Adhesion-dependent modulation of actin dynamics in Jurkat T cells.

Contact formation of T cells with antigen presenting cells results in the engagement of T cell receptors (TCRs), recruitment and aggregation of signaling proteins into microclusters and ultimately, T cell activation. During this process, T cells undergo dramatic changes in cell shape and reorganization of the cytoskeleton. While the importance of the cytoskeleton in T cell activation is well known, the dynamics of the actin cytoskeleton and how it correlates with signaling clusters during the early stages of spreading is not well understood. Here, we used total internal reflection fluorescence microscopy to study the dynamics of actin reorganization during Jurkat T cell spreading and the role of integrin ligation by the adhesion molecule, vascular cell adhesion molecule (VCAM), in modulating actin dynamics. We found that when T cells spread on anti-CD3 antibody-coated glass surfaces, the cell edge exhibited repeated protrusions and retractions, which were driven by wave like patterns of actin that emerged from signaling microclusters. Addition of VCAM on the activating substrate altered the dynamics of actin both globally and locally, leading to a smooth expansion of the cell edge and the disappearance of waves. Our results suggest that the actin cytoskeleton in Jurkat cells is capable of organizing into spatial patterns initiated by TCR signaling and regulated by integrin signaling.

Membrane dynamics correlate with formation of signaling clusters during cell spreading.

The morphology and duration of contacts between cells and adhesive surfaces play a key role in several biological processes, such as cell migration, cell differentiation, and the immune response. The interaction of receptors on the cell membrane with ligands on the adhesive surface leads to triggering of signaling pathways, which allow cytoskeletal rearrangement, and large-scale deformation of the cell membrane, which allows the cell to spread over the substrate. Despite numerous studies of cell spreading, the nanometer-scale dynamics of the membrane during formation of contacts, spreading, and initiation of signaling are not well understood. Using interference reflection microscopy, we study the kinetics of cell spreading at the micron scale, as well as the topography and fluctuations of the membrane at the nanometer scale during spreading of Jurkat T cells on antibody-coated substrates. We observed two modes of spreading, which were characterized by dramatic differences in membrane dynamics and topography. Formation of signaling clusters was closely related to the movement and morphology of the membrane in contact with the activating surface. Our results suggest that cell membrane morphology may be a critical constraint on signaling at the cell-substrate interface.