Dilated cardiomyopathy (DCM) is a leading cause of morbidity and mortality worldwide; yet how genetic variation and environmental factors impact DCM heritability remains unclear. Here, we Reprints and permissions information is available at www.nature.com/reprints.

Contractile actomyosin bundles are key force-producing and mechanosensing elements in muscle and non-muscle tissues. Whereas the organization of muscle myofibrils and mechanism regulating their contractility are relatively well-established, the principles by which myosin-II activity and force-balance are regulated in non-muscle cells have remained elusive. We show that Caldesmon, an important component of smooth muscle and non-muscle cell actomyosin bundles, is an elongated protein that functions as a dynamic cross-linker between myosin-II and tropomyosin-actin filaments. Depletion of Caldesmon results in aberrant lateral movement of myosin-II filaments along actin bundles, leading to irregular myosin distribution within stress fibers. This manifests as defects in stress fiber network organization and contractility, and accompanied problems in cell morphogenesis, migration, invasion, and mechanosensing. These results identify Caldesmon as critical factor that ensures regular myosin-II spacing within non-muscle cell actomyosin bundles, and reveal how stress fiber networks are controlled through dynamic cross-linking of tropomyosin-actin and myosin filaments.

The aggressive brain tumor glioblastoma (GBM) is characterized by rapid cellular infiltration of brain tissue, raising the possibility that disease progression could potentially be slowed by disrupting the machinery of cell migration. The LIM kinase isoforms LIMK1 and LIMK2 (LIMK1/2) play important roles in cell polarization, migration, and invasion and are markedly upregulated in GBM and many other infiltrative cancers. Yet, it remains unclear whether LIMK suppression could serve as a viable basis for combating GBM infiltration. In this study, we investigated effects of LIMK1/2 suppression on GBM invasion by combining GBM culture models, engineered invasion paradigms, and mouse xenograft models. While knockdown of either LIMK1 or LIMK2 only minimally influenced invasion in culture, simultaneous knockdown of both isoforms strongly reduced the invasive motility of continuous culture models and human GBM tumor-initiating cells (TIC) in both Boyden chamber and 3D hyaluronic acid spheroid invasion assays. Furthermore, LIMK1/2 functionally regulated cell invasiveness, in part, by disrupting polarized cell motility under confinement and cell chemotaxis. In an orthotopic xenograft model, TICs stably transduced with LIMK1/2 shRNA were implanted intracranially in immunocompromised mice. Tumors derived from LIMK1/2 knockdown TICs were substantially smaller and showed delayed growth kinetics and more distinct margins than tumors derived from control TICs. Overall, LIMK1/2 suppression increased mean survival time by 30%. These findings indicate that LIMK1/2 strongly regulate GBM invasive motility and tumor progression and support further exploration of LIMK1/2 as druggable targets.Significance: Targeting the actin-binding proteins LIMK1 and LIMK2 significantly diminishes glioblastoma invasion and spread, suggesting the potential value of these proteins as therapeutic targets.