Proteinase-Activated Receptor 4 (PAR4) Activation Triggers Cell Membrane Blebbing through RhoA and β-arrestin

Proteinase-Activated Receptors (PARs) are a four-member family of G-protein coupled receptors that are activated via proteolysis. PAR4 is a member of this family that is cleaved and activated by serine proteinases such as thrombin, trypsin and cathepsin-G. PAR4 is expressed in a variety of tissues and cell types including platelets, vascular smooth muscle cells and neuronal cells. In studying PAR4 signalling and trafficking, we observed dynamic changes in the cell membrane with spherical membrane protrusions that resemble plasma membrane blebbing. Since non-apoptotic membrane blebbing is now recognized as an important regulator of cell migration, cancer cell invasion, and vesicular content release we sought to elucidate the signalling pathway downstream of PAR4 activation that leads to such events. Using a combination of pharmacological inhibition and CRISPR/Cas9-mediated gene-editing approaches we establish that PAR4-dependent membrane blebbing occurs independently of the Gαq/11 and Gαi signalling pathways and is dependent on signalling via the β-arrestin-1/-2 and RhoA signalling pathways. In order to gain a more comprehensive understanding of β-arrestin-mediated signalling downstream of PAR4 and to guide future studies, we undertook RNA-seq analysis of PAR4 activated genes in control cells and in cells lacking β-arrestin-1/-2. A list of differentially expressed genes was generated followed by Gene Ontology (GO) and enrichment analysis, revealing PAR4 regulation of genes involved in processes including blood coagulation and circulation, cell-cell adhesion, sensory perception and neuron-neuron synaptic transmission-terms that relate back to known functions of PAR4 and are consistent with our finding of membrane blebbing triggered by PAR4 activation. Together these studies provide further mechanistic insight into PAR4 regulation of cellular function.