In addition, we have found that two members of the Rho family of proteins, RhoA and Rac1 have a regulatory function on starvation-mediated autophagy, but with opposite roles. Indeed, RhoA has an activatory role whereas Rac has an inhibitory one. We have also found that inhibition of the RhoA effector ROCK impaired the starvation-mediated autophagic response.  We propose that actin participates in the initial membrane remodeling stage when cells require an enhanced rate of autophagosome formation, and this actin function would be tightly regulated by different members of the Rho family.