Lymphocyte polarity, the immunological synapse and the scope of biological analogy

The Scribble Complex PDZ Proteins in Immune Cell Polarities

hScrib and hDlg belong to the PDZ family of proteins. Since the identification of these highly phylogenetically conserved scaffolds, an increasing amount of experiments has elucidated the roles of hScrib and hDlg in a variety of cell functions. Remarkably, their participation during the establishment of polarity in epithelial cells is well documented. Although the role of both proteins in the immune system is scantly known, it has become a growing field of investigation. Here, we summarize the interactions and functions of hScrib and hDlg1, which participate in diverse functions involving cell polarization in immune cells, and discuss their relevance in the immune cell biology. The fundamental role of hScrib and hDlg1 during the establishment of the immunological synapse, hence T cell activation, and the recently described role of hScrib in reactive oxygen species production in macrophages and of hDlg1 in cytokine production by dendritic cells highlight the importance of both proteins in immune cell biology. The expression of these proteins in other leukocytes can be anticipated and needs to be confirmed. Due to their multiple interaction domains, there is a wide range of possible interactions of hScrib and hDlg1 that remains to be explored in the immune system.

Viral targeting of PDZ polarity proteins in the immune system as a potential evasion mechanism

PDZ proteins are highly conserved through evolution; the principal function of this large family of proteins is to assemble protein complexes that are involved in many cellular processes, such as cell-cell junctions, cell polarity, recycling, or trafficking. Many PDZ proteins that have been identified as targets of viral pathogens by promoting viral replication and spread are also involved in epithelial cell polarity. Here, we briefly review the PDZ polarity proteins in cells of the immune system to subsequently focus on our hypothesis that the viral PDZ-dependent targeting of PDZ polarity proteins in these cells may alter the cellular fitness of the host to favor that of the virus; we further hypothesize that this modification of the cellular fitness landscape occurs as a common and widespread mechanism for immune evasion by viruses and possibly other pathogens.-Gutiérrez-González, L. H., Santos-Mendoza, T. Viral targeting of PDZ polarity proteins in the immune system as a potential evasion mechanism.

PDZ proteins are expressed and regulated in antigen-presenting cells and are targets of influenza A virus

In this work, we identified the expression, regulation, and viral targeting of Scribble and Dlg1 in antigen-presenting cells. Scribble and Dlg1 belong to the family of PDZ (postsynaptic density (PSD95), disc large (Dlg), and zonula occludens (ZO-1)) proteins involved in cell polarity. The relevance of PDZ proteins in cellular functions is reinforced by the fact that many viruses interfere with host PDZ-dependent interactions affecting cellular mechanisms thus favoring viral replication. The functions of Scribble and Dlg have been widely studied in polarized cells such as epithelial and neuron cells. However, within the cells of the immune system, their functions have been described only in T and B lymphocytes. Here we demonstrated that Scribble and Dlg1 are differentially expressed during antigen-presenting cell differentiation and dendritic cell maturation. While both Scribble and Dlg1 seem to participate in distinct dendritic cell functions, both are targeted by the viral protein NS1 of influenza A in a PDZ-dependent manner in dendritic cells. Our findings suggest that these proteins might be involved in the mechanisms of innate immunity and/or antigen processing and presentation that can be hijacked by viral pathogens.

Lymphocyte Fate and Metabolism: A Clonal Balancing Act

Activated lymphocytes perform a clonal balancing act, yielding a daughter cell that differentiates owing to intense PI3K signaling, alongside a self-renewing sibling cell with blunted anabolic signaling. Divergent cellular anabolism versus catabolism is emerging as a feature of several developmental and regenerative paradigms. Metabolism can dictate cell fate, in part, because lineage-specific regulators are embedded in the circuitry of conserved metabolic switches. Unequal transmission of PI3K signaling during regenerative divisions is reminiscent of compartmentalized PI3K activity during directed motility or polarized information flow in non-dividing cells. The diverse roles of PI3K pathways in membrane traffic, cell polarity, metabolism, and gene expression may have converged to instruct sibling cell feast and famine, thereby enabling clonal differentiation alongside self-renewal.

Building tolerance by dismantling synapses: inhibitory receptor signaling in natural killer cells

Cell surface receptors bearing immunotyrosine-based inhibitory motifs (ITIMs) maintain natural killer (NK) cell tolerance to normal host tissues. These receptors are difficult to analyze mechanistically because they block activating responses in a rapid and comprehensive manner. The advent of high-resolution single cell imaging techniques has enabled investigators to explore the cell biological basis of the inhibitory response. Recent studies using these approaches indicate that ITIM-containing receptors function at least in part by structurally undermining the immunological synapse between the NK cell and its target. In this review, we discuss these new advances and how they might relate to what is known about the biochemistry of inhibitory signaling in NK cells and other cell types.

BioArchitecture: the organization and regulation of biological space

BioArchitecture is a term used to describe the organization and regulation of biological space. It applies to the principles which govern the structure of molecules, polymers and mutiprotein complexes, organelles, membranes and their organization in the cytoplasm and the nucleus. It also covers the integration of cells into their three dimensional environment at the level of cell-matrix, cell-cell interactions, integration into tissue/organ structure and function and finally into the structure of the organism. This review will highlight studies at all these levels which are providing a new way to think about the relationship between the organization of biological space and the function of biological systems.