No abstract

The mating pathway in yeast Saccharomyces cerevisiae has long been used to reveal new mechanisms of signal transduction. The pathway comprises a pheromone receptor, a heterotrimeric G protein, and intracellular effectors of morphogenesis and transcription. Polarized cell growth, in the direction of a potential mating partner, is accomplished by the G-protein ␤␥ subunits and the small G-protein Cdc42. Transcription induction, needed for cell-cell fusion, is mediated by G␤␥ and the mitogen-activated protein kinase (MAPK) scaffold protein Ste5. A potential third pathway is initiated by the G-protein ␣ subunit Gpa1. Gpa1 signaling was shown previously to involve the F-box adaptor protein Dia2 and an endosomal effector protein, the phosphatidylinositol 3-kinase Vps34. Vps34 is also required for proper vacuolar sorting and autophagy. Here, using a panel of reporter assays, we demonstrate that mating pheromone stimulates vacuolar targeting of a cytoplasmic reporter protein and that this process depends on Vps34. Through a systematic analysis of F-box deletion mutants, we show that Dia2 is required to sustain pheromone-induced vacuolar targeting. We also found that other F-box proteins selectively regulate morphogenesis (Ydr306, renamed Pfu1) and transcription (Ucc1). These findings point to the existence of a new and distinct branch of the pheromone-signaling pathway, one that likely leads to vacuolar engulfment of cytoplasmic proteins and recycling of cellular contents in preparation for mating. Many extracellular signals are detected by G-proteincoupled receptors (GPCRs). 10 In animals, these signals include odors, tastes, light, pH, nucleotides, biogenic amines, peptides, steroids, and phospholipids. In each case, receptor activation results in binding of GTP to a G-protein ␣ subunit and dissociation of G␣ from the ␤␥ subunit dimer. Both G␣ and G␤␥ can then transduce signals through the activation of intracellular enzymes and ion channels. G-protein signaling ends when GTP is hydrolyzed to GDP, a process that is accelerated by members of the regulator of G-protein signaling (RGS) family (1). GPCRs also play an important role in yeast mating. Genetic analysis in yeast Saccharomyces cerevisiae has led to the identification and characterization of several new signaling proteins, including the first RGS protein Sst2 (2). Sst2 is required for pheromone gradient tracking (3-5), adaptation (6, 7), and noise suppression (8). Other pathway components were identified from mutants that produce an unresponsive sterile (ste) phenotype, including the mating pheromone receptors (Ste2 and Ste3), the G-protein ␤␥ subunits (Ste4 and Ste18), a G␤␥ effector (Ste5), downstream protein kinases (Ste20, Ste11, and Ste7), and a transcription factor (Ste12) (2). Further analysis revealed that the G-protein ␤␥ dimer recruits and activates Far1 in complex with Cdc24 (9-13), an exchange factor for the small G-protein Cdc42 (14), as well as Ste5, a scaffold protein required for activation of the MAPKs Fus3 and Kss1 (15-22). Cdc42 promotes cell cy...

An integral component of the antiviral response, Type I IFNs require regulation to modulate immune activation. We identify β-arrestin 2 as a key modulator of Type I IFN in primary human macrophages, an essential component of the innate immune response. β-arrestin 2 was selectively activated by CCL2/CCR2 signaling, which induced a decrease in IFN-α, but not IFN-β expression. siRNA knockdown of β-arrestin 2 demonstrated its role in IFNAR1 internalization, as well as STAT1 and IRF3 activation. As a result, cytokine responses were not propagated following HIV infection and TLR3 activation. However, remnants of IFN signaling remained intact, despite β-arrestin 2 activation, as IFN-β, IFN-γ, IFN-λ1, IRF7, TRAIL, and MxA expression were sustained. Similar effects of β-arrestin 2 on IFN signaling occurred in hepatocytes, suggesting that arrestins may broadly modulate IFN responses in multiple cell types. In summary, we identify a novel role of β-arrestin 2 as an integral regulator of Type I IFN through its internalization of IFNAR1 and a subsequent selective loss of downstream IFN signaling.

The use of beneficial bacteria to promote gastrointestinal heath is widely practiced, however, the mechanisms whereby many of these microbes elicit their beneficial effects remain elusive. Previously, we conducted a screen for the discovery of novel beneficial microbes and identified the potent cytoprotective effects of a strain of Lactococcus lactis subsp. cremoris. Here, we show that dietary supplementation with L. lactis subsp. cremoris induced transcript enrichment of a set of genes within the colon whose functions are associated with host cell and microbe interactions. Specifically, L. lactis subsp. cremoris induced the expression of tlr2, which we show was required for L. lactis subsp. cremoris to elicit its beneficial effects on the intestine. L. lactis subsp. cremoris did not confer beneficial effects in mice deficient in TLR-2, or deficient in its adaptor protein Myd88 in chronic gut injury models. In addition to cytoprotection, culture supernatant from L. lactis subsp. cremoris accelerated epithelial migration in a cultured epithelial cell scratch wound assay; and effect that was abrogated by a TLR-2 antagonist. Furthermore, L. lactis subsp. cremoris accelerated epithelial tissue restitution following the infliction of a colonic wound biopsy in a TLR-2 and Myd88-dependent manner. Within colonic wounds, L. lactis subsp. cremoris induced the activation of signaling pathways that function in tissue restitution following injury, including the ERK signaling pathway, and of focal adhesion complex (FAC) proteins. Together, these data demonstrate that L. lactis subsp. cremoris signals via the TLR2/MyD88-axis to confer cytoprotection and accelarated tissue restituion in the gut epithelium. These data point to evolving adaptations where beneficial gut microbes moduate innate immune signaling to excert positive influnces on host physiology.