Obscurin a localizes near the cell membrane to modulate stress fiber dynamics and cell migration

Obscurin is a giant (720-900 kDa) modular cytoskeletal protein with multiple signaling domains. While it is most highly expressed in myocytes, obscurin is also the second most mutated protein in breast and colorectal cancers and is significantly downregulated in pancreatic cancer. Obscurin derives its antioncogenic properties, at least in part, through its ability to modulate cellular motility and migration; obscurin knockdown in cultured epithelial cells leads to increased migration and an epithelial-to-mesenchymal transition (EMT). Obscurin likely controls cell motility through the obscurin RhoGEF domain interaction with the RhoA/ROCK pathway and/or the obscurin PH domain interaction with a PI3K/PIP3 pathway. Here, we more fully describe which obscurin domains dictate subcellular localization and regulate cellular motility. The obscurin C-terminus adenovirally infected into MDCK and MCF - 10A cells localizes to adhesion structures at the plasma membrane. This localization is driven by four regions in obscurin: the obscurin RhoGEF and PH domains, along with two regions in the unstructured C-terminus. Infected cells lack central stress fibers, and this morphology is linked to the RhoGEF domain, the PH domain, and the C-terminal 76 residues. These three obscurin regions also inhibit cell motility. Together these data demonstrate how both specific obscurin domains and specific cellular localization regulate cellular velocity.