APP controls the formation of PI(3,5)P2 vesicles through its binding of the PIKfyve complex

Abstract

Phosphoinositides are signalling lipids that are crucial for major signalling events as well as established regulators of membrane trafficking. Control of endosomal sorting and endosomal homeostasis requires phosphatidylinositol-3-phosphate (PI(3)P) and phosphatidylinositol-3,5-bisphosphate (PI(3,5)P2), the latter a lipid of low abundance but significant physiological relevance. PI(3,5)P2 is formed by phosphorylation of PI(3)P by the PIKfyve complex which is crucial for maintaining endosomal homeostasis. Interestingly, loss of PIKfyve function results in dramatic neurodegeneration. Despite the significance of PIKfyve, its regulation is still poorly understood. Here we show that the Amyloid Precursor Protein (APP), a central molecule in Alzheimer’s disease, associates with the PIKfyve complex (consisting of Vac14, PIKfyve and Fig4) and that the APP intracellular domain directly binds purified Vac14. We also show that the closely related APP paralogues, APLP1 and 2 associate with the PIKfyve complex. Whether APP family proteins can additionally form direct protein–protein interaction with PIKfyve or Fig4 remains to be explored. We show that APP binding to the PIKfyve complex drives formation of PI(3,5)P2 positive vesicles and that APP gene family members are required for supporting PIKfyve function. Interestingly, the PIKfyve complex is required for APP trafficking, suggesting a feedback loop in which APP, by binding to and stimulating PI(3,5)P2 vesicle formation may control its own trafficking. These data suggest that altered APP processing, as observed in Alzheimer’s disease, may disrupt PI(3,5)P2 metabolism, endosomal sorting and homeostasis with important implications for our understanding of the mechanism of neurodegeneration in Alzheimer’s disease.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-015-1993-0) contains supplementary material, which is available to authorized users.

PIKfyve complex regulates early melanosome homeostasis required for physiological amyloid formation

“…In view of the interesting similarities between intracellular trafficking and processing of PMEL and amyloid precursor protein (APP), which is involved in Alzheimer's disease (Bissig et al, 2016;Sannerud et al, 2016), our studies may also have important implications for pathological amyloid formation during Alzheimer's disease. Intriguingly, PIKfyve depletion leads to massive neurodegeneration in individuals with mutations of FIG4 and VAC14 (Baulac et al, 2014;Campeau et al, 2013;Chow et al, 2007;Lenk et al, 2011;Lenk et al, 2016), and PIKfyve influences APP (Balklava et al, 2015;Currinn et al, 2016). It is therefore tempting to speculate that, in neurons, PIKfyve activity regulates the abundance of an amyloidogenic substrate and its proteases in a compartment known to generate the Aβ intracellular pool (Peric and Annaert, 2015;Rajendran and Annaert, 2012;Sannerud et al, 2016).…”

The amyloid precursor protein (APP) binds the PIKfyve complex and modulates its function

“…PIKfyve was inhibited for a brief amount of time (46). While so far we have not been able to measure PI(3,5)P2 levels biochemically, all our cell biological findings suggest that APP gene family members modulate PIKfyve function.…”

“…Using a novel PI(3,5)P2 specific probe (47) we showed that overexpression of APP or ACID increased the number of PI(3,5)P2 positive vesicles in both HeLa and SH-SY5Y neuroblastoma cells. Conversely, knock-down of APP or the APP paralogue APLP2 reduced the number of PI(3,5)P2 positive vesicles in HeLa cells, suggesting that APP and its paralogues APLP2 are both able to stimulate PIKfyve function (46). RNAi Suppression of APP and APLP2 also increased the number of cells that display vacuoles, similar to the phenotype observed with PIKfyve RNAi, although to a lower extent (22,46).…”

“…Using a recently developed methodology for analysing the interactome of the intracellular domains of transmembrane receptors using proteo-liposomes we surprisingly identified the PIKfyve complex as a putative interactor of the APP intracellular domain (45,46). We analysed this interaction in detail and found that the highly conserved YENPTY motif of the APP intracellular domain is crucial for directly binding the Vac14 subunit of the PIKfyve complex (46). Using a novel PI(3,5)P2 specific probe (47) we showed that overexpression of APP or ACID increased the number of PI(3,5)P2 positive vesicles in both HeLa and SH-SY5Y neuroblastoma cells.…”

Defective phosphoinositide metabolism in autism

“…Mutations in FIG4 were also found in Yunis‐Varon syndrome, a neurological disorder with skeletal defects and severe neuronal loss in the central nervous system (Nakajima et al, ), as well as in some forms of amyloid lateral sclerosis, although a causal link has not yet been proved (Chow et al, ). Last but not least and as discussed above, FIG4 is part of the PIKfyve complex, which has been shown to be regulated by APP and, thus, may play a role in Alzheimer's disease (Currinn et al, ; Currinn and Wassmer, ). Mutations in a different phosphoinositide phosphatase, MTM‐related 2 ( MTMR2 ), which dephosphorylates both PI(3,5)P 2 and PI(3)P at the third hydroxyl group, lead to another form of Charcot‐Marie‐Tooth disease, CMT4B1 (Bolino et al, ).…”