Richard A. Flavell

Bio: Richard A. Flavell is an academic researcher from Yale University. The author has contributed to research in topics: Immune system & T cell. The author has an hindex of 231, co-authored 1328 publications receiving 205119 citations. Previous affiliations of Richard A. Flavell include National Institute for Medical Research & University of Michigan.

Roles of IL-4 and IFN-gamma in stabilizing the T helper cell type 1 and 2 phenotype.

Abstract: It has previously been reported that Th1 CD4 T cell populations can be converted to IL-4 producers, whereas Th2 populations are refractory to IL-12-mediated IFN-gamma production. We have recently shown that CD30 is a marker for the IL-4 response and have therefore used CD30 here to study Th1 and Th2 commitment. We show that Th2 cell populations normally show a stable phenotype and fail to respond to IL-12 because of endogenous IL-4 production. IFN-gamma abrogates this antagonistic effect of IL-4 and permits the conversion of Th2 populations to IFN-gamma producers by IL-12. In the complete absence of IL-4, however, IFN-gamma is not required for this transformation, and Th1 cells generated by IL-12 become committed to the Th1 pathway and lose the ability to respond to IL-4. Thus, the balance between local IL-4 and IFN-gamma in an immune response is a key factor in determining the outcome of the CD4 effector T cell response.

c-Jun NH2-Terminal Kinase (JNK)1 and JNK2 Have Distinct Roles in CD8+ T Cell Activation

Abstract: The c-Jun NH2-terminal kinase (JNK) signaling pathway is induced by cytokines and stress stimuli and is implicated in cell death and differentiation, but the specific function of this pathway depends on the cell type. Here we examined the role of JNK1 and JNK2 in CD8+ T cells. Unlike CD4+ T cells, the absence of JNK2 causes increased interleukin (IL)-2 production and proliferation of CD8+ T cells. In contrast, JNK1-deficient CD8+ T cells are unable to undergo antigen-stimulated expansion in vitro, even in the presence of exogenous IL-2. The hypoproliferation of these cells is associated with impaired IL-2 receptor α chain (CD25) gene and cell surface expression. The reduced level of nuclear activating protein 1 (AP-1) complexes in activated JNK1-deficient CD8+ T cells can account for the impaired IL-2 receptor α chain gene expression. Thus, JNK1 and JNK2 play different roles during CD8+ T cell activation and these roles differ from those in CD4+ T cells.

c-Jun NH2-Terminal Kinase Inhibits Targeting of the Protein Phosphatase Calcineurin to NFATc1

Abstract: The c-Jun NH2-terminal kinase (JNK) group of mitogen-activated protein kinases is activated by treatment of cells with cytokines or exposure to environmental stress (19). Gene disruption studies indicate that JNK protein kinases are required for multiple biological processes (15, 23, 32, 41, 42). However, the molecular mechanisms that account for the phenotypes displayed by JNK knockout mice remain unclear. For example, the disruption of the Jnk1 gene causes a severe defect in the response of CD4+ helper T (TH) cells to antigen-presenting cells (15). Wild-type naive TH cells can differentiate to TH1 or TH2 effector cells, which mediate inflammatory and humoral responses, respectively. In contrast, Jnk1−/− CD4 TH cells preferentially differentiate to TH2 effector cells and secrete large amounts of the TH2 cytokines, including interleukin-4 (IL-4). As a consequence, these mice are highly susceptible to infection with Leishmania. These effects of Jnk1 gene disruption were associated with increased nuclear accumulation of the NFATc1 transcription factor (15), which is known to act at the IL-4 promoter and is essential for TH2 responses (30, 44). The phenotype of Jnk1−/− mice suggests that NFATc1 is negatively regulated by JNK1 (15). However, this phenotype could be a direct or an indirect consequence of Jnk1 gene disruption. Transcription factor NFAT was first identified as an important regulator of IL-2 gene expression (16, 20). More recently, it has been established that NFAT contributes to the expression of several cytokines and participates in multiple physiological processes (12, 31). In resting T cells, NFAT is restricted to the cytoplasm (12, 31). Following T-cell activation, a sustained increase in intracellular calcium (37) activates the phosphatase calcineurin (11, 21). The activated calcineurin dephosphorylates NFAT and leads to increased nuclear accumulation (12, 31). The nuclear NFAT transcription factor then increases the expression of target genes, including IL-2, IL-4, and Fas ligand. The interaction of calcineurin with NFAT is a critical element in the signal transduction pathway that leads to increased NFAT-dependent gene expression. Interestingly, this interaction is mediated by a targeting domain (PxIxIT motif) that is present in the NH2-terminal region of the NFAT transcription factor (1, 2, 8). This targeting domain is required for efficient NFAT activation in vivo. Furthermore, ectopic expression of the targeting domain causes profound and specific inhibition of NFAT-mediated gene expression in cultured cells (2, 8). Studies of transgenic mice also demonstrate inhibition of NFAT-mediated gene expression caused by expression of the calcineurin targeting domain (8). Together, these data indicate that the calcineurin targeting domain is a critical component of the regulatory mechanism that controls NFAT activity. The purpose of this study was to examine the role of JNK1 in NFATc1 regulation. Since the phenotype of Jnk1−/− mice suggests a correlation between the JNK1 signaling pathway and NFATc1 (15), we tested whether NFATc1 is directly regulated by JNK1. We report that JNK1 binds and phosphorylates NFATc1 on sites located near the PxIxIT calcineurin targeting domain. This phosphorylation inhibits the interaction of calcineurin with the targeting domain and blocks nuclear accumulation. This observation provides a molecular mechanism for the observation of increased NFATc1 nuclear accumulation in Jnk1−/− mice.

Caspase-3 is a pivotal mediator of apoptosis during regression of the ovarian corpus luteum.

Abstract: Because caspase-3 is considered a primary executioner of apoptosis and has been implicated as a mediator of luteal regression, we hypothesized that corpora lutea (CL) derived from caspase-3 null mice would exhibit a delayed onset of apoptosis during luteal regression, when compared with CL derived from wild-type (WT) mice. To test this hypothesis, ovulation was synchronized in immature (postpartum d 24 –27) WT and caspase-3-deficient female littermates by exogenous gonadotropins. Individual CL were isolated by manual dissection, 30 h after ovulation, and placed in organ culture dishes in the absence of serum and growth factors. At the time of isolation (0 h) and after 24, 48, and 72 h in culture, the CL were removed and assessed for the presence of processed (active) caspase-3 enzyme and for apoptosis by multiple criteria. There was no evidence of active caspase-3 enzyme or apoptosis in either WT or caspase-3-deficient CL before culture. However, CL derived from the WT mice exhibited a time-dependent increase in the level of active caspase-3 and apoptosis during culture. By comparison, CL derived from caspase-3-deficient mice, cultured in parallel, failed to exhibit any detectable active caspase-3 and showed attenuated rates of apoptosis. To extend these findings derived from ex vivo culture experiments, ovaries were collected from WT and caspase-3 null female littermates at 2, 4, or 6 d post ovulation, and the occurrence of apoptosis within the CL was analyzed. Whereas ovaries of WT mice had only residual luteal tissue at d 6 post ovulation, ovaries collected from caspase-3-deficient mice retained many CL, at d 6 post ovulation, that were similar in size to those observed in the early luteal phase of WT mice. Importantly, there was no dramatic increase in apoptosis in CL of caspase-3-deficient mice at any time point examined post ovulation, indicating that the involution process had indeed been delayed. In contrast, the levels of progesterone declined regardless of genotype. These data provide the first direct evidence that caspase-3 is functionally required for apoptosis to proceed normally during luteal regression. However, caspase-3 is not a direct mediator of the decrease in steroidogenesis associated with luteolysis. (Endocrinology 143: 1495–1501, 2002)

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Accurate transcription initiation by RNA polymerase II in a soluble extract from isolated mammalian nuclei

Abstract: We have developed a procedure for preparing extracts from nuclei of human tissue culture cells that directs accurate transcription initiation in vitro from class II promoters. Conditions of extraction and assay have been optimized for maximum activity using the major late promoter of adenovirus 2. The extract also directs accurate transcription initiation from other adenovirus promoters and cellular promoters. The extract also directs accurate transcription initiation from class III promoters (tRNA and Ad 2 VA).

Apoptosis: A Review of Programmed Cell Death

Abstract: The process of programmed cell death, or apoptosis, is generally characterized by distinct morphological characteristics and energy-dependent biochemical mechanisms. Apoptosis is considered a vital component of various processes including normal cell turnover, proper development and functioning of the immune system, hormone-dependent atrophy, embryonic development and chemical-induced cell death. Inappropriate apoptosis (either too little or too much) is a factor in many human conditions including neurodegenerative diseases, ischemic damage, autoimmune disorders and many types of cancer. The ability to modulate the life or death of a cell is recognized for its immense therapeutic potential. Therefore, research continues to focus on the elucidation and analysis of the cell cycle machinery and signaling pathways that control cell cycle arrest and apoptosis. To that end, the field of apoptosis research has been moving forward at an alarmingly rapid rate. Although many of the key apoptotic proteins have been identified, the molecular mechanisms of action or inaction of these proteins remain to be elucidated. The goal of this review is to provide a general overview of current knowledge on the process of apoptosis including morphology, biochemistry, the role of apoptosis in health and disease, detection methods, as well as a discussion of potential alternative forms of apoptosis.