The Transposon-Encoded Protein TnpB Processes Its Own mRNA into ωRNA for Guided Nuclease Activity.

TnpB is a member of the Obligate Mobile Element Guided Activity (OMEGA) RNA-guided nuclease family, is harbored in transposons, and likely functions to maintain the transposon in genomes. Previously, it was shown that TnpB cleaves double- and single-stranded DNA substrates in an RNA-guided manner, but the biogenesis of the TnpB ribonucleoprotein (RNP) complex is unknown. Using in vitro purified apo TnpB, we demonstrate the ability of TnpB to generate guide omegaRNA (ωRNA) from its own mRNA through 5' processing. We also uncover a potential cis-regulatory mechanism whereby a region of the TnpB mRNA inhibits DNA cleavage by the RNP complex. We further expand the characterization of TnpB by examining ωRNA processing and RNA-guided nuclease activity in 59 orthologs spanning the natural diversity of the TnpB family. This work reveals a new functionality, ωRNA biogenesis, of TnpB, and characterizes additional members of this biotechnologically useful family of programmable enzymes.

Structure of the OMEGA nickase IsrB in complex with ωRNA and target DNA.

RNA-guided systems, such as CRISPR-Cas, combine programmable substrate recognition with enzymatic function, a combination that has been used advantageously to develop powerful molecular technologies1,2. Structural studies of these systems have illuminated how the RNA and protein jointly recognize and cleave their substrates, guiding rational engineering for further technology development3. Recent work identified a new class of RNA-guided systems, termed OMEGA, which include IscB, the likely ancestor of Cas9, and the nickase IsrB, a homologue of IscB lacking the HNH nuclease domain4. IsrB consists of only around 350 amino acids, but its small size is counterbalanced by a relatively large RNA guide (roughly 300-nt ωRNA). Here, we report the cryogenic-electron microscopy structure of Desulfovirgula thermocuniculi IsrB (DtIsrB) in complex with its cognate ωRNA and a target DNA. We find the overall structure of the IsrB protein shares a common scaffold with Cas9. In contrast to Cas9, however, which uses a recognition (REC) lobe to facilitate target selection, IsrB relies on its ωRNA, part of which forms an intricate ternary structure positioned analogously to REC. Structural analyses of IsrB and its ωRNA as well as comparisons to other RNA-guided systems highlight the functional interplay between protein and RNA, advancing our understanding of the biology and evolution of these diverse systems.

Crystal structure of Drosophila Piwi.

PIWI-clade Argonaute proteins associate with PIWI-interacting RNAs (piRNAs), and silence transposons in animal gonads. Here, we report the crystal structure of the Drosophila PIWI-clade Argonaute Piwi in complex with endogenous piRNAs, at 2.9 Å resolution. A structural comparison of Piwi with other Argonautes highlights the PIWI-specific structural features, such as the overall domain arrangement and metal-dependent piRNA recognition. Our structural and biochemical data reveal that, unlike other Argonautes including silkworm Siwi, Piwi has a non-canonical DVDK tetrad and lacks the RNA-guided RNA cleaving slicer activity. Furthermore, we find that the Piwi mutant with the canonical DEDH catalytic tetrad exhibits the slicer activity and readily dissociates from less complementary RNA targets after the slicer-mediated cleavage, suggesting that the slicer activity could compromise the Piwi-mediated co-transcriptional silencing. We thus propose that Piwi lost the slicer activity during evolution to serve as an RNA-guided RNA-binding platform, thereby ensuring faithful co-transcriptional silencing of transposons.

Structural basis for the promiscuous PAM recognition by Corynebacterium diphtheriae Cas9.

The RNA-guided DNA endonuclease Cas9 cleaves double-stranded DNA targets bearing a protospacer adjacent motif (PAM) and complementarity to an RNA guide. Unlike other Cas9 orthologs, Corynebacterium diphtheriae Cas9 (CdCas9) recognizes the promiscuous NNRHHHY PAM. However, the CdCas9-mediated PAM recognition mechanism remains unknown. Here, we report the crystal structure of CdCas9 in complex with the guide RNA and its target DNA at 2.9 Å resolution. The structure reveals that CdCas9 recognizes the NNRHHHY PAM via a combination of van der Waals interactions and base-specific hydrogen bonds. Moreover, we find that CdCas9 exhibits robust DNA cleavage activity with the optimal 22-nucleotide length guide RNAs. Our findings highlight the mechanistic diversity of the PAM recognition by Cas9 orthologs, and provide a basis for the further engineering of the CRISPR-Cas9 genome-editor nucleases.

Cap-specific terminal N 6-methylation of RNA by an RNA polymerase II-associated methyltransferase.

N 6-methyladenosine (m6A), a major modification of messenger RNAs (mRNAs), plays critical roles in RNA metabolism and function. In addition to the internal m6A, N 6, 2'-O-dimethyladenosine (m6Am) is present at the transcription start nucleotide of capped mRNAs in vertebrates. However, its biogenesis and functional role remain elusive. Using a reverse genetics approach, we identified PCIF1, a factor that interacts with the serine-5-phosphorylated carboxyl-terminal domain of RNA polymerase II, as a cap-specific adenosine methyltransferase (CAPAM) responsible for N 6-methylation of m6Am. The crystal structure of CAPAM in complex with substrates revealed the molecular basis of cap-specific m6A formation. A transcriptome-wide analysis revealed that N 6-methylation of m6Am promotes the translation of capped mRNAs. Thus, a cap-specific m6A writer promotes translation of mRNAs starting from m6Am.

Structural insights into cGAMP degradation by Ecto-nucleotide pyrophosphatase phosphodiesterase 1.

ENPP1 (Ecto-nucleotide pyrophosphatase phosphodiesterase 1), a type II transmembrane glycoprotein, hydrolyzes ATP to produce AMP and diphosphate, thereby inhibiting bone mineralization. A recent study showed that ENPP1 also preferentially hydrolyzes 2'3'-cGAMP (cyclic GMP-AMP) but not its linkage isomer 3'3'-cGAMP, and negatively regulates the cGAS-STING pathway in the innate immune system. Here, we present the high-resolution crystal structures of ENPP1 in complex with 3'3'-cGAMP and the reaction intermediate pA(3',5')pG. The structures revealed that the adenine and guanine bases of the dinucleotides are recognized by nucleotide- and guanine-pockets, respectively. Furthermore, the structures indicate that 2'3'-cGAMP, but not 3'3'-cGAMP, binds to the active site in a conformation suitable for catalysis, thereby explaining the specific degradation of 2'3'-cGAMP by ENPP1. Our findings provide insights into how ENPP1 hydrolyzes both ATP and cGAMP to participate in the two distinct biological processes.

Engineered CRISPR-Cas9 nuclease with expanded targeting space.

The RNA-guided endonuclease Cas9 cleaves its target DNA and is a powerful genome-editing tool. However, the widely used Streptococcus pyogenes Cas9 enzyme (SpCas9) requires an NGG protospacer adjacent motif (PAM) for target recognition, thereby restricting the targetable genomic loci. Here, we report a rationally engineered SpCas9 variant (SpCas9-NG) that can recognize relaxed NG PAMs. The crystal structure revealed that the loss of the base-specific interaction with the third nucleobase is compensated by newly introduced non-base-specific interactions, thereby enabling the NG PAM recognition. We showed that SpCas9-NG induces indels at endogenous target sites bearing NG PAMs in human cells. Furthermore, we found that the fusion of SpCas9-NG and the activation-induced cytidine deaminase (AID) mediates the C-to-T conversion at target sites with NG PAMs in human cells.

Use of endoscopic balloon dilation for benign esophageal stenosis in children: our 11 year experience.

Endoscopic balloon dilation (EBD) is an established therapy for esophageal stenosis. To assess its usefulness in children, we reviewed 11 years of pediatric cases of EBD in our hospital. Over the last 11 years, EBD was performed on 14 pediatric patients (10 boys and four girls; 7 months-11 years) at our hospital. All EBD sessions were performed under general anesthesia and fluoroscopic monitoring. The sessions were repeated every week or alternate weeks until resolution of dysphagia or development of smooth endoscope passage. Stenosis was resolved in 14 of 14 patients (100%). None of the patients (0%) showed recurrence of stenosis. As for postoperative complications, mediastinitis occurred only in one patient (7.1%). The median number of session repeats for an individual patient was three (range 1-10). EBD is a safe and effective therapeutic modality for esophageal stenosis in children.

[A Case of Pathologically Complete Response in Ruptured Hepatocellular Carcinoma Treated with Transcatheter Arterial Embolization].

We report a case of pathologicallycomplete response in ruptured hepatocellular carcinoma(HCC)treated with transcatheter arterial embolization(TAE). A 56-year-old man presented to our hospital with a hepatic tumor. Enhanced computed tomography(CT)revealed a tumor 65mm in diameter at S7/8 of the liver and the presence of abdominal fluid collection around the tumor. We diagnosed rupture of HCC and selective TAE was subsequentlyperformed. After TAE, the elevated PIVKA- / Ⅱ tumor marker level(1,008mAU/mL)decreased to the normal level. Three weeks after TAE, we performed right hepatectomy. The resected specimen revealed that the tumor consisted of necrotic tissue. Viable tumor cells were absent in this tumor. The pathological diagnosis was therefore HCC in which complete response was obtained with TAE.

Real-space and real-time dynamics of CRISPR-Cas9 visualized by high-speed atomic force microscopy.

The CRISPR-associated endonuclease Cas9 binds to a guide RNA and cleaves double-stranded DNA with a sequence complementary to the RNA guide. The Cas9-RNA system has been harnessed for numerous applications, such as genome editing. Here we use high-speed atomic force microscopy (HS-AFM) to visualize the real-space and real-time dynamics of CRISPR-Cas9 in action. HS-AFM movies indicate that, whereas apo-Cas9 adopts unexpected flexible conformations, Cas9-RNA forms a stable bilobed structure and interrogates target sites on the DNA by three-dimensional diffusion. These movies also provide real-time visualization of the Cas9-mediated DNA cleavage process. Notably, the Cas9 HNH nuclease domain fluctuates upon DNA binding, and subsequently adopts an active conformation, where the HNH active site is docked at the cleavage site in the target DNA. Collectively, our HS-AFM data extend our understanding of the action mechanism of CRISPR-Cas9.

Augmented O-GlcNAcylation of AMP-activated kinase promotes the proliferation of LoVo cells, a colon cancer cell line.

Increasing incidence of various cancers has been reported in diabetic patients. O-linked N-acetylglucosamine (O-GlcNAc) modification of proteins at serine/threonine residues (O-GlcNAcylation) is an essential post-translational modification that is upregulated in diabetic patients and has been implicated in tumor growth. However, the mechanisms by which O-GlcNAcylation promotes tumor growth remain unclear. Given that AMP-activated kinase (AMPK) has been thought to play important roles in suppressing tumor growth, we evaluated the involvement of AMPK O-GlcNAcylation on the growth of LoVo cells, a human colon cancer cell line. Results revealed that treatment with Thiamet G (TMG), an inhibitor of O-GlcNAc hydrolase, increased both anchorage-dependent and -independent growth of the cells. O-GlcNAc transferase overexpression also increased the growth. These treatments increased AMPK O-GlcNAcylation in a dose-dependent manner, which led to reduced AMPK phosphorylation and mTOR activation. Chemical inhibition or activation of AMPK led to increased or decreased growth, respectively, which was consistent with the data with genetic inhibition of AMPK. In addition, TMG-mediated acceleration of tumor growth was abolished by both chemical and genetic inhibition of AMPK. To examine the effects of AMPK O-GlcNAcylation in vivo, the LoVo cells were s.c. transplanted onto the backs of BALB/c-nu/nu mice. Injection of TMG promoted the growth and enhanced O-GlcNAcylation of the tumors of the mice. Consistent with in vitro data, AMPK O-GlcNAcylation was increased, which reduced AMPK phosphorylation and resulted in activation of mTOR. Collectively, the higher colon cancer risk of diabetic patients could be due to O-GlcNAcylation-mediated AMPK inactivation and subsequent activation of mTOR.

Applications of the CRISPR-Cas9 system in kidney research.

The recently discovered clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated protein 9 (Cas9) is an RNA-guided DNA nuclease, and has been harnessed for the development of simple, efficient, and relatively inexpensive technologies to precisely manipulate the genomic information in virtually all cell types and organisms. The CRIPSR-Cas9 systems have already been effectively used to disrupt multiple genes simultaneously, create conditional alleles, and generate reporter proteins, even in vivo. The ability of Cas9 to target a specific genomic region has also been exploited for various applications, such as transcriptional regulation, epigenetic control, and chromosome labeling. Here we first describe the molecular mechanism of the RNA-guided DNA targeting by the CRISPR-Cas9 system and then outline the current applications of this system as a genome-editing tool in mice and other species, to better model and study human diseases. We also discuss the practical and potential uses of the CRISPR-Cas9 system in kidney research and highlight the further applications of this technology beyond genome editing. Undoubtedly, the CRISPR-Cas9 system holds enormous potential for revolutionizing and accelerating kidney research and therapeutic applications in the future.

Structural Basis for the Altered PAM Specificities of Engineered CRISPR-Cas9.

The RNA-guided endonuclease Cas9 cleaves double-stranded DNA targets bearing a PAM (protospacer adjacent motif) and complementarity to the guide RNA. A recent study showed that, whereas wild-type Streptococcus pyogenes Cas9 (SpCas9) recognizes the 5'-NGG-3' PAM, the engineered VQR, EQR, and VRER SpCas9 variants recognize the 5'-NGA-3', 5'-NGAG-3', and 5'-NGCG-3' PAMs, respectively, thus expanding the targetable sequences in Cas9-mediated genome editing applications. Here, we present the high-resolution crystal structures of the three SpCas9 variants in complexes with a single-guide RNA and its altered PAM-containing, partially double-stranded DNA targets. A structural comparison of the three SpCas9 variants with wild-type SpCas9 revealed that the multiple mutations synergistically induce an unexpected displacement in the phosphodiester backbone of the PAM duplex, thereby allowing the SpCas9 variants to directly recognize the altered PAM nucleotides. Our findings explain the altered PAM specificities of the SpCas9 variants and establish a framework for further rational engineering of CRISPR-Cas9.

[A Case of Mucinous Adenocarcinoma of the Descending Colon with Extramural Progression].

A 63-year-old man was admitted to our hospital with a cough. Based on imaging studies, the patient was diagnosed with locally advanced descending colon cancer with extensive infiltration into peripheral organs by extramural progression. There was no distant metastasis. Therefore, he received left hemicolectomy with splenectomy, partial gastrectomy, and partial diaphragm resection. Histopathological examination showed a mucinous adenocarcinoma, pT4b, pN1, cM0, fStage III A. We report a rare case of extramural progression colon cancer with invasion of various organs and review 12 previous case reports.

Significance of liver biopsy for the evaluation of methotrexate-induced liver damage in patients with rheumatoid arthritis.

It is well recognized that long-term administration of methotrexate (MTX) in patients with rheumatoid arthritis (RA) can induce liver fibrosis via a steatohepatitis-like inflammatory process. Several non-invasive tests have been investigated as alternatives to liver biopsy, which is, however, still recognized as a final diagnostic modality to detect the MTX-induced liver damage. To clarify whether there is a significant discrepancy between clinical estimations and pathologic findings of this hepatic condition, we performed a following comparative study. Four RA patients (4 women, age 67-80 yr) with MTX-induced liver damage were reviewed. The severity of hepatic damage estimated clinically was compared with histopathologic findings. Consequently, the liver biopsies showed the relatively earlier stages of and milder degrees of hepatic damages than the clinical estimations. The histopathologic findings were more reliable and useful than any other clinical examinations, to plan and modify the treatment strategies, especially in cases of liver damages with multiple etiologies besides MTX. These findings suggest that liver biopsy is an unavoidable examination to assess precisely MTX-induced liver damage. Non-invasive tests may be useful to monitor the hepatic condition of RA patients receiving MTX but do not constitute an acceptable alternative to liver biopsy.

Structural Basis for the Catalytic Mechanism of DncV, Bacterial Homolog of Cyclic GMP-AMP Synthase.

Cyclic dinucleotides (CDNs) play key roles as second messengers and signaling molecules in bacteria and metazoans. The newly identified dinucleotide cyclase in Vibrio cholerae (DncV) produces three different CDNs containing two 3'-5' phosphodiester bonds, and its predominant product is cyclic GMP-AMP, whereas mammalian cyclic GMP-AMP synthase (cGAS) produces only cyclic GMP-AMP containing mixed 2'-5' phosphodiester bonds. We report the crystal structures of V. cholerae and Escherichia coli DncV in complex with various nucleotides in the pre-reaction states. The high-resolution structures revealed that DncV preferably recognizes ATP and GTP as acceptor and donor nucleotides, respectively, in the first nucleotidyl transfer reaction. Considering the recently reported intermediate structures, our pre-reaction state structures provide the precise mechanism of 3'-5' linked cyclic AMP-GMP production in bacteria. A comparison with cGAS in the pre-reaction states suggests that the orientation of the acceptor nucleotide primarily determines the distinct linkage specificities between DncV and cGAS.

[A case of multiple skin metastases from cancer of the descending colon responding to FOLFIRI/cetuximab therapy].

A 64-year-old woman presented to our hospital with subcutaneous tumors in the right thoracic region. After undergoing a thorough medical evaluation, she was diagnosed with multiple skin metastases arising from cancer of the descending colon. Surgical resection of the primary lesion was performed and FOLFIRI (5-fluorouracil, levofolinate calcium, irinotecan) and cetuximab chemotherapy for the metastases was initiated. The patient subsequently entered remission and did not experience any major side effects. This case report details an effective therapy for colon cancer with multiple skin metastases and presents a discussion of the expression profiles of epidermal growth factor receptor in both the primary and metastatic lesions.

Low-dose aspirin-induced gastroduodenal mucosal injury in Japanese patients with arteriosclerotic disease.

BACKGROUND: We aimed to elucidate the risk factors and preventive factors associated with chronic low-dose aspirin (L-ASA)-induced gastroduodenal mucosal injury in Japanese patients with arteriosclerotic disease. METHODS: This retrospective observational study included 400 L-ASA users who underwent upper gastrointestinal endoscopy. We investigated patients' clinical characteristics, including age, peptic ulcer history, concomitant drugs [i.e. gastric agents, antiplatelet drugs, anticoagulants, non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids], abdominal symptoms, endoscopic findings, and interruption of L-ASA before endoscopy. The severity of gastroduodenal mucosal lesions was evaluated using the modified LANZA score (MLS). RESULTS: Of 400 patients, 249 (62%) and 41 (10%) had gastroduodenal mucosal lesions (MLS ≥1) and gastroduodenal ulcers, respectively. Peptic ulcer history, abdominal symptoms, proton pump inhibitor (PPI), histamine type 2-receptor antagonists (H2RA), and the cessation of L-ASA before endoscopy were significantly associated with L-ASA-induced gastroduodenal ulcers; the odds ratio (OR) (confidence interval (CI)) was 5.49 (1.82-16.55), 4.56 (1.93-10.75), 0.12 (0.03-0.42), 0.13 (0.04-0.40) and 0.11 (0.04-0.29), respectively. Moreover, patients having two or more of five factors [i.e. advanced age (≥75), anticoagulants, antiplatelet drugs, NSAIDs and corticosteroids] had a significantly higher prevalence of L-ASA-induced gastroduodenal ulcers [OR (CI): 2.39 (1.002-5.69)]. CONCLUSION: Peptic ulcer history, abdominal symptoms and the summation of risk factors increased the risk for L-ASA-induced gastroduodenal ulcers. H2RAs and PPIs were effective for the prevention of L-ASA-induced gastroduodenal ulcers. The cessation of L-ASA before endoscopy might lead to the underestimation of L-ASA-induced gastroduodenal injury.