Molecular mechanisms by which cells sense and directionally migrate in response to mechanical perturbation, which is critical in homeostasis and many diseases, are not well understood. Dictyostelium discoideum cells exposed to a brief burst of shear flow show rapid and transient activation of multiple components of the signal transduction network that participates in directed migration of these cells. Previous data from our laboratory demonstrated that actin crosslinking protein filamin is involved in the ability of cells to respond to shear flow. We also found that the actin-binding domain is required for filamin’s function in this context. To determine if the dimerization domain (DD) is also required for filamin’s role in sensing/transmitting mechanical stimuli we generated a truncation construct of filamin lacking DD (FLNΔDD) and expressed it in wild-type or filamin-null cells. We found that FLNΔDD was able to relocalize to the cortex of both wild-type and filamin-null cells following 2-sec stimulation with shear flow, suggesting that dimerization between filamin molecules is not required for their recruitment to the cortex. To detect activation of the signal transduction network in the presence or absence of FLNΔDD, we used fluorescently-tagged Ras binding domain biosensor that detects active Ras and was previously shown to relocalize to the cortex following mechanical stimulation. Surprisingly, FLNΔDD was able to rescue the reduced response of filamin-null cells to shear flow stimulation, suggesting that dimerization of filamin may not be needed for its ability to sense or transmit mechanical cues. However, the presence of FLNΔDD may also alter the overall organization of the cytoskeletal network, potentially explaining changes in mechanotransduction. We are currently investigating these possibilities.
