Membrane Targeting of C2GAP1 Enables Dictyostelium discoideum to Sense Chemoattractant Gradient at a Higher Concentration Range

Abstract

Chemotaxis, which is G protein-coupled receptor (GPCR)-mediated directional cell migration, plays pivotal roles in diverse human diseases, including recruitment of leukocytes to inflammation sites and metastasis of cancer. It is still not fully understood how eukaryotes sense and chemotax in response to chemoattractants with an enormous concentration range. A genetically traceable model organism, Dictyostelium discoideum, is the best-studied organism for GPCR-mediated chemotaxis. Recently, we have shown that C2GAP1 controls G protein coupled receptor-mediated Ras adaptation and chemotaxis. Here, we investigated the molecular mechanism and the biological function of C2GAP1 membrane targeting for chemotaxis. We show that calcium and phospholipids on the plasma membrane play critical roles in membrane targeting of C2GAP1. Cells lacking C2GAP1 (c2gapA–) displayed an improved chemotaxis in response to chemoattractant gradients at subsensitive or low concentrations (<100 nM), while exhibiting impaired chemotaxis in response to gradients at high concentrations (>1 μM). Taken together, our results demonstrate that the membrane targeting of C2GAP1 enables Dictyostelium to sense chemoattractant gradients at a higher concentration range. This mechanism is likely an evolutionarily conserved molecular mechanism of Ras regulation in the adaptation and chemotaxis of eukaryotes.

Ras inhibitors gate chemoattractant concentration range for chemotaxis through controlling GPCR-mediated adaptation and cell sensitivity

“…Unexpectedly, the interaction between C2GAP1 and Ras is significantly reduced with the presence of high [Ca 2+ ]. Consistent with the above, iplA−cells, which lack the IP 3 receptor and triggers no [Ca 2+ ] increase upon cAMP stimulation, display a prolonged membrane translocation of C2GAP1 (27), indicating that the GPCR-mediated calcium signaling negatively regulates the membrane translocation of C2GAP1. On the plasma membrane, C2GAP1 binds phospholipids, including the substrates and products of PI 3 K and PTEN (27,37,55,61).…”

“…Consistent with the above, iplA−cells, which lack the IP 3 receptor and triggers no [Ca 2+ ] increase upon cAMP stimulation, display a prolonged membrane translocation of C2GAP1 (27), indicating that the GPCR-mediated calcium signaling negatively regulates the membrane translocation of C2GAP1. On the plasma membrane, C2GAP1 binds phospholipids, including the substrates and products of PI 3 K and PTEN (27,37,55,61). However, C2GAP1 still translocates to the plasma membrane in cells treated with the PI 3 K inhibitors (25), indicating the products of PI 3 K are not essential for its membrane targeting and PIP 3 might provide another layer of regulation for the recruitment of C2GAP1.…”

“…Interestingly, both cells spread faster morphologically and have very active protrusion formation. Both c2gapA− and capri kd cells are more sensitive to chemoattractant stimuli and show improved chemotaxis in low- or subsensitive-concentration gradients while displaying impaired chemotaxis in response to high-concentration gradients ( 12 , 27 ), demonstrating that c2gapA− and capri kd cells display an upshifted concentration range of chemoattractant gradient for chemotaxis. Hence, Dictyostelium and neutrophils employ RasGAP proteins to control GPCR-mediated adaptation and cell sensitivity and consequently gate a chemoattractant concentration range for chemotaxis.…”

“…Both molecules target the plasma membrane independent of the active state of Ras and RasGAP activity ( 12 , 25 ). Both bind phospholipids of PI 3 K activation on the plasma membrane ( 27 , 79 , 83 ). Both bind F-actin but do not rely on F-actin for their membrane targeting ( 25 , 75 ).…”

“…Here, we first review temporospatial features of chemoattractant GPCR-mediated Ras adaptation and then summarize recent findings on two membrane-targeting Ras inhibitors, C2GAP1 and CAPRI in D. discoideum and human neutrophils, respectively, that control the GPCR-mediated adaptation and sensitivity of cells ( 12 , 25 , 27 ). The functions of these two molecules suggest an evolutionarily conserved molecular mechanism by which eukaryotic cells gate the concentration range of chemoattractant gradients for chemotaxis.…”