A novel TIP30 protein complex regulates EGF receptor signaling and endocytic degradation

A multiprotein signaling complex sustains AKT and mTOR/S6K activity necessary for the survival of cancer cells undergoing stress

Cancer cells encounter stresses during tumor progression and metastatic spread, however, how they survive these challenges is not fully understood. We now identify a mechanism for cancer cell survival through the discovery of a multiprotein signaling complex that includes the GTPase Cdc42, the Cdc42 GEF/effector protein Dock7, AKT, mTOR and the mTORC1 regulatory partners TSC1, TSC2, and Rheb. This pro-survival signaling complex sustains the activated state of AKT by preventing its dephosphorylation at Ser473 during serum starvation, resulting in a low but critical activation of a Raptor-independent mTOR/S6K activity. We demonstrate that the Dock7 DHR1 domain, previously of unknown function, is responsible for preserving AKT phosphorylation through an interaction requiring its C2-like motif. Collectively, these findings help address long-standing questions of how Cdc42 signals mTOR activation by elucidating the unique functions of its signaling partner Dock7 as an AKT regulator necessary for resistance to anoikis and apoptosis in cancer cells.

Hyperpolarization-activated cyclic nucleotide-gated cation channel 3 promotes HCC development in a female-biased manner

Sex differences in hepatocellular carcinoma (HCC) development are regulated by sex and non-sex chromosomes, sex hormones, and environmental factors. We previously reported that Ncoa5+/- mice develop HCC in a male-biased manner. Here we show that NCOA5 expression is reduced in male patient HCCs while the expression of an NCOA5-interacting tumor suppressor, TIP30, is lower in female HCCs. Tip30 heterozygous deletion does not change HCC incidence in Ncoa5+/- male mice but dramatically increases HCC incidence in Ncoa5+/- female mice, accompanied by hepatic hyperpolarization-activated cyclic nucleotide-gated cation channel 3 (HCN3) overexpression. HCN3 overexpression cooperates with MYC to promote mouse HCC development, whereas Hcn3 knockout preferentially hinders HCC development in female mice. Furthermore, HCN3 amplification and overexpression occur in human HCCs and correlate with a poorer prognosis of patients in a female-biased manner. Our results suggest that TIP30 and NCOA5 protect against female liver oncogenesis and that HCN3 is a female-biased HCC driver.

Epigenetic silencing of HTATIP2 in glioblastoma contributes to treatment resistance by enhancing nuclear translocation of the DNA repair protein MPG

Glioblastoma, the most malignant brain tumor in adults, exhibits characteristic patterns of epigenetic alterations that await elucidation. The DNA methylome of glioblastoma revealed recurrent epigenetic silencing of HTATIP2, which encodes a negative regulator of importin β-mediated cytoplasmic-nuclear protein translocation. Its deregulation may thus alter the functionality of cancer-relevant nuclear proteins, such as the base excision repair (BER) enzyme N-methylpurine DNA glycosylase (MPG), which has been associated with treatment resistance in GBM. We found that induction of HTATIP2 expression in GBM cells leads to a significant shift of predominantly nuclear to cytoplasmic MPG, whereas depletion of endogenous HTATIP2 results in enhanced nuclear MPG localization. Reduced nuclear MPG localization, prompted by HTATIP2 expression or by depletion of MPG, yielded less phosphorylated-H2AX-positive cells upon treatment with an alkylating agent. This suggested reduced MPG-mediated formation of apurinic/apyrimidinic sites, leaving behind unrepaired DNA lesions, reflecting a reduced capacity of BER in response to the alkylating agent. Epigenetic silencing of HTATIP2 may thus increase nuclear localization of MPG, thereby enhancing the capacity of the glioblastoma cells to repair treatment-related lesions and contributing to treatment resistance.

The ACSL4 Network Regulates Cell Death and Autophagy in Diseases

Lipid metabolism, cell death, and autophagy are interconnected processes in cells. Dysregulation of lipid metabolism can lead to cell death, such as via ferroptosis and apoptosis, while lipids also play a crucial role in the regulation of autophagosome formation. An increased autophagic response not only promotes cell survival but also causes cell death depending on the context, especially when selectively degrading antioxidant proteins or organelles that promote ferroptosis. ACSL4 is an enzyme that catalyzes the formation of long-chain acyl-CoA molecules, which are important intermediates in the biosynthesis of various types of lipids. ACSL4 is found in many tissues and is particularly abundant in the brain, liver, and adipose tissue. Dysregulation of ACSL4 is linked to a variety of diseases, including cancer, neurodegenerative disorders, cardiovascular disease, acute kidney injury, and metabolic disorders (such as obesity and non-alcoholic fatty liver disease). In this review, we introduce the structure, function, and regulation of ACSL4; discuss its role in apoptosis, ferroptosis, and autophagy; summarize its pathological function; and explore the potential implications of targeting ACSL4 in the treatment of various diseases.

Genome-wide association study of the age of onset of type 1 diabetes reveals HTATIP2 as a novel T cell regulator

Introduction

Type 1 diabetes, a disorder caused by autoimmune destruction of pancreatic insulin-producing cells, is more difficult to manage when it presents at a younger age. We sought to identify genetic correlates of the age of onset by conducting the first genome-wide association study (GWAS) treating the age of first diagnosis as a quantitative trait.

Methods

We performed GWAS with a discovery cohort of 4,014 cases and a replication cohort of 493 independent cases. Genome-wide significant SNPs were mapped to a causal variant by Bayesian conditional analysis and gel shift assay. The causal protein-coding gene was identified and characterized by RNA interference treatment of primary human pan-CD4+ T cells with RNA-seq of the transcriptome. The candidate gene was evaluated functionally in primary cells by CD69 staining and proliferation assays.

Results

Our GWAS replicated the known association of the age of diagnosis with the human leukocyte antigen complex (HLA-DQB1). The second signal identified was in an intron of the NELL1 gene on chromosome 11 and fine-mapped to variant rs10833518 (P < 1.54 × 10^-9). Homozygosity for the risk allele leads to average age of onset one year earlier. Knock-down of HIV TAT-interacting protein 2 (HTATIP2), but not other genes in the locus, resulted in alterations to gene expression in signal transduction pathways including MAP kinases and PI3-kinase. Higher levels of HTATIP2 expression are associated with increased viability, proliferation, and activation of T cells in the presence of signals from antigen and cytokine receptors.

Discussion

This study implicates HTATIP2 as a new type 1 diabetes gene acting via T cell regulation. Larger population sample sizes are expected to reveal additional loci.

Peroxisome Proliferator-Activated Receptor Activation in Precision-Cut Bovine Liver Slices Reveals Novel Putative PPAR Targets in Periparturient Dairy Cows

Metabolic challenges experienced by dairy cows during the transition between pregnancy and lactation (also known as peripartum), are of considerable interest from a nutrigenomic perspective. The mobilization of large amounts of non-esterified fatty acids (NEFA) leads to an increase in NEFA uptake in the liver, the excess of which can cause hepatic accumulation of lipids and ultimately fatty liver. Interestingly, peripartum NEFA activate the Peroxisome Proliferator-activated Receptor (PPAR), a transcriptional regulator with known nutrigenomic properties. The study of PPAR activation in the liver of periparturient dairy cows is thus crucial; however, current in vitro models of the bovine liver are inadequate, and the isolation of primary hepatocytes is time consuming, resource intensive, and prone to errors, with the resulting cells losing characteristic phenotypical traits within hours. The objective of the current study was to evaluate the use of precision-cut liver slices (PCLS) from liver biopsies as a model for PPAR activation in periparturient dairy cows. Three primiparous Jersey cows were enrolled in the experiment, and PCLS from each were prepared prepartum (−8.0 ± 3.6 DIM) and postpartum (+7.7± 1.2 DIM) and treated independently with a variety of PPAR agonists and antagonists: the PPARα agonist WY-14643 and antagonist GW-6471; the PPARδ agonist GW-50156 and antagonist GSK-3787; and the PPARγ agonist rosiglitazone and antagonist GW-9662. Gene expression was assayed through RT-qPCR and RNAseq, and intracellular triacylglycerol (TAG) concentration was measured. PCLS obtained from postpartum cows and treated with a PPARγ agonist displayed upregulation of ACADVL and LIPC while those treated with PPARδ agonist had increased expression of LIPC, PPARD, and PDK4. In PCLS from prepartum cows, transcription of LIPC was increased by all PPAR agonists and NEFA. TAG concentration tended to be larger in tissue slices treated with PPARδ agonist compared to CTR. Use of PPAR isotype-specific antagonists in PCLS cultivated in autologous blood serum failed to decrease expression of PPAR targets, except for PDK4, which was confirmed to be a PPARδ target. Transcriptome sequencing revealed considerable differences in response to PPAR agonists at a false discovery rate-adjusted p-value of 0.2, with the most notable effects exerted by the PPARδ and PPARγ agonists. Differentially expressed genes were mainly related to pathways involved with lipid metabolism and the immune response. Among differentially expressed genes, a subset of 91 genes were identified as novel putative PPAR targets in the bovine liver, by cross-referencing our results with a publicly available dataset of predicted PPAR target genes, and supplementing our findings with prior literature. Our results provide important insights on the use of PCLS as a model for assaying PPAR activation in the periparturient dairy cow.

An evaluation of maternal serum dynamic thiol-disulfide homeostasis and ischemia modified albumin changes in pregnant women with COVID-19

Objective:

It is thought that oxidative stress, free radicals, reactive oxygen species and reactive nitrogen species affect the pathophysiology of coronavirus disease-2019 (COVID-19). This study aimed to evaluate the oxidative status in pregnant patients with COVID-19 infection according to the changes seen in the levels of maternal serum thiol-disulfide and ischemia-modified albumin (IMA).

Materials and Methods:

A study group was formed of 40 pregnant women with confirmed COVID-19 infection (study group) and a control group of 40 healthy pregnant women with no risk factors determined. In this prospective, case-controlled study, analyses were made of the maternal serum native thiol, total thiol, disulfide, IMA, and disulfide/native thiol concentrations.

Results:

The maternal serum native thiol and total thiol concentrations in the study group were determined to be statistically significantly lower (p=0.007 and p=0.006, respectively), and the disulfide/native thiol ratio was higher but not to a level of statistical significance (p=0.473). There was no difference between the two groups regarding IMA levels (p=0.731).

Conclusion:

The thiol-disulfide balance was seen to shift in the oxidant direction in pregnancies with COVID-19, which might support the view that ischemic processes play a role in the etiopathogenesis of this novel disease.

TIP30 overcomes gefitinib resistance by regulating cytoplasmic and nuclear EGFR signaling in non-small-cell lung cancer

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) (eg, gefitinib) exert potent therapeutic efficacy in non–small‐cell lung cancer (NSCLC) harboring EGFR‐activating mutations. However, the resistance to EGFR TKIs limits their clinical therapeutic efficacy. TIP30, a newly identified tumor suppressor, appears to be involved in the regulation of cytoplasmic and nuclear EGFR signaling in NSCLC. Our previous study demonstrated that TIP30 regulated EGF‐dependent cyclin D1 transcription in human lung adenocarcinoma and suppressed tumorigenesis. In the present study, the involvement of TIP30 in combating gefitinib resistance in NSCLC was determined for the first time in vitro and in vivo. Gain and loss of function studies showed that overexpression of TIP30 effectively sensitized cells to gefitinib in vitro, whereas TIP30 inhibition promoted gefitinib cell resistance. Moreover, TIP30 negatively regulated the activation of the p‐AKT and p‐MEK signaling pathways in PC9/GR. Importantly, PC9/GR harbored high levels of nuclear EGFR, and overexpression of TIP30 restored irregular EGFR trafficking and degradation from early endosomes to the late endosomes, decreasing the nuclear accumulation of EGFR, which may partly or totally inhibit EGFR‐mediated induction of c‐Myc transcription. Xenographic tumors induced by overexpression of TIP30 by PC9/GR cells in nude mice were suppressed compared with their original counterparts. Overall, it was revealed that TIP30 overexpression restored gefitinib sensitivity in NSCLC cells and attenuated the cytoplasmic and nuclear EGFR signaling pathways and may be a promising biomarker in gefitinib resistance in NSCLC.

The Multifunctional Role of EMP3 in the Regulation of Membrane Receptors Associated with IDH-Wild-Type Glioblastoma

Epithelial membrane protein 3 (EMP3) is a tetraspan membrane protein overexpressed in isocitrate dehydrogenase-wild-type (IDH-wt) glioblastoma (GBM). Several studies reported high EMP3 levels as a poor prognostic factor in GBM patients. Experimental findings based on glioma and non-glioma models have demonstrated the role of EMP3 in the regulation of several membrane proteins known to drive IDH-wt GBM. In this review, we summarize what is currently known about EMP3 biology. We discuss the regulatory effects that EMP3 exerts on a variety of oncogenic receptors and discuss how these mechanisms may relate to IDH-wt GBM. Lastly, we enumerate the open questions towards EMP3 function in IDH-wt GBM.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Pancreatic Ductal Adenocarcinoma: MicroRNAs Affecting Tumor Growth and Metastasis in Preclinical In Vivo Models

Patients with pancreatic ductal adenocarcinoma have a dismall prognosis because at the time of diagnosis, in the vast majority of patients the tumor has already disseminated to distant organs and the therapeutic benefit of approved agents such as gemcitabine is limited. Therefore, the identification and preclinical and clinical validation of therapeutic agents covering new targets is of paramount importance. In this review we have summarized microRNAs and corresponding targets which affect growth and metastasis of pancreatic tumors in preclinical mouse in vivo models. We identified four up-regulated and 16 down-regulated miRs in PDAC in comparison to corresponding normal tissues. Three sub-categories of miRs have emerged: miRs affecting tumor growth and miRs with an impact on both, tumor growth and metastasis or metastasis only. Finally, we discuss technical and therapeutic aspects of miR-related therapeutic agents for the treatment of pancreatic ductal adenocarcinoma.

Mechanism of membrane fusion: protein-protein interaction and beyond

Membrane fusion is a universal event in all living organism. It is at the heart of intracellular organelle biogenesis and membrane traffic processes such as endocytosis and exocytosis, and is also used by enveloped viruses to enter hosting cells. Regarding the cellular mechanisms underlying membrane fusion, pioneering studies by Randy Schekman, James Rothman, Thomas C. Südhof and their colleagues have demonstrated the function of specific proteins and protein-protein interactions as essential fusogenic factor to initiate membrane fusion. Since then, function of lipids and protein-lipid interaction has also been identified as important players in membrane fusion. Based on that NSF (NEM-sensitive factor where NEM stands for N-ethyl-maleimide) and acyl-CoA are required for the membrane fusion of transporting vesicles with Golgi cisternae, it is further suggested that the transfer of the acyl chain to a molecule(s) is essential for membrane fusion. Among the previously identified fusogens, phosphatidic acid (PA) is found as an acyl chain recipient. Functionally, acylation of PA is required for tethering the membranes of Rab5a vesicles and early endosomes together during membrane fusion. As certain threshold of proximity between the donor and acceptor membrane is required to initiate membrane fusion, fusogenic factors beyond protein-protein and protein-lipid interaction need to be identified.

TIP30 counteracts cardiac hypertrophy and failure by inhibiting translational elongation

Pathological cardiac overload induces myocardial protein synthesis and hypertrophy, which predisposes to heart failure. To inhibit hypertrophy therapeutically, the identification of negative regulators of cardiomyocyte protein synthesis is needed. Here, we identified the tumor suppressor protein TIP30 as novel inhibitor of cardiac hypertrophy and dysfunction. Reduced TIP30 levels in mice entailed exaggerated cardiac growth during experimental pressure overload, which was associated with cardiomyocyte cellular hypertrophy, increased myocardial protein synthesis, reduced capillary density, and left ventricular dysfunction. Pharmacological inhibition of protein synthesis improved these defects. Our results are relevant for human disease, since we found diminished cardiac TIP30 levels in samples from patients suffering from end‐stage heart failure or hypertrophic cardiomyopathy. Importantly, therapeutic overexpression of TIP30 in mouse hearts inhibited cardiac hypertrophy and improved left ventricular function during pressure overload and in cardiomyopathic mdx mice. Mechanistically, we identified a previously unknown anti‐hypertrophic mechanism, whereby TIP30 binds the eukaryotic elongation factor 1A (eEF1A) to prevent the interaction with its essential co‐factor eEF1B2 and translational elongation. Therefore, TIP30 could be a therapeutic target to counteract cardiac hypertrophy.

Subcongenic analysis of a quantitative trait locus affecting body weight and glucose metabolism in zinc transporter 7 (znt7)-knockout mice

Background

A genome-wide mapping study using male F₂zinc transporter 7-knockout mice (znt7-KO) and their wild type littermates in a mixed 129P1/ReJ (129P1) and C57BL/6J (B6) background identified a quantitative trait locus (QTL) on chromosome 7, which had a synergistic effect on body weight gain and fat deposit with the znt7-null mutation.

Results

The genetic segment for body weight on mouse chromosome 7 was investigated by newly created subcongenic znt7-KO mouse strains carrying different lengths of genomic segments of chromosome 7 from the 129P1 donor strain in the B6 background. We mapped the sub-QTL for body weight in the proximal region of the previously mapped QTL, ranging from 47.4 to 64.4 megabases (Mb) on chromosome 7. The 129P1 donor allele conferred lower body weight gain and better glucose handling during intraperitoneal glucose challenge than the B6 allele control. We identified four candidate genes, including Htatip2, E030018B13Rik, Nipa1, and Atp10a, in this sub-QTL using quantitative RT-PCR and cSNP detection (single nucleotide polymorphisms in the protein coding region).

Conclusions

This study dissected the genetic determinates of body weight and glucose metabolism in znt7-KO mice. The study demonstrated that a 17-Mb long 129P1 genomic region on mouse chromosome 7 conferred weight reduction and improved glucose tolerance in znt7-KO male mice. Among the four candidate genes identified, Htatip2 is the most likely candidate gene involved in the control of body weight based on its function in regulation of lipid metabolism. The candidate genes discovered in this study lay a foundation for future studies of their roles in development of metabolic diseases, such as obesity and type 2 diabetes.

Electronic supplementary material

The online version of this article (10.1186/s12863-019-0715-2) contains supplementary material, which is available to authorized users.

Characterization of the epithelial membrane protein 3 interaction network reveals a potential functional link to mitogenic signal transduction regulation

Epithelial Membrane Protein 3 (EMP3), a 4-transmembrane glycoprotein, first gained attention as a putative tumor suppressor. Accumulating evidence, however, points to a more tumor promotive function of EMP3. The biological function of EMP3 remains largely unclear. To elucidate more of EMP3's interaction network, we performed a Yeast-Two-Hybrid (Y2H) screening, followed by validation of candidate interactors by Biomolecular Fluorescence Complementation (BiFC) and Proximity Ligation Assay (PLA). Furthermore, we generated stable EMP3 knockdown cell lines and measured cell proliferation, migration and sensitivity to apoptosis induction as well as the expression and activation levels of important signal pathway components. The Y2H screening yielded 10 novel interactions of EMP3, eight of which could also be detected by BiFC and PLA interaction assays. All newly discovered interaction partners are involved in signaling or trafficking regulation. Most notably, FLOT1 and HTATIP2 have well described roles in the regulation of EGFR signaling. In addition, knockdown of EMP3 resulted in reduced levels of p-AKT, p-ERK and p-EGFR, attenuated cell proliferation and migration and sensitized cells to apoptosis induction by TRAIL and Staurosporine. Based on these observations we hypothesize that EMP3 might be involved in the regulation of receptor-tyrosine-kinase mediated mitogenic signaling.

Relevance of Rab Proteins for the Life Cycle of Hepatitis C Virus

Although potent direct-acting antiviral drugs for the treatment of chronic hepatitis C virus (HCV) infection are licensed, there are more than 70 million individuals suffering from chronic HCV infection. In light of the limited access to these drugs, high costs, and a lot of undiagnosed cases, it is expected that the number of HCV cases will not decrease worldwide in the next years. Therefore, and due to the paradigmatic character of HCV for deciphering the crosstalk between viral pathogens and the host cell, characterization of HCV life cycle remains a challenge. HCV belongs to the family of Flaviviridae. As an enveloped virus HCV life cycle depends in many steps on intracellular trafficking. Rab GTPases, a large family of small GTPases, play a central role in intracellular trafficking processes controlling fusion, uncoating, vesicle budding, motility by recruiting specific effector proteins. This review describes the relevance of various Rab proteins for the different steps of the HCV life cycle.

Evasion of phagotrophic predation by protist hosts and innate immunity of metazoan hosts by Legionella pneumophila

Legionella pneumophila is a ubiquitous environmental bacterium that has evolved to infect and proliferate within amoebae and other protists. It is thought that accidental inhalation of contaminated water particles by humans is what has enabled this pathogen to proliferate within alveolar macrophages and cause pneumonia. However, the highly evolved macrophages are equipped with more sophisticated innate defence mechanisms than are protists, such as the evolution of phagotrophic feeding into phagocytosis with more evolved innate defence processes. Not surprisingly, the majority of proteins involved in phagosome biogenesis (~80%) have origins in the phagotrophy stage of evolution. There are a plethora of highly evolved cellular and innate metazoan processes, not represented in protist biology, that are modulated by L. pneumophila, including TLR2 signalling, NF-κB, apoptotic and inflammatory processes, histone modification, caspases, and the NLRC-Naip5 inflammasomes. Importantly, L. pneumophila infects haemocytes of the invertebrate Galleria mellonella, kill G. mellonella larvae, and proliferate in and kill Drosophila adult flies and Caenorhabditis elegans. Although coevolution with protist hosts has provided a substantial blueprint for L. pneumophila to infect macrophages, we discuss the further evolutionary aspects of coevolution of L. pneumophila and its adaptation to modulate various highly evolved innate metazoan processes prior to becoming a human pathogen.

Association of Endophilin B1 with Cytoplasmic Vesicles

Endophilins are SH3- and BAR domain-containing proteins implicated in membrane remodeling and vesicle formation. Endophilins A1 and A2 promote the budding of endocytic vesicles from the plasma membrane, whereas endophilin B1 has been implicated in vesicle budding from intracellular organelles, including the trans-Golgi network and late endosomes. We previously reported that endophilins A1 and A2 exist almost exclusively as soluble dimers in the cytosol. Here, we present results of fluorescence fluctuation spectroscopy analyses indicating that, in contrast, the majority of endophilin B1 is present in multiple copies on small, highly mobile cytoplasmic vesicles. Formation of these vesicles was enhanced by overexpression of wild-type dynamin 2, but suppressed by expression of a catalytically inactive dynamin 2 mutant. Using dual-color heterospecies partition analysis, we identified the epidermal growth factor receptor on endophilin B1 vesicles. Moreover, a proportion of endophilin B1 vesicles also contained caveolin, whereas clathrin was almost undetectable on those vesicles. These results raise the possibility that endophilin B1 participates in dynamin 2-dependent formation of a population of transport vesicles distinct from those generated by A-type endophilins.

Endophilin B2 facilitates endosome maturation in response to growth factor stimulation, autophagy induction, and influenza A virus infection

Endocytosis, and the subsequent trafficking of endosomes, requires dynamic physical alterations in membrane shape that are mediated in part by endophilin proteins. The endophilin B family of proteins contains an N-terminal Bin/amphiphysin/Rvs (N-BAR) domain that induces membrane curvature to regulate intracellular membrane dynamics. Whereas endophilin B1 (SH3GLB1/Bif-1) is known to be involved in a number of cellular processes, including apoptosis, autophagy, and endocytosis, the cellular function of endophilin B2 (SH3GLB2) is not well understood. In this study, we used genetic approaches that revealed that endophilin B2 is not required for embryonic development in vivo but that endophilin B2 deficiency impairs endosomal trafficking in vitro, as evidenced by suppressed endosome acidification, EGFR degradation, autophagic flux, and influenza A viral RNA nuclear entry and replication. Mechanistically, although the loss of endophilin B2 did not affect endocytic internalization and lysosomal function, endophilin B2 appeared to regulate the trafficking of endocytic vesicles and autophagosomes to late endosomes or lysosomes. Moreover, we also found that despite having an intracellular localization and tissue distribution similar to endophilin B1, endophilin B2 is dispensable for mitochondrial apoptosis. Taken together, our findings suggest that endophilin B2 positively regulates the endocytic pathway in response to growth factor signaling, autophagy induction, and viral entry.

TIP30 regulates lipid metabolism in hepatocellular carcinoma by regulating SREBP1 through the Akt/mTOR signaling pathway

Lipid reprogramming has been considered as a crucial characteristic in hepatocellular carcinoma (HCC) initiation and progression. However, detailed molecular mechanisms have yet to be clearly defined. Here, we examined the effects of tumor suppressor TIP30 on the regulation of HCC lipid metabolism. We found that decreased TIP30 expression leads to elevated fatty acid synthesis and enhanced levels of lipogenic enzymes SCD and FASN in HCC cells. Moreover, SREBP1 is one of the key transcription factors regulating liver lipid metabolism, and TIP30 deficiency significantly increased SREBP1 expression and nuclear accumulation. Small interfering RNAs targeting SREBP1 could reverse fatty acid synthesis induced by TIP30 deficiency. Furthermore, downregulating TIP30 activated the Akt/mTOR signaling pathway to upregulate SREBP1 expression, which promoted lipid metabolism by activating gene transcription of lipogenesis, including fasn and scd. We also showed that TIP30 deficiency-regulated lipid metabolism promoted proliferation of HCC cells. Clinically, our data revealed that TIP30 expression significantly correlated with SREBP1 in patients with HCC and that a combination of TIP30 and SREBP1 is a powerful predictor of HCC prognosis. Together, our data suggested a novel function of TIP30 in HCC progression and indicate that TIP30 regulation of SREBP1 may represent a novel target for HCC treatment.

Never let it go: Stopping key mechanisms underlying metastasis to fight pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive neoplasm, predicted to become the second leading cause of cancer-related deaths before 2030. This dismal trend is mainly due to lack of effective treatments against its metastatic behavior. Therefore, a better understanding of the key mechanisms underlying metastasis should provide new opportunities for therapeutic purposes. Genomic analyses revealed that aberrations that fuel PDAC tumorigenesis and progression, such as SMAD4 loss, are also implicated in metastasis. Recently, microRNAs have been shown to play a regulatory role in the metastatic behavior of many tumors, including PDAC. In particular, miR-10 and miR-21 have appeared as master regulators of the metastatic program, while members of the miR-200 family are involved in the epithelial-to-mesenchymal switch, favoring cell migration and invasiveness. Several studies have also found a close relationship between cancer stem cells (CSCs) and biological features of metastasis, and the CSC markers ALDH1, ABCG2 and c-Met are expressed at high levels in metastatic PDAC cells. Emerging evidence reveals that exosomes are involved in the modulation of the tumor microenvironment and can initiate PDAC pre-metastatic niche formation in the liver and lungs. In this review, we provide an overview of the role of all these pivotal factors in the metastatic behavior of PDAC, and discuss their potential exploitation in the clinic to improve current therapeutics and identify new drug targets.

Calpain mobilizes Atg9/Bif-1 vesicles from Golgi stacks upon autophagy induction by thapsigargin

CAPNS1 is essential for stability and function of the ubiquitous calcium-dependent proteases micro- and milli-calpain. Upon inhibition of the endoplasmic reticulum Ca²⁺ ATPase by 100 nM thapsigargin, both micro-calpain and autophagy are activated in human U2OS osteosarcoma cells in a CAPNS1-dependent manner. As reported for other autophagy triggers, thapsigargin treatment induces Golgi fragmentation and fusion of Atg9/Bif-1-containing vesicles with LC3 bodies in control cells. By contrast, CAPNS1 depletion is coupled with an accumulation of LC3 bodies and Rab5 early endosomes. Moreover, Atg9 and Bif-1 remain in the GM130-positive Golgi stacks and Atg9 fails to interact with the endocytic route marker transferrin receptor and with the core autophagic protein Vps34 in CAPNS1-depleted cells. Ectopic expression of a Bif-1 point mutant resistant to calpain processing is coupled to endogenous p62 and LC3-II accumulation. Altogether, these data indicate that calpain allows dynamic flux of Atg9/Bif-1 vesicles from the Golgi toward the budding autophagosome.

Summary: ER stress triggers calpain-dependent Bif-1 activation and induction of autophagosome maturation by promoting ATG9/Bif-1 vesicle trafficking and fusion with LC3 bodies.

Regulated Entry of Hepatitis C Virus into Hepatocytes

Hepatitis C virus (HCV) is a model for the study of virus–host interaction and host cell responses to infection. Virus entry into hepatocytes is the first step in the HCV life cycle, and this process requires multiple receptors working together. The scavenger receptor class B type I (SR-BI) and claudin-1 (CLDN1), together with human cluster of differentiation (CD) 81 and occludin (OCLN), constitute the minimal set of HCV entry receptors. Nevertheless, HCV entry is a complex process involving multiple host signaling pathways that form a systematic regulatory network; this network is centrally controlled by upstream regulators epidermal growth factor receptor (EGFR) and transforming growth factor β receptor (TGFβ-R). Further feedback regulation and cell-to-cell spread of the virus contribute to the chronic maintenance of HCV infection. A comprehensive and accurate disclosure of this critical process should provide insights into the viral entry mechanism, and offer new strategies for treatment regimens and targets for HCV therapeutics.

A microRNA signature in circulating exosomes is superior to exosomal glypican-1 levels for diagnosing pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that often presents clinically at an advanced stage and that may be confused with chronic pancreatitis (CP). Conversely, CP may be misdiagnosed as PDAC leading to unwarranted pancreas resection. Therefore, early PDAC diagnosis and clear differentiation between PDAC and CP are crucial for improved care. Exosomes are circulating microvesicles whose components can serve as cancer biomarkers. We compared exosomal glypican-1 (GPC1) and microRNA levels in normal control subjects and in patients with PDAC and CP. We report that exosomal GPC1 is not diagnostic for PDAC, whereas high exosomal levels of microRNA-10b, (miR-10b), miR-21, miR-30c, and miR-181a and low miR-let7a readily differentiate PDAC from normal control and CP samples. By contrast with GPC1, elevated exosomal miR levels decreased to normal values within 24 h following PDAC resection. All 29 PDAC cases exhibited significantly elevated exosomal miR-10b and miR-30c levels, whereas 8 cases had normal or slightly increased CA 19-9 levels. Thus, our exosomal miR signature is superior to exosomal GPC1 or plasma CA 19-9 levels in establishing a diagnosis of PDAC and differentiating between PDAC and CP.

Genomics of human fatty liver disease reveal mechanistically linked lipid droplet-associated gene regulations in bland steatosis and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a common disorder hallmarked by excessive lipid deposits. Based on our recent research on lipid droplet (LD) formation in hepatocytes, we investigated LD-associated gene regulations in NAFLD of different grades, that is, steatosis vs steatohepatitis by comparing liver biopsies from healthy controls (N = 13) and NAFLD patients (N = 102). On average, more than 700 differentially expressed genes (DEGs) were identified of which 146 are mechanistically linked to LD formation. We identified 51 LD-associated DEGs frequently regulated in patient samples (range ≥5 to ≤102) with the liver-receptor homolog-1(NR5A2), that is, a key regulator of cholesterol metabolism being commonly repressed among 100 patients examined. With bland steatosis, notable regulations involved hypoxia-inducible lipid droplet-associated-protein and diacylglycerol-O-acyltransferase-2 renowned for their role in LD-growth. Conversely, nonalcoholic steatohepatitis-associated DEGs coded for epidermal growth factor receptor and TLR4 signaling with decreased expression of the GTPase Rab5 and the lipid phosphohydrolase PPAP2B thus highlighting adaptive responses to inflammation, LDL-mediated endocytosis and lipogenesis, respectively. Studies with steatotic primary human hepatocyte cultures demonstrated induction of LD-associated PLIN2, CIDEC, DNAAF1, whereas repressed expression of CPT1A, ANGPTL4, and PKLR informed on burdened mitochondrial metabolism. Equally, repressed expression of the B-lymphocyte chemoattractant CXCL13 and STAT4 as well as induced FGF21 evidenced amelioration of steatosis-related inflammation. In-vitro/in-vivo patient sample comparisons confirmed C-reactive protein, SOCS3, NR5A2, and SOD2 as commonly regulated. Lastly, STRING network analysis highlighted potential "druggable" targets with PLIN2, CIDEC, and hypoxia-inducible lipid droplet-associated-protein being confirmed by immunofluorescence microscopy. In conclusion, steatosis and steatohepatitis specific gene regulations informed on the pathogenesis of NAFLD to broaden the perspective of targeted therapies.

Progress of endocytic CHRN to autophagic degradation is regulated by RAB5-GTPase and T145 phosphorylation of SH3GLB1 at mouse neuromuscular junctions in vivo

Endocytosed nicotinic acetylcholine receptors (CHRN) are degraded via macroautophagy/autophagy during atrophic conditions and are accompanied by the autophagic regulator protein SH3GLB1. The present study addressed the functional role of SH3GLB1 on CHRN trafficking and its implementation. We found an augmented ratio of total SH3GLB1 to threonine-145 phosphorylated SH3GLB1 (SH3GLB1:p-SH3GLB1) under conditions of increased CHRN vesicle numbers. Overexpression of T145 phosphomimetic (T145E) and phosphodeficient (T145A) mutants of SH3GLB1, was found to either slow down or augment the processing of endocytic CHRN vesicles, respectively. Co-expression of the early endosomal orchestrator RAB5 largely rescued the slow processing of endocytic CHRN vesicles induced by T145E. SH3GLB1 phosphomutants did not modulate the expression or colocalization of RAB5 with CHRN vesicles, but instead altered the expression of RAB5 activity regulators. In summary, these findings suggest that SH3GLB1 controls CHRN endocytic trafficking in a phosphorylation- and RAB5-dependent manner at steps upstream of autophagosome formation.

TIP30: A Novel Tumor-Suppressor Gene

TIP30/CC3 was first identified and characterized as a "candidate" tumor-suppressor gene in 1997. Recently, the TIP30 tumor-suppressor status has been fully established since several studies have described that TIP30 protein expression is frequently downregulated in diverse types of human tumors, and the downregulation is often associated with tumor progression. TIP30 is involved in the control of cell apoptosis, growth, metastasis, angiogenesis, DNA repair, and tumor cell metabolism. Moreover, TIP30(-/-) mice spontaneously develop hepatocellular carcinoma and other tumors at a higher incidence than that of wild-type mice. In this review, we provide an overview of current knowledge concerning the role of TIP30 in tumor development and progression. To our knowledge, this is the first review about the role of novel tumor-suppressor gene TIP30 in tumor development and progression.

Association of TIP30 expression and prognosis of hepatocellular carcinoma in patients with HBV infection

Altered expression of TIP30, a tumor suppressor, has been observed in many cancers. In this study, we have evaluated the expression of TIP30 in the tissues of 209 hepatocellular carcinomas (HCC) and their adjacent tissues by using a high‐density tissue microarray, and analyzed its correlation with the clinical pathological parameters of the patients. The results revealed negative or weak expression of TIP30 in 43.5% (91/209) of the HCC tissues, and in only 27% (56/209) of the adjacent tissues. The expression level of TIP30 in HCC was inversely correlated with serum alpha‐fetoprotein (AFP) levels, HBV infection, and tumor differentiation. Multivariate analysis for survival indicated that serum HBV infection was the most significant predictor of poor prognosis in HCC (P = 0.0023), and TIP30 expression and tumor differentiation were also independent indicators in this respect (P = 0.0364 and P = 0.0397, respectively). Patients with medium or high expression levels of TIP30 (TIP30^++/+++) had a better 5‐year overall survival rate than those with low/negative (TIP30^+/−) expression (P < 0.001). TIP30^+/−/HBV⁺ patients had the worst 5‐year overall survival rate, whereas TIP30^++/+++/HBV⁻ patients had the best. To further explore the correlation between TIP30 and HBV infection in HCC, HBV⁺ hepatoblastoma cell‐line HepG2 2.2.15 and HCC cell‐line Hep3B were used. Upon silencing of HBV, we observed an upregulation of TIP30 and decreased cell proliferation. In the in vivo studies, we found that the mice inoculated with HepG2 2.2.15 cells with HBV silencing had a prolonged tumor latency and a longer life span, as compared to the control mice inoculated with untreated control cells. In conclusion, the results suggest that downregulation of TIP30 may result from HBV infection, and subsequently promotes the progression of HCC.

Overexpression of TIP30 inhibits the growth and invasion of glioma cells

Glioma is an aggressive malignancy with limited effective treatment and poor prognosis. Therefore, the identification of novel prognostic markers and effective therapeutic targets is important for the treatment of human glioma. TIP30 is a tumor suppressor involved in the regulation of numerous cellular processes, including tumor cell growth, metastasis, and angiogenesis in various human cancers. The present study investigated whether Tat-interacting protein (TIP)30 was able to regulate tumorigenesis and predict the clinical outcome of patients with glioma. A total of 92 human glioma tissue samples and 10 normal brain tissue samples were examined by immunostaining. The results indicated that the expression levels of TIP30 significantly decreased in glioma tissue samples. as compared with normal brain tissue samples. Furthermore, TIP30 expression was inversely correlated with tumor histological classification, pathological grade, tumor size, and epidermal growth factor receptor (EGFR) expression; however, no association was detected between TIP30 expression and patient age and gender. In addition, patients with positive TIP30 expression exhibited significantly longer median overall survival rates, as compared with those with negative TIP30 expression. In vitro experiments revealed that upregulation of TIP30 expression by lentiviral vector transfection inhibited cell growth and induced cell apoptosis, as determined by MTT assay and Annexin V-fluorescein isothiocyanate staining, respectively. In addition, TIP30 expression markedly attenuated cell migration and invasion, as determined by wound healing and transwell assays. Upregulation of TIP30 expression in glioma cells decreased the expression levels of EGFR and its associated downstream molecules phosphorylated extracellular signal-regulated kinases (ERK) and phosphorylated AKT, as determined by western blot analysis. The results of the present study indicated that TIP30 may suppress oncogenesis and glioma progression, thereby improving the prognosis of patients with glioma. Therefore, TIP30 may prove useful as a prognostic biomarker, and as a potential target for glioma therapy.

TGF-β1 induces epigenetic silence of TIP30 to promote tumor metastasis in esophageal carcinoma

TGF-β1, a potent EMT (epithelial-mesenchymal transition) inducer present in the tumor microenvironment, is involved in the metastasis and progression of various carcinomas, including esophageal squamous cell carcinoma (ESCC). TIP30 (30kDa HIV-1 Tat interacting protein) is a putative tumor metastasis suppressor. Here, we found TIP30 was decreased in cells undergoing EMT induced by TGF-β1, an occurrence that was related to promoter hypermethylation. TGF-β1 induced TIP30 hypermethylation via increasing DNMT1 and DNMT3A expression, which could be restored by TGF-β antibodies. In our in vitro and in vivo studies, we showed that silence of TIP30 led to EMT, enhanced migrative and invasive abilities of ESCC cells, promoted tumor metastasis in xenografted mice; alternatively, overexpression of TIP30 inhibited TGF-β1-induced EMT, and metastatic abilities of ESCC cells. Mechanically, TIP30 silencing induced the nuclear translocation and transcriptional activation of β-catenin in an AKT-dependent manner, which further resulted in the initiation of EMT. Consistently, TIP30 was frequently methylated and downregulated in ESCC patients. Loss of TIP30 correlated with nuclear β-catenin and aberrant E-cadherin expression. TIP30 was a powerful marker in predicting the prognosis of ESCC. Taken together, our results suggest a novel and critical role of TIP30 involved in TGF-β1-induced activation of AKT/β-catenin signaling and ESCC metastasis.

Proteomic analysis of livers from fat-fed mice deficient in either PKCδ or PKCε identifies Htatip2 as a regulator of lipid metabolism

Insulin resistance contributes to the development of Type 2 diabetes, and is associated with lipid oversupply. Deletion of isoforms of the lipid-activated protein kinase C (PKC) family, PKCδ or PKCε, improves insulin action in fat-fed mice, but differentially affects hepatic lipid metabolism. To investigate the mechanisms involved, we employed an in vivo adaptation of SILAC to examine the effects of a fat diet together with deletion of PKCδ or PKCε on the expression of liver proteins. We identified a total of 3359 and 3488 proteins from the PKCδ and PKCε knockout study groups, respectively, and showed that several enzymes of lipid metabolism were affected by the fat diet. In fat-fed mice, 23 proteins showed changes upon PKCδ deletion while 19 proteins were affected by PKCε deletion. Enzymes of retinol metabolism were affected by the absence of either PKC. Pathway analysis indicated that monosaccharide metabolism was affected only upon PKCδ deletion, while isoprenoid biosynthesis was affected in a PKCε-specific manner. Certain proteins were regulated inversely, including HIV-1 tat interactive protein 2 (Htatip2). Overexpression or knockdown of Htatip2 in hepatocytes affected fatty acid storage and oxidation, consistent with a novel role in mediating the differential effects of PKC isoforms on lipid metabolism. All MS data have been deposited in the ProteomeXchange with identifier PXD000971 (http://proteomecentral.proteomexchange.org/dataset/PXD000971).

Tip30 controls differentiation of murine mammary luminal progenitor to estrogen receptor-positive luminal cell through regulating FoxA1 expression

Estrogen receptor-alpha positive (ER⁺) breast cancers comprise the majority of human breast cancers, but molecular mechanisms underlying this subtype of breast cancers remain poorly understood. Here, we show that ER⁺ mammary luminal tumors arising in Tip30^−/−MMTV-Neu mice exhibited increased enrichment of luminal progenitor gene signature. Deletion of the Tip30 gene increased proportion of mammary stem and progenitor cell populations, and raised susceptibility to ER⁺ mammary luminal tumors in female Balb/c mice. Moreover, Tip30^−/− luminal progenitors displayed increases in propensity to differentiate to mature ER⁺ luminal cells and FoxA1 expression. Knockdown of FoxA1 expression in Tip30^−/− progenitors by shRNA specific for FoxA1 reduced their differentiation toward ER⁺ mature luminal cells. Taken together, our results suggest that TIP30 is a key regulator for maintaining ER⁺ and ER⁻luminal pools in the mammary luminal lineage, and loss of it promotes expansion of ER⁺ luminal progenitors and mature cells and ER⁺ mammary tumorigenesis.

Oncogenic protein MTBP interacts with MYC to promote tumorigenesis

Despite its involvement in most human cancers, MYC continues to pose a challenge as a readily tractable therapeutic target. Here we identify the MYC transcriptional cofactors TIP48 and TIP49 and MYC as novel binding partners of Mdm2-binding protein (MTBP), a functionally undefined protein that we show is oncogenic and overexpressed in many human cancers. MTBP associated with MYC at promoters and increased MYC-mediated transcription, proliferation, neoplastic transformation, and tumor development. In breast cancer specimens, we determined overexpression of both MYC and MTBP was associated with a reduction in 10-year patient survival compared with MYC overexpression alone. MTBP was also frequently co-amplified with MYC in many human cancers. Mechanistic investigations implicated associations with TIP48/TIP49 as well as MYC in MTBP function in cellular transformation and the growth of human breast cancer cells. Taken together, our findings show MTBP functions with MYC to promote malignancy, identifying this protein as a novel general therapeutic target in human cancer.

dAcsl, the Drosophila ortholog of acyl-CoA synthetase long-chain family member 3 and 4, inhibits synapse growth by attenuating bone morphogenetic protein signaling via endocytic recycling

Fatty acid metabolism plays an important role in brain development and function. Mutations in acyl-CoA synthetase long-chain family member 4 (ACSL4), which converts long-chain fatty acids to acyl-CoAs, result in nonsyndromic X-linked mental retardation. ACSL4 is highly expressed in the hippocampus, a structure critical for learning and memory. However, the underlying mechanism by which mutations of ACSL4 lead to mental retardation remains poorly understood. We report here that dAcsl, the Drosophila ortholog of ACSL4 and ACSL3, inhibits synaptic growth by attenuating BMP signaling, a major growth-promoting pathway at neuromuscular junction (NMJ) synapses. Specifically, dAcsl mutants exhibited NMJ overgrowth that was suppressed by reducing the doses of the BMP pathway components, accompanied by increased levels of activated BMP receptor Thickveins (Tkv) and phosphorylated mothers against decapentaplegic (Mad), the effector of the BMP signaling at NMJ terminals. In addition, Rab11, a small GTPase involved in endosomal recycling, was mislocalized in dAcsl mutant NMJs, and the membrane association of Rab11 was reduced in dAcsl mutant brains. Consistently, the BMP receptor Tkv accumulated in early endosomes but reduced in recycling endosomes in dAcsl mutant NMJs. dAcsl was also required for the recycling of photoreceptor rhodopsin in the eyes, implying a general role for dAcsl in regulating endocytic recycling of membrane receptors. Importantly, expression of human ACSL4 rescued the endocytic trafficking and NMJ phenotypes of dAcsl mutants. Together, our results reveal a novel mechanism whereby dAcsl facilitates Rab11-dependent receptor recycling and provide insights into the pathogenesis of ACSL4-related mental retardation.

The EGFR signalling system in the liver: from hepatoprotection to hepatocarcinogenesis

The liver displays an outstanding wound healing and regenerative capacity unmatched by any other organ. This reparative response is governed by a complex network of inflammatory mediators, growth factors and metabolites that are set in motion in response to hepatocellular injury. However, when liver injury is chronic, these regenerative mechanisms become dysregulated, facilitating the accumulation of genetic alterations leading to unrestrained cell proliferation and the development of hepatocellular carcinoma (HCC). The epidermal growth factor receptor (EGFR or ErbB1) signaling system has been identified as a key player in all stages of the liver response to injury, from early inflammation and hepatocellular proliferation to fibrogenesis and neoplastic transformation. The EGFR system engages in extensive crosstalk with other signaling pathways, acting as a true signaling hub for other growth factors, cytokines and inflammatory mediators. Here, we briefly review essential aspects of the biology of the EGFR, the other ErbB receptors, and their ligands in liver injury, regeneration and HCC development. Some aspects of the preclinical and clinical experience with EGFR therapeutic targeting in HCC are also discussed.

Role of autophagy, SQSTM1, SH3GLB1, and TRIM63 in the turnover of nicotinic acetylcholine receptors

Removal of ubiquitinated targets by autophagosomes can be mediated by receptor molecules, like SQSTM1, in a mechanism referred to as selective autophagy. While cytoplasmic protein aggregates, mitochondria, and bacteria are the best-known targets of selective autophagy, their role in the turnover of membrane receptors is scarce. We here showed that fasting-induced wasting of skeletal muscle involves remodeling of the neuromuscular junction (NMJ) by increasing the turnover of muscle-type CHRN (cholinergic receptor, nicotinic/nicotinic acetylcholine receptor) in a TRIM63-dependent manner. Notably, this process implied enhanced production of endo/lysosomal carriers of CHRN, which also contained the membrane remodeler SH3GLB1, the E3 ubiquitin ligase, TRIM63, and the selective autophagy receptor SQSTM1. Furthermore, these vesicles were surrounded by the autophagic marker MAP1LC3A in an ATG7-dependent fashion, and some of them were also positive for the lysosomal marker, LAMP1. While the amount of vesicles containing endocytosed CHRN strongly augmented in the absence of ATG7 as well as upon denervation as a model for long-term atrophy, denervation-induced increase in autophagic CHRN vesicles was completely blunted in the absence of TRIM63. On a similar note, in trim63(-/-) mice denervation-induced upregulation of SQSTM1 and LC3-II was abolished and endogenous SQSTM1 did not colocalize with CHRN vesicles as it did in the wild type. SQSTM1 and LC3-II coprecipitated with surface-labeled/endocytosed CHRN and SQSTM1 overexpression significantly induced CHRN vesicle formation. Taken together, our data suggested that selective autophagy regulates the basal and atrophy-induced turnover of the pentameric transmembrane protein, CHRN, and that TRIM63, together with SH3GLB1 and SQSTM1 regulate this process.

microRNA-10b enhances pancreatic cancer cell invasion by suppressing TIP30 expression and promoting EGF and TGF-β actions

Increased microRNA-10b (miR-10b) expression in the cancer cells in pancreatic ductal adenocarcinoma (PDAC) is a marker of disease aggressiveness. In the present study, we determined that plasma miR-10b levels are significantly increased in PDAC patients by comparison with normal controls. By gene profiling, we identified potential targets downregulated by miR-10b, including Tat-interacting protein 30 (TIP30). Immunoblotting and luciferase reporter assays confirmed that TIP30 was a direct miR-10b target. Downregulation of TIP30 by miR-10b or siRNA-mediated silencing of TIP30 enhanced epidermal growth factor (EGF)-dependent invasion. The actions of miR-10b were abrogated by expressing a modified TIP30 cDNA resistant to miR-10b. EGF-induced EGF receptor (EGFR) tyrosine phosphorylation and extracellular signal-regulated kinase phosphorylation were enhanced by miR-10b, and these effects were mimicked by TIP30 silencing. The actions of EGF in the presence of miR-10b were blocked by EGFR kinase inhibition with erlotinib and by dual inhibition of PI3K (phosphatidylinositol 3'-kinase) and MEK. Moreover, miR-10b, EGF and transforming growth factor-beta (TGF-β) combined to markedly increase cell invasion, and this effect was blocked by the combination of erlotinib and SB505124, a type I TGF-β receptor inhibitor. miR-10b also enhanced the stimulatory effects of EGF and TGF-β on cell migration and epithelial-mesenchymal transition (EMT) and decreased the expression of RAP2A, EPHB2, KLF4 and NF1. Moreover, miR-10b overexpression accelerated pancreatic cancer cell (PCC) proliferation and tumor growth in an orthotopic model. Thus, plasma miR-10b levels may serve as a diagnostic marker in PDAC, whereas intra-tumoral miR-10b promotes PCC proliferation and invasion by suppressing TIP30, which enhances EGFR signaling, facilitates EGF-TGF-β cross-talk and enhances the expression of EMT-promoting genes, whereas decreasing the expression of several metastasis-suppressing genes. Therefore, therapeutic targeting of miR-10b in PDAC may interrupt growth-promoting deleterious EGF-TGF-β interactions and antagonize the metastatic process at various levels.

Decreased TIP30 expression predicts poor prognosis in pancreatic cancer patients

Pancreatic ductal adenocarcinoma (PDAC) is known for its aggressive growth, and is characterized by early tissue invasion and metastasis with poor prognosis. Identifying prognostic markers and delineating the underlying mechanisms that promote progression of PDAC are important for the treatment of pancreatic cancer. TIP30, a newly identified tumor suppressor, appears to be involved in multiple processes during tumor development and metastasis. Here, we investigated the expression of TIP30 in PDAC and its prognostic value in PDAC patients. We examined the expression of TIP30 by immunohistochemistry in tissue microarrays containing 106 surgically resected PDAC. Kaplan-Meier analysis and Cox proportional hazards regression modeling analysis showed that TIP30 expression independently predicted better survival in pancreatectomy patients (p < 0.01). Moreover, decreased TIP30 expression was associated with lymph node metastasis (p < 0.05) and loss of E-cadherin expression (r = 0.329, p < 0.01). Suppression of TIP30 resulted in upregulation of Snail and subsequent downregulation of E-cadherin in SW1990 cells containing high-level of endogenous TIP30. However, in the PANC-1 cells containing low level of endogenous TIP30, suppressing TIP30 caused upregulation of Slug instead of Snail, followed by upregulation of MMP9 rather than E-cadherin. Taken together, our work reveals that decreased TIP30 expression is able to enhance invasion and metastasis of pancreatic cancer cells through upregulation of the Snail family members and may serve as an independent predictor for poor outcomes in PDAC patients.

Bif-1 suppresses breast cancer cell migration by promoting EGFR endocytic degradation

Dysregulation of EGFR expression and signaling is well documented to contribute to disease progression and metastasis in many types of cancer including breast cancer. EGF-stimulated EGFR activation leads to receptor internalization and endocytic degradation to control EGFR-mediated signaling. This process is frequently deregulated in cancer cells, leading to increased EGFR expression and mitogenic signaling. Here, we demonstrate that Bif-1, a tumor suppressor, plays a role in EGFR endocytic degradation and chemotactic migration in MDA-MB-231 breast cancer cells. Our data reveal that suppression of Bif-1 expression delays EGFR degradation and sustains Erk1/2 activation in response to EGF stimulation. Mechanistically, loss of Bif-1 sequesters internalized EGF in Rab5-positive endosomes and delays EGFR trafficking to lysosomes. Recruitment of Rab7 to EGF-positive vesicles and the activation of Rab7 are impaired in Bif-1 knockdown cells. Additionally, intracellular pH and the localization of acidic vesicles are altered by suppression of Bif-1. Furthermore, inhibition of Bif-1 increases chemotactic cell migration in response to EGF or serum, which correlates with prolonged cytoskeletal reorganization. Importantly, the effect of Bif-1 on EGF-induced cell migration is abolished by gefitinib, an EGFR-specific inhibitor. Taken together, these data suggest a novel function for Bif-1 as a suppressor of breast cancer cell migration by promoting EGFR degradation through the regulation of endosome maturation.

TIP30 loss enhances cytoplasmic and nuclear EGFR signaling and promotes lung adenocarcinogenesis in mice

Lung adenocarcinoma, the most common type of human non-small cell lung cancer (NSCLC), frequently overexpresses EGFR. However, the mechanisms underlying EGFR overexpression are not completely understood. Recent studies have identified that decreased expression of TIP30 is associated with the metastasis of human NSCLCs, but a causative relationship between TIP30 deficiency and NSCLC development remains unclear. We show here that Tip30 deletion leads to spontaneous development of lung adenomas and adenocarcinomas in mice. Lung tumor development was preceded by aberrant expansion of bronchioalveolar stem/progenitor and alveolar type II cells, as well as increased expression of EGFR and its downstream signaling factors in the lung of Tip30^−/− mice. Moreover, TIP30 knockdown in human lung adenocarcinoma cells resulted in prolonged EGFR activity in early endosomes, delayed EGFR degradation, increased EGFR nuclear localization, leading to up-regulated pAKT and pERK1/2 expression. Importantly, in human lung adenocarcinomas, low TIP30 expression correlates with prolonged patient overall and post-progression survival times. Together, these results suggest that TIP30 functions as a tumor suppressor to inhibit EGFR cytoplasmic and nuclear signaling and suppress adenocarcinogenesis in the lung and highlight the potential of therapeutic strategies aiming at inhibiting EGFR signaling for patients with low TIP30 expression lung adenocarcinoma.

NOK/STYK1 has a strong tendency towards forming aggregates and colocalises with epidermal growth factor receptor in endosomes

Our previous studies showed that the overexpression of Novel Oncogene with Kinase-domain (NOK)/STYK1 led to cellular transformation, tumorigenesis and metastasis. This report characterises the subcellular distribution of NOK in HeLa cells and its localisation in early endosomes. Confocal immunolocalisation studies indicated that NOK had structural subtypes and was distributed into two distinct expression patterns: a dot pattern (DP) and an aggregation pattern (AP). The results of an immunohistochemistry (IHC) analysis of pathological tissues also showed that high expression level of endogenous NOK was expressed in an aggregate-like structure in vivo. Importantly, we found that NOK was localised in endosomes and colocalised with epidermal growth factor receptor (EGFR) in activated endosomal vesicles. However, as the stimulation time increased, NOK and EGFR began to progress through different pathways. EGFR was gradually degraded after treatment with EGF for approximately 20 min, whereas NOK levels were not reduced. This result suggests that NOK mainly plays a role in facilitating the trafficking of EGFR from early endosomes to later endosomes/lysosomes. Taken together, NOK has a strong tendency towards forming aggregates, which may have physiological implications and provide the first evidence that this novel receptor kinase is colocalised with EGFR in endosomes to participate in a post-internalisation step of EGFR.

Sendai virus-based liposomes enable targeted cytosolic delivery of nanoparticles in brain tumor-derived cells

Background

Nanotechnology-based bioassays that detect the presence and/or absence of a combination of cell markers are increasingly used to identify stem or progenitor cells, assess cell heterogeneity, and evaluate tumor malignancy and/or chemoresistance. Delivery methods that enable nanoparticles to rapidly detect emerging, intracellular markers within cell clusters of biopsies will greatly aid in tumor characterization, analysis of functional state and development of treatment regimens.

Results

Experiments utilized the Sendai virus to achieve in vitro, cytosolic delivery of Quantum dots in cells cultured from Human brain tumors. Using fluorescence microscopy and Transmission Electron Microscopy, in vitro experiments illustrated that these virus-based liposomes decreased the amount of non-specifically endocytosed nanoparticles by 50% in the Human glioblastoma and medulloblastoma samples studied. Significantly, virus-based liposome delivery also facilitated targeted binding of Quantum dots to cytosolic Epidermal Growth Factor Receptor within cultured cells, focal to the early detection and characterization of malignant brain tumors.

Conclusions

These findings are the first to utilize the Sendai virus to achieve cytosolic, targeted intracellular binding of Qdots within Human brain tumor cells. The results are significant to the continued applicability of nanoparticles used for the molecular labeling of cancer cells to determine tumor heterogeneity, grade, and chemotherapeutic resistivity.

APLP1 and Rab5A interact with the II-III loop of the voltage-gated Ca-channel Ca(v)2.3 and modulate its internalization differently

BACKGROUND

Voltage gated calcium channels (VGCCs) regulate cellular activity in response to membrane depolarization by altering calcium homeostasis. Because calcium is the most versatile second messenger, regulation of the amount of VGCCs at the plasma membrane is highly critical for several essential cellular processes. Among the different types of VGCCs, the Ca(v)2.3 calcium channel and its regulation mechanisms are least understood due to Ca(v)2.3's resistance to most pharmacological agents.

METHODS

In order to study regulation and surface expression of Ca(v)2.3, a yeast two hybrid (Y2H) screen with the II-III loop of human Ca(v)2.3 as bait, was performed. APLP1, a member of the APP gene family and Rab5A, an endocytotic catalyst were identified as putative interaction partners. The interaction were confirmed by immunoprecipitation. To study the functional importance of the interaction, patch-clamp recordings in Ca(v)2.3 stably transfected HEK-293 cells (2C6) and surface biotin endocytosis assays were performed.

RESULTS

We are able to show that the II-III loop of the Ca(v)2.3 calcium channel binds APLP1 and that this binding promotes internalization of the channel. In addition, Rab5A also binds to the same loop of the channel and exerts an inhibitory effect on APLP1 mediated channel internalization.

CONCLUSIONS

This study identifies a regulation mechanism of Ca(v)2.3's surface expression, which implicates APLP1 as a regulator of calcium homeostasis. Thus APLP1 may play a crucial role in neuropathological mechanisms, which involve modulation of surface expression of voltage-gated Ca(2+) channels.

The TIP30 protein complex, arachidonic acid and coenzyme A are required for vesicle membrane fusion

Efficient membrane fusion has been successfully mimicked in vitro using artificial membranes and a number of cellular proteins that are currently known to participate in membrane fusion. However, these proteins are not sufficient to promote efficient fusion between biological membranes, indicating that critical fusogenic factors remain unidentified. We have recently identified a TIP30 protein complex containing TIP30, acyl-CoA synthetase long-chain family member 4 (ACSL4) and Endophilin B1 (Endo B1) that promotes the fusion of endocytic vesicles with Rab5a vesicles, which transport endosomal acidification enzymes vacuolar (H⁺)-ATPases (V-ATPases) to the early endosomes in vivo. Here, we demonstrate that the TIP30 protein complex facilitates the fusion of endocytic vesicles with Rab5a vesicles in vitro. Fusion of the two vesicles also depends on arachidonic acid, coenzyme A and the synthesis of arachidonyl-CoA by ACSL4. Moreover, the TIP30 complex is able to transfer arachidonyl groups onto phosphatidic acid (PA), producing a new lipid species that is capable of inducing close contact between membranes. Together, our data suggest that the TIP30 complex facilitates biological membrane fusion through modification of PA on membranes.