Lois S. Weisman

Two major protein recycling pathways have emerged as key regulators of enduring forms of synaptic plasticity, such as long-term potentiation (LTP), yet how these pathways are recruited during plasticity is unknown. Phosphatidylinositol-3-phosphate (PI(3)P) is a key regulator of endosomal trafficking and alterations in this lipid have been linked to neurodegeneration. Here, using primary hippocampal neurons, we demonstrate dynamic PI(3)P synthesis during chemical induction of LTP (cLTP), which drives coordinate recruitment of the SNX17–Retriever and SNX27–Retromer pathways to endosomes and synaptic sites. Both pathways are necessary for the cLTP-dependent structural enlargement of dendritic spines and act in parallel by recycling distinct sets of cell surface proteins at synapses. Importantly, preventing PI(3)P synthesis blocks synaptic recruitment of SNX17 and SNX27, decreases cargo recycling, and blocks LTP in cultured neurons and hippocampal slices. These findings provide mechanistic insights into the regulation of endocytic recycling at synapses and define a role for dynamic PI(3)P synthesis in synaptic plasticity.

The PIKfyve–VAC14–FIG4 complex synthesizes and turns over phosphatidylinositol-3,5-bisphosphate, PI(3,5)P₂, an essential signaling lipid. A medium-resolution structure revealed that VAC14 forms a star-shaped pentamer scaffold. Two legs of VAC14 bind FIG4, with one leg also occupied by PIKfyve. The significance of VAC14 oligomerization was unknown. Here, using Alphafold2 and cryogenic electron microscopy maps we generated an atomic-resolution prediction, and found that some mutations linked to pediatric neurodegenerative diseases reside in the VAC14–VAC14 interfaces. A corresponding yeast mutation, along with additional mutations, demonstrates that VAC14 oligomerization is critical for Fab1/PIKfyve function. These mutations cause defects in the generation of PI(3,5)P₂, in VAC14 localization, and in VAC14 oligomerization. Similarly, VAC14 patient mutations expressed in human VAC14 knockout (KO) cells, are defective in the formation of the PIKfyve–VAC14–FIG4 complex, as measured by pull-down assays, are defective in VAC14 oligomerization as measured by fluorescence-detection size-exclusion chromatography of cell lysates, and are defective in colocalization with VPS35-containing endosomes. These studies show that VAC14 oligomerization plays a crucial role in the regulation of PIKfyve/FAB1 and provide insights into selected patient mutations. Moreover, they suggest that small molecules that stabilize the VAC14 complex may provide an intervention for diseases linked to mutations in VAC14.

Myo2, a class V myosin motor, is essential for organelle transport in budding yeast. Its association with cargo is regulated by adaptor proteins that mediate both attachment and release. Vac17, a vacuole-specific adaptor, links Myo2 to the vacuole membrane protein Vac8 and plays a key role in assembling and disassembling the Myo2–Vac17–Vac8 complex during vacuole inheritance. Using genetics, cryo-EM, and structure prediction, we find that Vac17 interacts with Myo2 at two distinct sites rather than a single interface. Similarly, the peroxisome adaptor Inp2 engages two separate regions of Myo2, one of which overlaps with a Vac17-binding site. These findings support a “handhold” model, in which cargo adaptors occupy multiple surfaces on the Myo2 tail, which likely enhances motor–cargo associations as well as provide additional regulatory control over motor recruitment.

Pancreatic ductal adenocarcinoma (PDAC) subsists in a nutrient-deregulated microenvironment, making it particularly susceptible to treatments that interfere with cancer metabolism^1,2. For example, PDAC uses, and is dependent on, high levels of autophagy and other lysosomal processes^3–5. Although targeting these pathways has shown potential in preclinical studies, progress has been hampered by the difficulty in identifying and characterizing favourable targets for drug development⁶. Here, we characterize PIKfyve, a lipid kinase that is integral to lysosomal functioning⁷, as a targetable vulnerability in PDAC. Using a genetically engineered mouse model, we established that PIKfyve is essential to PDAC progression. Furthermore, through comprehensive metabolic analyses, we found that PIKfyve inhibition forces PDAC to upregulate a distinct transcriptional and metabolic program favouring de novo lipid synthesis. In PDAC, the KRAS–MAPK signalling pathway is a primary driver of de novo lipid synthesis. Accordingly, simultaneously targeting PIKfyve and KRAS–MAPK resulted in the elimination of the tumour burden in numerous preclinical human and mouse models. Taken together, these studies indicate that disrupting lipid metabolism through PIKfyve inhibition induces synthetic lethality in conjunction with KRAS–MAPK-directed therapies for PDAC.

Myo2, a myosin V motor, is essential for organelle transport in budding yeast. Its attachment to and detachment from cargo are mediated by adaptor molecules. Vac17, a vacuole-specific adaptor, links Myo2 to Vac8 on the vacuole membrane, and plays a key role in the formation and dissociation of the Myo2-Vac17-Vac8 complex. Using genetics, cryo-electron microscopy and structure prediction, we find that Vac17 interacts with Myo2 through two distinct sites rather than a single interface. Similarly, the peroxisome adapter Inp2 engages two separate regions of Myo2, one of which overlaps with Vac17. These findings support a “handhold” model, in which cargo adaptors occupy multiple sites on the Myo2 tail, enhancing motor-cargo interactions and likely providing additional regulatory control over motor recruitment. Summary This study provides insights into how cargo adaptors bind myosin V. Genetics, cell-based assays, cryo-EM, and AlphaFold, reveal that the vacuole-specific adaptor uses a handhold mechanism to attach to two areas on the myosin V tail. Moreover, evidence is presented that other adaptors use a similar strategy.

Environmental stress induces an arrest of the cell cycle. Thus, release from this arrest is essential for cell survival. The cell-cycle-arrest occurs via the down regulation of the cyclins that drive the main cyclin dependent kinase, CDK1/Cdc28. However, it was not clear how cells escape this potentially fatal arrest. Here we show that prior to the restoration of CDK1/Cdc28 cyclins, a non-canonical CDK, Pho85, initiates a cascade to restart the cell cycle. We demonstrate that following stress, Pho85 phosphorylates the Sch9 kinase, which in turn directly phosphorylates the transcriptional inhibitor Whi5, the yeast analog of RB1/retinoblastoma, and a CDK1 target. This promotes Whi5 translocation from the nucleus, and the release of the stress-induced arrest at G ₁ phase. In addition, we find that in parallel with Pho85, CDK1/Cdc28 also plays a role in the control of Whi5. Together, these findings provide insights into how cells re-enter the cell cycle during recovery from stress and reveal that a non-canonical CDK and cyclin takes on essential roles and acts via a pathway that functions in parallel with CDK1/Cdc28.

Phosphatidylinositol 3,5-bisphosphate enables transport of proteins to synaptic sites.