The coronin family of actin-binding proteins regulate actin branching by inhibiting Arp2/3. We recently reported 2 interactions that were unique to coronin-1C: binding of a Rac1 inhibitor, RCC2, to the unique linker region and Rac1 itself to the propeller domain in a manner that differs from that proposed for other coronins. Through these interactions coronin-1C redistributes Rac1 from the back of the cell to the leading edge for either activation or sequestration by the associated Rac1-inhibitor, RCC2. Here we investigate the relationship between the Rac1- and actin-binding properties of coronin-1C and find that, although actin appears to be involved in the retrafficking of Rac1, signaling by Rac1 lies upstream of the stress fiber-formation, for which the coronins were originally characterized.
Keywords: CRIB: Cdc42/Rac-interacting binding domain; Coronin-1C; ECM: extracellular matrix; GEF: guanine nucleotide exchange factor; PAK: p21-activated kinase; Rac1; actin; endocytosis; trafficking.