Quantitative proteomics reveals potential anti-inflammatory protein targets of radial extracorporeal shock wave therapy in TNF-α-induced model of acute inflammation in primary human tenocytes.

Tendinopathy refers to a type of tendon disease with a multifactorial spectrum. Recent research has begun to reveal the effects of inflammation on the tendinopathic process, especially in the first stage of tendinopathy. Radial extracorporeal shock wave therapy (rESWT) has been successfully used to treat orthopedic diseases. However, the molecular mechanisms underlying the anti-inflammatory effects of rESWT on tumor necrosis factor-α treated tenocytes have not been fully elucidated. In this study, we applied total protein tandem mass tag-labeled quantitative proteomics with liquid chromatography-mass spectrometer/mass spectrometer technology to identify differentially expressed proteins (DEPs) among inflammatory tenocytes, rESWT inflammatory tenocytes, and controls using three biological replicates. Human tenocytes were used and they were cultured in vitro. In total, 1028 and 40 DEPs were detected for control versus inflammatory tenocytes and for inflammatory tenocytes versus rESWT inflammatory tenocytes, respectively. Further, we identified integrin α2, selenoprotein S, and NLR family CARD domain-containing protein 4 as pivotal molecular targets of the anti-inflammatory effects of rESWT. This is the first study to provide a reference proteomic map for inflammatory tenocytes and rESWT inflammatory tenocytes. Our findings provide crucial insight into the molecular mechanisms underscoring the anti-inflammatory effects of rESWT in tendinopathy.

Chk1 Inhibition Hinders the Restoration of H3.1K56 and H3.3K56 Acetylation and Reprograms Gene Transcription After DNA Damage Repair.

H3K56 acetylation (H3K56Ac) was reported to play a critical role in chromatin assembly; thus, H3K56ac participates in the regulation of DNA replication, cell cycle progression, DNA repair, and transcriptional activation. To investigate the influence of DNA damage regulators on the acetylation of histone H3 and gene transcription, U2OS cells expressing SNAP-labeled H3.1 or SNAP-labeled H3.3 were treated with ATM, ATR, or a Chk1 inhibitor after ultraviolet (UV) radiation. The levels of H3.1K56ac, H3.3K56ac, and other H3 site-specific acetylation were checked at different time points until 24 h after UV radiation. The difference in gene transcription levels was also examined by mRNA sequencing. The results identified Chk1 as an important regulator of histone H3K56 acetylation in the restoration of both H3.1K56ac and H3.3K56ac. Moreover, compromising Chk1 activity via chemical inhibitors suppresses gene transcription after UV radiation. The study suggests a previously unknown role of Chk1 in regulating H3K56 and some other site-specific H3 acetylation and in reprograming gene transcription during DNA damage repair.

Timely upstream events regulating nucleotide excision repair by ubiquitin-proteasome system: ubiquitin guides the way.

The ubiquitin-proteasome system (UPS) plays crucial roles in regulation of multiple DNA repair pathways, including nucleotide excision repair (NER), which eliminates a broad variety of helix-distorting DNA lesions that can otherwise cause deleterious mutations and genomic instability. In mammalian NER, DNA damage sensors, DDB and XPC acting in global genomic NER (GG-NER), and, CSB and RNAPII acting in transcription-coupled NER (TC-NER) sub-pathways, undergo an array of post-translational ubiquitination at the DNA lesion sites. Accumulating evidence indicates that ubiquitination orchestrates the productive assembly of NER preincision complex by driving well-timed compositional changes in DNA damage-assembled sensor complexes. Conversely, the deubiquitination is also intimately involved in regulating the damage sensing aftermath, via removal of degradative ubiquitin modification on XPC and CSB to prevent their proteolysis for the factor recycling. This review summaries the relevant research efforts and latest findings in our understanding of ubiquitin-mediated regulation of NER and active participation by new regulators of NER, e.g., Cullin-Ring ubiquitin ligases (CRLs), ubiquitin-specific proteases (USPs) and ubiquitin-dependent segregase, valosin-containing protein (VCP)/p97. We project hypothetical step-by-step models in which VCP/p97-mediated timely extraction of damage sensors is integral to overall productive NER. The USPs and proteasome subtly counteract in fine-tuning the vital stability and function of NER damage sensors.

Investigation of perioperative blood loss of femoral shaft fractures treated with intramedullary nail or locking compression plate.

INTRODUCTION: Femoral shaft fractures (FSFs) are associated with significant blood loss, resulting in anemia and hemorrhagic shock. However, there has been limited data for the blood loss of FSFs during the whole perioperative period. Our primary aim is to quantify the blood loss associated with FSFs treated with intramedullary nail or locking compression plate fixation, as well as to identify the relative affecting factors for perioperative hidden blood loss (HBL). PATIENTS AND METHODS: 131 consecutive patients with FSFs were enrolled in the retrospective study between January 2009 and January 2020, including 90 cases for intramedullary nail (Nail group) and 41 cases for locking compression plate fixation (Plate group). Demographics and perioperative data were collected and analyzed. Total blood loss (TBL), visible blood loss (VBL), HBL, and percentage of HBL (PHBL) were calculated based on hematocrit (Hct) changes. RESULTS: There was a large drop of hemoglobin (Hb) during the perioperative time. Of all 131 patients, the average HBL was 1445.5 ± 443.2 mL, accounting for 78.7% of TBL (1815.1 ± 446.3 mL). TBL and HBL in Nail group were 1886.1 ± 438.6 mL and 1546.0 ± 424.7 mL; while TBL and HBL in Plate group were 1659.5 ± 427.9 mL and 1225.1 ± 405.7 mL. The differences between the two groups were statistically significant (p = 0.007, p < 0.001, respectively). Besides, statistical significance (p< 0.05, p< 0.05, respectively) was also reported in HBL between Type-A and Type-C, and between Type-B and Type-C (1395.8 ± 444.8 mL vs. 1651.6 ± 495.7 mL; and 1411.2 ± 383.4 mL vs. 1651.6 ± 495.7 mL, respectively). CONCLUSIONS: Patients of FSFs had significant TBL and HBL, the amount of which was much larger than that observed intra-operatively. Moreover, two readily available preoperative factors for nail fixation and Type-C were associated with a higher likelihood of more HBL. Therefore, it was argued that regular perioperative monitoring and timely blood transfusion were crucially important for patients to avoid possible risks of anemia and facilitate recovery.

Spironolactone-induced XPB degradation requires TFIIH integrity and ubiquitin-selective segregase VCP/p97.

Mineralocorticoid and androgen receptor antagonist, spironolactone, was recently identified as an inhibitor of nucleotide excision repair (NER), acting via induction of proteolysis of TFIIH component Xeroderma Pigmentosum B protein (XPB). This activity provides a strong rationale for repurposing spironolactone for cancer therapy. Here, we report that the spironolactone-induced XPB proteolysis is mediated through ubiquitin-selective segregase, valosin-containing protein (VCP)/p97. We show that spironolactone induces a dose- and time-dependent degradation of XPB but not XPD, and that the XPB degradation is blocked by VCP/p97 inhibitors DBeQ, NMS-873, and neddylation inhibitor MLN4924. Moreover, the cellular treatment by VCP/p97 inhibitors leads to the accumulation of ubiquitin conjugates of XPB but not XPD. VCP/p97 knockdown by inducible shRNA does not affect XPB level but compromises the spironolactone-induced XPB degradation. Also, VCP/p97 interacts with XPB upon treatment of spironolactone and proteasome inhibitor MG132, while the VCP/p97 adaptor UBXD7 binds XPB and its ubiquitin conjugates. Additionally, ATP analog-mediated inhibition of Cdk7 significantly decelerates spironolactone-induced XPB degradation. Likewise, engaging TFIIH to NER by UV irradiation slows down spironolactone-induced XPB degradation. These results indicate that the spironolactone-induced XPB proteolysis requires VCP/p97 function and that XPB within holo-TFIIH rather than core-TFIIH is more vulnerable to spironolactone-induced proteolysis. Abbreviations NER: nucleotide excision repair; TFIIH: transcription factor II H; CAK: Cdk-activating kinase (CAK) complex; XPB: Xeroderma Pigmentosum type B; VCP/p97: valosin-containing protein/p97; Cdk7: cyclin-dependent kinase 7; NAE: NEDD8-activating enzyme; IP: immunoprecipitation.

USP7-mediated deubiquitination differentially regulates CSB but not UVSSA upon UV radiation-induced DNA damage.

Cockayne syndrome group B (CSB) protein participates in transcription-coupled nucleotide excision repair. The stability of CSB is known to be regulated by ubiquitin-specific protease 7 (USP7). Yet, whether USP7 acts as a deubiquitinating enzyme for CSB is not clear. Here, we demonstrate that USP7 deubiquitinates CSB to maintain its levels after ultraviolet (UV)-induced DNA damage. While both CSB and UV-stimulated scaffold protein A (UVSSA) exhibit a biphasic decrease and recovery upon UV irradiation, only CSB recovery depends on USP7, which physically interacts with and deubiquitinates CSB. Meanwhile, CSB overexpression stabilizes UVSSA, but decrease UVSSA's presence in nuclease-releasable/soluble chromatin, and increase the presence of ubiquitinated UVSSA in insoluble chromatin alongside CSB-ubiquitin conjugates. Remarkably, CSB overexpression also decreases CSB association with USP7 and UVSSA in soluble chromatin. UVSSA exists in several ubiquitinated forms, of which mono-ubiquitinated form and other ubiquitinated UVSSA forms are detectable upon 6xHistidine tag-based purification. The ubiquitinated UVSSA forms, however, are not cleavable by USP7 in vitro. Furthermore, USP7 disruption does not affect RNA synthesis but decreases the recovery of RNA synthesis following UV exposure. These results reveal a role of USP7 as a CSB deubiquitinating enzyme for fine-tuning the process of TC-NER in human cells.

Prevalence and associated factors of intra-articular lesions in acute ankle fractures evaluated by arthroscopy and clinical outcomes with minimum 24-month follow-up.

BACKGROUND: Acute ankle fractures can lead to high rate of concomitant intra-articular lesions which may compromise clinical results. The purpose of this study was to evaluate the incidence of concomitant intra-articular lesions in acute ankle fractures with arthroscopy. We also sought to analyze the relationship between intra-articular lesions and the fracture type, as well as the severity of the fracture. METHODS: It was a retrospective cohort study. From April 2014 to December 2015, we have chosen arthroscopy-assisted open reduction and internal fixation (AORIF) for the treatment of unstable acute ankle fractures. All concomitant intra-articular lesions were assessed and documented carefully and prospectively, such as ligament injuries, osteochondral lesions, and tibiofibular syndesmosis injuries. All fractures were classified according to the Lauge-Hansen classification system. The American Orthopedic Foot and Ankle Society's (AOFAS) ankle-hindfoot scale was used to assess post-operative function. Statistical comparisons between the intra-articular lesions, the fracture type, and the severity of the presenting fracture were performed using a Chi-squared analysis. RESULTS: Data of 36 patients were analyzed in the study, including 23 supination-type fractures and 13 pronation-type fractures. The incidence of tibiofibular syndesmosis injuries, chondral lesions, and loose bodies were 92%, 72%, and 39%, respectively. Avulsion fractures of the anterior tibiofibular syndesmosis were more commonly found in supination-type fractures than pronation-type fracture (45% vs. 15%, χ = 5.78, P = 0.02), which would cause mechanical blocking in the anterior portion of the ankle. On the contrary, chondral lesions were more commonly found in the more severe fractures than mild fractures (86% vs. 53%, χ = 4.57, P = 0.03). A mean 41.7 months (range, 33.0-51.0 months) of follow-up was achieved. A mean AOFAS's ankle-hindfoot scale was 96.9, and 97.2% of the patients were satisfied with the procedure. CONCLUSIONS: Acute ankle fractures have a high incidence of concomitant intra-articular lesions. Avulsion fractures of the anterior tibiofibular syndesmosis are more commonly found in supination-type fractures. Chondral lesions are related to the severity of the fractures, but not with the classification of the fractures. AORIF can be one reliable solution in dealing with the associated injuries seen with acute ankle fractures.

Efficacy and Safety of Tranexamic Acid for Blood Salvage in Intertrochanteric Fracture Surgery: A Meta-Analysis.

The use of tranexamic acid (TXA) for reducing blood loss in intertrochanteric fracture (IF) surgery remains controversial. We therefore performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the efficacy and safety of TXA in reducing transfusion requirements and blood loss for IF surgery. Databases, including PubMED, Cochrane, and Embase, were searched for RCTs that were published before February 2018 and that addressed the efficacy and safety of TXA in patients who underwent IF surgery. A total of 746 patients from 7 RCTs were subjected to meta-analysis. The results showed that TXA group had reduced surgical blood loss (weighted mean difference [WMD] = -37.24, 95% confidence interval [CI]: -48.70 to -25.77, P <.00001), reduced total blood loss (WMD = -199.08, 95% CI: -305.16 to -93.01, P = .0002), higher postoperative hemoglobin (WMD = 0.46, 95% CI: 0.12 to 0.79, P = .007), and hematocrit levels (WMD = 1.55, 95% CI: 0.64 to 2.47, P = .008) compared to control group, while no significant differences were found in transfusion rates (relative risk [RR] = 0.75, 95% CI: 0.50 to 1.11, P = .15), postoperative drainage (WMD = -38.82, 95% CI: -86.87 to 9.22, P = .11), and thromboembolic events (RR = 0.94, 95% CI: 0.41 to 2.19, P = .89). In patients undergoing IF surgery, the administration of TXA significantly reduced surgical blood loss and total blood loss, while it had no significant effect on transfusion rate, postoperative drainage, and the risk of thromboembolic events. Nevertheless, due to the variations in the included studies, additional RCTs are required to further validate these conclusions.

Human CRL4DDB2 ubiquitin ligase preferentially regulates post-repair chromatin restoration of H3K56Ac through recruitment of histone chaperon CAF-1.

Acetylated histone H3 lysine 56 (H3K56Ac) diminishes in response to DNA damage but is restored following DNA repair. Here, we report that CRL4DDB2 ubiquitin ligase preferentially regulates post-repair chromatin restoration of H3K56Ac through recruitment of histone chaperon CAF-1. We show that H3K56Ac accumulates at DNA damage sites. The restoration of H3K56Ac but not H3K27Ac, H3K18Ac and H3K14Ac depends on CAF-1 function, whereas all these acetylations are mediated by CBP/p300. The CRL4DDB2 components, DDB1, DDB2 and CUL4A, are also required for maintaining the H3K56Ac and H3K9Ac level in chromatin, and for restoring H3K56Ac following induction of DNA photolesions and strand breaks. Depletion of CUL4A decreases the recruitment of CAF-1 p60 and p150 to ultraviolet radiation- and phleomycin-induced DNA damage. Neddylation inhibition renders CRL4DDB2 inactive, decreases H3K56Ac level, diminishes CAF-1 recruitment and prevents H3K56Ac restoration. Mutation in the PIP box of DDB2 compromises its capability to elevate the H3K56Ac level but does not affect XPC ubiquitination. These results demonstrated a function of CRL4DDB2 in differential regulation of histone acetylation in response to DNA damage, suggesting a novel role of CRL4DDB2 in repair-driven chromatin assembly.

Intramedullary nails versus sliding hip screws for AO/OTA 31-A2 trochanteric fractures in adults: A meta-analysis.

OBJECTIVES: The optimum treatment with intramedullary nails (IMN) or sliding hip screws (SHS) for type 31-A2 trochanteric fractures remains controversial. Therefore, we performed a meta-analysis of randomized controlled trials (RCTs) to compare IMN with SHS in AO/OTA 31-A2 trochanteric fractures. MATERIAL AND METHODS: Databases including PubMed, Cochrane, and Embase were searched to identify RCTs published before December 2016, which compared IMN with SHS for intraoperative and postoperative outcomes in AO/OTA 31-A2 trochanteric fractures. RESULTS: A total of 909 patients from six RCTs were subjected to the meta-analysis. The results showed that the IMN group was associated with less operative blood loss, leg shortening, wound infections, length of hospital stay, and days to mobilization with walking aids and also yielded a higher Parker score as compared to the SHS group. No significant difference was seen in the other parameters including operative details, fracture fixation complications, postoperative complications, and 1 year mortality. CONCLUSION: IMN fixation was found to be the superior treatment of choice for 31-A2 trochanteric fractures as compared with SHS fixation in our meta-analysis. The adverse effects appeared comparable between the two groups. However, due to the variations in the included studies, more large-sample, measures-unified, and high-quality RCTs are needed to validate these conclusions.

Nucleotide Excision Repair: Finely Tuned Molecular Orchestra of Early Pre-incision Events.

Nucleotide excision repair (NER) eliminates a broad variety of helix-distorting DNA lesions that can otherwise cause genomic instability. NER comprises two distinct subpathways: global genomic NER (GG-NER) operating throughout the genome, and transcription-coupled NER (TC-NER) preferentially removing DNA lesions from transcribing DNA strands of transcriptionally active genes. Several NER factors undergo post-translational modifications, including ubiquitination, occurring swiftly and reversibly at DNA lesion sites. Accumulating evidence indicates that ubiquitination not only orchestrates the spatio-temporal recruitment of key protein factors to DNA lesion sites but also the productive assembly of NER pre-incision complex. This review will be restricted to the latest conceptual understanding of ubiquitin-mediated regulation of initial damage sensors of NER, that is DDB, XPC, RNAPII and CSB. We project hypothetical NER models in which ubiquitin-specific segregase, valosin-containing protein (VCP)/p97, plays an essential role in timely extraction of the congregated DNA damage sensors to functionally facilitate the DNA lesion elimination from the genome.

UV-induced proteolysis of RNA polymerase II is mediated by VCP/p97 segregase and timely orchestration by Cockayne syndrome B protein.

RNA polymerase II (RNAPII) acts as a damage sensor for transcription-coupled nucleotide excision repair (TC-NER) and undergoes proteolytic clearance from damaged chromatin by the ubiquitin-proteasome system (UPS). Here, we report that Valosin-containing protein (VCP)/p97, a druggable oncotarget, is essential for RNAPII's proteolytic clearance in mammalian cells. We show that inhibition of VCP/p97, or siRNA-mediated ablation of VCP/p97 and its cofactors UFD1 and UBXD7 severely impairs ultraviolet radiation (UVR)-induced RNAPII degradation. VCP/p97 interacts with RNAPII, and the interaction is enhanced by Cockayne syndrome B protein (CSB). However, the VCP/p97-mediated RNAPII proteolysis occurs independent of CSB. Surprisingly, CSB enhances UVR-induced RNAPII ubiquitination but delays its turnover. Additionally, VCP/p97-mediated RNAPII turnover occurs with and without Von Hippel-Lindau tumor suppressor protein (pVHL), a known substrate receptor of Elongin E3 ubiquitin ligase for RNAPII. Moreover, pVHL re-expression improves cell viability following UVR. Whereas, VCP/p97 inhibition decreases cell viability and enhances a low-dose UVR killing in presence of pVHL. These findings reveal a function of VCP/p97 segregase in UVR-induced RNAPII degradation in mammalian cells, and suggest a role of CSB in coordinating VCP/p97-mediated extraction of ubiquitinated RNAPII and CSB itself from chromatin.

Valosin-containing Protein (VCP)/p97 Segregase Mediates Proteolytic Processing of Cockayne Syndrome Group B (CSB) in Damaged Chromatin.

Cockayne syndrome group A and B (CSB) proteins act in transcription-coupled repair, a subpathway of nucleotide excision repair. Here we demonstrate that valosin-containing protein (VCP)/p97 segregase functions in ultraviolet radiation (UVR)-induced ubiquitin-mediated CSB degradation. We show that VCP/p97 inhibition and siRNA-mediated ablation of VCP/p97 and its cofactors UFD1 and UBXD7 impair CSB degradation. VCP/p97 inhibition also results in the accumulation of CSB in chromatin. Moreover, VCP/p97 interacts with both native and ubiquitin-conjugated forms of CSB. The localized cellular UVR exposures lead to VCP/p97 accumulation at DNA damage spots, forming distinct UVR-induced foci. However, manifestation of VCP/p97 foci is independent of CSB and UBXD7. Furthermore, VCP/p97 and UBXD7 associate with the Cockayne syndrome group A-DDB1-Cul4A complex, an E3 ligase responsible for CSB ubiquitination. Compromising proteasome and VCP/p97 function allows accumulation of both native and ubiquitinated CSB and results in an increase of UBXD7, proteasomal RPN2, and Sug1 in the chromatin compartment. Surprisingly, both biochemical inhibition and genetic defect of VCP/p97 enhance the recovery of RNA synthesis following UVR, whereas both VCP/p97 and proteasome inhibitions decrease cell viability. Our findings reveal a new role of VCP/p97 segregase in the timely processing of ubiquitinated CSB from damaged chromatin.

Damaged DNA-binding protein down-regulates epigenetic mark H3K56Ac through histone deacetylase 1 and 2.

Acetylated histone H3 lysine 56 (H3K56Ac) is one of the reversible histone post-translational modifications (PTMs) responsive to DNA damage. We previously described a biphasic decrease and increase of epigenetic mark H3K56Ac in response to ultraviolet radiation (UVR)-induced DNA damage. Here, we report a new function of UV damaged DNA-binding protein (DDB) in deacetylation of H3K56Ac through specific histone deacetylases (HDACs). We show that simultaneous depletion of HDAC1/2 compromises the deacetylation of H3K56Ac, while depletion of HDAC1 or HDAC2 alone has no effect on H3K56Ac. The H3K56Ac deacetylation does not require functional nucleotide excision repair (NER) factors XPA and XPC, but depends on the function of upstream factors DDB1 and DDB2. UVR enhances the association of DDB2 with HDAC1 and, enforced DDB2 expression leads to translocation of HDAC1 to UVR-damaged chromatin. HDAC1 and HDAC2 are recruited to UVR-induced DNA damage spots, which are visualized by anti-XPC immunofluorescence. Dual HDAC1/2 depletion decreases XPC ubiquitination, but does not affect the recruitment of DDB2 to DNA damage. By contrast, the local accumulation of γH2AX at UVR-induced DNA damage spots was compromised upon HDAC1 as well as dual HDAC1/2 depletions. Additionally, UVR-induced ATM activation decreased in H12899 cells expressing H3K56Ac-mimicing H3K56Q. These results revealed a novel role of DDB in H3K56Ac deacetylation during early step of NER and the existence of active functional cross-talk between DDB-mediated damage recognition and H3K56Ac deacetylation.

USP7 deubiquitinase promotes ubiquitin-dependent DNA damage signaling by stabilizing RNF168.

During DNA damage response (DDR), histone ubiquitination by RNF168 is a critical event, which orchestrates the recruitment of downstream DDR factors, e.g. BRCA1 and 53BP1. Here, we report USP7 deubiquitinase regulates the stability of RNF168. We showed that USP7 disruption impairs H2A and ultraviolet radiation (UVR)-induced γH2AX monoubiquitination, and decreases the levels of pBmi1, Bmi1, RNF168 and BRCA1. The effect of USP7 disruption was recapitulated by siRNA-mediated USP7 depletion. The USP7 disruption also compromises the formation of UVR-induced foci (UVRIF) and ionizing radiation-induced foci (IRIF) of monoubiquitinated H2A (uH2A) and polyubiquitinated H2AX/A, and subsequently affects UVRIF and IRIF of BRCA1 as well as the IRIF of 53BP1. USP7 was shown to physically bind RNF168 in vitro and in vivo. Overexpression of wild-type USP7, but not its interaction-defective mutant, prevents UVR-induced RNF168 degradation. The USP7 mutant is unable to cleave Ub-conjugates of RNF168 in vivo. Importantly, ectopic expression of RNF168, or both RNF8 and RNF168 together in USP7-disrupted cells, significantly rescue the formation of UVRIF and IRIF of polyubiquitinated H2A and BRCA1. Taken together, these findings reveal an important role of USP7 in regulating ubiquitin-dependent signaling via stabilization of RNF168.

Arthroscopy-assisted surgery for tibial plateau fractures.

PURPOSE: This study aimed to summarize the recent clinical outcomes of patients undergoing arthroscopy-assisted reduction and internal fixation (ARIF) for tibial plateau fractures. METHODS: A systematic electronic search of the PubMed and Cochrane databases was performed in January 2014. All English-language clinical studies on tibial plateau fractures treated with ARIF that were published after January 1, 2000 were eligible for inclusion. Basic information related to the surgery was collected. RESULTS: The search criteria initially identified 141 articles, and 19 studies were included in this systematic review. There were 2 retrospective comparative studies, 16 case series studies, and one clinical series based on a technique note. There were a total of 609 patients in this systematic review, with a mean follow-up time of 52.5 months. The most common fracture types were Schatzker types II and III. Concomitant injuries were common: 42.2% of the patients had meniscal injuries, and 21.3% had anterior cruciate ligament (ACL) injuries. In addition, the status of 90.5% of the patients was classified as good or excellent according to the clinical Rasmussen scoring system, and 90.9% of the patients were satisfied with the treatment. Only 6 severe complications were reported, including one case of compartment syndrome. CONCLUSIONS: ARIF is a reliable, effective, and safe method for the treatment of tibial plateau fractures, especially when they present with concomitant injuries. LEVEL OF EVIDENCE: Level IV, systematic review of Level III and Level IV studies.

Cdt2-mediated XPG degradation promotes gap-filling DNA synthesis in nucleotide excision repair.

Xeroderma pigmentosum group G (XPG) protein is a structure-specific repair endonuclease, which cleaves DNA strands on the 3' side of the DNA damage during nucleotide excision repair (NER). XPG also plays a crucial role in initiating DNA repair synthesis through recruitment of PCNA to the repair sites. However, the fate of XPG protein subsequent to the excision of DNA damage has remained unresolved. Here, we show that XPG, following its action on bulky lesions resulting from exposures to UV irradiation and cisplatin, is subjected to proteasome-mediated proteolytic degradation. Productive NER processing is required for XPG degradation as both UV and cisplatin treatment-induced XPG degradation is compromised in NER-deficient XP-A, XP-B, XP-C, and XP-F cells. In addition, the NER-related XPG degradation requires Cdt2, a component of an E3 ubiquitin ligase, CRL4(Cdt2). Micropore local UV irradiation and in situ Proximity Ligation assays demonstrated that Cdt2 is recruited to the UV-damage sites and interacts with XPG in the presence of PCNA. Importantly, Cdt2-mediated XPG degradation is crucial to the subsequent recruitment of DNA polymerase δ and DNA repair synthesis. Collectively, our data support the idea of PCNA recruitment to damage sites which occurs in conjunction with XPG, recognition of the PCNA-bound XPG by CRL4(Cdt2) for specific ubiquitylation and finally the protein degradation. In essence, XPG elimination from DNA damage sites clears the chromatin space needed for the subsequent recruitment of DNA polymerase δ to the damage site and completion of gap-filling DNA synthesis during the final stage of NER.