Structural basis of semaphorin-plexin recognition and viral mimicry from Sema7A and A39R complexes with PlexinC1.

Repulsive signaling by Semaphorins and Plexins is crucial for the development and homeostasis of the nervous, immune, and cardiovascular systems. Sema7A acts as both an immune and a neural Semaphorin through PlexinC1, and A39R is a Sema7A mimic secreted by smallpox virus. We report the structures of Sema7A and A39R complexed with the Semaphorin-binding module of PlexinC1. Both structures show two PlexinC1 molecules symmetrically bridged by Semaphorin dimers, in which the Semaphorin and PlexinC1 beta propellers interact in an edge-on, orthogonal orientation. Both binding interfaces are dominated by the insertion of the Semaphorin's 4c-4d loop into a deep groove in blade 3 of the PlexinC1 propeller. A39R appears to achieve Sema7A mimicry by preserving key Plexin-binding determinants seen in the mammalian Sema7A complex that have evolved to achieve higher affinity binding to the host-derived PlexinC1. The complex structures support a conserved Semaphorin-Plexin recognition mode and suggest that Plexins are activated by dimerization.

Transient CSF1R inhibition ameliorates behavioral deficits in Cntnap2 knockout and valproic acid-exposed mouse models of autism.

Microglial abnormality and heterogeneity are observed in autism spectrum disorder (ASD) patients and animal models of ASD. Microglial depletion by colony stimulating factor 1-receptor (CSF1R) inhibition has been proved to improve autism-like behaviors in maternal immune activation mouse offspring. However, it is unclear whether CSF1R inhibition has extensive effectiveness and pharmacological heterogeneity in treating autism models caused by genetic and environmental risk factors. Here, we report pharmacological functions and cellular mechanisms of PLX5622, a small-molecule CSF1R inhibitor, in treating Cntnap2 knockout and valproic acid (VPA)-exposed autism model mice. For the Cntnap2 knockout mice, PLX5622 can improve their social ability and reciprocal social behavior, slow down their hyperactivity in open field and repetitive grooming behavior, and enhance their nesting ability. For the VPA model mice, PLX5622 can enhance their social ability and social novelty, and alleviate their anxiety behavior, repetitive and stereotyped autism-like behaviors such as grooming and marble burying. At the cellular level, PLX5622 restores the morphology and/or number of microglia in the somatosensory cortex, striatum, and hippocampal CA1 regions of the two models. Specially, PLX5622 corrects neurophysiological abnormalities in the striatum of the Cntnap2 knockout mice, and in the somatosensory cortex, striatum, and hippocampal CA1 regions of the VPA model mice. Incidentally, microglial dynamic changes in the VPA model mice are also reported. Our study demonstrates that microglial depletion and repopulation by transient CSF1R inhibition is effective, and however, has differential pharmacological functions and cellular mechanisms in rescuing behavioral deficits in the two autism models.

KIT mutations and expression: current knowledge and new insights for overcoming IM resistance in GIST.

Gastrointestinal stromal tumor (GIST) is the most common sarcoma located in gastrointestinal tract and derived from the interstitial cell of Cajal (ICC) lineage. Both ICC and GIST cells highly rely on KIT signal pathway. Clinically, about 80-90% of treatment-naive GIST patients harbor primary KIT mutations, and special KIT-targeted TKI, imatinib (IM) showing dramatic efficacy but resistance invariably occur, 90% of them was due to the second resistance mutations emerging within the KIT gene. Although there are multiple variants of KIT mutant which did not show complete uniform biologic characteristics, most of them have high KIT expression level. Notably, the high expression level of KIT gene is not correlated to its gene amplification. Recently, accumulating evidences strongly indicated that the gene coding, epigenetic regulation, and pre- or post- protein translation of KIT mutants in GIST were quite different from that of wild type (WT) KIT. In this review, we elucidate the biologic mechanism of KIT variants and update the underlying mechanism of the expression of KIT gene, which are exclusively regulated in GIST, providing a promising yet evidence-based therapeutic landscape and possible target for the conquer of IM resistance. Video Abstract.

Down-regulation of SLC35C1 induces colon cancer through over-activating Wnt pathway.

The canonical Wnt signalling pathway is a critical pathway involved in the proliferation of cells. It has been well-established that it plays the central role during colorectal carcinogenesis and development. Yet the exact molecular mechanism of how the canonical Wnt pathway is fine-tuned remains elusive. We found that SLC35C1, a GDP-fucose transporter, negatively regulates the Wnt signalling pathway. We show here that SLC35C1 is reduced in all colon cancer by both immunohistochemistry images and TCGA data, whereas ß-catenin is increased. Down-regulation of SLC35C1 is also detected by real-time PCR in stage 3 and stage 4 colorectal cancer tissues. Moreover, analysing the TCGA database with cBioPortal reveals the negative correlation of SLC35C1 mRNA level to the expression of ß-catenin. Reduced SLC35C1 significantly promotes cell proliferation and colony formation of HEK293 cells. Meanwhile, in HEK293 cells silencing SLC35C1 activates canonical Wnt pathway, whereas overexpressing SLC35C1 inhibits it. Consistently, the reduction of SLC35C1 in HEK293 cells also elevated the mRNA level of Wnt target genes C-myc, Axin2 and Cyclin D1, as well as the secretion of Wnt3a. In conclusion, we identified SLC35C1 as a negative regulator of the Wnt signalling pathway in colon cancer. Decreased SLC35C1 may cause over-activation of Wnt signalling in colorectal cancer.

Preoperative adjuvant therapy for locally advanced and recurrent/metastatic gastrointestinal stromal tumors: a retrospective study.

BACKGROUND: Preoperative imatinib mesylate therapy for gastrointestinal stromal tumors (GISTs) is controversial. This study aimed to explore the clinical efficacy and optimal duration of preoperative imatinib mesylate (IM) therapy in patients with locally advanced and recurrent/metastatic GISTs. METHODS: We retrospectively examined patients who received preoperative imatinib mesylate therapy from January 2013 to December 2018 at Xiangya Hospital, Central South University and the Second Xiangya Hospital of Central South University, China. Clinical data, including the results of tests for mutations in KIT and PDGFR, findings from regularly conducted re-examinations, abdominal-enhanced computed tomography/magnetic resonance imaging data, responses to imatinib, progression-free survival, and overall cancer-specific survival, were recorded. RESULTS: A total of 25 patients were enrolled in our study, including 18 with a locally advanced GIST and 7 with recurrent or metastatic GISTs. Their ages ranged from 22 to 70 years (M:F = 1.6:0.9), with a mean age of 50.48 ± 12.51 years. The tumor locations included the stomach (56.0%), rectum (16.0%), enterocoelic/retroperitoneal sites (12.0%), and the small intestine (12.0%). Based on testing for mutations in KIT and PDGFR, 22 patients received 400 mg/day KIT, and 3 patients received 600 mg/day PDGFR. The median duration of preoperative IM therapy was 8.96 ± 4.81 months, ranging from 3 to 26 months. According to the Choi criteria, 24 patients achieved a partial response (PR), and 1 patient had stable disease (SD). All patients underwent surgery after preoperative IM therapy, and no postoperative complications appeared. The 2-year PFS and 5-year PFS were 92% and 60%, respectively, and the total 5-year cancer-specific survival (CSS) was 92%. CONCLUSION: Preoperative imatinib therapy is feasible for locally advanced and recurrent/metastatic GISTs and can effectively shrink the tumor size, allow organ sparing, and avoid extensive organ resection. Moreover, the optimal duration of preoperative IM therapy in patients with locally advanced and recurrent/metastatic GISTs was 8.96 ± 4.81 months, ranging from 3 to 26 months, and gastric GISTs had a better response to preoperative IM therapy than did non-gastric GISTs.

Status and progress in the treatment for locally resectable progressive gastric cancer and metastatic gastric cancer. / 可切除的局部进展期胃癌及转移性胃癌治疗现状及进展.

For resectable gastric cancer, although radical surgery is still the main treatment, methods of operation and the curative effect of operation are still in the stage of exploration for metastatic gastric cancer. Radiotherapy, chemotherapy and molecular targeted therapy also play an important role in prolonging the survival period of patients with gastric cancer. Postoperative radiotherapy and chemotherapy can prolong the survival time, but for patients with locally advanced gastric cancer, the preoperative radiotherapy and chemotherapy can also further improve the survival period of patients compared with direct operation. In addition, with the development and using of molecular targeted drugs, such as antiangiogenic agents, immunosuppressive drugs and so on, the survival period of patients with gastric cancer has been further extended.

Matrix stiffness mediates stemness characteristics via activating the Yes-associated protein in colorectal cancer cells.

Matrix stiffness is an essential physical microenvironment in solid cancer. However, its influence on cancer stemness still remains elusive. Colorectal cancer (CRC) cell line HCT-116 was cultured in the matrix with various stiffness. The siYAP was applied to detect the changes of stemness markers. The cancer stemness markers, Yes-associated protein (YAP), Lamin A/C and downstream protein molecules, and their activation were measured after the treatment with anti-ß1-integrin and FAK inhibitors. In CRC tissue samples, collagen deposition and the expression of α-SMA and CD133 were detected. The study found that the expression level of stemness markers and Lamin A/C increased as the matrix stiffness raised and was regulated by YAP activation in CRC stem cells. Inhibition of ß1-integrin and FAK activation in a high stiffness cell culture medium significantly decreased the activation of YAP, PI3K, and AKT. Collagen was highly deposited in the CRC invasive tumor front (ITF), and the expression of CD133 was higher in ITF compared with normal tissue and the tumor cells. Moreover, the expression level of α-SMA was positively correlated with CD133 expression level. Together, our results suggest that activation of YAP in CRC plays an important role in the promotion of cancer stem cell properties by extracellular matrix stiffness in CRC.

Structural mapping of hot spots within human CASPR2 discoidin domain for autoantibody recognition.

Accumulating evidence has showed that anti-CASPR2 autoantibodies occur in a long list of neurological immune disorders including limbic encephalitis (LE). Belonging to the well-known neurexin superfamily, CASPR2 has been suggested to be a central node in the molecular networks controlling neurodevelopment. Distinct from other subfamilies in the neurexin superfamily, the CASPR subfamily features a unique discoidin (Disc) domain. As revealed by our and others' recent studies, CASPR2 Disc domain bears a major epitope for autoantibodies. However, structural information on CASPR2 recognition by autoantibodies has been lacking. Here, we report the crystal structure of human CASPR2 Disc domain at a high resolution of 1.31 Å, which is the first atomic-resolution structure of the CASPR subfamily members. The Disc domain adopts a total ß structure and folds into a distorted jellyroll-like barrel with a conserved disulfide-bond interlocking its N- and C-termini. Defined by four loops and located in one end of the barrel, the "loop-tip surface" is totally polar and easily available for protein docking. Based on structure-guided epitope prediction, we generated nine mutants and evaluated their binding to autoantibodies of cerebrospinal fluid from twelve patients with limbic encephalitis. The quadruple mutant G69N/A71S/S77N/D78R impaired CASPR2 binding to autoantibodies from eleven LE patients, which indicates that the loop L1 in the Disc domain bears hot spots for autoantibody interaction. Structural mapping of autoepitopes within human CASPR2 Disc domain sheds light on how autoantibodies could sequester CASPR2 ectodomain and antagonize its functionalities in the pathogenic processes.

What are the reasons for a longer operation time in robotic gastrectomy than in laparoscopic gastrectomy for stomach cancer?

BACKGROUND: Many studies have shown that robotic gastrectomy requires a longer operation time than laparoscopic gastrectomy. However, no study has analyzed the exact reason for this difference in detail. We therefore investigated the reasons why more time is needed in robotic gastrectomy. METHODS: Ten consecutive cases of robotic distal gastrectomy (RDG) performed in our institution were selected to measure the operation time in detail. Ten cases of laparoscopic distal gastrectomy (LDG) performed during the same period were chosen for comparison. The operation videos and electronic medical records of these 20 patients were retrospectively reviewed. The overall operation time, operation time in each step, and time required for instrument changes were measured. The number of intraoperative instrument changes and camera cleanings were also counted. RESULTS: The overall operation time (including effective time and junk time) was 56.8 min longer for RDG than LDG (273.7 vs. 216.9 min, respectively; p = 0.000). The effective time was only 15.3 min longer for RDG than LDG (145.9 vs. 130.6 min, respectively; p = 0.094). The time needed for the six technical steps was also not significantly different between the two groups. However, the junk time (instrument setup and docking or positioning of surgical arms) was 41.5 min longer for RDG than LDG (127.8 vs. 86.2 min, respectively; p = 0.001). The number of instrument changes was not different between RDG and LDG (p = 0.277), but the time required for each was longer for RDG than LDG (p = 0.000). The number of camera cleanings was lower for RDG than LDG (10.7 vs. 15.5 times, respectively; p = 0.005). CONCLUSIONS: To reduce the operation time in RDG, a smarter and simpler system for setup should be developed to reduce the junk time. Additionally, a system for swifter instrument changes and more sophisticated energy devices are warranted to reduce the effective time.

The crystal structure of full-length Sizzled from Xenopus laevis yields insights into Wnt-antagonistic function of secreted Frizzled-related proteins.

The Wnt-signaling pathway is crucial to cell proliferation, differentiation, and migration. The secreted Frizzled-related proteins (sFRPs) represent the largest family of secreted Wnt inhibitors. However, their function in antagonizing Wnt signaling has remained somewhat controversial. Here, we report the crystal structure of Sizzled from Xenopus laevis, the first full-length structure of an sFRP. Tethered by an inter-domain disulfide bond and a linker, the N-terminal cysteine-rich domain (CRD) and the C-terminal netrin-like domain (NTR) of Sizzled are arranged in a tandem fashion, with the NTR domain occluding the groove of CRD for Wnt accessibility. A Dual-Luciferase assay demonstrated that removing the NTR domain and replacing the CRD groove residues His-116 and His-118 with aromatic residues may significantly enhance antagonistic function of Sizzled in inhibiting Wnt3A signaling. Sizzled is a monomer in solution, and Sizzled CRD exhibited different packing in the crystal, suggesting that sFRPs do not have a conserved CRD dimerization mode. Distinct from the canonical NTR domain, the Sizzled NTR adopts a novel α/ß folding with two perpendicular helices facing the central mixed ß-sheet. The subgroup of human sFRP1/2/5 and Sizzled should have a similar NTR domain that features a highly positively charged region, opposite the NTR-CRD interface, suggesting that the NTR domain in human sFRPs, at least sFRP1/2/5, is unlikely to bind to Wnt but is likely involved in biphasic Wnt signaling modulation. In summary, the Sizzled structure provides the first insights into how the CRD and the NTR domains relate to each other for modulating Wnt-antagonistic function of sFRPs.

[Expression of regulatory factor R-spondin family in Wnt signaling pathway in colorectal cancer and its clinical significance].

OBJECTIVE: To explore the expression of R-spondin family in colorectal cancer tissues and adjacent tissues, and to evaluate its relationship with clinic-pathological stage.
 Methods: A total of 64 samples of colorectal cancer tissues and adjacent tissues were collected from the patients, who received radical surgery in Xiangya Hospital, Central South University between January 2014 and August 2014. The mRNA and protein expression levels of R-spondin 1-4 and ß-catenin in the colorectal cancer tissues and adjacent tissues were detected by qRT-PCR and immunohistochemistry. The relationship between the expression level of R-spondin 1-4 and the clinic-pathological factors were analyzed to explore the correlation between the expression level of R-spondin 1-4 and ß-catenin in colorectal cancer.
 Results: Compared with the adjacent tissues, the mRNA and protein expression levels of R-spondin 1 were elevated in the colorectal cancer tissues (P<0.05). The mRNA and protein expression levels of R-spondin 2-4 were increased in the colorectal cancer tissues than those in the normal tissues (P<0.05), but there was no significant difference between the colorectal cancer tissues and adjacent tissues (P>0.05). The expression level of R-spondin 1 was positively correlated with the nuclear expression of ß-catenin in the colorectal cancer tissues (r=0.6307, P<0.05).
 Conclusion: Compared with the adjacent tissues, the mRNA and protein expression levels of R-spondin 1 are significantly elevated in the colorectal cancer tissues. R-spondin 1 may play a role in promoting carcinogenesis by regulating the activity of ß-catenin in the downstream of Wnt signaling pathway.

[Diagnostic analysis for 52 cases of gastrointestinal neuroendocrine tumor].

OBJECTIVE: To investigate the clinical features, diagnosis, treatments and prognosis for gastrointestinal neuroendocrine tumors (GI-NETs).
 METHODS: Clincal data of 52 patients, who were diagnosed as GI-NETs between January 2004 and October 2014, were reviewed. The patients were divided into a local excision group (n=21) and a transabdominal excision group (n=30), and the major clinical features, treatment modalities and outcomes were analyzed.
 RESULTS: The clinical features of GI-NETs were nonspecific, and most of the clinical manifestation were local invasiveness. CT scan was lack of specific findings. GI-NETs greater than 1 cm often showed local incrassation, upheaval and soft tissue shadow. In the case of lager GI-NETs, necrosis and moderate enhancement could be seen. Positive ratio for expression of chromogranin A (CgA) and synaptophysin (Syn) in the 52 cases of specimen were 63.5% and 88.5%, respectively. Except 1 patient, whose surgery was canceled because of poor health, other 51 patients were treated with surgery through different approaches. Among them, 30 cases were transabdominal resection (57.7%) and 21 were local resection (40.4%). Chemotherapy and/or radiotherapy was only applied for 7 patients. After a follow-up of 40 (3-132) months, 7 patients died, the rest were alive. The median survival in the local resection group and the transabdominal resection group was 43.0 and 39.5 months, respectively (P>0.05).
 CONCLUSION: Under the condition of fully understanding the biological characteristics of GI-NETs, early diagnosis and timely personalized treatment is hopeful to reach the relative good prognosis and survival.

Evidence for Follicle-stimulating Hormone Receptor as a Functional Trimer.

Follicle-stimulating hormone receptor (FSHR), a G-protein coupled receptor, is an important drug target in the development of novel therapeutics for reproductive indications. The FSHR extracellular domains were observed in the crystal structure as a trimer, which enabled us to propose a novel model for the receptor activation mechanism. The model predicts that FSHR binds Asnα(52)-deglycosylated FSH at a 3-fold higher capacity than fully glycosylated FSH. It also predicts that, upon dissociation of the FSHR trimer into monomers, the binding of glycosylated FSH, but not deglycosylated FSH, would increase 3-fold, and that the dissociated monomers would in turn enhance FSHR binding and signaling activities by 3-fold. This study presents evidence confirming these predictions and provides crystallographic and mutagenesis data supporting the proposed model. The model also provides a mechanistic explanation to the agonist and antagonist activities of thyroid-stimulating hormone receptor autoantibodies. We conclude that FSHR exists as a functional trimer.

Structure of follicle-stimulating hormone in complex with the entire ectodomain of its receptor.

FSH, a glycoprotein hormone, and the FSH receptor (FSHR), a G protein-coupled receptor, play central roles in human reproduction. We report the crystal structure of FSH in complex with the entire extracellular domain of FSHR (FSHR(ED)), including the enigmatic hinge region that is responsible for signal specificity. Surprisingly, the hinge region does not form a separate structural unit as widely anticipated but is part of the integral structure of FSHR(ED). In addition to the known hormone-binding site, FSHR(ED) provides interaction sites with the hormone: a sulfotyrosine (sTyr) site in the hinge region consistent with previous studies and a potential exosite resulting from putative receptor trimerization. Our structure, in comparison to others, suggests FSHR interacts with its ligand in two steps: ligand recruitment followed by sTyr recognition. FSH first binds to the high-affinity hormone-binding subdomain of FSHR and reshapes the ligand conformation to form a sTyr-binding pocket. FSHR then inserts its sTyr (i.e., sulfated Tyr335) into the FSH nascent pocket, eventually leading to receptor activation.

Treatment strategy of rectal gastrointestinal stromal tumor (GIST).

BACKGROUND: Rectal gastrointestinal stromal tumor (GIST) is a rare entity. A retrospective analysis of outcomes from a single institution to identify treatment strategies associated with improved outcomes. METHODS: Records of patients with GIST of the rectum were retrospectively reviewed. Patient and tumor characteristics, treatment details, and outcome were evaluated. RESULTS: Compared with the trans-abdominal approach group, the local excision group patients had smaller size and lower location tumors (P < 0.05). Positive resection margin was an important hazard factor for DFS (OR, 7.63; P = 0.015). Among the patients with the tumor size >5 cm, those with preoperative Imatinib therapy had higher rate of a negative resection margin than those without (100% vs. 20%, P = 0.048). Among the patients with intermediate and high-risk tumors, those who received peri-operative Imatinib therapy had longer DFS compared with those without (61.3 ± 6.1 months vs. 20.2 ± 4.4 months, P = 0.030). CONCLUSIONS: The location of rectal GIST impacts the choice of resection type. Most patients with tumors within 5 cm of the anal verge can be treated with local excision. Positive resection margin is the independent hazard factor for poorer survival. Peri-operative Imatinib therapy is associated with a prolonged DFS in patients with intermediate and high-risk tumors.

Spatiotemporal Mapping of the Oxytocin Receptor at Single-Cell Resolution in the Postnatally Developing Mouse Brain.

The oxytocin receptor (OXTR) has garnered increasing attention for its role in regulating both mature behaviors and brain development. It has been established that OXTR mediates a range of effects that are region-specific or period-specific. However, the current studies of OXTR expression patterns in mice only provide limited help due to limitations in resolution. Therefore, our objective was to generate a comprehensive, high-resolution spatiotemporal expression map of Oxtr mRNA across the entire developing mouse brain. We applied RNAscope in situ hybridization to investigate the spatiotemporal expression pattern of Oxtr in the brains of male mice at six distinct postnatal developmental stages (P7, P14, P21, P28, P42, P56). We provide detailed descriptions of Oxtr expression patterns in key brain regions, including the cortex, basal forebrain, hippocampus, and amygdaloid complex, with a focus on the precise localization of Oxtr+ cells and the variance of expression between different neurons. Furthermore, we identified some neuronal populations with high Oxtr expression levels that have been little studied, including glutamatergic neurons in the ventral dentate gyrus, Vgat+Oxtr+ cells in the basal forebrain, and GABAergic neurons in layers 4/5 of the cortex. Our study provides a novel perspective for understanding the distribution of Oxtr and encourages further investigations into its functions.

Pathologic Response of Phase III Study: Perioperative Camrelizumab Plus Rivoceranib and Chemotherapy Versus Chemotherapy for Locally Advanced Gastric Cancer (DRAGON IV/CAP 05).

PURPOSE: This multicenter, randomized phase III trial evaluated the efficacy and safety of perioperative camrelizumab (an anti-PD-1 antibody) plus low-dose rivoceranib (a VEGFR-2 inhibitor) and S-1 and oxaliplatin (SOX) (SOXRC), high-dose rivoceranib plus SOX (SOXR), and SOX alone (SOX) for locally advanced gastric or gastroesophageal junction (G/GEJ) adenocarcinoma. METHODS: Patients with T3-4aN + M0 G/GEJ adenocarcinoma were randomly assigned (1:1:1) to receive perioperative treatment with SOXRC, SOXR, or SOX. The primary end points were pathologic complete response (pCR) and event-free survival. The Independent Data Monitoring Committee recommended stopping enrollment in the SOXR group on the basis of the safety data of the first 103 randomly assigned patients in the three groups. The patients were then randomly assigned 1:1 to the SOXRC or SOX groups. This report presents the pCR results obtained per protocol for the first 360 randomly assigned patients who had the opportunity for surgery in the SOXRC and SOX groups. RESULTS: In the SOXRC and SOX groups, of the 180 patients in each group, 99% and 98% of patients received neoadjuvant therapy, 91% and 94% completed planned neoadjuvant therapy, and 86% and 87% underwent surgery, respectively. The pCR was significantly higher in the SOXRC group at 18.3% (95% CI, 13.0 to 24.8) compared with 5.0% (95% CI, 2.3 to 9.3) in the SOX group (difference of 13.7%; 95% CI, 7.2 to 20.1; odds ratio of 4.5 [95% CI, 2.1 to 9.9]). The one-sided P value was <.0001, crossing the prespecified statistical significance threshold of P = .005. Surgical complications and grade ≥3 neoadjuvant treatment-related adverse events were 27% versus 33% and 34% versus 17% for SOXRC and SOX, respectively. CONCLUSION: The SOXRC regimen significantly improved pCR compared with SOX alone in patients with G/GEJ adenocarcinoma with a tolerable safety profile.

The mechanism of shared but distinct CSF-1R signaling by the non-homologous cytokines IL-34 and CSF-1.

Interleukin-34 (IL-34) and colony stimulating factor-1 (CSF-1) both signal through the CSF-1R receptor tyrosine kinase, but they have no sequence homology, and their functions and signaling activities are not identical. We report the crystal structures of mouse IL-34 alone and in complex with the N-terminal three immunoglobulin-like domains (D1-D3) of mouse CSF-1R. IL-34 is structurally related to other helical hematopoietic cytokines, but contains two additional helices integrally associated with the four shared helices. The non-covalently linked IL-34 homodimer recruits two copies of CSF-1R on the sides of the helical bundles, with an overall shape similar to the CSF-1:CSF-1R complex, but the flexible linker between CSF-1R D2 and D3 allows these domains to clamp IL-34 and CSF-1 at different angles. Functional dissection of the IL-34:CSF-1R interface indicates that the hydrophobic interactions, rather than the salt bridge network, dominate the biological activity of IL-34. To degenerately recognize two ligands with completely different surfaces, CSF-1R apparently takes advantage of different subsets of a chemically inert surface that can be tuned to fit different ligand shapes. Differentiated signaling between IL-34 and CSF-1 is likely achieved by the relative thermodynamic independence of IL-34 vs. negative cooperativity of CSF-1 at the receptor-recognition sites, in combination with the difference in hydrophobicity which dictates a more stable IL-34:CSF-1R complex compared to the CSF-1:CSF-1R complex.

Structures of a platelet-derived growth factor/propeptide complex and a platelet-derived growth factor/receptor complex.

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) are prototypic growth factors and receptor tyrosine kinases which have critical functions in development. We show that PDGFs share a conserved region in their prodomain sequences which can remain noncovalently associated with the mature cystine-knot growth factor domain after processing. The structure of the PDGF-A/propeptide complex reveals this conserved, hydrophobic association mode. We also present the structure of the complex between PDGF-B and the first three Ig domains of PDGFRbeta, showing that two PDGF-B protomers clamp PDGFRbeta at their dimerization seam. The PDGF-B:PDGFRbeta interface is predominantly hydrophobic, and PDGFRs and the PDGF propeptides occupy overlapping positions on mature PDGFs, rationalizing the need of propeptides by PDGFs to cover functionally important hydrophobic surfaces during secretion. A large-scale structural organization and rearrangement is observed for PDGF-B upon receptor binding, in which the PDGF-B L1 loop, disordered in the structure of the free form, adopts a highly specific conformation to form hydrophobic interactions with the third Ig domain of PDGFRbeta. Calorimetric data also shows that the membrane-proximal homotypic PDGFRalpha interaction, albeit required for activation, contributes negatively to ligand binding. The structural and biochemical data together offer insights into PDGF-PDGFR signaling, as well as strategies for PDGF-antagonism.

Investigation of Crack Propagation Behaviour in Thin-Rim Gears: Experimental Tests and Numerical Simulations.

Thin-rim gears are widely used in industrial fields such as aerospace and electric vehicles due to the advantage of light weight. Yet, the root crack fracture failure of thin-rim gears significantly limits their application and further affects the reliability and safety of high-end equipment. In this work, the root crack propagation behavior of thin-rim gears is experimentally and numerically investigated. The crack initiation position and crack propagation path for different backup ratio gears are simulated using gear finite element (FE) models. The crack initiation position is determined using the maximum gear root stress position. An extended FE method coupled with commercial software ABAQUS is used to simulate the gear root crack propagation. The simulation results are then verified by conducting experimental tests for different backup ratio gears based on a dedicated designed single-tooth bending test device.