GABARAP sequesters the FLCN-FNIP tumor suppressor complex to couple autophagy with lysosomal biogenesis.

Adaptive changes in lysosomal capacity are driven by the transcription factors TFEB and TFE3 in response to increased autophagic flux and endolysosomal stress, yet the molecular details of their activation are unclear. LC3 and GABARAP members of the ATG8 protein family are required for selective autophagy and sensing perturbation within the endolysosomal system. Here, we show that during the conjugation of ATG8 to single membranes (CASM), Parkin-dependent mitophagy, and Salmonella-induced xenophagy, the membrane conjugation of GABARAP, but not LC3, is required for activation of TFEB/TFE3 to control lysosomal capacity. GABARAP directly binds to a previously unidentified LC3-interacting motif (LIR) in the FLCN/FNIP tumor suppressor complex and mediates sequestration to GABARAP-conjugated membrane compartments. This disrupts FLCN/FNIP GAP function toward RagC/D, resulting in impaired substrate-specific mTOR-dependent phosphorylation of TFEB. Thus, the GABARAP-FLCN/FNIP-TFEB axis serves as a molecular sensor that coordinates lysosomal homeostasis with perturbations and cargo flux within the autophagy-lysosomal network.

Discrete molecular classes of ovarian cancer suggestive of unique mechanisms of transformation and metastases.

PURPOSE: Tumor heterogeneity and subsistence of high-grade serous ovarian adenocarcinoma (HGSC) classes can be speculated from clinical incidences suggesting passive tumor dissemination versus active invasion and metastases. EXPERIMENTAL DESIGN: We explored this theme toward tumor classification through two approaches of gene expression pattern clustering: (i) derivation of a core set of metastases-associated genes and (ii) resolution of independent weighted correlation networks. Further identification of appropriate cell and xenograft models was carried out for resolution of class-specific biologic functions. RESULTS: Both clustering approaches achieved resolution of three distinct tumor classes, two of which validated in other datasets. Networks of enriched gene modules defined biologic functions of quiescence, cell division-differentiation-lineage commitment, immune evasion, and cross-talk with niche factors. Although deviant from normal homeostatic mechanisms, these class-specific profiles are not totally random. Preliminary validation of these suggests that Class 1 tumors survive, metastasize in an epithelial-mesenchymal transition (EMT)-independent manner, and are associated with a p53 signature, aberrant differentiation, DNA damage, and genetic instability. These features supported by association of cell-specific markers, including PAX8, PEG3, and TCF21, led to the speculation of their origin being the fimbrial fallopian tube epithelium. On the other hand, Class 2 tumors activate extracellular matrix-EMT-driven invasion programs (Slug, SPARC, FN1, THBS2 expression), IFN signaling, and immune evasion, which are prospectively suggestive of ovarian surface epithelium associated wound healing mechanisms. Further validation of these etiologies could define a new therapeutic framework for disease management.