Transcriptional activation of histone subtypes is coordinately regulated and tightly coupled with the onset of DNA replication during S-phase entry. The underlying molecular mechanisms for such coordination and coupling are not well understood. The cyclin E-Cdk2 substrate NPAT has been shown to play an essential role in the transcriptional activation of histone genes at the G1/S-phase transition. Here, we show that NPAT interacts with components of the Tip60 histone acetyltransferase complex through a novel amino acid motif, which is functionally conserved in E2F and adenovirus E1A proteins. In addition, we demonstrate that transformation/transactivation domain-associated protein (TRRAP) and Tip60, two components of the Tip60 complex, associate with histone gene promoters at the G1/S-phase boundary in an NPAT-dependent manner. In correlation with the association of the TRRAP-Tip60 complex, histone H4 acetylation at histone gene promoters increases at the G1/S-phase transition, and this increase involves NPAT function. Suppression of TRRAP or Tip60 expression by RNA interference inhibits histone gene activation. Thus, our data support a model in which NPAT recruits the TRRAP-Tip60 complex to histone gene promoters to coordinate the transcriptional activation of multiple histone genes during the G1/S-phase transition.

Schistosomiasis is a major public health problem that primarily affects developing countries. Although schistosomicidal drugs exist, the development of an efficacious vaccine would potentially be the most powerful means of controlling this disease. Previous studies have shown that vaccination with selected protective epitopes successfully induced partial protection and/or reduced female fecundity in animal models. Thus, we investigated whether the T cell epitope P5 from the host-interactive tegument of Schistosoma japonicum 22.6 (S. japonicum) could act as a protective epitope. The protective potential of P5 in a vaccine against S. japonicum was determined by using a T cell epitope based peptide-DNA dual vaccine (PDDV). In our experiments, the vaccine construct (P5e18K-PDDV) contains the peptide of the T cell epitope (P5) and plasmid DNA, encoding P5 and adjuvant GM-CSF. We show that P5e18K-PDDV induced both cell-mediated and humoral immune responses in vivo and achieved partial protection against S. japonicum infection in C57BL/6J mice. Histopathological studies reveal that P5e18K-PDDV immunized mice had substantially reduced liver pathology compared to the control groups. Together, these results suggest that P5 could be used as a vaccine immunogen for both worm killing and disease prevention against S. japonicum.

A number of epidemiological and clinical studies have suggested an inverse association between allergy and helminth infection, such as Schistosomiasis. Therefore, we hypothesize that Schistosoma japonicum egg antigens, a type of native antigen, can induce production of CD4+ CD25+ T cells with regulatory activity, modulating airway inflammation and inhibiting asthma development. The frequency of CD4+ CD25+ T cells was determined by flow cytometry for mice treated with ovalbumin (OVA), CD25+ depletion/OVA, schistosome egg antigens, schistosome egg antigens/OVA and for control mice. The ability of CD25+ T cells from these mice to suppress T-cell proliferation and cytokine production was investigated both in vivo and in vitro. Results showed that the CD4+ CD25+ T cells of OVA-treated mice exhibited impaired control of dysregulated mucosal T helper 2 responses compared to the controls (P<0.05). Depletion of CD25+ cells accelerated OVA-induced airway inflammation and increased the expression of interleukin (IL)-5 and IL-4. Treatment with schistosome egg antigens increased the number and suppressive activity of CD4+ CD25+ T cells, which made IL-10, but little IL-4. In a murine model of asthma, S. japonicum egg antigens decreased the expression of Th2 cytokines, relieved antigen-induced airway inflammation, and inhibited asthma development. Thus, we provided evidence that S. japonicum egg antigens induced the production of CD4+ CD25+ T cells, resulting in constitutive immunosuppressive activity and inhibition of asthma development. These results reveal a novel form of protection against asthma and suggest a mechanistic explanation for the protective effect of helminth infection on the development of allergy.

目的：探讨CD4+CD25+调节性T（Treg）细胞在慢性丙型肝炎患者免疫下调中的意义。方法：流式细胞仪检测慢性丙型肝炎患者外周血中CD4+CD25+Treg细胞的数量；与CD4+CD25-T细胞共同培养，检测其抑制功能；流式细胞仪检测其对CD4+CD25-T细胞合成IFN-γ和IL-4的影响；RTPCR检测CD4+CD25+Treg细胞中Foxp3的mRNA表达。结果：CD4+CD25+Treg细胞约占慢性丙型肝炎患者外周血中CD4+T细胞的14.1±1.6%，显著高于正常对照5.3±0.8%（P<0.01），显著抑制CD4+T细胞的增殖（P=0.002），以及合成IFN-γ。CD4+CD25+Treg细胞高表达Foxp3。结论：持续性HCV感染患者CD4+CD25+Treg细胞表达增加，特异性抑制Th1细胞反应。

Activation of the G1 checkpoint following DNA damage leads to inhibition of cyclin E-Cdk2 and subsequent G1 arrest in higher eucaryotes. Little, however, is known about the molecular events downstream of cyclin E-Cdk2 inhibition. Here we show that, in addition to the inhibition of DNA synthesis, ionizing radiation induces downregulation of histone mRNA levels in mammalian cells. This downregulation occurs at the level of transcription and requires functional p53 and p21CIP1/WAF1 proteins. We demonstrate that DNA damage induced by ionizing radiation results in the suppression of phosphorylation of NPAT, an in vivo substrate of cyclin E-Cdk2 kinase and an essential regulator of histone gene transcription, and its dissociation from histone gene clusters in a p53/p21-dependent manner. Inhibition of Cdk2 activity by specific inhibitors in the absence of DNA damage similarly disperses NPAT from histone gene clusters and represses histone gene expression. Our results thus suggest that inhibition of Cdk2 activity following DNA damage results in the downregulation of histone gene transcription through dissociation of NPAT from histone gene clusters.