Biology subjects

Bakun, M.

Publications and source records attributed to Bakun, M..

2 recordsLinked to original sources

bioRxiv2022

Dynactin interaction with AP-2 adaptor complex requires CLIP-170 and autophagy

The endocytic adaptor protein 2 (AP-2) complex binds dynactin as part of its noncanonical function, which is necessary for dynein-driven autophagosome transport along microtubules in neuronal axons. The absence of this AP-2-dependent transport causes neuronal morphology simplification and neurodegeneration. The mechanisms that lead to formation of the AP-2-dynactin complex have not been studied to date. However, the inhibition of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) enhances the transport of newly formed autophagosomes by influencing the biogenesis and protein interactions of Rab-interacting lysosomal protein (RILP), another dynein cargo adaptor. We tested effects of mTORC1 inhibition on interactions between the AP-2 and dynactin complexes, with a focus on their two essential subunits, AP-2{beta} and p150Glued. We found that the mTORC1 inhibitor rapamycin enhanced p150Glued-AP-2{beta} complex formation in both neurons and non-neuronal cells. Additional analysis revealed that the p150Glued-AP-2{beta} interaction was indirect and required integrity of the dynactin complex. In non-neuronal cells rapamycin-driven enhancement of the p150Glued-AP-2{beta} interaction also required the presence of cytoplasmic linker protein 170 (CLIP-170), the activation of autophagy, and an undisturbed endolysosomal system. The rapamycin-dependent p150Glued-AP-2{beta} interaction occurred on lysosomal-associated membrane protein 1 (Lamp-1)-positive organelles but without the need for autolysosome formation. Rapamycin treatment also increased the acidification and number of acidic organelles and increased speed of the long-distance retrograde movement of Lamp-1-positive organelles. Altogether, our results indicate that autophagy regulates the p150Glued-AP-2{beta} interaction, possibly to coordinate sufficient motor-adaptor complex availability for effective lysosome transport.

cell biology↗

bioRxiv2021

ApoE4 disrupts interaction of sortilin with fatty acid-binding protein 7 essential to promote lipid signaling

Sortilin is a receptor for neuronal uptake of apolipoprotein E. Sortilin-dependent uptake of lipidated apoE promotes conversion of polyunsaturated fatty acids (PUFA) into neuromodulators that induce anti-inflammatory gene expression in the brain. This neuroprotective pathway works with apoE3 but is lost with apoE4, the main risk factor for Alzheimers disease (AD). Here, we elucidated steps in cellular handling of lipids through sortilin, and why they are disrupted by apoE4. Combining unbiased proteome screens with analyses in mouse models, we uncover interaction of sortilin with fatty acid-binding protein (FABP) 7, the intracellular carrier for PUFA in the brain. In the presence of apoE3, sortilin promotes functional expression of FABP7 and its ability to elicit lipid-dependent gene transcription. By contrast, apoE4 binding blocks sortilin sorting, causing catabolism of FABP7 and impairing lipid signaling. Reduced FABP7 levels in the brain of AD patients expressing apoE4 substantiate the relevance of these interactions for neuronal lipid homeostasis. Taken together, we document interaction of sortilin with mediators of extracellular and intracellular lipid transport that provides a mechanistic explanation for loss of a neuroprotective lipid metabolism in AD. SUMMARY STATEMENTLipids are central to brain health and defects in brain lipid homeostasis are causal to neurodegenerative processes in Alzheimers disease. Here, we uncovered how the neuronal lipoprotein receptor sortilin interacts with apoE and FABP7, the carriers for extra- and intracellular transport of lipids in the brain, respectively. We show that this interaction enables lipids to control gene transcription via nuclear receptors; and why this presumed neuroprotective lipid action is disturbed in humans who carry the {varepsilon}4 variant of apoE, the most important risk factor for sporadic Alzheimers disease.

cell biology↗