Granberg, K. L. | bioRxiv Science

bioRxiv2022

Signals Generated by Neutrophil Receptors for Danger Molecules Transactivate Allosterically Modulated FFA2R: Distinct response patterns are mediated by modulators recognized by different allosteric receptor sites

Positive allosteric modulators for free fatty acid receptor 2 (FFA2R/GPR43), that affect receptor function through binding to two distinct allosteric binding sites, were used to determine the correlation between the responses induced in neutrophils by two distinct activation modes; FFA2R was activated either by the orthosteric agonist propionate or by a receptor transactivation mechanism that activated FFA2R from the cytosolic side of the neutrophil plasma membrane by signals generated by the neutrophil PAFR (receptor for platelet activating factor), P2Y2R (receptor for ATP), FPR1 (receptor for fMLF) and FPR2 (receptor for WKYMVM). We show that the transactivation signals that activate FFA2R in the absence of any orthosteric agonist were generated downstream of the signaling G protein that couple to PAFR and P2Y2R. This transactivation of allosterically modulated FFA2Rs, by signals generated by PAFR/P2Y2R, represents a novel mechanism by which a G protein coupled receptor can be activated. Weak correlations were obtained when the FFA2R activity was induced by the transactivation signals generated by PAFRs and P2Y2Rs were compared with the FFA2R activity induced by the orthosteric agonist propionate. Comparison of the responses for each allosteric modulator revealed that the ratio values, calculated from the peak values of the ATP and propionate responses, varied from 0.2 to 1. Depending on the allosteric modulator, the response induced by the two different mechanisms (orthosteric activation and receptor transactivation, respectively), was equal or the propionate response was more pronounced. Importantly, we conclude that FFA2R activation from outside (orthosteric activation) and inside (receptor cross-talk/transactivation) can be selectively affected by an allosteric FFA2R modulator. O_LIThe allosterically modulated FFA2R is transactivated by signals generated by other GPCRs. C_LIO_LIThe PAF and ATP receptors transactivate FFA2R from the cytosolic side of the membrane. C_LIO_LIThe mechanisms that regulates activation of FFA2R from outside and inside differ. C_LI

cell biology↗

bioRxiv2020

Multiple ligand recognition sites in free fatty acid receptor 2 (FFAR2) direct distinct neutrophil activation patterns

Non-activating positive allosteric modulators specific for free fatty acid receptor 2 (FFAR2) increased the activity induced by orthosteric agonists to trigger a rise in intracellular Ca2+ ([Ca2+]i) and activate the O2- producing neutrophil NADPH-oxidase. In addition, two allosteric modulators (Cmp58 and AZ1729) recognized by different receptor domains on FFAR2, cooperatively triggered activation without any rise in [Ca2+]i. To gain insights into FFAR2 modulation and signaling, we set out to identify structurally diverse allosteric FFAR2 modulators. Initially, we identified two molecules that directly activate neutrophils and these were classified as an allosteric FFAR2 agonists and an orthosteric agonist, respectively. Based on the sensitizing effect on the neutrophil response to propionate, ten non-direct-activating molecules were classified as allosteric FFAR2 modulators. One of these synergistically activated neutrophils when combined with AZ1729, but not when combined with Cmp58. The remaining nine compounds synergistically induced the same type of biased neutrophil signaling but only when combined with Cmp58. The activation signals down-stream of FFAR2 when stimulated by two allosteric modulators with different binding sites were in most cases biased in that two complementary modulators together triggered an activation of the NADPH-oxidase, but no increase in [Ca2+]i. The neutrophil activation pattern achieved when two functionally "AZ1729- or "Cmp58-like" allosteric FFAR2 modulators were combined, supporting a model for activation in which FFAR2 has two different sites that selectively bind allosteric modulators. The novel neutrophil activation patterns and receptor down-stream signaling mediated by two cross-sensitizing allosteric modulators represent a new regulatory mechanism that controls FFAR2 receptor function.

cell biology↗