Direct Modulation of Heterotrimeric G Protein-coupled Signaling by a Receptor Kinase Complex

Plants and some protists have heterotrimeric G protein complexes that activate spontaneously without canonical G protein-coupled receptors (GPCRs). In Arabidopsis, the sole 7-transmembrane regulator of G protein signaling 1 (AtRGS1) modulates the G protein complex by keeping it in the resting state (GDP-bound). However, it remains unknown how a myriad of biological responses is achieved with a single G protein modulator. We propose that in complete contrast to G protein activation in animals, plant leucine-rich repeat receptor-like kinases (LRR RLKs), not GPCRs, provide this discrimination through phosphorylation of AtRGS1 in a ligand-dependent manner. G protein signaling is directly activated by the pathogen-associated molecular pattern flagellin peptide 22 through its LRR RLK, FLS2, and co-receptor BAK1

Sequential Transphosphorylation of the BRI1/BAK1 Receptor Kinase Complex Impacts Early Events in Brassinosteroid Signaling

SummaryBrassinosteroids (BRs) regulate plant development through a signal transduction pathway involving the BRI1 and BAK1 transmembrane receptor kinases. The detailed molecular mechanisms of phosphorylation, kinase activation, and oligomerization of the BRI1/BAK1 complex in response to BRs are uncertain. We demonstrate that BR-dependent activation of BRI1 precedes association with BAK1 in planta, and that BRI1 positively regulates BAK1 phosphorylation levels in vivo. BRI1 transphosphorylates BAK1 in vitro on specific kinase-domain residues critical for BAK1 function. BAK1 also transphosphorylates BRI1, thereby quantitatively increasing BRI1 kinase activity toward a specific substrate. We propose a sequential transphosphorylation model in which BRI1 controls signaling specificity by direct BR binding followed by substrate phosphorylation. The coreceptor BAK1 is then activated by BRI1-dependent transphosphorylation and subsequently enhances signaling output through reciprocal BRI1 transphosphorylation. This model suggests both conservation and distinct differences between the molecular mechanisms regulating phosphorylation-dependent kinase activation in plant and animal receptor kinases

Genome-wide cloning and sequence analysis of leucine-rich repeat receptor-like protein kinase genes in Arabidopsis thaliana

Abstract Background Transmembrane receptor kinases play critical roles in both animal and plant signaling pathways regulating growth, development, differentiation, cell death, and pathogenic defense responses. In Arabidopsis thaliana, there are at least 223 Leucine-rich repeat receptor-like kinases (LRR-RLKs), representing one of the largest protein families. Although functional roles for a handful of LRR-RLKs have been revealed, the functions of the majority of members in this protein family have not been elucidated. Results As a resource for the in-depth analysis of this important protein family, the complementary DNA sequences (cDNAs) of 194 LRR-RLKs were cloned into the GatewayR donor vector pDONR/ZeoR and analyzed by DNA sequencing. Among them, 157 clones showed sequences identical to the predictions in the Arabidopsis sequence resource, TAIR8. The other 37 cDNAs showed gene structures distinct from the predictions of TAIR8, which was mainly caused by alternative splicing of pre-mRNA. Most of the genes have been further cloned into GatewayR destination vectors with GFP or FLAG epitope tags and have been transformed into Arabidopsis for in planta functional analysis. All clones from this study have been submitted to the Arabidopsis Biological Resource Center (ABRC) at Ohio State University for full accessibility by the Arabidopsis research community. Conclusions Most of the Arabidopsis LRR-RLK genes have been isolated and the sequence analysis showed a number of alternatively spliced variants. The generated resources, including cDNA entry clones, expression constructs and transgenic plants, will facilitate further functional analysis of the members of this important gene family

Calcium/calmodulin inhibition of the Arabidopsis BRASSINOSTEROID-INSENSITIVE 1 receptor kinase provides a possible link between calcium and brassinosteroid signalling

The receptor kinase BRI1 (BRASSINOSTEROID-INSENSITIVE 1) is a key component in BR (brassinosteroid) perception and signal transduction, and has a broad impact on plant growth and development. In the present study, we demonstrate that Arabidopsis CaM (calmodulin) binds to the recombinant cytoplasmic domain of BRI1 in a Ca2+-dependent manner in vitro. In silico analysis predicted binding to Helix E of the BRI1 kinase subdomain VIa and a synthetic peptide based on this sequence interacted with Ca2+/CaM. Co-expression of CaM with the cytoplasmic domain of BRI1 in Escherichia coli strongly reduced autophosphorylation of BRI1, in particular on tyrosine residues, and also reduced the BRI1-mediated transphosphorylation of E. coli proteins on tyrosine, threonine and presumably serine residues. Several isoforms of CaM and CMLs (CaM-like proteins) were more effective (AtCaM6, AtCaM7 and AtCML8, where At is Arabidopsis thaliana) than others (AtCaM2, AtCaM4 and AtCML11) when co-expressed with BRI1 in E. coli. These results establish a novel assay for recombinant BRI1 transphosphorylation activity and collectively uncover a possible new link between Ca2+ and BR signalling

Methods and timing of biliary drainage for acute cholangitis: Tokyo Guidelines

Biliary drainage is a radical method to relieve cholestasis, a cause of acute cholangitis, and takes a central part in the treatment of acute cholangitis. Emergent drainage is essential for severe cases, whereas patients with moderate and mild disease should also receive drainage as soon as possible if they do not respond to conservative treatment, and their condition has not improved. Biliary drainage can be achieved via three different routes/procedures: endoscopic, percutaneous transhepatic, and open methods. The clinical value of both endoscopic and percutaneous transhepatic drainage is well known. Endoscopic drainage is associated with a low morbidity rate and shorter duration of hospitalization; therefore, this approach is advocated whenever it is applicable. In endoscopic drainage, either endoscopic nasobiliary drainage (ENBD) or tube stent placement can be used. There is no significant difference in the success rate, effectiveness, and morbidity between the two procedures. The decision to perform endoscopic sphincterotomy (EST) is made based on the patient’s condition and the number and diameter of common bile duct stones. Open drainage, on the other hand, should be applied only in patients for whom endoscopic or percutaneous transhepatic drainage is contraindicated or has not been successfully performed. Cholecystectomy is recommended in patients with gallbladder stones, following the resolution of acute cholangitis with medical treatment, unless the patient has poor operative risk factors or declines surgery

Genetic Evidence for an Indispensable Role of Somatic Embryogenesis Receptor Kinases in Brassinosteroid Signaling

The authors are grateful to the Arabidopsis Biological Resource Center for providing the T-DNA insertion lines discussed in this work. We thank Dr. Yanhai Yin (Iowa State University) for providing anti-BES1 antibody, Dr. Jiayang Li (Institute of Genetics and Developmental Biology, Chinese Academy of Sciences) for bri1-301 seeds, and Dr. Xing-wang Deng (Yale University) for cop1-4 and cop1-6 seeds as controls.Author Summary Brassinosteroids (BRs) are a group of plant hormones critical for plant growth and development. BRs are perceived by a cell-surface receptor complex including two distinctive receptor kinases, BRI1 and BAK1. Whereas BRI1 is a true BR-binding receptor, BAK1 does not appear to have BR-binding activity. Therefore, BAK1 is likely a co-receptor in BR signal transduction. The genetic significance of BAK1 was not clearly demonstrated in previous studies largely due to functional redundancy of BAK1 and its closely related homologues. It was not clear whether BAK1 plays an essential role or only an enhancing role in BR signaling. In this study, we identified all possible BAK1 redundant genes in the Arabidopsis thaliana genome and generated single, double, triple, and quadruple mutants. Detailed analysis indicated that, without BAK1 and its functionally redundant proteins, BR signaling is completely disrupted, largely because BRI1 has lost its ability to activate downstream components. These studies provide the first piece of loss-of-functional genetic evidence that BAK1 is indispensable to the early events of the BR signaling pathway.Yeshttp://www.plosgenetics.org/static/editorial#pee

Cell line-dependent variability in HIV activation employing DNMT inhibitors

Long-lived reservoirs of Human Immunodeficiency Virus (HIV) latently infected cells present the main barrier to a cure for HIV infection. Much interest has focused on identifying strategies to activate HIV, which would be used together with antiretrovirals to attack reservoirs. Several HIV activating agents, including Tumor Necrosis Factor alpha (TNFα) and other agents that activate via NF-kB are not fully effective in all latent infection models due to epigenetic restrictions, such as DNA methylation and the state of histone acetylation. DNA methyltransferases (DNMT) inhibitors like 5-aza-2'deoxycytidine (Aza-CdR) and histone deacetylase (HDAC) inhibitors like Trichostatin A (TSA) have been proposed as agents to enhance reactivation and have shown activity in model systems. However, it is not clear how the activities of DNMT and HDAC inhibitors range across different latently infected cell lines, potential models for the many different latently infected cells within an HIV patient. We determined HIV activation following treatment with TNFα, TSA and Aza-CdR across a range of well known latently infected cell lines. We assessed the activity of these compounds in four different Jurkat T cell-derived J-Lat cell lines (6.3, 8.4, 9.2 and 10.6), which have a latent HIV provirus in which GFP replaces Nef coding sequence, and ACH-2 and J1.1 (T cell-derived), and U1 (promonocyte-derived) cell lines with full-length provirus. We found that Aza-CdR plus TNFα activated HIV at least twice as well as TNFα alone for almost all J-Lat cells, as previously described, but not for J-Lat 10.6, in which TNFα plus Aza-CdR moderately decreased activation compared to TNFα alone. Surprisingly, a much greater reduction of TNFα-stimulated activation with Aza-CdR was detected for ACH-2, J1.1 and U1 cells. Reaching the highest reduction in U1 cells with a 75% reduction. Interestingly, Aza-CdR not only decreased TNFα induction of HIV expression in certain cell lines, but also decreased activation by TSA. Since DNMT inhibitors reduce the activity of provirus activators in some HIV latently infected cell lines the use of epigenetic modifying agents may need to be carefully optimized if they are to find clinical utility in therapies aimed at attacking latent HIV reservoirs