Eri1 regulates microRNA homeostasis and mouse lymphocyte development and anti-viral function.

Natural killer (NK) cells play a critical role in early host defense to infected and transformed cells. Here we show that mice deficient in Eri1, a conserved 3'-to-5' exoribonuclease that represses RNA interference, have a cell-intrinsic defect in NK cell development and maturation. Eri1(-/-) NK cells displayed delayed acquisition of Ly49 receptors in the bone marrow and a selective reduction in Ly49D and Ly49H activating receptors in the periphery. Eri1 was required for immune-mediated control of mouse cytomegalovirus (MCMV) infection. Ly49H(+) NK cells deficient in Eri1 failed to expand efficiently during MCMV infection, and virus-specific responses were also diminished among Eri1(-/-) T cells. We identified miRNAs as the major endogenous small RNA target of Eri1 in mouse lymphocytes. Both NK and T cells deficient in Eri1 displayed a global, sequence-independent increase in miRNA abundance. Ectopic Eri1 expression rescued defective miRNA expression in mature Eri1(-/-) T cells. Thus, mouse Eri1 regulates miRNA homeostasis in lymphocytes and is required for normal NK cell development and anti-viral immunity

Critical Roles of Phosphorylation and Actin Binding Motifs, but Not the Central Proline-rich Region, for Ena/Vasodilator-stimulated Phosphoprotein (VASP) Function during Cell Migration

The Ena/vasodilator-stimulated phosphoprotein (VASP) protein family is implicated in the regulation of a number of actin-based cellular processes, including lamellipodial protrusion necessary for whole cell translocation. A growing body of evidence derived largely from in vitro biochemical experiments using purified proteins, cell-free extracts, and pathogen motility has begun to suggest various mechanistic roles for Ena/VASP proteins in the control of actin dynamics. Using complementation of phenotypes in Ena/VASP-deficient cells and overexpression in normal fibroblasts, we have assayed the function of a panel of mutants in one member of this family, Mena, by mutating highly conserved sequence elements found in this protein family. Surprisingly, deletion of sites required for binding of the actin monomer-binding protein profilin, a known ligand of Ena/VASP proteins, has no effect on the ability of Mena to regulate random cell motility. Our analysis revealed two features essential for Ena/VASP function in cell movement, cyclic nucleotide-dependent kinase phosphorylation sites and an F-actin binding motif. Interestingly, expression of the C-terminal EVH2 domain alone is sufficient to complement loss of Ena/VASP function in random cell motility