Fabrication of a dual substrate display to test roles of cell adhesion proteins in vesicle targeting to plasma membrane domains

Micro- and nanoscale engineering of cell signaling

It is increasingly recognized that cell signaling, as a chemical process, must be considered at the local, micrometer scale. Micro- and nanofabrication techniques provide access to these dimensions, with the potential to capture and manipulate the spatial complexity of intracellular signaling in experimental models. This review focuses on recent advances in adapting surface engineering for use with biomolecular systems that interface with cell signaling, particularly with respect to surfaces that interact with multiple receptor systems on individual cells. The utility of this conceptual and experimental approach is demonstrated in the context of epithelial cells and T lymphocytes, two systems whose ability to perform their physiological function is dramatically impacted by the convergence and balance of multiple signaling pathways.

Investigative and clinical applications of synthetic immune synapses

The immune synapse (IS) has emerged as a compelling model of cell-cell communication. This interface between a T cell and antigen-presenting cell (APC) serves as a key point in coordinating the immune response. A distinguishing feature of this interface is that juxtacrine signaling molecules form complex patterns that are defined at micrometer and submicrometer scales. Moreover, these patterns are highly dynamic. While cellular and molecular approaches have provided insight into the influence of these patterns on cell-cell signaling, replacing the APC with a synthetic, micro/nanoengineered surface promises a new level of sophistication to these studies. Micropatterning of multiple ligands onto a surface, for example, allowed the direct demonstration that T cells can sense and respond to microscale geometry of the IS. Supported lipid bilayers have captured the lateral mobility of natural ligands, allowing insight into this complex property of the cell-cell interface in model systems. Finally, engineered surfaces have allowed the study of forces and mechanosensing in T cell activation, an emerging area of immune cell research. In addition to providing new insight into biophysical principles, investigations into IS function may allow control over ex vivo T cell expansion. Bioreactors based on these concepts may find immediate application in enhancing cellular-based immunotherapy.

The study of polarisation in single cells using model cell membranes

The apicobasal polarisation of epithelial cells within an epithelium is critical for its function as a selective barrier. Microenvironmental parameters, including cell-matrix and cell-cell interactions, contribute to the initiation and orientation of this polarity. However, it is often non-trivial to decipher the differential effects of these parameters in a controlled manner using traditional in vitro platforms. A reductionist platform, consisting of E-cadherin coupled onto laterally mobile supported lipid bilayers, was utilised to mimic E-cadherin presentation in the cell membrane. These functionalised bilayers were generated either on flat 2D surfaces or the interior surfaces of round microwells. This platform enabled the study of E-cadherin adhesion and the initiation of polarisation in a controlled environment, where the dimensionality of the microenvironment, type of protein coating and cell shape could be independently studied. A high proportion of single epithelial cells interacted with and clustered cellular E-cadherin in the presence of E-cadherin functionalised bilayers, which was reduced in the presence of integrin-mediated adhesion. The differential response in E-cadherin clustering correlated with the polarisation of E-cadherin and Na,K-ATPase, a reporter for the induction of basolateral polarity. Neither the three-dimensional presentation of E-cadherin nor the cell shape affected E-cadherin clustering or polarisation in single cells. Thus, the mobile presentation of E-cadherin was sufficient to mimic a cell-cell contact and induce basolateral polarisation in single cells.

Rigidity-dependent cross talk between integrin and cadherin signaling

Integrin-cadherin cross talk is an important aspect of cell function. We explored this signaling using substrates micropatterned with islands of fibronectin surrounded by E-cadherin, capturing the segregation of these signals in normal tissue. While MDCK cells were able to concurrently form adhesive structures with these two proteins, engagement of fibronectin by MCF-7 cells, an adenocarcinoma cell line, inhibited response of these cells to E-cadherin. We further demonstrated that this inhibition is rigidity dependent; on soft elastomer substrates with Young's modulus in the range of tens of kiloPascals, MCF-7 cells were able to engage both integrin and cadherin ligands.