The Nonstructural NS1 Protein of Influenza Viruses Modulates TP53 Splicing through Host Factor CPSF4.

Influenza A viruses (IAV) are known to modulate and "hijack" several cellular host mechanisms, including gene splicing and RNA maturation machineries. These modulations alter host cellular responses and enable an optimal expression of viral products throughout infection. The interplay between the host protein p53 and IAV, in particular through the viral nonstructural protein NS1, has been shown to be supportive for IAV replication. However, it remains unknown whether alternatively spliced isoforms of p53, known to modulate p53 transcriptional activity, are affected by IAV infection and contribute to IAV replication. Using a TP53 minigene, which mimics intron 9 alternative splicing, we have shown here that the NS1 protein of IAV changes the expression pattern of p53 isoforms. Our results demonstrate that CPSF4 (cellular protein cleavage and polyadenylation specificity factor 4) independently and the interaction between NS1 and CPSF4 modulate the alternative splicing of TP53 transcripts, which may result in the differential activation of p53-responsive genes. Finally, we report that CPSF4 and most likely beta and gamma spliced p53 isoforms affect both viral replication and IAV-associated type I interferon secretion. All together, our data show that cellular p53 and CPSF4 factors, both interacting with viral NS1, have a crucial role during IAV replication that allows IAV to interact with and alter the expression of alternatively spliced p53 isoforms in order to regulate the cellular innate response, especially via type I interferon secretion, and perform efficient viral replication.IMPORTANCE Influenza A viruses (IAV) constitute a major public health issue, causing illness and death in high-risk populations during seasonal epidemics or pandemics. IAV are known to modulate cellular pathways to promote their replication and avoid immune restriction via the targeting of several cellular proteins. One of these proteins, p53, is a master regulator involved in a large panel of biological processes, including cell cycle arrest, apoptosis, or senescence. This "cellular gatekeeper" is also involved in the control of viral infections, and viruses have developed a wide diversity of mechanisms to modulate/hijack p53 functions to achieve an optimal replication in their hosts. Our group and others have previously shown that p53 activity is finely modulated by different multilevel mechanisms during IAV infection. Here, we characterized IAV nonstructural protein NS1 and the cellular factor CPSF4 as major partners involved in the IAV-induced modulation of the TP53 alternative splicing that was associated with a strong modulation of p53 activity and notably the p53-mediated antiviral response.

Mast cells and eosinophils in mastocytosis, chronic eosinophilic leukemia, and non-clonal disorders.

Mast cells and eosinophils often travel in the same biologic circles. In non-clonal states, such as allergic and inflammatory conditions, cell-to-cell contact and the pleiotropic actions of multiple cytokines and chemokines, derived from local tissues or mast cells themselves, foster the co-recruitment of these cells to the same geographic cellular niche. While eosinophils and mast cells serve critical roles as part of the host immune response and in maintenance of normal homeostasis, these cell types can undergo neoplastic transformation due to the development of clonal molecular abnormalities that arise in early hematopoietic progenitors. The dysregulated tyrosine kinases, D816V KIT and FIP1L1-PDGFRA, are the prototypic oncogenic lesions resulting in systemic mastocytosis (SM) and chronic eosinophilic leukemia, respectively. We review the pathobiology of these myeloproliferative neoplasms (MPNs) with a focus on the relationship between mast cells and eosinophils, and discuss murine models, which further elucidate how the phenotype of these diseases can be influenced by stem cell factor (SCF) and expression of the potent eosinophilopoietic cytokine, interleukin-5 (IL-5). Therapy of SM and FIP1L1-PDGFRA-positive disease and the prognostic relevance of increased peripheral blood and tissue mast cells in hematolymphoid malignancies will also be addressed.

Hypereosinophilic syndrome: a multicenter, retrospective analysis of clinical characteristics and response to therapy.

BACKGROUND: Hypereosinophilic syndrome (HES) is a heterogeneous group of rare disorders defined by persistent blood eosinophilia > or =1.5 x 10(9)/L, absence of a secondary cause, and evidence of eosinophil-associated pathology. With the exception of a recent multicenter trial of mepolizumab (anti-IL-5 mAb), published therapeutic experience has been restricted to case reports and small case series. OBJECTIVE: The purpose of the study was to collect and summarize baseline demographic, clinical, and laboratory characteristics in a large, diverse cohort of patients with HES and to review responses to treatment with conventional and novel therapies. METHODS: Clinical and laboratory data from 188 patients with HES, seen between January 2001 and December 2006 at 11 institutions in the United States and Europe, were collected retrospectively by chart review. RESULTS: Eighteen of 161 patients (11%) tested were Fip1-like 1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRA) mutation-positive, and 29 of 168 patients tested (17%) had a demonstrable aberrant or clonal T-cell population. Corticosteroid monotherapy induced complete or partial responses at 1 month in 85% (120/141) of patients with most remaining on maintenance doses (median, 10 mg prednisone equivalent daily for 2 months to 20 years). Hydroxyurea and IFN-alpha (used in 64 and 46 patients, respectively) were also effective, but their use was limited by toxicity. Imatinib (used in 68 patients) was more effective in patients with the FIP1L1-PDGFRA mutation (88%) than in those without (23%; P < .001). CONCLUSION: This study, the largest clinical analysis of patients with HES to date, not only provides useful information for clinicians but also should stimulate prospective trials to optimize treatment of HES.

T-cell abnormalities are present at high frequencies in patients with hypereosinophilic syndrome.

BACKGROUND: A T-cell clone, thought to be the source of eosinophilopoietic cytokines, identified by clonal rearrangement of the T-cell receptor and by the presence of aberrant T-cell immunophenotype in peripheral blood defines lymphocytic variant of hypereosinophilic syndrome (L-HES). DESIGN AND METHODS: Peripheral blood samples from 42 patients who satisfied the diagnostic criteria for HES were studied for T-cell receptor clonal rearrangement by polymerase chain reaction according to BIOMED-2. The T-cell immunophenotype population was assessed in peripheral blood by flow cytometry. The FIP1L1-PDGFRA fusion gene was detected by nested polymerase chain reaction. RESULTS: Forty-two HES patients (18 males and 24 females) with a median age at diagnosis of 56 years (range 17-84) were examined in this study. Their median white blood cell count was 12.9 x 10(9)/L (range 5.3-121), with an absolute eosinophil count of 4.5 x 10(9)/L (range 1.5-99) and a median eosinophilic bone marrow infiltration of 30% (range 11-64). Among the 42 patients, clonal T-cell receptor rearrangements were detected in 18 patients (42.8%). Patients with T-cell receptor clonality included: T-cell receptor beta in 15 patients (35%), T-cell receptor gamma in 9 (21%) and T-cell receptor delta in 9 (21%) patients, respectively. Clonality was detected in all three T-cell receptor loci in 4 cases, in two loci in 7 patients and in one T-cell receptor locus in the remaining 7 patients. The FIP1L1-PDGFRA fusion transcript was absent in all but 2 patients with T-cell receptor clonality. Three patients out of 42 revealed an aberrant T-cell immunophenotype. In some patients, an abnormal CD4:CD8 ratio was demonstrated. CONCLUSIONS: T-cell abnormalities are present at high frequencies in patients with HES.

SLBP is associated with histone mRNA on polyribosomes as a component of the histone mRNP.

The stem-loop binding protein (SLBP) binds the 3' end of histone mRNA and is present both in nucleus, and in the cytoplasm on the polyribosomes. SLBP participates in the processing of the histone pre-mRNA and in translation of the mature message. Histone mRNAs are rapidly degraded when cells are treated with inhibitors of DNA replication and are stabilized by inhibitors of translation, resulting in an increase in histone mRNA levels. Here, we show that SLBP is a component of the histone messenger ribonucleoprotein particle (mRNP). Histone mRNA from polyribosomes is immunoprecipitated with anti-SLBP. Most of the SLBP in cycloheximide-treated cells is present on polyribosomes as a result of continued synthesis and transport of the histone mRNP to the cytoplasm. When cells are treated with inhibitors of DNA replication, histone mRNAs are rapidly degraded but SLBP levels remain constant and SLBP is relocalized to the nucleus. SLBP remains active both in RNA binding and histone pre-mRNA processing when DNA replication is inhibited.