ERK1 is important for Th2 differentiation and development of experimental asthma.

The ERK1/2 signaling pathway regulates a variety of T-cell functions. We observed dynamic changes in the expression of ERK1/2 during T-helper cell differentiation. Specifically, the expression of ERK1/2 was decreased and increased by IL-12 and IL-4, respectively. To address this subject further, we examined the specific role of ERK1 in Th2 differentiation and development of experimental asthma using ERK1(-/-) mice. ERK1(-/-) mice were unable to mount airway inflammation and hyperreactivity in two different models of asthma, acute and chronic. ERK1(-/-) mice had reduced expression of Th2 cytokines IL-4 and IL-5 but not IL-17A or IFN-γ. They had reduced levels of allergen-specific IgE and blood eosinophils. T cells from immunized ERK1(-/-) mice manifested reduced proliferation in response to the sensitizing allergen. ERK1(-/-) T cells had reduced and short-lived expression of JunB following TCR stimulation, which likely contributed to their impaired Th2 differentiation. Immunized ERK1(-/-) mice showed reduced numbers of CD44(high) CD4 T cells in the spleen. In vitro studies demonstrated that Th2 but not Th1 cells from ERK1(-/-) mice had reduced numbers of CD44(high) cells. Finally, CD4 T cells form ERK1(-/-) mice expressed higher levels of BIM under growth factor-deprived conditions and reduced Mcl-1 on stimulation. As a result, the survival of CD4 T cells, especially CD44(high) Th2 cells, was much reduced in ERK1(-/-) mice. We conclude that ERK1 plays a nonredundant role in Th2 differentiation and development of experimental asthma. ERK1 controls Th2 differentiation and survival through its effect on JunB and BIM, respectively.

IL-2 and IL-4 stimulate MEK1 expression and contribute to T cell resistance against suppression by TGF-beta and IL-10 in asthma.

The T cell-driven airway inflammation in chronic asthma is uninhibited and sustained. We examined the resistance of T cells from asthmatic patients against suppression by TGF-ß, IL-10 and glucocorticoids and explored its signaling mechanism. CD4(+)CD25(-) T cells from allergic asthmatic subjects demonstrated increased TCR-stimulated proliferation as compared with healthy and chronic obstructive pulmonary disease controls. This proliferation was resistant to inhibition by TGF-ß, IL-10, and dexamethasone and to anergy induction. CD4 T cells from asthmatic patients, but not chronic obstructive pulmonary disease, allergic rhinitis, and healthy subjects, showed increased expression of MEK1, heightened phosphorylation of ERK1/2, and increased levels of c-Fos. IL-2 and IL-4 stimulated the expression of MEK1 and c-Fos and induced T cell resistance. The inhibition of MEK1 reversed, whereas induced expression of c-Fos and JunB promoted T cell resistance against TGF-ß- and IL-10-mediated suppression. We have uncovered an IL-2- and IL-4-driven MEK1 induction mechanism that results in heightened ERK1/2 activation in asthmatic T cells and make them resistant to certain inhibitory mechanisms.

UNC119 inhibits dynamin and dynamin-dependent endocytic processes.

Unc119 is an adapter signaling molecule, which regulates activation of tyrosine kinases in T cells, eosinophils and fibroblasts. It plays an important role in the photoreceptor synapses of the retina. Recently, we have shown that it inhibits bacterial uptake through macropinocytosis. In this paper we demonstrate a role for Unc119 in clathrin- and caveolae-based endocytosis as well as macropinocytosis. Depletion of Unc119 in fibroblasts increases, whereas overexpression inhibits uptake of transferrin, FM4-64, albumin, viruses, and ligand-coated beads. Physiological stimuli that upregulate the expression of Unc119 also inhibits endocytosis. Unc119 has the opposite effect on cholera toxin B uptake, which represents a clathrin- and dynamin-independent endocytic process. Unc119 interacts with dynamin, a key effector molecule of many endocytic processes. More importantly, Unc119 inhibits the GTPase activity of dynamin. Binding of Unc119 to dynamin decreases the association with its binding partner amphiphysin, a known regulator of dynamin activation. Thus, Unc119 regulates various endocytic pathways through dynamin and sets a threshold point for vesicular trafficking.

Uncoordinated 119 protein controls trafficking of Lck via the Rab11 endosome and is critical for immunological synapse formation.

The activation of T cells through the TCR is essential for development of the adaptive immune response. TCR does not have any enzymatic activity and relies on the plasma membrane-associated lymphocyte-specific protein tyrosine kinase (Lck) for initiation of signaling. Here we uncover a mechanism that is responsible for plasma membrane targeting of Lck. We show that Lck is transported to the membrane via a specific endosomal compartment. The transport depends on the adaptor protein Uncoordinated 119 (Unc119), on the GTPase rat brain 11 (Rab11), and on the actin cytoskeleton. Unc119 regulates the activation of Rab11. Consequently, Unc119 orchestrates the recruitment of the actin-based motor protein, myosin 5B, and the organization of multiprotein complexes on endosomes. The Unc119-regulated pathway is essential for immunological synapse formation and T cell activation.

Unc119 protects from Shigella infection by inhibiting the Abl family kinases.

BACKGROUND: Bacteria engage cell surface receptors and intracellular signaling molecules to enter the cell. Unc119 is an adaptor protein, which interacts with receptors and tyrosine kinases. Its role in bacterial invasion of cells is unknown. METHODOLOGY/PRINCIPAL FINDINGS: We used biochemical, molecular and cell biology approaches to identify the binding partners of Unc119, and to study the effect of Unc119 on Abl family kinases and Shigella infection. We employed loss-of-function and gain-in-function approaches to study the effect of Unc119 in a mouse model of pulmonary shigellosis. Unc119 interacts with Abl family kinases and inhibits their kinase activity. As a consequence, it inhibits Crk phosphorylation, which is essential for Shigella infection. Unc119 co-localizes with Crk and Shigella in infected cells. Shigella infectivity increases in Unc119-deficient epithelial and macrophage cells. In a mouse model of shigellosis cell-permeable TAT-Unc119 inhibits Shigella infection. Conversely, Unc119 knockdown in vivo results in enhanced bacterial invasion and increased lethality. Unc119 is an inducible protein. Its expression is upregulated by probacteria and bacterial products such as lipopolysacharide and sodium butyrate. The latter inhibits Shigella infection in mouse lungs but is ineffective in Unc119 deficiency. CONCLUSIONS: Unc119 inhibits signaling pathways that are used by Shigella to enter the cell. As a consequence it provides partial but significant protection from Shigella infections. Unc119 induction in vivo boosts host defense against infections.