Module 4: Figure actin remodelling
Actin remodelling mechanisms.
Actin remodelling is regulated by different signalling pathways. Protein tyrosine kinase-linked receptors (PTKRs) and G protein-coupled receptors (GPCRs) act through the Rac signalling pathway (Module 2: Figure Rac signalling) and initiate polymerization by recruiting the Arp2/3 complex. An increase in Ca2+ activates Gelsolin that inhibits polymerization by capping the growing end and also functions to sever existing filaments into short capped fragments that have two fates. The pointed-end can be depolymerized with the help of cofilin that then donates actin monomers to the pool of actin bound to profilin and thymosin-β4 (Tβ4). Some of these short fragments can also be uncapped through a mechanism that depends on the formation of PtdIns4,5P2 that inactivates gelsolin resulting in uncapping such that polymerization can continue. This Figure is based on the information shown in Figure 10 in Shalini et al. (2013).