LPP3 mediates self-generation of chemotactic LPA gradients by melanoma cells

Melanoma cells steer out of tumours using self-generated lysophosphatidic acid (LPA) gradients. The cells break down LPA, which is present at high levels around the tumours, creating a dynamic gradient that is low in the tumour and high outside. They then also migrate up this gradient, creating a complex and evolving outward chemotactic stimulus. Here we introduce a new assay for self-generated chemotaxis, and show that raising LPA levels causes a delay in migration rather than loss of chemotactic efficiency. Knockdown of the lipid phosphatase LPP3 - but not its homologues LPP1 or LPP2 - diminishes the cell's ability to break down LPA. This is specific for chemotactically active LPAs, such as the 18:1 and 20:4 species. Inhibition of autotaxin-mediated LPA production does not diminish outward chemotaxis, but loss of LPP3-mediated LPA breakdown blocks it. Similarly, in both 2D and 3D invasion assays, knockdown of LPP3 diminishes melanoma cells' ability to invade. Our results demonstrate that LPP3 is the key enzyme in melanoma cells' breakdown of LPA, and confirm the importance of attractant breakdown in LPA-mediated cell steering

Melanoma cells break down LPA to establish local gradients that drive chemotactic dispersal.

The high mortality of melanoma is caused by rapid spread of cancer cells, which occurs unusually early in tumour evolution. Unlike most solid tumours, thickness rather than cytological markers or differentiation is the best guide to metastatic potential. Multiple stimuli that drive melanoma cell migration have been described, but it is not clear which are responsible for invasion, nor if chemotactic gradients exist in real tumours. In a chamber-based assay for melanoma dispersal, we find that cells migrate efficiently away from one another, even in initially homogeneous medium. This dispersal is driven by positive chemotaxis rather than chemorepulsion or contact inhibition. The principal chemoattractant, unexpectedly active across all tumour stages, is the lipid agonist lysophosphatidic acid (LPA) acting through the LPA receptor LPAR1. LPA induces chemotaxis of remarkable accuracy, and is both necessary and sufficient for chemotaxis and invasion in 2-D and 3-D assays. Growth factors, often described as tumour attractants, cause negligible chemotaxis themselves, but potentiate chemotaxis to LPA. Cells rapidly break down LPA present at substantial levels in culture medium and normal skin to generate outward-facing gradients. We measure LPA gradients across the margins of melanomas in vivo, confirming the physiological importance of our results. We conclude that LPA chemotaxis provides a strong drive for melanoma cells to invade outwards. Cells create their own gradients by acting as a sink, breaking down locally present LPA, and thus forming a gradient that is low in the tumour and high in the surrounding areas. The key step is not acquisition of sensitivity to the chemoattractant, but rather the tumour growing to break down enough LPA to form a gradient. Thus the stimulus that drives cell dispersal is not the presence of LPA itself, but the self-generated, outward-directed gradient

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Melanomas’ fatal attraction to lysophosphatidic acid trails: a new prognostic and therapeutic approach?

No abstract available

Visualizing cancer cell chemotaxis and invasion in 2D and 3D

We describe three chemotaxis assays—Insall chambers, circular invasion assays, and 3D organotypic assays—that are particularly appropriate for measuring migration of cancer cells in response to gradients of soluble attractants. Each assay has defined advantages, and together they provide the best possible quantitative assessment of cancer chemotaxis

LPA gradients across melanomas <i>in vivo</i>.

<p>(A) TYR::CreER^T2BRAF^V600E/+PTEN^lox/+ mice, a genetically appropriate melanoma model, were treated with tamoxifen as described in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio.1001966-Garcia1" target="_blank">[56]</a>, grown until melanomas spontaneously developed. Dashed box shows the region used for the samples shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio-1001966-g001" target="_blank">Figure 1C</a>. (B) Haematoxylin and eosin-stained biopsies of murine melanomas demonstrating the dispersal of cells from a representative tumour from <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio-1001966-g005" target="_blank">Figure 5A</a>, with cells spreading directly away from the tumour. Upper image 2.5× magnification; lower image 20× magnification from dashed box above, showing melanoma cells invading toward the muscle layer (D, dermis; M, muscle layer). (C) Biopsies from mouse melanomas. Several sites in a linear distribution were biopsied using a 6 mm punch biopsy tool within 5 minutes of the mouse being sacrificed and immediately frozen in liquid nitrogen. The positions of biopsies used for LPA measurement are indicated (too few distant samples were obtained for a significant measurement). Bar shows 5 mm. (D) LPA concentration gradients across the margin of a melanoma. Four melanomas were sampled at three sites in a line as shown in (A) (A, tumour body; B, tumour edge; C, skin surrounding tumour). Total LPA per mg tissue was quantified by mass spectrometry after weighing the tissue specimens and extracting the LPA. Outward-directed gradients of LPA were found across the margin of all the melanomas tested. Bars show SEM. (E) Analysis of LPA subspecies. 18∶2-LPA, 20∶4-LPA and 22∶6-LPA show a clearer gradient than 16∶0-LPA, which is though to be less active as a signalling molecule.</p

Chemotaxis of cells from different melanoma stages.

<p>(A) Chemotaxis of a panel of six cell lines from different melanoma stages (RGP, green; VGP, purple; metastatic, red) up a 0%–10% FBS gradient was measured as above (<i>n</i>≥45 cells per cell line). (B) Chemotactic index of cells from different stages. Data from (A) were collated by melanoma stage. Chemotaxis improves as the stage of melanoma progresses, although even the earliest RGP cells show clear chemotaxis. (C) Speeds of cells from different stages. Data from (A) were collated by melanoma stage. Metastatic lines are conspicuously faster (<i>p</i>-values from unpaired <i>t</i>-tests), although again the speed of RGP and VGP cells is still relatively high for non-haematopoietic cells.</p

Density-dependent dispersal of melanoma cells.

<p>(A) Schematic showing the stages of melanoma spread. (B) WM239A metastatic melanoma cells dispersing in uniform medium. 2×10⁴ cells were introduced into one reservoir of an Insall chamber containing complete medium with 10% FBS throughout, and observed by time-lapse phase contrast microscopy. See <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio.1001966.s004" target="_blank">Movie S1</a>. The left side of each image shows the reservoir containing cells, while the right side is the viewing bridge of the chamber. (C–D) Migration is density-dependent. WM1158 metastatic melanoma cells were seeded at different densities in full medium with 10% FBS, and observed as before. At 2×10⁴ cells/well and above, peak migration distances increase sharply, as confirmed by the distance at 17 hours (D; graph shows mean ± SEM). (E) Migration is not driven by production of a repellent. 2×10⁴ WM1158 cells were introduced into a chamber in minimal medium without serum and observed at 17 hours as before. Cells survive and adhere, but do not disperse. (F) Migration is not driven by production of a serum-derived repellent. 2×10⁴ WM1158 cells were introduced into a chamber in minimal medium without serum and observed at 17 hours as before. Cells disperse less efficiently in conditioned medium than in fresh medium. (G) Migration mediated by chemotaxis up a serum gradient is similar to density-induced migration. Left panel: 2×10⁴ WM1158 cells were introduced into a chamber in the presence of a gradient from 0% FBS around the cells to 10% in the opposite reservoir <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio.1001966-MuinonenMartin1" target="_blank">[15]</a>. The cells rapidly migrate towards the well containing serum. Right panel: similar assay with 10% serum in both reservoirs. Panels taken from <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio.1001966.s006" target="_blank">Movies S3</a> and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001966#pbio.1001966.s004" target="_blank">S1</a>, respectively.</p