The transcription factor Zbtb32 controls the proliferative burst of virus-specific natural killer cells responding to infection.

Natural killer (NK) cells are innate lymphocytes that exhibit many features of adaptive immunity, including clonal proliferation and long-lived memory. Here we demonstrate that the BTB-ZF transcription factor Zbtb32 (also known as ROG, FAZF, TZFP and PLZP) was essential for the proliferative burst and protective capacity of virus-specific NK cells. Signals from proinflammatory cytokines were both necessary and sufficient to induce high expression of Zbtb32 in NK cells. Zbtb32 facilitated NK cell proliferation during infection by antagonizing the anti-proliferative factor Blimp-1 (Prdm1). Our data support a model in which Zbtb32 acts as a cellular 'hub' through which proinflammatory signals instruct a 'proliferation-permissive' state in NK cells, thereby allowing their prolific expansion in response to viral infection.

A Single miRNA-mRNA Interaction Affects the Immune Response in a Context- and Cell-Type-Specific Manner.

MicroRNA (miRNA)-dependent regulation of gene expression confers robustness to cellular phenotypes and controls responses to extracellular stimuli. Although a single miRNA can regulate expression of hundreds of target genes, it is unclear whether any of its distinct biological functions can be due to the regulation of a single target. To explore in vivo the function of a single miRNA-mRNA interaction, we mutated the 3' UTR of a major miR-155 target (SOCS1) to specifically disrupt its regulation by miR-155. We found that under physiologic conditions and during autoimmune inflammation or viral infection, some immunological functions of miR-155 were fully or largely attributable to the regulation of SOCS1, whereas others could be accounted only partially or not at all by this interaction. Our data suggest that the role of a single miRNA-mRNA interaction is dependent on cell type and biological context.

Stage-specific regulation of natural killer cell homeostasis and response against viral infection by microRNA-155.

Natural killer (NK) cells function in the recognition and destruction of host cells infected with pathogens. Many regulatory mechanisms govern the potent responses of NK cells, both at the cellular and molecular level. Ablation of microRNA (miRNA) processing enzymes demonstrated that miRNAs play critical roles in NK cell differentiation and function; however, the role of individual miRNAs requires further investigation. Using mice containing a targeted deletion of microRNA-155 (miR-155), we observed defects in NK cell maintenance and maturation at steady state, as well as in homeostatic proliferation in lymphopenic mice. In addition, we discovered that miR-155 is up-regulated in activated NK cells during mouse cytomegalovirus (MCMV) infection in response to signals from the proinflammatory cytokines IL-12 and IL-18 and through signal transducer and activator of transcription 4 (STAT4) signaling. Although miR-155 was found to be dispensable for cytotoxicity and cytokine production when triggered through activating receptors, NK cells lacking miR-155 exhibited severely impaired effector and memory cell numbers in both lymphoid and nonlymphoid tissues after MCMV infection. We demonstrate that miR-155 differentially targets Noxa and suppressor of cytokine signaling 1 (SOCS1) in NK cells at distinct stages of homeostasis and activation. NK cells constitutively expressing Noxa and SOCS1 exhibit profound defects in expansion during the response to MCMV infection, suggesting that their regulation by miR-155 promotes antiviral immunity.

Protein kinase C-θ clustering at immunological synapses amplifies effector responses in NK cells.

In lymphocytes, stimulation of cell surface activating receptors induces the formation of protein microclusters at the plasma membrane that contain the receptor itself, along with other signaling molecules. Although these microclusters are generally thought to be crucial for promoting downstream cellular responses, evidence that specifically links clustering potential to signaling output is lacking. We found that protein kinase C-θ (PKCθ), a key signaling molecule in multiple lymphocyte subsets, formed microclusters in activated NK cells. These microclusters coalesced within the immunological synapse between the NK cell and its target cell. Clustering was mediated by the regulatory region of PKCθ and specifically required a putative phosphotyrosine-binding site within its N-terminal C2 domain. Whereas expression of wild-type PKCθ rescued the cytokine production defect displayed by PKCθ-deficient NK cells, expression of a PKCθ point-mutant incapable of forming microclusters had little to no effect. Hence, PKCθ clustering was necessary for optimal effector function. Notably, only receptors containing ITAMs induced PKCθ microclusters on their own, explaining previous observations that ITAM-coupled receptors promote stronger activating signals and effector responses than do receptors lacking these motifs. Taken together, our results provide a cell biological basis for the role of PKCθ clustering during NK cell activation, and highlight the importance of subcellular compartmentalization for lymphocyte signal transduction.

Growth, metastasis, and expression of CCL2 and CCL5 by murine mammary carcinomas are dependent upon Myd88.

Previously we reported that lipopolysaccharide (LPS) treatment of murine mammary carcinomas resulted in decreased growth of the tumors. Here we show the decreased growth following LPS treatment was mediated through effects downstream of TLR4 and Myd88. Perhaps more notably, simply reducing TLR4 or Myd88 levels was sufficient to slow tumor growth rates. Moreover, reduced levels of Myd88 correlated with a significant reduction in lung metastasis as well as decreased CCL2 and CCL5 expression. To determine whether inhibiting Myd88 function could also alter tumor growth and chemokine expression we used a Myd88 homodimerization inhibitory peptide. Indeed, inhibiting Myd88 function in four different murine mammary carcinomas as well as the human breast cancer cell line MDA-MB-231 led to decreased growth as well as CCL2 and CCL5 expression. These data imply that Myd88 is important for growth and metastasis of breast cancer, and expression of at least two proinflammatory chemokines.