Cell clusters adopt a collective amoeboid mode of migration in confined nonadhesive environments

Cell migration is essential to living organisms and deregulated in cancer. Single cell's migration ranges from traction-dependent mesenchymal motility to contractility-driven propulsive amoeboid locomotion, but collective cell migration has only been described as a focal adhesion-dependent and traction-dependent process. Here, we show that cancer cell clusters, from patients and cell lines, migrate without focal adhesions when confined into nonadhesive microfabricated channels. Clusters coordinate and behave like giant super cells, mobilizing their actomyosin contractility at the rear to power their migration. This polarized cortex does not sustain persistent retrograde flows, of cells or actin, like in the other modes of migration but rather harnesses fluctuating cell deformations, or jiggling. Theoretical physical modeling shows this is sufficient to create a gradient of friction forces and trigger directed cluster motion. This collective amoeboid mode of migration could foster metastatic spread by enabling cells to cross a wide spectrum of environments.

Mutant p53s generate pro-invasive niches by influencing exosome podocalyxin levels

Mutant p53s (mutp53) increase cancer invasiveness by upregulating Rab-coupling protein (RCP) and diacylglycerol kinase-α (DGKα)-dependent endosomal recycling. Here we report that mutp53-expressing tumour cells produce exosomes that mediate intercellular transfer of mutp53's invasive/migratory gain-of-function by increasing RCP-dependent integrin recycling in other tumour cells. This process depends on mutp53's ability to control production of the sialomucin, podocalyxin, and activity of the Rab35 GTPase which interacts with podocalyxin to influence its sorting to exosomes. Exosomes from mutp53-expressing tumour cells also influence integrin trafficking in normal fibroblasts to promote deposition of a highly pro-invasive extracellular matrix (ECM), and quantitative second harmonic generation microscopy indicates that this ECM displays a characteristic orthogonal morphology. The lung ECM of mice possessing mutp53-driven pancreatic adenocarcinomas also displays increased orthogonal characteristics which precedes metastasis, indicating that mutp53 can influence the microenvironment in distant organs in a way that can support invasive growth.

Cancer cells with trapped nuclei cut their way through the extracellular matrix

When an invading cancer cell attempts to pass through a hole in the extracellular matrix (ECM) which is too small for its nucleus, this generates physical tension. This tension is sensed by a nucleus–centrosome connection that activates trafficking of endosomal vesicles containing the matrix metalloprotease, MT1-MMP1 to the site of constraint. Recent evidence shows how focussed ECM degradation relieves the constraint and allows cancer cells to continue invading.

Increased formate overflow is a hallmark of oxidative cancer

Formate overflow coupled to mitochondrial oxidative metabolism\ has been observed in cancer cell lines, but whether that takes place in the tumor microenvironment is not known. Here we report the observation of serine catabolism to formate in normal murine tissues, with a relative rate correlating with serine levels and the tissue oxidative state. Yet, serine catabolism to formate is increased in the transformed tissue of in vivo models of intestinal adenomas and mammary carcinomas. The increased serine catabolism to formate is associated with increased serum formate levels. Finally, we show that inhibition of formate production by genetic interference reduces cancer cell invasion and this phenotype can be rescued by exogenous formate. We conclude that increased formate overflow is a hallmark of oxidative cancers and that high formate levels promote invasion via a yet unknown mechanism.

Glutaminolysis drives membrane trafficking to promote invasiveness of breast cancer cells

The role of glutaminolysis in providing metabolites to support tumour growth is well-established, but the involvement of glutamine metabolism in invasive processes is yet to be elucidated. Here we show that normal mammary epithelial cells consume glutamine, but do not secrete glutamate. Indeed, low levels of extracellular glutamate are necessary to maintain epithelial homoeostasis, and provision of glutamate drives disruption of epithelial morphology and promotes key characteristics of the invasive phenotype such as lumen-filling and basement membrane disruption. By contrast, primary cultures of invasive breast cancer cells convert glutamine to glutamate which is released from the cell through the system Xc- antiporter to activate a metabotropic glutamate receptor. This contributes to the intrinsic aggressiveness of these cells by upregulating Rab27-dependent recycling of the transmembrane matrix metalloprotease, MT1-MMP to promote invasive behaviour leading to basement membrane disruption. These data indicate that acquisition of the ability to release glutamate is a key watershed in disease aggressiveness.

New insights into the tetraspanin Tspan5 using novel monoclonal antibodies

Tspan5 is a member of a subgroup of tetraspanins referred to as TspanC8. These tetraspanins directly interact with the metalloprotease ADAM10, regulate its exit from the endoplasmic reticulum and subsequent trafficking, and differentially regulate its ability to cleave various substrates and activate Notch signaling. The study of Tspan5 has been limited by the lack of good antibodies. This study provides new insights into Tspan5 using new monoclonal antibodies (mAbs), including two mAbs recognizing both Tspan5 and the highly similar tetraspanin Tspan17. Using these mAbs, we show that endogenous Tspan5 associates with ADAM10 in human cell lines and in mouse tissues where it is the most abundant, such as the brain, the lung, the kidney, or the intestine. We also uncover two TspanC8-specific motifs in the large extracellular domain of Tspan5 that are important for ADAM10 interaction and exit from the endoplasmic reticulum. One of the anti-Tspan5 mAbs does not recognize Tspan5 associated with ADAM10, providing a convenient way to measure the fraction of Tspan5 not associated with ADAM10. This fraction is minor in the cell lines tested, and it increases upon transfection of cells with TspanC8 tetraspanins such as Tspan15 or Tspan33 that inhibit Notch signaling. Finally, two antibodies inhibit ligand-induced Notch signaling, and this effect is stronger in cells depleted of the TspanC8 tetraspanin Tspan14, further indicating that Tspan5 and Tspan14 can compensate for each other in Notch signaling.

Tensin links energy metabolism to extracellular matrix assembly

The regulation of integrin function is key to fundamental cellular processes, including cell migration and extracellular matrix (ECM) assembly. In this issue, Georgiadou et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201609066) report that the metabolic sensor adenosine monophosphate-activated protein kinase influences tensin production to regulate α5β1-integrin and fibrillar adhesion assembly and thus reveal an important connection between energy metabolism and ECM assembly.

Phosphorylation of Rab-coupling protein by LMTK3 controls Rab14-dependent EphA2 trafficking to promote cell:cell repulsion

The Rab GTPase effector, Rab-coupling protein (RCP) is known to promote invasive behaviour in vitro by controlling integrin and receptor tyrosine kinase (RTK) trafficking, but how RCP influences metastasis in vivo is unclear. Here we identify an RTK of the Eph family, EphA2, to be a cargo of an RCP-regulated endocytic pathway which controls cell:cell repulsion and metastasis in vivo. Phosphorylation of RCP at Ser435 by Lemur tyrosine kinase-3 (LMTK3) and of EphA2 at Ser897 by Akt are both necessary to promote Rab14-dependent (and Rab11-independent) trafficking of EphA2 which generates cell:cell repulsion events that drive tumour cells apart. Genetic disruption of RCP or EphA2 opposes cell:cell repulsion and metastasis in an autochthonous mouse model of pancreatic adenocarcinoma-whereas conditional knockout of another RCP cargo, α5 integrin, does not suppress pancreatic cancer metastasis-indicating a role for RCP-dependent trafficking of an Eph receptor to drive tumour dissemination in vivo.

A proteomic approach to identify endosomal cargoes controlling cancer invasiveness

We have previously shown that Rab17, a small GTPase associated with epithelial polarity, is specifically suppressed by ERK2 (also known as MAPK1) signalling to promote an invasive phenotype. However, the mechanisms through which Rab17 loss permits invasiveness, and the endosomal cargoes that are responsible for mediating this, are unknown. Using quantitative mass spectrometry-based proteomics, we have found that knockdown of Rab17 leads to a highly selective reduction in the cellular levels of a v-SNARE (Vamp8). Moreover, proteomics and immunofluorescence indicate that Vamp8 is associated with Rab17 at late endosomes. Reduced levels of Vamp8 promote transition between ductal carcinoma in situ (DCIS) and a more invasive phenotype. We developed an unbiased proteomic approach to elucidate the complement of receptors that redistributes between endosomes and the plasma membrane, and have pin-pointed neuropilin-2 (NRP2) as a key pro-invasive cargo of Rab17- and Vamp8-regulated trafficking. Indeed, reduced Rab17 or Vamp8 levels lead to increased mobilisation of NRP2-containing late endosomes and upregulated cell surface expression of NRP2. Finally, we show that NRP2 is required for the basement membrane disruption that accompanies the transition between DCIS and a more invasive phenotype.

Abstract P6-01-06: Glutamine metabolism drives breast cancer invasion by providing a source of extracellular glutamate to activate the GRM3 metabotropic glutamate receptor

Glutamine metabolism is well-established to contribute to cancer cell growth and proliferation by providing a source of nitrogen for nucleotide and amino acid biosynthesis as well as TCA cycle intermediates. There is also accumulating evidence that glutamine metabolism may contribute to metastasis although mechanistic links to tumour cell migration and invasion remain unclear. We have generated a number of highly invasive primary cell lines from the polyoma middle-T genetically engineered mouse model of breast cancer (MMTV-PyMT) and found that withdrawal of glutamine from these cells reduces not only their proliferation, but also their invasive migration into 'stroma-like' preparations of fibroblast-derived extracellular matrix. Our metabolomic analyses indicate that invasive MMTV-PyMT cells actively secrete glutamate, a product of glutamine metabolism, into the extracellular milieu. Moreover, addition of glutamate is sufficient to restore invasiveness (but not cell growth or proliferation) to glutamine-starved MMTV-PyMT cells. We have pursued these findings by investigating the role played by plasma membrane receptors for glutamate in cell migration and invasion in PyMT cells and in MDA-MB-231 triple negative breast cancer cells. We provide evidence that glutamate generated within the cell by deamidation of glutamine leaves the cell via the xCT antiporter to activate the GRM3 metabotropic glutamate receptor at the cell surface. This, in turn, suppresses adenylate cyclase activity to prevent protein kinase A activation and to drive an invasive programme. Indeed, knocking out GRM3 with CRISPR technology or inhibition using a selective GRM3 antagonist (LY341495) is sufficient to oppose invasiveness without compromising proliferation. Conversely, a specific GRM3 agonist (LY354740) drives invasiveness without increasing proliferation. Consistently, treatment with LY341495 was sufficient to abrogate lung colonisation following tail vein injection whilst tumour growth after orthotopic injection was unaffected. Our results provide a mechanistic link between glutamine metabolism and invasion and identify GRM3 as a potential therapeutic target in breast cancer.

Citation Format: Macpherson IR, Dornier E, Rabas N, Rainero E, Norman JC. Glutamine metabolism drives breast cancer invasion by providing a source of extracellular glutamate to activate the GRM3 metabotropic glutamate receptor [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-01-06.

TspanC8 tetraspanins regulate ADAM10/Kuzbanian trafficking and promote Notch activation in flies and mammals

TspanC8 tetraspanins have a conserved function in the regulation of ADAM10 trafficking and activity, thereby positively regulating Notch activation.

The metalloprotease ADAM10/Kuzbanian catalyzes the ligand-dependent ectodomain shedding of Notch receptors and activates Notch. Here, we show that the human tetraspanins of the evolutionary conserved TspanC8 subfamily (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17, and Tspan33) directly interact with ADAM10, regulate its exit from the endoplasmic reticulum, and that four of them regulate ADAM10 surface expression levels. In an independent RNAi screen in Drosophila, two TspanC8 genes were identified as Notch regulators. Functional analysis of the three Drosophila TspanC8 genes (Tsp3A, Tsp86D, and Tsp26D) indicated that these genes act redundantly to promote Notch signaling. During oogenesis, TspanC8 genes were up-regulated in border cells and regulated Kuzbanian distribution, Notch activity, and cell migration. Furthermore, the human TspanC8 tetraspanins Tspan5 and Tspan14 positively regulated ligand-induced ADAM10-dependent Notch1 signaling. We conclude that TspanC8 tetraspanins have a conserved function in the regulation of ADAM10 trafficking and activity, thereby positively regulating Notch receptor activation.