Aragay, A. M. | Search bioRxiv

bioRxiv2021

A novel Alex3/Gαq protein complex regulating mitochondrial dynamics, dendritic complexity, and neuronal survival

In neurons, mitochondrial dynamics and trafficking are essential to provide the energy required for neurotransmission and neuronal activity. Recent studies point to GPCR and G proteins as important regulators of mitochondrial dynamics and energy metabolism. Here we show that activation of Gq negatively regulates mitochondrial dynamics and trafficking in neurons. Gq interacts with the mitochondrial trafficking protein Alex3. By generating a CNS-specific armcx3 knock-out mouse line, we demonstrate that Alex3 is required for Gq effects on mitochondrial dynamics and trafficking, and dendritic growth. Armcx3-deficient mice present decreased OXPHOS complex and ER stress response protein levels, which correlate with increased neuronal death, motor neuron and neuromuscular synaptic loss, and severe motor alterations. Finally, we show that Alex3 disassembles from the Miro1/Gq complex upon calcium rise. These data uncover a novel Alex3/Gq complex that regulates neuronal mitochondrial dynamics and neuronal death and allows the control of mitochondrial functions by GPCRs.

cell biology↗

bioRxiv2021

Kazrin C entraps early endosomes at the pericentriolar region and facilitates endocytic recycling

Kazrin is a protein widely expressed in vertebrates whose depletion causes a myriad of developmental defects, in part derived from altered cell adhesion, impaired cell migration and failure to undergo Epidermal to Mesenchymal Transition (EMT). However, the primary molecular role of kazrin, which might contribute to all these functions, has not been elucidated yet. We previously identified one of its isoforms, kazrin C, as a protein that potently inhibits clathrin-mediated endocytosis when overexpressed. We now generated kazrin knock out Mouse Embryonic Fibroblasts (MEFs) to investigate its endocytic function. We found that kazrin depletion delays perinuclear enrichment of internalized material, indicating a role in endocytic traffic from Early (EE) to Recycling Endosomes (REs). Consistently, we found that the C-terminal domain of kazrin C, predicted to be an Intrinsically Disordered Region (IDR), directly interacts with several components of the EEs, and that kazrin depletion impairs centripetal motility of EEs. Further, we noticed that the N-terminus of kazrin C shares homology with dynein/dynactin adaptors and that it directly interacts with the dynactin complex and the dynein Light Intermediate Chain 1 (LIC1). Altogether, the data indicate that one of the primary kazrin functions is to facilitate endocytic recycling via the perinuclear endocytic compartment, by promoting microtubule and dynein/dynactin-dependent transport of EEs or EE-derived transport intermediates to the RE.

cell biology↗