Homeostatic cell cycle and the origin of autophagosomal vesicles ()
ABSTRACT
The autophagosomes were
identified in the viable cycloheximide (CHX)-treated cells which had an incapacitated
translational process and thus disabled synthesis of endoplasmic reticulum
(ER)-derived vesicular transporters. They were found devoid of the proteins
transported from ER to cell organelles, were unable to fuse with ER, Golgi or
mitochondria, and displayed affinity with lysosomes. The analysis of autophagosomes,
derived from the CHX cell organelles, revealed that their lipid composition
resemble that of the maternal organelle. Thus, the ER-derived autophagosomes
were marked with the presence of phosphatidylinositol (PI), Golgi-derived
vesicles contained sphingomyelin (SM) and glycosphingolipids (GLL), and the
mitochondria-derived autophagosomes contained phosphatidylglycerol (PG) and
cardiolipin (CL). The incubation of the vesicles with intact lysosomes
afforded their and the lysosome membrane lipids degradation. The analysis of
the products derived from incubation of lysosomes and autophagosomes with
radiolabeled SM, in the presence and the absence of TritonX100,
allowed us to conclude that during autophagosome degradation the lysosomal enzymes
are not released to cytosol, and that only lysosomes contain the enzymes
degrading membrane lipids. In summary, our findings allowed us to authenticate
the vesicles generated in the CHX-treated cells as organelle-specific
autophagosomes and to determine that complete cycle of cell restitution and
debridement includes intralysosomal degradation of the lysosomal membrane
engulfing the autophagosomes vesicles.
Share and Cite:
Slomiany, A. and Slomiany, B. (2013) Homeostatic cell cycle and the origin of autophagosomal vesicles.
Advances in Biological Chemistry,
3, 275-287. doi:
10.4236/abc.2013.33031.