<P> Several experiments have been done with mice and varying Beclin1, a protein that regulates autophagy . When the Beclin1 gene was altered to be heterozygous (Beclin 1 + / -), the mice were found to be tumor prone . However, when Beclin1 was overexpressed, tumor development was inhibited . Care should be exercised when interpreting phenotypes of beclin mutants and attributing the observations to a defect in autophagy, however: Beclin1 is generally required for phosphatidylinositol 3 - phosphate production and as such it affects numerous lysosomal and endosomal functions, including endocytosis and endocytic degradation of activated growth factor receptors . In support of the possibility that Beclin1 affects cancer development through an autophagy - independent pathway is the fact that core autophagy factors which are not known to affect other cellular processes and are definitely not known to affect cell proliferation and cell death, such as Atg7 or Atg5, show a much different phenotype when the respective gene is knocked out, which does not include tumor formation . In addition, full knockout of Beclin1 is embryonic lethal whereas knockout of Atg7 or Atg5 is not . </P> <P> Necrosis and chronic inflammation also has been shown to be limited through autophagy which helps protect against the formation of tumor cells . Thus these experiments show autophagy's role as a tumor suppressor . </P> <P> Alternatively, autophagy has also been shown to play a huge role in tumor cell survival . In cancerous cells, autophagy is used as a way to deal with stress on the cell . Once these autophagy related genes were inhibited, cell death was potentiated . The increase in metabolic energy is offset by autophagy functions . These metabolic stresses include hypoxia, nutrient deprivation, and an increase in proliferation . These stresses activate autophagy in order to recycle ATP and maintain survival of the cancerous cells . Autophagy has been shown to enable continued growth of tumor cells by maintaining cellular energy production . By inhibiting autophagy genes in these tumors cells, regression of the tumor and extended survival of the organs affected by the tumors were found . Furthermore, inhibition of autophagy has also been shown to enhance the effectiveness of anticancer therapies . </P> <P> Cells that undergo an extreme amount of stress experience cell death either through apoptosis or necrosis . Prolonged autophagy activation leads to a high turnover rate of proteins and organelles . A high rate above the survival threshold may kill cancer cells with a high apoptotic threshold . This technique can be utilized as a therapeutic cancer treatment . </P>

What is the lysosomes role in maintaining homeostasis in the cell