Michalke, E. | Search bioRxiv

bioRxiv2024

Structure and mechanism of the RalGAP tumor suppressor complex

The RalGAP (GTPase activating protein) complexes are negative regulators of the Ral GTPases and thus crucial components that counteract (oncogenic) Ras signaling. However, no structural information on the architecture of this tumor suppressor complex is available hampering a mechanistic understanding of its functionality. Here, we present a cryo-EM structure of RalGAP that reveals an extended 58 nm tetrameric architecture comprising two heterodimers of the RalGAP and RalGAP{beta} subunits. We show that the catalytic domain of RalGAP requires stabilization by a unique domain of RalGAP{beta}, providing the molecular basis for why RalGAP complexes are obligatory heterodimers. Formation of RalGAP tetramers is not required for activity in vitro, but essential for function of the complex in vivo. Structural analysis of RalGAP subunit variants reported in cancer patients suggests effects on complex formation and thus functional relevance in tumor development, emphasizing the significance of the obtained structural information for medical research.

biochemistry↗

bioRxiv2022

TORC1 regulation of dendrite regrowth after pruning is linked to actin and exocytosis

Neurite pruning and regrowth are important mechanisms to adapt neural circuits to distinct developmental stages. Neurite regrowth after pruning often depends on differential regulation of growth signaling pathways, but their precise mechanisms of action during regrowth are unclear. Here, we show that the PI3K/TORC1 pathway is required for dendrite regrowth after pruning in Drosophila peripheral neurons during metamorphosis. TORC1 impinges on translation initiation, and our analysis of 5 untranslated regions (UTRs) of remodeling factor mRNAs linked to actin suggests that TOR selectively stimulates the translation of regrowth over pruning factors. Furthermore, we find that dendrite regrowth also requires the GTPase RalA and the exocyst complex as regulators of polarised secretion, and we provide evidence that this pathway is also regulated by TOR. We propose that TORC1 coordinates dendrite regrowth after pruning by coordinately stimulating the translation of regrowth factors involved in cytoskeletal regulation and secretion. Author SummaryDuring development, neurons grow axons and dendrites that they use to make synaptic connections. Such connections are often fine-tuned through pruning and regrowth of axons and dendrites, but the coordination of the two processes is not well understood. It had previously been shown that hormone signaling suppresses the TORC1 growth pathway during pruning of Drosophila sensory neuron dendrites. We found that TORC1 is required for the subsequent regrowth of these dendrites. TORC1 activates protein biosynthesis, and our analyses suggest that it primarily targets neurite growth pathways, but not degenerative pathways. These growth pathways include the actin cytoskeleton and the secretion machinery with the small GTPase RalA. Thus, the TORC1 growth pathway is a major hub coordinating neurite pruning and regrowth.

developmental biology↗