Class III PI3K as an Autophagy Reactivation Switch in Malignant Transformation

项目总结

Project Summary Macroautophagy (hereafter autophagy) is crucial to cellular homeostasis. In healthy cells, high levels of basal autophagy are necessary for proper homeostasis and are required for anticancer immunosurveillance. Malignant transformations can arise when autophagy is impaired. Autophagic activity is low until the tumor outpaces its available nutrient supply. As the tumor outgrows its blood supply, the environment become hypoxic, and autophagy re-activation is necessary for tumor proliferation and invasion. Pharmological inhibition of autophagy by antimalarial drug chloroquine leads to tumor regression, however, this drug is not specific to cancerous cells and has many off-target paths. This dual role of autophagy in cancer complicates our ability to target it therapeutically. It is unknown how autophagic function is restored, and this is a central question in the field. All autophagy activation mechanisms involve the lipid kinase class III phosphatidylinositol 3-kinase complex I (PI3KC3-C1) containing tumor suppressor protein BECN1. PI3KC3-C1 is a central initiator, however, its activation mechanism is unknown and this makes it a challenging enzyme to target therapeutically. Discovery of the activation mechanism, at the atomic level, of this central lipid kinase complex through cryo-electron microscopy will greatly aid the ability to rationally design therapeutics to selectively activate or inhibit PI3KC3-C1 at various stages in cancer transformation or proliferation. To identify large-scale changes in the proteome during autophagy reactivation in SILAC (Stable Isotope Labeling with Amino acids in Cell culture) coupled with mass spectrometry will be performed. The objective here is to determine if there is a unique target in proliferating tumors, dependent on a specific autophagy activation mechanism or on a selective autophagy pathway. Ideally, this study would produce new protein candidates to target therapeutically, which would be more specific and less toxic than hydroxychloroquine to treat pancreatic cancers.