The Molecular Basis for Cellular Contractility Driven Mechanosensing

Abstract

Internal and external mechanical forces govern many cellular processes in normal and diseased states such as muscle contraction, tissue invasion and metastasis of tumor cells. Thus a cell's ability to sense and respond to mechanical stimuli is critical for cell behavior and survival. In Dictyostelium, the mechanoenzyme myosin II and the actin crosslinker cortexillin I work cooperatively to control cellular contractility in response to deformation. The scaffolding proteins IQGAP1 and IQGAP2, which can bind to cortexillin I, further regulate this mechanosensory system through feedback loops. The IQGAPs are not required for mechanosensing, but affect the stress-dependent myosin accumulation in the cortex. IQGAP1 inhibits mechanosensing, while IQGAP2 is required for suppressing this inhibition. A molecular understanding of how this mechanosensory system works to modulate contractility remains elusive. By measuring protein dynamics using fluorescence recovery after photobleaching (FRAP), we observed stress-dependent reduction in the mobility of many of the proteins in the mechanosensory system. Further, these dynamics are dependent on the integrity of the mechanosensory system, as mutant cells with disrupted mechanosensing typically show slower protein dynamics and increased cortical association of the proteins than in wild type cells. In addition, we are also characterizing the biochemical interactions important for mechanosensory response. These experiments will allow us to develop a molecular model to explain how mechanical forces are transmitted within the cell. The knowledge of the molecular underpinnings of this myosin II-based feedback control system will be applicable to other contractile systems such as those involved in development and morphogenesis of multicellular organisms.