MOLECULAR COMPONENTS INVOLVED IN SPECIFIC STEPS OF THE AUTOPHAGY/MULTIVESICULAR BODY (MVB) PATHWAYS

FADER, C. M.; SÁNCHEZ, D.; MESTRE MB AND COLOMBO M.I

Villa Carlos Paz. Cordoba. Argentina.

Congreso; XLIV reunión anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2008

Autophagy is a normal degradative pathway that involves the sequestration of cytoplasmic components and organelles in a vacuole called autophagosome which finally fuses with the lysosome to degrade the sequestered material. In mammalian cells, different extracellular signals can trigger autophagy such as nutrient starvation, stress, or treatment with hormones. Morphological and biochemical studies have shown that autophagosomes fuse with endosomes (e.g. MVBs) forming a so called amphisome. We have analyzed at the molecular level the interaction of MVBs with the autophagic pathway in K562 cells. Our results indicate that a functional Rab11 is required for the interaction between MVBs and autophagosomes, whereas Rab7 was essential for fusion with lysosomes. Moreover, knocking down Beclin-1, to specifically affect the PI3K involved in autophagy, also alters MVB formation indicating that both pathways share molecular components. SNAREs are key molecules of the vesicle fusion machinery. We present evidence indicating that VAMP3/cellubrevin, a v-SNARE protein involved in the endocytic pathway, is necessary for fusion between MVBs and autophagosomes to generate the amphisome. In contrast, VAMP3 does not seem to be required for fusion with lysosomes, which is a microtubule-dependent event, supporting the existence of an alternative direct fusion between autophagosomes and lysosomes.