The characteristic pathologic features of asthma in adults and school-aged children develop in preschool children with confirmed wheeze between the ages of 1 and 3 years, a time when intervention may modify the natural history of asthma.

The contribution of human subtelomeric DNA and chromatin organization to telomere integrity and chromosome end protection is not yet understood in molecular detail. Here, we show by ChIP-Seq that most human subtelomeres contain a CTCF-and cohesin-binding site within B1-2 kb of the TTAGGG repeat tract and adjacent to a CpG-islands implicated in TERRA transcription control. ChIP-Seq also revealed that RNA polymerase II (RNAPII) was enriched at sites adjacent to the CTCF sites and extending towards the telomere repeat tracts. Mutation of CTCF-binding sites in plasmid-borne promoters reduced transcriptional activity in an orientation-dependent manner. Depletion of CTCF by shRNA led to a decrease in TERRA transcription, and a loss of cohesin and RNAPII binding to the subtelomeres. Depletion of either CTCF or cohesin subunit Rad21 caused telomere-induced DNA damage foci (TIF) formation, and destabilized TRF1 and TRF2 binding to the TTAGGG proximal subtelomere DNA. These findings indicate that CTCF and cohesin are integral components of most human subtelomeres, and important for the regulation of TERRA transcription and telomere end protection.

Telomeres repress the DNA damage response at the natural chromosome ends to prevent cell-cycle arrest and maintain genome stability. Telomeres are elongated by telomerase in a tightly regulated manner to ensure a sufficient number of cell divisions throughout life, yet prevent unlimited cell division and cancer development. Hoyeraal-Hreidarsson syndrome (HHS) is characterized by accelerated telomere shortening and a broad range of pathologies, including bone marrow failure, immunodeficiency, and developmental defects. HHS-causing mutations have previously been found in telomerase and the shelterin component telomeric repeat binding factor 1 (TRF1)-interacting nuclear factor 2 (TIN2). We identified by whole-genome exome sequencing compound heterozygous mutations in four siblings affected with HHS, in the gene encoding the regulator of telomere elongation helicase 1 (RTEL1). Rtel1 was identified in mouse by its genetic association with telomere length. However, its mechanism of action and whether it regulates telomere length in human remained unknown. Lymphoblastoid cell lines obtained from a patient and from the healthy parents carrying heterozygous RTEL1 mutations displayed telomere shortening, fragility and fusion, and growth defects in culture. Ectopic expression of WT RTEL1 suppressed the telomere shortening and growth defect, confirming the causal role of the RTEL1 mutations in HHS and demonstrating the essential function of human RTEL1 in telomere protection and elongation. Finally, we show that human RTEL1 interacts with the shelterin protein TRF1, providing a potential recruitment mechanism of RTEL1 to telomeres. dyskeratosis congenita | genomic instability | aging | telomeropathies H uman telomeres are composed of tandem TTAGGG DNA repeats, ending with an essential single-stranded 3′-overhang (reviewed in refs. 1 and 2). This overhang can be elongated by the enzyme telomerase to make up for losses caused by incomplete DNA replication and degradation. The expression of the telomerase reverse-transcriptase subunit (hTERT) is suppressed in most human somatic tissues; consequently, telomeres gradually shorten with each cell division. Critically short telomeres activate the DNA damage response (DDR) and cause cell-cycle arrest or apoptosis. Thus, telomere length and integrity control cellular lifespan and provide a tumor-suppressing mechanism (3). Shelterin, a complex of six core proteins, assembles at mammalian telomeres to suppress DDR and regulate telomere length (4, 5). Shelterin was suggested to facilitate the formation of a telomere (T)-loop, via invasion of double-stranded telomeric DNA by the 3′ overhang, where it is inaccessible to DDR factors and to telomerase.Dyskeratosis congenita (DC) and its severe form HoyeraalHreidarsson syndrome (HHS) are hereditary disorders associated with severely shortened telomeres and diverse clinical symptoms (6-8). The major cause of death in DC and HHS is bone marrow failure, but mortality from cancer and pulmonary fibrosis also occurs at frequencies above normal. Mu...

Telomerase is a regulated enzyme and its activity is tightly associated with cell proliferation. The mechanisms of this association are unclear, but speci®c growth factors may regulate telomerase activity. The present study examines the eect of epidermal growth factor (EGF) on telomerase activity and identi®es the signal transduction pathway involved in this process. EGF upregulated telomerase activity in EGF receptor-positive cells after the activation of telomerase reverse transcriptase (TERT) mRNA expression. This activation was rapid, peaked after 6 or 12 h and was not blocked by the concurrent exposure to cycloheximide, suggesting a direct eect of EGF on TERT transcription. Transient expression assays revealed that EGF activates the hTERT promoter and that the proximal core promoter is responsible for this regulation. The activation of hTERT mRNA expression by EGF was speci®cally blocked by MEK inhibitor, and in vitro kinase assays demonstrated that ERK is activated in response to EGF. Transient expression assays using mutant reporter plasmids revealed that an ETS motif located in the core promoter of hTERT is required for the EGF-induced transactivation of hTERT. Overexpression of wild type Ets in cells enhanced the EGF eect on hTERT transcription, while that of dominant negative Ets signi®cantly repressed EGF action. These ®ndings suggest that EGF activates telomerase through the direct activation of TERT transcription, in which the Ras/ MEK/ERK pathway and Ets factor play major roles. Our data support the notion that growth factors directly regulate telomerase via speci®c signal transduction pathways.

Macrophages dictate both initiation and resolution of inflammation. During acute inflammation classically activated macrophages (M1) predominate, and during the resolution phase alternative macrophages (M2) are dominant. The molecular mechanisms involved in macrophage polarization are understudied. MicroRNAs are differentially expressed in M1 and M2 macrophages that influence macrophage polarization. We identified a role of miR-21 in macrophage polarization, and found that cross-talk between miR-21 and the lipid mediator prostaglandin E2 (PGE2) is a determining factor in macrophage polarization. miR-21 inhibition impairs expression of M2 signature genes but not M1 genes. PGE2 and its downstream effectors PKA and Epac inhibit miR-21 expression and enhance expression of M2 genes, and this effect is more pronounced in miR-21-/- cells. Among potential targets involved in macrophage polarization, we found that STAT3 and SOCS1 were enhanced in miR-21-/- cells and further enhanced by PGE2. We found that STAT3 was a direct target of miR-21 in macrophages. Silencing the STAT3 gene abolished PGE2-mediated expression of M2 genes in miR-21-/- macrophages. These data shed light on the molecular brakes involved in homeostatic macrophage polarization and suggest new therapeutic strategies to prevent inflammatory responses.