Heterochromatin domains play important roles in chromosome biology, organismal development, and aging, including centromere function, mammalian female X chromosome inactivation, and senescence-associated heterochromatin foci. In the fission yeast Schizosaccharomyces pombe and metazoans, heterochromatin contains histone H3 that is dimethylated at lysine 9.

Pseudomonas aeruginosa is an opportunistic pathogen that is capable of causing acute and chronic pulmonary infection in the immunocompromised host. In the case of cystic fibrosis (CF), chronic P. aeruginosa infection causes increased mortality by promoting overly exuberant airway inflammation and cumulative lung damage. Identifying the key regulators of this inflammation may lead to the development of new therapies that improve P. aeruginosa-related mortality. We report here that interleukin-23 (IL-23), the cytokine most clearly tied to IL-17-mediated inflammation, also promotes IL-17-independent inflammation during P. aeruginosa pulmonary infection. During the early innate immune response, prior to IL-17 induction, IL-23 acts synergistically with IL-1␤ to promote early neutrophil (polymorphonuclear leukocyte [PMN]) recruitment. However, at later time points, IL-23 also promoted IL-17 production by lung ␥␦ T cells, which was greatly augmented in the presence of IL-1␤. These studies show that IL-23 controls two independent phases of neutrophil recruitment in response to P. aeruginosa infection: early PMN emigration that is IL-17 independent and later PMN emigration regulated by IL-17. Pseudomonas aeruginosa pulmonary infection occurs in immunocompromised hosts and is associated with significant morbidity and mortality. The pathogen induces a robust neutrophil response that causes significant airway damage and does not always eliminate the pathogen. In cystic fibrosis (CF), where infection is chronic, the inflammation causes cumulative airway damage that is a major contributor to morbidity and mortality (41,46,62). Identifying the immune mediators that promote this inflammation is the first step in developing new therapies that can improve outcomes in chronic P. aeruginosa pulmonary infection.We and others have previously shown that airway interleukin-23 (IL-23) and IL-17 levels correlate with infection status and inflammation in individuals with CF (12,15,38) and that lymphocytes from CF-derived draining lymph nodes produce higher levels of IL-17 than non-CF disease controls (3). We have also shown that both IL-23 and IL-17 are critical for neutrophil recruitment in a murine model of chronic P. aeruginosa pulmonary infection (14). While these data demonstrate that the IL-23/ IL-17 proinflammatory axis is active during P. aeruginosa airway infection and in CF, the studies did not isolate the actions of IL-23 from those of IL-17.Historically, IL-17 has been credited with promoting both neutrophil recruitment and granulopoiesis through its induction of neutrophil growth factors and chemokines, including IL-6, granulocyte colony-stimulating factor (G-CSF), keratinocyte chemoattractant (KC), and macrophage inflammatory protein 2 (MIP-2) (14,24,30,38,49,54,64). IL-23, a recently identified IL-12 family member (42, 60), has been primarily characterized in the context of this Th17 response (1,25,33). Of note, however, IL-23-overexpressing mice have a hyperinflammatory phenotype and notable elevations in serum IL-1␤ and t...

Restricting the localization of the histone H3 variant CENP-A (Cse4 in yeast, CID in flies) to centromeres is essential for faithful chromosome segregation. Mislocalization of CENP-A leads to chromosomal instability (CIN) in yeast, fly and human cells. Overexpression and mislocalization of CENP-A has been observed in many cancers and this correlates with increased invasiveness and poor prognosis. Yet genes that regulate CENP-A levels and localization under physiological conditions have not been defined. In this study we used a genome-wide genetic screen to identify essential genes required for Cse4 homeostasis to prevent its mislocalization for chromosomal stability. We show that two Skp, Cullin, Fbox (SCF) ubiquitin ligases with the evolutionarily conserved F-box proteins Met30 and Cdc4 interact and cooperatively regulate proteolysis of endogenous Cse4 and prevent its mislocalization for faithful chromosome segregation under physiological conditions. The interaction of Met30 with Cdc4 is independent of the D domain, which is essential for their homodimerization and ubiquitination of other substrates. The requirement for both Cdc4 and Met30 for ubiquitination is specifc for Cse4; and a common substrate for Cdc4 and Met30 has not previously been described. Met30 is necessary for the interaction between Cdc4 and Cse4, and defects in this interaction lead to stabilization and mislocalization of Cse4, which in turn contributes to CIN. We provide the first direct link between Cse4 mislocalization to defects in kinetochore structure and show that SCF-mediated proteolysis of