Exosomes bind to autotaxin and act as a physiological delivery mechanism to stimulate LPA receptor signalling in cells

Abstract

Autotaxin (ATX; also known as ENPP2), the lysophospholipase responsible for generating the lipid receptor agonist lysophosphatidic acid (LPA), is a secreted enzyme. Here we show that, once secreted, ATX can bind to the surface of cell-secreted exosomes. Exosomebound ATX is catalytically active and carries generated LPA. Once bound to a cell, through specific integrin interactions, ATX releases the LPA to activate cell surface G-protein-coupled receptors of LPA; inhibition of signalling by the receptor antagonist Ki1642 suggests that these receptors are LPAR1 and LPAR3. The binding stimulates downstream signalling, including phosphorylation of AKT and mitogenactivated protein kinases, the release of intracellular stored Ca 2+ and cell migration. We propose that exosomal binding of LPA-loaded ATX provides a means of efficiently delivering the lipid agonist to cell surface receptors to promote signalling. We further propose that this is a means by which ATX-LPA signalling operates physiologically.

The potential of different Autotaxin inhibitor types regulating catalysis-dependent and -independent signalling

“…Such an event could hypothetically lead to LPA-bound ATX at the cell surface, after which ATX would release LPA and activate LPARs. Indeed, the authors indicated that it was by this mechanism that ATX yielded activation of LPA 1 and LPA 3 in the employed in vitro experimental setup [29]. Taken together, the evidence is consistent with a role of ATX as an LPA carrier, transporting LPA to distal locations from those where LPC can be taken.…”

“…Although these observations appear contradictory, the loop insertions could have induced structural changes destabilising the orthosteric site, and resulting in catalytically inactive ATX without just occluding substrate trafficking through the tunnel. Interestingly, a recent study indicated that active ATX can bind to the surface of secreted exosomes and carry LPA [29]. Such an event could hypothetically lead to LPA-bound ATX at the cell surface, after which ATX would release LPA and activate LPARs.…”

Glycosylated extracellular vesicles released by glioblastoma cells are decorated by CCL18 allowing for cellular uptake via chemokine receptor CCR8

“…Here, we show that CCL18 functions as bridging adaptor for GBM EVs, and CCL18 expression has been identified as an important prognostic factor in GBM [90]. Recently, it was shown that EVs can also be decorated by autotaxin resulting in binding to integrins expressed on cell surfaces [32]. Similarly, it was reported that heparan sulphates exposed on EVs can bind to fibronectin, serving as a connecting molecule to heparan sulphates expressed on cell membranes [34].…”

“…We observed that pretreatment of cells with heparin reduces EV uptake to a lesser extent than pretreatment of EVs with heparin (data not shown), suggesting that both mechanisms (direct heparin sulphate- and CCR8-mediated endocytosis) can occur simultaneously. An important consequence of the ‘connectokine’ model is that it implies a complex level of regulation of EV transfer, perhaps similarly as observed for decoration of EVs with autotoxin [32] or fibronectin.…”

miR-122-5p Expression and Secretion in Melanoma Cells Is Amplified by the LPAR3 SH3–Binding Domain to Regulate Wnt1

“…One method for miRNA secretion from the cell is via exosomes, 30-100 nm vesicles that are released when multivesicular endosomes fuse with the plasma membrane (8,9). Exosomes can also contain DNA, RNA, proteins, lipids, and enzymes that metabolize lipids (10)(11)(12). Exosome secretion appears to be a signature of tumor cell aggressiveness, which serves as communication with the microenvironment to precondition tissue and facilitate tumorigenesis (13)(14)(15)(16)(17)(18).…”