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Autophagy is the bulk degradation of cellular proteins through the autophagosomic-lysosomal pathway. This process is important for normal cell growth, and may be disrupted in tumor cells. Beclin is a Bcl-2 binding protein that is homologous to the yeast autophagy gene, apg6/vps30. The structure of beclin includes a Bcl-2 binding coiled-coil region, and a leucine-rich nuclear export signal (NES). Beclin protein colocalizes with intracytoplasmic organelles and nuclei in normal COS7 and MCF7 cells. However, inhibition of CRM1-dependent nuclear export leads to beclin localization primarily in the nucleus. Mutation of the NES domain of beclin also prevents nuclear export, as well as suppresses beclin-mediated nutrient deprivation-induced autophagy. In addition, these beclin mutants can not inhibit in vitro clonigenicity and in vivo tumorigenicity of MCF7 cells. Beclin interaction with Bcl-2 may be involved with host viral defense, since overexpression of beclin inhibits Sindbis virus replication and expression of beclin lacking the Bcl-2 binding domain has no antiviral effects. Thus, beclin may be an important component of complexes involved in autophagy.Western Blotting
