ER-PM Contact Sites - SNARING Actors in Emerging Functions

VAP27-1 interacts with KCS6 and CER2 to facilitate the biosynthesis of very- long-chain fatty acids

Cuticular wax is primarily composed of very-long-chain fatty acids (VLCFAs) and their derivatives. It forms a critical hydrophobic layer on plant surfaces, acting as a protective barrier against biotic and abiotic stress. The biosynthesis of VLCFAs and their derivative wax occurs in endoplasmic reticulum (ER) and is subsequently transported to the plant surface. While substantial research has focused on cuticular wax biosynthesis enzymes and their transcriptional regulation, the mechanisms by which these enzymes are modulated by proteins within cytosol organelles remain poorly understood. In this study, we identified that β-ketoacyl-CoA synthase 6 (KCS6), an ER-localized rate-limiting enzyme in VLCFAs biosynthesis, also localized at ER-plasma membrane contact sites (EPCS). We further demonstrated that KCS6 and its cofactor ECERIFERUM 2 (CER2) interact with vesicle-associated membrane protein-associated protein 27-1 (VAP27-1), a key regulator of EPCS formation and stabilization. Overexpression of VAP27-1 in Arabidopsis thaliana resulted in a significant increase in almost all cuticular wax components compared to WT. Additionally, firefly luciferase complementation imaging assays (LCI) and yeast heterologous expression analysis revealed that VAP27-1 strengthens the interaction between the KCS6-CER2 complex, resulting in increased accumulation of VLCFAs. In conclusion, this study emphasized the critical role of VAP27-1 in regulating the biosynthesis of cuticular wax mediated by KCS6-CER2, providing new insights into the fine-tuning mechanisms of cuticular wax biosynthesis within the ER. Furthermore, the identification of VAP27-1 as a novel modulator of VLCFA synthases offers a potential target for enhancing plant resilience to environmental stresses.

Hsa_circ_0006006 is a potential biomarker for prognosis and cisplatin resistance in non-small cell lung cancer

BACKGROUND AND OBJECTIVE

Platinum-based drugs, such as cisplatin (DDP), are the standard treatment, yet drug resistance has become a key challenge. Previous studies have shown that hsa_circ_0006006 promotes non small cell lung cancer (NSCLC) progression. This study aimed to reveal the role of specific circRNAs in DDP resistance in NSCLC and their potential clinical applications.

METHODS

CircRNA sequencing data of three NSCLC tissue and three normal tissue samples were extracted from the GEO database based on conditions that matched the microarray expression profiles of circRNAs from human NSCLC lung samples and matched neighboring samples and raw matrix data and platform annotation data, and differential expression analysis was performed using the R language. Log2 Fold change > 1 and P < 0.05 were labeled as differential genes. Serum samples were collected from 31 NSCLC patients and 21 DDP-resistant NSCLC patients. The Kaplan-Meier method was used to detect the correlation between circRNA levels and survival prognosis of NSCLC patients. The relationship between circRNAs and clinicopathological characteristics of patients was assessed by chi-square test. RT-qPCR was performed to detect the expression of key circRNAs associated with DDP drug resistance. circRNAs were analyzed by ROC curves to assess the diagnostic potential. A549 cells and A549/DDP cells were cultured to verify the effect of up- and down-regulation of hsa_circ_0006006 on DDP drug resistance in NSCLC cells using colony formation assay and flow cytometry.

RESULTS

Abnormally elevated hsa_circ_0006006 expression was closely associated with NSCLC survival prognosis as well as DDP resistance (p < 0.05) with good diagnostic efficacy (AUC for NSCLC = 0.91, p < 0.01; AUC for DDP resistant = 0.80, p = 0.00). This was further validated in the analysis of clinical samples (p < 0.05). Knockdown of hsa_circ_0006006 significantly reduced DDP resistance in NSCLC cells, while overexpression of hsa_circ_0006006 had the opposite effect (p < 0.05).

CONCLUSION

NSCLC survival prognosis is associated with aberrant expression of hsa_circ_0006006, which regulates NSCLC cell proliferation and apoptosis and thus promotes DDP drug resistance. These findings provide potential targets for patient prognosis and assessment of biomarkers of response to DDP therapies that can be used to aid in early diagnosis and prognostic assessment, as well as new options for the future development of relevant small-molecule inhibitors or nucleic acid drugs.

Calcium channel signalling at neuronal endoplasmic reticulum-plasma membrane junctions

Neurons are highly specialised cells that need to relay information over long distances and integrate signals from thousands of synaptic inputs. The complexity of neuronal function is evident in the morphology of their plasma membrane (PM), by far the most intricate of all cell types. Yet, within the neuron lies an organelle whose architecture adds another level to this morphological sophistication - the endoplasmic reticulum (ER). Neuronal ER is abundant in the cell body and extends to distant axonal terminals and postsynaptic dendritic spines. It also adopts specialised structures like the spine apparatus in the postsynapse and the cisternal organelle in the axon initial segment. At membrane contact sites (MCSs) between the ER and the PM, the two membranes come in close proximity to create hubs of lipid exchange and Ca2+ signalling called ER-PM junctions. The development of electron and light microscopy techniques extended our knowledge on the physiological relevance of ER-PM MCSs. Equally important was the identification of ER and PM partners that interact in these junctions, most notably the STIM-ORAI and VAP-Kv2.1 pairs. The physiological functions of ER-PM junctions in neurons are being increasingly explored, but their molecular composition and the role in the dynamics of Ca2+ signalling are less clear. This review aims to outline the current state of research on the topic of neuronal ER-PM contacts. Specifically, we will summarise the involvement of different classes of Ca2+ channels in these junctions, discuss their role in neuronal development and neuropathology and propose directions for further research.

The function of sphingolipids in membrane trafficking and cell signaling in plants, in comparison with yeast and animal cells

Sphingolipids are essential membrane components involved in a wide range of cellular, developmental and signaling processes. Sphingolipids are so essential that knock-out mutation often leads to lethality. In recent years, conditional or weak allele mutants as well as the broadening of the pharmacological catalog allowed to decipher sphingolipid function more precisely in a less invasive way. This review intends to provide a discussion and point of view on the function of sphingolipids with a main focus on endomembrane trafficking, Golgi-mediated protein sorting, cell polarity, cell-to-cell communication and cell signaling at the plasma membrane. While our main angle is the plant field research, we will constantly refer to and compare with the advances made in the yeast and animal field. In this review, we will emphasize the role of sphingolipids not only as a membrane component, but also as a key player at a center of homeostatic regulatory networks involving direct or indirect interaction with other lipids, proteins and ion fluxes.

Nanojunctions: Specificity of Ca2+ signaling requires nano-scale architecture of intracellular membrane contact sites

Spatio-temporal definition of Ca2+ signals involves the assembly of signaling complexes within the nano-architecture of contact sites between the sarco/endoplasmic reticulum (SR/ER) and the plasma membrane (PM). While the requirement of precise spatial assembly and positioning of the junctional signaling elements is well documented, the role of the nano-scale membrane architecture itself, as an ion-reflecting confinement of the signalling unit, remains as yet elusive. Utilizing the Na+/Ca2+ Exchanger-1 / SR/ER Ca2+ ATPase-2-mediated ER Ca2+ refilling process as a junctional signalling paradigm, we provide here the first evidence for an indispensable cellular function of the junctional membrane architecture. Our stochastic modeling approach demonstrates that junctional ER Ca2+ refilling operates exclusively at nano-scale membrane spacing, with a strong inverse relationship between junctional width and signaling efficiency. Our model predicts a breakdown of junctional Ca2+ signaling with loss of reflecting membrane confinement. In addition we consider interactions between Ca2+ and the phospholipid membrane surface, which may support interfacial Ca2+ transport and promote receptor targeting. Alterations in the molecular and nano-scale membrane organization at organelle-PM contacts are suggested as a new concept in pathophysiology.

Controlling contacts-Molecular mechanisms to regulate organelle membrane tethering

In recent years, membrane contact sites (MCS), which mediate interactions between virtually all subcellular organelles, have been extensively characterized and shown to be essential for intracellular communication. In this review essay, we focus on an emerging topic: the regulation of MCS. Focusing on the tether proteins themselves, we discuss some of the known mechanisms which can control organelle tethering events and identify apparent common regulatory hubs, such as the VAP interface at the endoplasmic reticulum (ER). We also highlight several currently hypothetical concepts, including the idea of tether oligomerization and redox regulation playing a role in MCS formation. We identify gaps in our current understanding, such as the identity of the majority of kinases/phosphatases involved in tether modification and conclude that a holistic approach-incorporating the formation of multiple MCS, regulated by interconnected regulatory modulators-may be required to fully appreciate the true complexity of these fascinating intracellular communication systems.

Extended-synaptotagmin 1 engages in unconventional protein secretion mediated via SEC22B+ vesicle pathway in liver cancer

Protein secretion in cancer cells defines tumor survival and progression by orchestrating the microenvironment. Studies suggest the occurrence of active secretion of cytosolic proteins in liver cancer and their involvement in tumorigenesis. Here, we investigated the identification of extended-synaptotagmin 1 (E-Syt1), an endoplasmic reticulum (ER)-bound protein, as a key mediator for cytosolic protein secretion at the ER-plasma membrane (PM) contact sites. Cytosolic proteins interacted with E-Syt1 on the ER, and then localized spatially inside SEC22B⁺ vesicles of liver cancer cells. Consequently, SEC22B on the vesicle tethered to the PM via Q-SNAREs (SNAP23, SNX3, and SNX4) for their secretion. Furthermore, inhibiting the interaction of protein kinase Cδ (PKCδ), a liver cancer-specific secretory cytosolic protein, with E-Syt1 by a PKCδ antibody, decreased in both PKCδ secretion and tumorigenicity. Results reveal the role of ER-PM contact sites in cytosolic protein secretion and provide a basis for ER-targeting therapy for liver cancer.

Annexins Bridging the Gap: Novel Roles in Membrane Contact Site Formation

Membrane contact sites (MCS) are specialized small areas of close apposition between two different organelles that have led researchers to reconsider the dogma of intercellular communication via vesicular trafficking. The latter is now being challenged by the discovery of lipid and ion transfer across MCS connecting adjacent organelles. These findings gave rise to a new concept that implicates cell compartments not to function as individual and isolated entities, but as a dynamic and regulated ensemble facilitating the trafficking of lipids, including cholesterol, and ions. Hence, MCS are now envisaged as metabolic platforms, crucial for cellular homeostasis. In this context, well-known as well as novel proteins were ascribed functions such as tethers, transporters, and scaffolds in MCS, or transient MCS companions with yet unknown functions. Intriguingly, we and others uncovered metabolic alterations in cell-based disease models that perturbed MCS size and numbers between coupled organelles such as endolysosomes, the endoplasmic reticulum, mitochondria, or lipid droplets. On the other hand, overexpression or deficiency of certain proteins in this narrow 10-30 nm membrane contact zone can enable MCS formation to either rescue compromised MCS function, or in certain disease settings trigger undesired metabolite transport. In this "Mini Review" we summarize recent findings regarding a subset of annexins and discuss their multiple roles to regulate MCS dynamics and functioning. Their contribution to novel pathways related to MCS biology will provide new insights relevant for a number of human diseases and offer opportunities to design innovative treatments in the future.