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Background
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Autophagy, the process of bulk degradation of cellular proteins through an autophagosomic-lysosomal pathway is important for normal growth control and may be defective in tumor cells. It is involved in the preservation of cellular nutrients under starvation conditions as well as the normal turnover of cytosolic components. In mammalian cells, APG7 is essential for autophagy conjugation systems, autophagosome formation, starvation-induced bulk degradation of proteins and organelles. Beclin-1, a coiled-coil Bcl-2-interacting protein homologous to the yeast autophagy gene apg6, is a mammalian autophagy gene that can inhibit tumorigenesis and is expressed at reduced levels in human breast carcinoma, suggesting that defects in autophagy proteins may contribute to the development or progression of tumors. PIST is a protein that interacts with Beclin-1 through its coiled-coil domain and can modulate Beclin-1 activity. LAMP1 and LAMP2 are homologous, highly glycosylated proteins associated with the lysosome and are thought to have overlapping functions. Mice lacking LAMP1 have very minor defects compared to those deficient in LAMP2 expression. However, the loss of both proteins results in embryonic lethality, suggesting that each protein possesses some unique and necessary functions.
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