Adhesion‐dependent modulation of actin dynamics in Jurkat T cells

Abstract

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.

Self-organization of protrusions and polarity during eukaryotic chemotaxis

“…What is the basic unit of actin assembly for eukaryotic chemotaxis? It has long been known that motile cells exhibit periodic changes in their morphology [1–3]; later work has observed that actin-binding proteins (e.g., WAVE regulatory complex (WRC), Arp2/3 complex, and coronin) exhibit oscillatory localization dynamics in Dictyostelium [4–10], neutrophils [11,12], and other mammalian cells [5,13–15], which take the form of either stationary oscillations or propagating waves at the plasma membrane (Figure 1A). A useful framework in which to conceptualize these waves has been to view them as an excitable system, similar to the action potentials which neurons use to transmit information.…”

Mechanosensing in the immune response

“…T cells also express the α4β1 integrin VLA-4, which influences T cell activation. Interestingly, VLA-4 ligation to its ligand, VCAM-1, leads to a dramatic arrest of actin retrograde flow [48, 49] but its effect on cellular forces and microcluster dynamics remain to be tested.…”

“…At the rear of the lamellipodium, the linear bundles condense into arc-like structures under the action of myosin II motors. Interestingly, unlike adherent cells, myosin activity is not required for maintenance of retrograde flow [48, 49], raising questions about the role of myosin contractility in force generation and T cell activation.…”

“…Such dense localization of actin regulators at microclusters primes them to being “hotspots” of actin dynamics. Indeed we have observed ‘actin waves’ or bursts of actin polymerization originating from signaling microclusters [49]. …”

“…Whether TCR-associated signaling microclusters serve a similar role in T cells is not known, but it is interesting to speculate that they might do so given the similarities in the molecular players. Force transmission must involve coupling between microclusters and actin [49, 53, 104, 105, 109, 110], but what mediates this coupling is not known. Resolving this question requires measurement of forces with high spatial resolution while simultaneously monitoring actin dynamics and microcluster assembly with genetic manipulation of candidate molecules.…”