ABSTRACT
Ras GTPase-activating protein-binding proteins 1 and 2 (G3BP1 and G3BP2, respectively) are widely recognized as core components of stress granules (SGs). We report that G3BPs reside at the cytoplasmic surface of lysosomes. They act in a non-redundant manner to anchor the tuberous sclerosis complex (TSC) protein complex to lysosomes and suppress activation of the metabolic master regulator mechanistic target of rapamycin complex 1 (mTORC1) by amino acids and insulin. Like the TSC complex, G3BP1 deficiency elicits phenotypes related to mTORC1 hyperactivity. In the context of tumors, low G3BP1 levels enhance mTORC1-driven breast cancer cell motility and correlate with adverse outcomes in patients. Furthermore, G3bp1 inhibition in zebrafish disturbs neuronal development and function, leading to white matter heterotopia and neuronal hyperactivity. Thus, G3BPs are not only core components of SGs but also a key element of lysosomal TSC-mTORC1 signaling.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , DNA Helicases/metabolism , Lysosomes/metabolism , Mechanistic Target of Rapamycin Complex 1/metabolism , Poly-ADP-Ribose Binding Proteins/metabolism , RNA Helicases/metabolism , RNA Recognition Motif Proteins/metabolism , RNA-Binding Proteins/metabolism , Signal Transduction , Tuberous Sclerosis/metabolism , Amino Acid Sequence , Animals , Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Cell Line, Tumor , Cell Movement/drug effects , Cytoplasmic Granules/drug effects , Cytoplasmic Granules/metabolism , DNA Helicases/chemistry , Evolution, Molecular , Female , Humans , Insulin/pharmacology , Lysosomal Membrane Proteins/metabolism , Lysosomes/drug effects , Neurons/drug effects , Neurons/metabolism , Phenotype , Poly-ADP-Ribose Binding Proteins/chemistry , RNA Helicases/chemistry , RNA Recognition Motif Proteins/chemistry , Rats, Wistar , Signal Transduction/drug effects , Zebrafish/metabolismABSTRACT
Tuberous Sclerosis Complex (TSC) is a rare genetic disease that manifests with early symptoms, including cortical malformations, childhood epilepsy, and TSC-associated neuropsychiatric disorders (TANDs). Cortical malformations arise during embryonic development and have been linked to childhood epilepsy before, but the underlying mechanisms of this relationship remain insufficiently understood. Zebrafish have emerged as a convenient model to study elementary neurodevelopment; however, without in-depth functional analysis, the Tsc2-deficient zebrafish line cannot be used for studies of TANDs or new drug screening. In this study, we found that the lack of Tsc2 in zebrafish resulted in heterotopias and hyperactivation of the mTorC1 pathway in pallial regions, which are homologous to the mammalian cortex. We observed commissural thinning that was responsible for brain dysconnectivity, recapitulating TSC pathology in human patients. The lack of Tsc2 also delayed axonal development and caused aberrant tract fasciculation, corresponding to the abnormal expression of genes involved in axon navigation. The mutants underwent epileptogenesis that resulted in nonmotor seizures and exhibited increased anxiety-like behavior. We further mapped discrete parameters of locomotor activity to epilepsy-like and anxiety-like behaviors, which were rescued by reducing tyrosine receptor kinase B (TrkB) signaling. Moreover, in contrast to treatment with vigabatrin and rapamycin, TrkB inhibition rescued brain dysconnectivity and anxiety-like behavior. These data reveal that commissural thinning results in the aberrant regulation of anxiety, providing a mechanistic link between brain anatomy and human TANDs. Our findings also implicate TrkB signaling in the complex pathology of TSC and reveal a therapeutic target.
Subject(s)
Anxiety/metabolism , Epilepsy/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Receptor, trkB/metabolism , Tuberous Sclerosis/metabolism , Zebrafish Proteins/metabolism , Animals , Anxiety/genetics , Anxiety/psychology , Disease Models, Animal , Epilepsy/genetics , Epilepsy/psychology , Female , Humans , Intracellular Signaling Peptides and Proteins/genetics , Mechanistic Target of Rapamycin Complex 1/genetics , Mechanistic Target of Rapamycin Complex 1/metabolism , Receptor, trkB/genetics , Seizures/genetics , Seizures/metabolism , Seizures/psychology , Tuberous Sclerosis/genetics , Tuberous Sclerosis/psychology , Zebrafish , Zebrafish Proteins/geneticsABSTRACT
Mechanistic target of rapamycin complex 1 (mTORC1) is an integration hub for extracellular and intracellular signals necessary for brain development. Hyperactive mTORC1 is found in autism spectrum disorder (ASD) characterized by atypical reactivity to sensory stimuli, among other symptoms. In Tuberous sclerosis complex (TSC) inactivating mutations in the TSC1 or TSC2 genes result in hyperactivation of the mTORC1 pathway and ASD. Here, we show that lack of light preference of the TSC zebrafish model, tsc2 vu242/vu242 is caused by aberrant processing of light stimuli in the left dorsal habenula and tsc2 vu242/vu242 fish have impaired function of the left dorsal habenula, in which neurons exhibited higher activity and lacked habituation to the light stimuli. These characteristics were rescued by rapamycin. We thus discovered that hyperactive mTorC1 caused aberrant habenula function resulting in lack of light preference. Our results suggest that mTORC1 hyperactivity contributes to atypical reactivity to sensory stimuli in ASD.