No abstract

Methyl jasmonate (MeJA) is one of the most effective inducers of taxol biosynthetic genes, particularly the tasy gene. However, the mechanism underlying the regulation of tasy by MeJA is still unknown. In this study, a 550-bp 5'-flanking sequence was obtained and confirmed as the promoter of the tasy gene. Deletion analysis revealed that the fragment containing a GCC-box from -150 to -131 was the crucial jasmonate (JA)-responsive element, designated as JRE. Using JRE as bait, two binding proteins, namely TcERF12 and TcERF15, were discovered. Sequence alignment and phylogenetic analysis showed that TcERF12 was related to the repressor AtERF3, while TcERF15 was more related to the activator ORA59; these are typical GCC-box-binding ethylene-responsive factors. Both could significantly respond to MeJA for 10 and 4.5 times, respectively, in 0.5 h. When the two TcERFs were overexpressed in Taxus cells, tasy gene expression decreased by 2.1 times in TcERF12-overexpressing cells, but increased by 2.5 times in TcERF15-overexpressing cells. Results indicated that TcERF12 and TcERF15 were negative and positive regulators, respectively, in the JA signal transduction to the tasy gene by binding the GCC-box in the JRE of the tasy promoter. Our results promote further research on regulatory mechanisms of taxol biosynthesis.

Summary The development of CD1d-restricted invariant NKT (iNKT) cells, a population that is critical for both innate and adaptive immunity, is regulated by multiple transcription factors, but the molecular mechanisms underlying how the transcriptional activation of these factors are regulated during iNKT development remain largely unknown. We found that the histone acetyltransferase GCN5 is essential for iNKT cell development during the maturation stage. GCN5 deficiency blocked iNKT cell development in a cell-intrinsic manner. At the molecular level, GCN5 is a specific lysine acetyltransferase of EGR2, a transcription factor required for iNKT cell development. GCN5-mediated acetylation positively regulated EGR2 transcriptional activity, and both genetic and pharmacological GCN5 suppression specifically inhibited the transcription of EGR2 target genes in iNKT cells, including Runx1, PLZF, IL-2Rb, and T-bet. Therefore, our study revealed GCN5-mediated EGR2 acetylation as a molecular mechanism that regulates iNKT development.

Humoral immunity involves multiple checkpoints during B-cell development, maturation, and activation. The cell death receptor CD95/Fas-mediated apoptosis plays a critical role in eliminating the unwanted activation of B cells by self-reactive antigens and in maintaining B-cell homeostasis through activation-induced B-cell death (AICD). The molecular mechanisms controlling AICD remain largely undefined. Herein, we show that the E3 ubiquitin ligase Hrd1 protected B cells from activation-induced cell death by degrading the death receptor Fas. Hrd1-null B cells exhibited high Fas expression during activation and rapidly underwent Fas-mediated apoptosis, which could be largely inhibited by FasL neutralization. Fas mutation in Hrd1 KO mice abrogated the increase in B-cell AICD. We identified Hrd1 as the first E3 ubiquitin ligase of the death receptor Fas and Hrd1-mediated Fas destruction as a molecular mechanism in regulating B-cell immunity.Hrd1 | Fas | B cells | ubiquitination B -cell immunity involves several checkpoints, which are important to orchestrate and balance survival and apoptotic signals and control the quality and size of the B-cell compartment (1, 2). The earliest steps in B-cell development occur in the bone marrow, where assembly of the pre-B-cell receptor (pre-BCR) followed by the mature BCR occurs in distinct stages. Once the mature BCR is expressed, B lymphocytes then progress into the immature B-cell stage, where further selection checkpoints occur before the immature B cells transition to the periphery and mature into circulating B cells (2, 3). Mature B cells are maintained through tonic BCR, CD40, and B-cell-activating factor receptor (BAFFR) signaling (4). Activation by cross-linking the BCR leads to rapid proliferation, somatic hypermutation, and further differentiation of B cells (5, 6). The expansion of activated B-cell compartment is subsequently downmodulated through activation-induced cell death (AICD) (7,8).The death receptor Fas has been identified as a key regulator of AICD of B cells (9-11). Fas is highly expressed on activated B cells, particularly in the germinal center, where it mediates the deletion of autoreactive or unproductive somatic hypermutated B cells (12)(13)(14). Fas, as well as its ligand FasL, play critical roles in B-cell apoptosis. The selective removal of Fas from activated B cells results in lupus-like disease and autoantibody production (15-17). It has been a widely accepted view that the Fas/FasL mutations result in, at least in part, a failure to eliminate self-reactive GC B cells in autoimmune patients and animal models (12, 18). However, more recent studies show that FAS is in fact not required for the elimination of self-reactive GC B cells. Instead, Fas inactivation led to accumulation of a population of unconventional GC B cells that underwent somatic hypermutation and survived despite losing antigen reactivity (8). Nevertheless, it is clear that Fasmediated B-cell death is critically involved in B-cell-mediated autoimmune diseases. However, the molecular...