Intracellular nanovesicles mediate α5β1 integrin trafficking during cell migration

ATG9A vesicles are a subtype of intracellular nanovesicle

Cells are filled with thousands of vesicles, which mediate protein transport and ensure homeostasis of the endomembrane system. Distinguishing these vesicles functionally and molecularly represents a major challenge. Intracellular nanovesicles (INVs) are a large class of transport vesicles that likely comprise multiple subtypes. Here, we define the INV proteome and find that it is molecularly heterogeneous and enriched for transmembrane cargo molecules, including integrins, transporters and ATG9A, a lipid scramblase associated with autophagy. ATG9A is known to reside in 'ATG9A vesicles' - small vesicles that contribute to autophagosome formation. Here, using in-cell vesicle capture assays, we found that ATG9A, as well as other ATG9A vesicle cargoes, are in INVs. Quantitative analysis showed that virtually all ATG9A vesicles are INVs, but that only ∼20% of INVs are ATG9A vesicles, suggesting that ATG9A vesicles are in fact a subtype of INV, which we term ATG9A-flavor INVs. Finally, we show that perturbing ATG9A-flavor INVs impairs the autophagy response induced by starvation.

Overexpression of TPD52L2 in HNSCC: prognostic significance and correlation with immune infiltrates

BACKGROUND

Evidence has been presented that the tumor protein D52 (TPD52) family plays a critical role in tumor development and progression. As a member of the TPD52 family, the changes in TPD52L2 gene status are instrumental in kinds of cancer development. However, its effects on patient prognosis and immune infiltration in Head and Neck Squamous Carcinoma (HNSCC) are still poorly understood.

METHODS

The Tumor Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and c-BioPortal database was used to explore the expression pattern, prognostic value, and variation of gene status in HNSCC. The LinkedOmics database was used to obtain the co-expression genes of TPD52L2 and identify the diagnostic value of TPD52L2 in HNSCC. The correlations between TPD52L2 expression and six main types of immune cell infiltrations and immune signatures were explored using Tumor Immune Estimation Resource (TIMER). The correlation between TPD52L2 expression and immune checkpoint genes (ICGs) was analyzed by TCGA database. Immunohistochemistry (IHC) was performed to validate the expression of three ICGs (PDL1, PDL2, EGFR) and TPD52L2 using 5 paired HNSCC and normal head and neck tissues. Polymerase Chain Reaction (PCR) and Western Blot (WB) of HNSCC and normal head and neck cell lines were performed to verify the high level of TPD52L2 mRNA and protein expression. protein expression of TPD52L2 in pan-cancer was also validated using UALCAN.

RESULTS

TPD52L2 was overexpressed in tumor tissues, and it predicted worse survival status in HNSCC. ROC analysis suggested that TPD52L2 had a diagnostic value. Multivariate Cox analysis identified TPD52L2 as an independent negative prognostic marker of overall survival. Functional network analysis suggested that TPD52L2 was associated with immune-related signaling pathways, cell migration pathways, and cancer-related pathways. High expression of TPD52L2 was associated with a more mutant frequency of TP53. Notably, we found that the expression of TPD52L2 was closely negatively correlated with the infiltration levels of 15 types of immune cells and positively correlated with several immune markers. PCR, WB experiments, and UALCAN database verified the high level of TPD52L2 mRNA and protein expression.

CONCLUSION

TPD52L2 is upregulated in HNSCC, which is an independent factor for adverse prognosis prediction. It probably plays a role in the negative regulation of immune cell infiltration. TPD52L2 might be a promising prognostic biomarker and therapeutic target in HNSCC.

Rab30 facilitates lipid homeostasis during fasting

To facilitate inter-tissue communication and the exchange of proteins, lipoproteins, and metabolites with the circulation, hepatocytes have an intricate and efficient intracellular trafficking system regulated by small Rab GTPases. Here, we show that Rab30 is induced in the mouse liver by fasting, which is amplified in liver-specific carnitine palmitoyltransferase 2 knockout mice (Cpt2L-/-) lacking the ability to oxidize fatty acids, in a Pparα-dependent manner. Live-cell super-resolution imaging and in vivo proximity labeling demonstrates that Rab30-marked vesicles are highly dynamic and interact with proteins throughout the secretory pathway. Rab30 whole-body, liver-specific, and Rab30; Cpt2 liver-specific double knockout (DKO) mice are viable with intact Golgi ultrastructure, although Rab30 deficiency in DKO mice suppresses the serum dyslipidemia observed in Cpt2L-/- mice. Corresponding with decreased serum triglyceride and cholesterol levels, DKO mice exhibit decreased circulating but not hepatic ApoA4 protein, indicative of a trafficking defect. Together, these data suggest a role for Rab30 in the selective sorting of lipoproteins to influence hepatocyte and circulating triglyceride levels, particularly during times of excessive lipid burden.

Passive diffusion accounts for the majority of intracellular nanovesicle transport

During membrane trafficking, a vesicle formed at the donor compartment must travel to the acceptor membrane before fusing. For large carriers, it is established that this transport is motor-driven; however, the mode by which small vesicles, which outnumber larger carriers, are transported is poorly characterized. Here, we show that intracellular nanovesicles (INVs), a substantial class of small vesicles, are highly mobile within cells and that this mobility depends almost entirely on passive diffusion (0.1-0.3 μm2 s-1). Using single particle tracking, we describe how other small trafficking vesicles have a similar diffusive mode of transport that contrasts with the motor-dependent movement of larger endolysosomal carriers. We also demonstrate that a subset of INVs is involved in exocytosis and that delivery of cargo to the plasma membrane during exocytosis is decreased when diffusion of INVs is specifically restricted. Our results suggest that passive diffusion is sufficient to explain the majority of small vesicle transport.

Genetically encoded imaging tools for investigating cell dynamics at a glance

The biology of a cell is the sum of many highly dynamic processes, each orchestrated by a plethora of proteins and other molecules. Microscopy is an invaluable approach to spatially and temporally dissect the molecular details of these processes. Hundreds of genetically encoded imaging tools have been developed that allow cell scientists to determine the function of a protein of interest in the context of these dynamic processes. Broadly, these tools fall into three strategies: observation, inhibition and activation. Using examples for each strategy, in this Cell Science at a Glance and the accompanying poster, we provide a guide to using these tools to dissect protein function in a given cellular process. Our focus here is on tools that allow rapid modification of proteins of interest and how observing the resulting changes in cell states is key to unlocking dynamic cell processes. The aim is to inspire the reader's next set of imaging experiments.

Integrin receptor trafficking in health and disease

Integrins are a family of 24 different heterodimers that are indispensable for multicellular life. Cell polarity, adhesion and migration are controlled by integrins delivered to the cell surface which in turn is regulated by the exo- and endocytic trafficking of integrins. The deep integration between trafficking and cell signaling determines the spatial and temporal output from any biochemical cue. Integrin trafficking plays a key role in development and many pathological conditions, especially cancer. Several novel regulators of integrin traffic have been discovered in recent times, including a novel class of integrin carrying vesicles, the intracellular nanovesicles (INVs). The tight regulation of trafficking pathways by cell signaling, where kinases phosphorylate key small GTPases in the trafficking pathway enable coordination of cell response to the extracellular milieu. Integrin heterodimer expression and trafficking differ in different tissues and contexts. In this Chapter, we discuss recent studies on integrin trafficking and its contribution to normal physiological and pathophysiological states.

Tumor protein D54 binds intracellular nanovesicles via an extended amphipathic region

Tumor Protein D54 (TPD54) is an abundant cytosolic protein that belongs to the TPD52 family, a family of four proteins (TPD52, 53, 54 and 55) that are overexpressed in several cancer cells. Even though the functions of these proteins remain elusive, recent investigations indicate that TPD54 binds to very small cytosolic vesicles with a diameter of ca. 30 nm, half the size of classical (e.g. COPI and COPII) transport vesicles. Here, we investigated the mechanism of intracellular nanovesicle capture by TPD54. Bioinformatical analysis suggests that TPD54 contains a small coiled-coil followed by four amphipathic helices (AH1-4), which could fold upon binding to lipid membranes. Limited proteolysis, circular dichroism (CD) spectroscopy, tryptophan fluorescence, and cysteine mutagenesis coupled to covalent binding of a membrane sensitive probe showed that binding of TPD54 to small liposomes is accompanied by large structural changes in the amphipathic helix region. Furthermore, site-directed mutagenesis indicated that AH2 and AH3 have a predominant role in TPD54 binding to membranes both in cells and using model liposomes. We found that AH3 has the physicochemical features of an Amphipathic Lipid Packing Sensor (ALPS) motif, which, in other proteins, enables membrane binding in a curvature-dependent manner. Accordingly, we observed that binding of TPD54 to liposomes is very sensitive to membrane curvature and lipid unsaturation. We conclude that TPD54 recognizes nanovesicles through a combination of ALPS-dependent and -independent mechanisms.

Integrating intracellular nanovesicles into integrin trafficking pathways and beyond

Membrane traffic controls the movement of proteins and lipids from one cellular compartment to another using a system of transport vesicles. Intracellular nanovesicles (INVs) are a newly described class of transport vesicles. These vesicles are small, carry diverse cargo, and are involved in multiple trafficking steps including anterograde traffic and endosomal recycling. An example of a biological process that they control is cell migration and invasion, due to their role in integrin recycling. In this review, we describe what is known so far about these vesicles. We discuss how INVs may integrate into established membrane trafficking pathways using integrin recycling as an example. We speculate where in the cell INVs have the potential to operate and we identify key questions for future investigation.