SLIT2/ROBO1-signaling inhibits macropinocytosis by opposing cortical cytoskeletal remodeling

Abstract

Macropinocytosis is essential for myeloid cells to survey their environment and for growth of RAS-transformed cancer cells. Several growth factors and inflammatory stimuli are known to induce macropinocytosis, but its endogenous inhibitors have remained elusive. Stimulation of Roundabout receptors by Slit ligands inhibits directional migration of many cell types, including immune cells and cancer cells. We report that SLIT2 inhibits macropinocytosis in vitro and in vivo by inducing cytoskeletal changes in macrophages. In mice, SLIT2 attenuates the uptake of muramyl dipeptide, thereby preventing NOD2-dependent activation of NF-κB and consequent secretion of pro-inflammatory chemokine, CXCL1. Conversely, blocking the action of endogenous SLIT2 enhances CXCL1 secretion. SLIT2 also inhibits macropinocytosis in RAS-transformed cancer cells, thereby decreasing their survival in nutrient-deficient conditions which resemble tumor microenvironment. Our results identify SLIT2 as a physiological inhibitor of macropinocytosis and challenge the conventional notion that signals that enhance macropinocytosis negatively regulate cell migration, and vice versa.

The Dual Role of Macropinocytosis in Cancers: Promoting Growth and Inducing Methuosis to Participate in Anticancer Therapies as Targets

“…Disruption of actin or microtubules in DCs with specific inhibitors significantly prevented macropinocytosis ( 38 ). Meanwhile, SLIT2, a Slit protein, was found to inhibit macropinocytosis by opposing cortical cytoskeletal remodeling ( 39 ). Ruffle membrane/lamellipodia form macropinocytic cups, and then form macropinosomes, involving a series of small GTPases and PIs ( Figure 2 .…”

The neurorepellent, Slit2, prevents macrophage lipid loading by inhibiting CD36-dependent binding and internalization of oxidized low-density lipoprotein

“…To determine whether the inhibitory effect of NSlit2 on lipid uptake is mediated by its receptor, Robo-1, we used Robo1N, a soluble N-terminal fragment of Robo-1, known to inhibit binding of Slit2 to Robo-1, thereby blocking any downstream effects [21][22][23] . In the presence of NSlit2, macrophages internalized significantly less oxLDL ( Fig.…”

“…www.nature.com/scientificreports/ Slit2 to Robo-1 can result in inactivation of Rac through the actions of slit-robo GTPase activating proteins, srGAPs 14,34 . Accordingly, we recently demonstrated that murine macrophages express srGAP2, and that exposure of mouse macrophages to Slit2 causes inactivation of Rac in these cells 23 . Our results are also consistent with work demonstrating a key role for Rac-mediated signaling in foam cell formation 35 .…”

“…Indeed, Slit2 has been shown to inhibit migration of aortic smooth muscle cells towards inflammatory cues, and acts as a potent anti-platelet agent both in vitro and in vivo 21,50 . We recently showed that Slit2 inhibits macropinocytosis of macrophages, and in this way, can inhibit their secretion of the inflammatory chemokine, CXCL1, following exposure to inflammatory stimuli 23 . We now report here that NSlit2 inhibits oxLDL uptake and foam cell formation by macrophages.…”

“…As such, in our studies, NSlit2-mediated inhibition of one or both of these processes could possibly contribute to the observed decrease in CD36-dependent lipid uptake by macrophages. However, we recently investigated the effects of Slit2 on Src signaling in macrophages, and did not observe any effects on activation of Src kinases 23 .…”