NF-kappaB is a core transcription factor, the activation of which can lead to hypoxic-ischemic brain damage (HIBD), while RCAN1 plays a protective role in HIBD. However, the relationship between NF-kappaB and RCAN1 in HIBD remains unclear. This study aimed to explore the mechanism of NF-kappaB signaling pathway in hippocampal neuron apoptosis and cognitive impairment of neonatal rats with HIBD in relation to RCAN1. Initially, microarray analysis was used to determine the differentially expressed genes related to HIBD. After the establishment of HIBD rat models, gain- or loss-of-function assay was performed to explore the functional role of NF-kappaB signaling pathway in HIBD. Then, the learning and memory ability of rats was evaluated. Expression of RCAN1, NF-kappaB signaling pathway-related genes and glial fibrillary acidic protein (GFAP), S-100beta and acetylcholine (Ach) level, and acetylcholinesterase (AchE) activity were determined with neuron apoptosis detected to further explore the function of NF-kappaB signaling pathway. RCAN1 could influence the development of HIBD. In the HIBD model, the expression of RCAN1 and NF-kappaB-related genes increased, and NF-kappaB p65 showed a significant nuclear shift. By activation of NF-kappaB or overexpression of RCAN1, the number of neuronal apoptosis, S-100beta protein level, and AchE level increased significantly, Ach activity decreased significantly, and GFAP positive cells increased. In addition, after the activation of NF-kappaB or overexpression of RCAN1, the learning and memory ability of HIBD rats was inhibited. All the results show that activation of NF-kappaB signaling pathway promotes RCAN1 expression, thus increasing neuronal apoptosis and aggravating cognitive impairment in HIBD rats.
Title: Thiolation Protein-Based Transfer of Indolyl to a Ribosomally Synthesized Polythiazolyl Peptide Intermediate during the Biosynthesis of the Side-Ring System of Nosiheptide Qiu Y, Du Y, Zhang F, Liao R, Zhou S, Peng C, Guo Y, Liu W Ref: Journal of the American Chemical Society, 139:18186, 2017 : PubMed
Nosiheptide, a potent bicyclic member of the family of thiopeptide antibiotics, possesses a distinctive l-Trp-derived indolyl moiety. The way in which this moiety is incorporated into a ribosomally synthesized and post-translationally modified thiopeptide remains poorly understood. Here, we report that NosK, an alpha/beta-hydrolase fold protein, mediates the transfer of indolyl from NosJ, a discrete thiolation protein, to a linear pentathiazolyl peptide intermediate rather than its genetically encoded untreated precursor. This intermediate results from enzymatic processing of the peptide precursor, in which five of the six l-Cys residues are transformed into thiazoles but Cys4 selectively remains unmodified for indolyl substitution via a thioester exchange. Determining the timing of indolyl incorporation, which expands the chemical space of a thiopeptide framework, facilitates mechanistic access to the unusual logic of post-translational modifications in the biosynthesis of nosiheptide-type thiopeptide members that share a similar compact side-ring system.
Monoacylglycerol lipase (MAGL) is a key enzyme in lipid metabolism that is demonstrated to be involved in tumor progression through both energy supply of fatty acid (FA) oxidation and enhancing cancer cell malignance. The aim of this study was to investigate whether MAGL could be a potential therapeutic target and prognostic indicator for hepatocellular carcinoma (HCC). To evaluate the relationship between MAGL levels and clinical characteristics, a tissue microarray (TMA) of 353 human HCC samples was performed. MAGL levels in HCC samples were closely linked to the degree of malignancy and patient prognosis. RNA interference, specific pharmacological inhibitor JZL-184 and gene knock-in of MAGL were utilized to investigate the effects of MAGL on HCC cell proliferation, apoptosis, and invasion. MAGL played important roles in both proliferation and invasion of HCC cells through mechanisms that involved prostaglandin E2 (PGE2) and lysophosphatidic acid (LPA). JZL-184 administration significantly inhibited tumor growth in mice. Furthermore, we confirmed that promoter methylation of large tumor suppressor kinase 1 (LATS1) resulted in dysfunction of the Hippo signal pathway, which induced overexpression of MAGL in HCC. These results indicate that MAGL could be a potentially novel therapeutic target and prognostic indicator for HCC.
Title: An alpha/beta-hydrolase fold protein in the biosynthesis of thiostrepton exhibits a dual activity for endopeptidyl hydrolysis and epoxide ring opening/macrocyclization Zheng Q, Wang S, Duan P, Liao R, Chen D, Liu W Ref: Proc Natl Acad Sci U S A, 113:14318, 2016 : PubMed
Thiostrepton (TSR), an archetypal bimacrocyclic thiopeptide antibiotic that arises from complex posttranslational modifications of a genetically encoded precursor peptide, possesses a quinaldic acid (QA) moiety within the side-ring system of a thiopeptide-characteristic framework. Focusing on selective engineering of the QA moiety, i.e., by fluorination or methylation, we have recently designed and biosynthesized biologically more active TSR analogs. Using these analogs as chemical probes, we uncovered an unusual indirect mechanism of TSR-type thiopeptides, which are able to act against intracellular pathogens through host autophagy induction in addition to direct targeting of bacterial ribosome. Herein, we report the accumulation of 6'-fluoro-7', 8'-epoxy-TSR, a key intermediate in the preparation of the analog 6'-fluoro-TSR. This unexpected finding led to unveiling of the TSR maturation process, which involves an unusual dual activity of TsrI, an alpha/beta-hydrolase fold protein, for cascade C-N bond cleavage and formation during side-ring system construction. These two functions of TsrI rely on the same catalytic triad, Ser72-His200-Asp191, which first mediates endopeptidyl hydrolysis that occurs selectively between the residues Met-1 and Ile1 for removal of the leader peptide and then triggers epoxide ring opening for closure of the QA-containing side-ring system in a regio- and stereo-specific manner. The former reaction likely requires the formation of an acyl-Ser72 enzyme intermediate; in contrast, the latter is independent of Ser72. Consequently, C-6' fluorination of QA lowers the reactivity of the epoxide intermediate and, thereby, allows the dissection of the TsrI-associated enzymatic process that proceeds rapidly and typically is difficult to be realized during TSR biosynthesis.
Title: Thiostrepton maturation involving a deesterification-amidation way to process the C-terminally methylated Peptide backbone Liao R, Liu W Ref: J Am Chem Soc, 133:2852, 2011 : PubMed
Thiopeptides are a class of clinically interesting and highly modified peptide antibiotics. Their biosyntheses share a common paradigm for characteristic core formation but differ in tailoring to afford individual members. Herein we report an unusual deesterification-amidation process in thiostrepton maturation to furnish the terminal amide moiety. TsrB, serving as a carboxylesterase, catalyzes the hydrolysis of the methyl ester intermediate to provide the carboxylate intermediate, which can be converted to the amide product by an amidotransferase, TsrC. These findings revealed a C-terminal methylation of the precursor peptide, which is cryptic in thiostrepton biosynthesis but potentially common in the formation of its homologous series of thiopeptides that vary in the C-terminal form as methyl ester, carboxylate, or amide.
Title: Thiopeptide biosynthesis featuring ribosomally synthesized precursor peptides and conserved posttranslational modifications Liao R, Duan L, Lei C, Pan H, Ding Y, Zhang Q, Chen D, Shen B, Yu Y, Liu W Ref: Chemical Biology, 16:141, 2009 : PubMed
Thiopeptides, with potent activity against various drug-resistant pathogens, contain a characteristic macrocyclic core consisting of multiple thiazoles, dehydroamino acids, and a 6-membered nitrogen heterocycle. Their biosynthetic pathways remain elusive, in spite of great efforts by in vivo feeding experiments. Here, cloning, sequencing, and characterization of the thiostrepton and siomycin A gene clusters unveiled a biosynthetic paradigm for the thiopeptide specific core formation, featuring ribosomally synthesized precursor peptides and conserved posttranslational modifications. The paradigm generality for thiopeptide biosynthesis was supported by genome mining and ultimate confirmation of the thiocillin I production in Bacillus cereus ATCC 14579, a strain that was previously unknown as a thiopeptide producer. These findings set the stage to accelerate the discovery of thiopeptides by prediction at the genetic level and to generate structural diversity by applying combinatorial biosynthesis methods.
Nosiheptide (NOS), belonging to the e series of thiopeptide antibiotics that exhibit potent activity against various bacterial pathogens, bears a unique indole side ring system and regiospecific hydroxyl groups on the characteristic macrocyclic core. Here, cloning, sequencing, and characterization of the nos gene cluster from Streptomyces actuosus ATCC 25421 as a model for this series of thiopeptides has unveiled new insights into their biosynthesis. Bioinformatics-based sequence analysis and in vivo investigation into the gene functions show that NOS biosynthesis shares a common strategy with recently characterized b or c series thiopeptides for forming the characteristic macrocyclic core, which features a ribosomally synthesized precursor peptide with conserved posttranslational modifications. However, it apparently proceeds via a different route for tailoring the thiopeptide framework, allowing the final product to exhibit the distinct structural characteristics of e series thiopeptides, such as the indole side ring system. Chemical complementation supports the notion that the S-adenosylmethionine-dependent protein NosL may play a central role in converting tryptophan to the key 3-methylindole moiety by an unusual carbon side chain rearrangement, most likely via a radical-initiated mechanism. Characterization of the indole side ring-opened analogue of NOS from the nosN mutant strain is consistent with the proposed methyltransferase activity of its encoded protein, shedding light into the timing of the individual steps for indole side ring biosynthesis. These results also suggest the feasibility of engineering novel thiopeptides for drug discovery by manipulating the NOS biosynthetic machinery.
