STARVATION INDUCES FUSION BETWEEN AUTOFAGIC VACUOLES AND MVBs IN K562 CELLS

FADER CM, SANCHEZ D AND COLOMBO MI.

Iguazú. Misiones. Argentina

Congreso; XL Annual Meeting SAIB 2004; 2004

Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB)

During maturation reticulocytes lose some membrane proteins and some organelles that are not required on the mature red cell. The proteins are released into the extracellular medium associated with vesicles that are formed by budding of the endosomal membrane into the lumen of the compartment, leading to multivesicular bodies (MVBs). Fusion of MVBs with plasma membrane results in secretion of the small internal vesicles, termed exosomes. It has been shown that during erythroid maturation, autophagy is required to eliminate organelles such ribosomes and mitochondria. Autophagy is a normal degradative pathway that involves the sequestration of cytoplasmic components and organelles in a vacuole called an autophagosome that finally fuses with the lysosome and the sequestered material is degraded. In the present report, we have examined by confocal microscopy how starvation affect the development of MVBs in K562 cells overexpresing wt GFP-Rab11 and RFP-LC3 (an autophagosomal marker) . Starvation coased an enlargement of the vacuoles decorated with GFP-Rab11wt and RFP-LC3, and an increased the colocalization beetwen GFP-Rab11wt and RFP-LC3, compared with its control. A similar effect was obtained when the cotranfected cells were incubated in starvation with vinblastin (an MT-depolymerizing agent) or incubated with rapamicin (an autophagy stimulator). The colocalization of RFP-LC3 with GFP-Rab11wt was abrogated by wortmanin and coased a marked enlargement of the vacuoles decorated with GFP-Rab11. Taken together our results suggest that interaction between autophagyc vacuoles and MVBs exist.