Tandem Deubiquitination and Acetylation of SPRTN Promotes DNA-Protein Crosslink Repair and Protects against Aging.

DNA-protein crosslinks (DPCs) are highly toxic DNA lesions that threaten genomic integrity. Recent findings highlight that SPRTN, a specialized DNA-dependent metalloprotease, is a central player in proteolytic cleavage of DPCs. Previous studies suggest that SPRTN deubiquitination is important for its chromatin association and activation. However, the regulation and consequences of SPRTN deubiquitination remain unclear. Here we report that, in response to DPC induction, the deubiquitinase VCPIP1/VCIP135 is phosphorylated and activated by ATM/ATR. VCPIP1, in turn, deubiquitinates SPRTN and promotes its chromatin relocalization. Deubiquitination of SPRTN is required for its subsequent acetylation, which promotes SPRTN relocation to the site of chromatin damage. Furthermore, Vcpip1 knockout mice are prone to genomic instability and premature aging. We propose a model where two sequential post-translational modifications (PTMs) regulate SPRTN chromatin accessibility to repair DPCs and maintain genomic stability and a healthy lifespan.

Sarcopenia as a predictor of mortality in kidney transplant recipients: A 5-year prospective cohort study with propensity score matching.

BACKGROUND: Sarcopenia is known to bring about adverse outcomes in elderly populations and dialysis patients. However, whether it is a risk factor in kidney transplant recipients (KTRs) has not yet been established. In the present study, the association of sarcopenia with mortality was investigated in KTRs. METHODS: We conducted a single-center prospective cohort study and recruited KTRs who were more than 1-year posttransplant from August 2017 to January 2018. The participants were followed for 5 years, and the Kaplan-Meier method and Cox proportional hazards model were used to assess patient survival. RESULTS: A total of 212 KTRs with a median age of 54 years and median transplant vintage of 79 months were enrolled in this study. Among them, 33 (16%) had sarcopenia according to the Asia Working Group for Sarcopenia 2019 at baseline. During the 5-year follow-up period, 20 (9.4%) died, 5 returned to dialysis after graft loss, and 4 were lost to follow-up. The 5-year overall survival rate was 90%. After 1:1 propensity score matching, a matched cohort with 60 KTRs was generated. The overall survival rate was significantly lower in the sarcopenia group compared to the non-sarcopenia group (p = 0.025, log-rank test). Furthermore, mortality risk was significantly higher in the sarcopenia group compared to the non-sarcopenia group (hazard ratio = 7.57, 95% confidence interval = 0.94-62). CONCLUSION: Sarcopenia was a predictor of mortality in KTRs. KTRs with suboptimal muscle status who were at risk for poor survival could have a clinical benefit by interventions for sarcopenia.

Comparison of Oncological Outcomes between Transperitoneal and Retroperitoneal Approaches in Laparoscopic Nephroureterectomies for Upper Tract Urothelial Carcinoma.

Background and Objectives: Our aim was to clarify the oncological outcomes of the two different approaches to laparoscopic nephroureterectomies (LNUs) in Japan, and to examine whether there were any significant differences between the transperitoneal approach and the retroperitoneal approach. Materials and Methods: We retrospectively evaluated patients who underwent an LNU for upper tract urothelial carcinoma (UTUC) from January 2013 to December 2022. We identified 52 patients who underwent a transperitoneal LNU (tLNU) and 93 who underwent a retroperitoneal LNU (rLNU). We adopted age, smoking, and pT-stage matching, and 43 patients were classified in each group. We investigated the time from surgery to recurrence (RFS: recurrence-free survival), the time to death (OS: overall survival), and the time to non-urothelial-tract recurrence-free survival (NUTRFS). A Cox regression analysis was performed to evaluate the risk factors that influenced recurrence. Results: There were no significant differences in the RFS, OS, and NUTRFS between the two matched groups. In the multivariate Cox regression analysis, the pT stage (pT3≥ vs. pT2≤) had an HR = 2.09 and a p = 0.01, and was an independent prognostic risk factor regarding cancer recurrence. Conclusions: There were no significant differences in the oncological outcomes between the tLNU and rLNU groups. It is suggested that the transperitoneal approach should be selected for LNUs.

Intra-S phase checkpoint kinase Chk1 dissociates replication proteins Treslin and TopBP1 through multiple mechanisms during replication stress.

Replication stress impedes DNA polymerase progression causing activation of the ataxia telangiectasia and Rad3-related signaling pathway, which promotes the intra-S phase checkpoint activity through phosphorylation of checkpoint kinase 1 (Chk1). Chk1 suppresses replication origin firing, in part, by disrupting the interaction between the preinitiation complex components Treslin and TopBP1, an interaction that is mediated by TopBP1 BRCT domain-binding to two cyclin-dependent kinase (CDK) phosphorylation sites, T968 and S1000, in Treslin. Two nonexclusive models for how Chk1 regulates the Treslin-TopBP1 interaction have been proposed in the literature: in one model, these proteins dissociate due to a Chk1-induced decrease in CDK activity that reduces phosphorylation of the Treslin sites that bind TopBP1 and in the second model, Chk1 directly phosphorylates Treslin, resulting in dissociation of TopBP1. However, these models have not been formally examined. We show here that Treslin T968 phosphorylation was decreased in a Chk1-dependent manner, while Treslin S1000 phosphorylation was unchanged, demonstrating that T968 and S1000 are differentially regulated. However, CDK2-mediated phosphorylation alone did not fully account for Chk1 regulation of the Treslin-TopBP1 interaction. We also identified additional Chk1 phosphorylation sites on Treslin that contributed to disruption of the Treslin-TopBP1 interaction, including S1114. Finally, we showed that both of the proposed mechanisms regulate origin firing in cancer cell line models undergoing replication stress, with the relative roles of each mechanism varying among cell lines. This study demonstrates that Chk1 regulates Treslin through multiple mechanisms to promote efficient dissociation of Treslin and TopBP1 and furthers our understanding of Treslin regulation during the intra-S phase checkpoint.

Enzalutamide versus flutamide for castration-resistant prostate cancer after combined androgen blockade therapy with bicalutamide: the OCUU-CRPC study.

BACKGROUND: Before the androgen target therapy era, flutamide was widely used for castration-resistant prostate cancer in Japan. Enzalutamide is currently the recommended treatment; however, the efficacy and safety of enzalutamide and flutamide after combined androgen blockade therapy with bicalutamide, has not been compared. METHODS: Patients with castration-resistant prostate cancer who received combined androgen blockade therapy with bicalutamide were randomly assigned to receive either enzalutamide or flutamide. The primary endpoint for efficacy was the 3-month prostate-specific antigen response rate. This trial is registered with ClinicalTrials.gov (NCT02346578) and the University hospital Medical Information Network (UMIN000016301). RESULTS: Overall, 103 patients were enrolled. The 3- (80.8% vs. 35.3%; p < 0.001) and 6-month (73.1% vs. 31.4%; p < 0.001) prostate-specific antigen response rates were higher in the enzalutamide than in the flutamide group. The 3-month disease progression rates (radiographic or prostate-specific antigen progression) were 6.4% and 38.8% in the enzalutamide and flutamide groups, respectively [hazard ratio (HR): 0.16; 95% confidence interval (CI): 0.05-0.47; p < 0.001]; the 6-month rates were 11.4% and 51.1%, respectively (HR 0.22; 95% CI 0.09-0.50; p < 0.001). Enzalutamide provided superior prostate-specific antigen progression-free survival compared with flutamide (HR 0.29; 95% CI 0.15-0.54; p < 0.001). Median time to prostate-specific antigen progression-free survival was not reached and was 6.6 months in the enzalutamide and flutamide groups, respectively. CONCLUSIONS: As an alternative anti-androgen therapy in patients with castration-resistant prostate cancer who fail bicalutamide-combined androgen blockade therapy, enzalutamide provides superior clinical outcomes compared with flutamide. Enzalutamide should be preferred over flutamide in these patients.

Spartan deficiency causes accumulation of Topoisomerase 1 cleavage complexes and tumorigenesis.

Germline mutations in SPRTN cause Ruijs-Aalfs syndrome (RJALS), a disorder characterized by genome instability, progeria and early onset hepatocellular carcinoma. Spartan, the protein encoded by SPRTN, is a nuclear metalloprotease that is involved in the repair of DNA-protein crosslinks (DPCs). Although Sprtn hypomorphic mice recapitulate key progeroid phenotypes of RJALS, whether this model expressing low amounts of Spartan is prone to DPC repair defects and spontaneous tumors is unknown. Here, we showed that the livers of Sprtn hypomorphic mice accumulate DPCs containing Topoisomerase 1 covalently linked to DNA. Furthermore, these mice exhibited DNA damage, aneuploidy and spontaneous tumorigenesis in the liver. Collectively, these findings provide evidence that partial loss of Spartan impairs DPC repair and tumor suppression.

BRCA1-associated protein 1 (BAP1) deubiquitinase antagonizes the ubiquitin-mediated activation of FoxK2 target genes.

BRCA1-associated protein 1 (BAP1), which is frequently mutated in cancer, functions as a deubiquitinase (DUB) for histone H2A. Although BAP1 interacts with a transcriptional regulator, HCF-1, and transcription factors FoxK1 and FoxK2, how BAP1 controls gene expression remains unclear. This study investigates the importance of BAP1 DUB activity and the interactions with FoxK2 and HCF-1 in the regulation of FoxK2 target genes. We show that FoxK2 recruits BAP1 to the target genes through the forkhead-associated domain, which interacts with Thr(P)-493 on BAP1. BAP1, in turn, recruits HCF-1, thereby forming a ternary complex in which BAP1 bridges FoxK2 and HCF-1. BAP1 represses FoxK2 target genes, and this effect requires BAP1 DUB activity but not interaction with HCF-1. Importantly, BAP1 depletion causes up-regulation of FoxK2 target genes only in the presence of the Ring1B-Bmi1 complex, an E3 ubiquitin ligase for histone H2A, indicating an antagonizing role of BAP1 against Ring1B-Bmi1. Our findings suggest that BAP1 deficiency causes increased expression of target genes in a Ring1B-Bmi1-dependent manner.

Regulation of error-prone translesion synthesis by Spartan/C1orf124.

Translesion synthesis (TLS) employs low fidelity polymerases to replicate past damaged DNA in a potentially error-prone process. Regulatory mechanisms that prevent TLS-associated mutagenesis are unknown; however, our recent studies suggest that the PCNA-binding protein Spartan plays a role in suppression of damage-induced mutagenesis. Here, we show that Spartan negatively regulates error-prone TLS that is dependent on POLD3, the accessory subunit of the replicative DNA polymerase Pol δ. We demonstrate that the putative zinc metalloprotease domain SprT in Spartan directly interacts with POLD3 and contributes to suppression of damage-induced mutagenesis. Depletion of Spartan induces complex formation of POLD3 with Rev1 and the error-prone TLS polymerase Pol ζ, and elevates mutagenesis that relies on POLD3, Rev1 and Pol ζ. These results suggest that Spartan negatively regulates POLD3 function in Rev1/Pol ζ-dependent TLS, revealing a previously unrecognized regulatory step in error-prone TLS.

Conversion of stable ABO-incompatible kidney transplant recipients from mycophenolate mofetil with standard exposure calcineurin inhibitors (CNIs) to everolimus with very low exposure CNIs-a short-term pilot study.

BACKGROUND: A recent report has demonstrated that as with mycophenolate mofetil (MMF), everolimus is capable of inhibiting human B-lymphocyte function and activation including B-lymphocyte proliferation, apoptosis, and immunoglobulin production in vitro. Everolimus may therefore be used as an immunosuppressant in ABO-incompatible kidney transplantation. METHODS: A three-month pilot study was performed to examine the efficacy and safety of conversion of stable ABO-incompatible kidney transplant recipients from MMF with standard exposure calcineurin inhibitors (CNIs) to everolimus with very low exposure CNIs. Sixteen recipients were enrolled in the study. The patients without acute rejection by graft biopsy were switched from MMF to everolimus with CNI minimization. At three months after conversion, graft biopsies were performed to check for acute rejection and C4d deposition. RESULTS: Conversion to everolimus with CNI minimization for three months did not induce acute rejection and C4d deposition in all of the ABO-incompatible kidney transplant recipients. A slight elevation of anti-A/B antibody titer occurred in our present study. Everolimus was associated with hyperlipidemia and edema. CONCLUSIONS: These results demonstrated that short-term conversion from MMF to everolimus after one yr post-transplant may be a safe and effective alternate for ABO-incompatible kidney transplant recipients requiring temporary discontinuation of MMF.

Daprodustat for Post-Transplant Anemia in Renal Transplant Recipients.

BACKGROUND: Daprodustat, a hypoxia-inducible factor prolyl hydroxylase inhibitor, has been reported to be effective in treating conservative renal failure and renal anemia in patients undergoing dialysis. However, its effects on post-transplant anemia have not yet been reported. This study aimed to determine whether daprodustat may be a useful treatment for post-transplant anemia. MATERIALS: Excluding 5 cases in which the drug was discontinued due to side effects, 21 post-transplant patients treated with daprodustat for ≥12 months and available for follow-up were analyzed. Changes in hemoglobin levels, iron metabolism, estimated glomerular filtration rate, and low-density lipoprotein levels were evaluated over 1 year. RESULTS: The average hemoglobin level was 10.1 g/dL before treatment, and after 1, 2, 3, 6, 9, and 12 months, these had increased significantly to 10.9, 11.2, 11.9, 12.3, 12.3, and 12.6, respectively. Ferritin levels were significantly lower throughout the 12-month study period. Transferrin saturation was significantly lower than before treatment during the first 6 months, with no significant differences after that. The participants' estimated glomerular filtration rate and low-density lipoprotein cholesterol levels did not change significantly throughout the treatment. CONCLUSION: Daprodustat significantly increased hemoglobin levels was easily dose-adjusted and was relatively safe for continuous use over 1 year. It was also effective in patients who had responded inadequately to erythropoiesis-stimulating agents. Therefore, we conclude that daprodustat may be a useful treatment for post-transplant anemia.

Experience with Tandem Pre-Dilution Online Hemodiafiltration and Centrifugal Plasma Exchange in Pretransplant Desensitization for Abo-Incompatible Kidney Transplantation: A Case Report.

BACKGROUND: In the use of therapeutic plasma exchange (TPE) as antibody removal therapy for ABO-incompatible (ABOi) kidney transplantation, it is technically possible to perform online hemodiafiltration (OHDF) and TPE simultaneously for patients who are receiving OHDF. In this study, we report tandem therapy of pre-dilution OHDF and centrifugal plasma exchange (cTPE), instead of membrane plasma exchange, which is the mainstay of TPE in Japan. METHODS: A total of 14 sessions of tandem cTPE and pre-dilution OHDF were performed as preoperative antibody removal therapy for 6 ABOi kidney transplant recipients. cTPE intra-circuit pressure, decreased antibody titer, and adverse events were evaluated. The study was carried out following the ethical standards of the Declaration of Helsinki and Istanbul. Donors were not prisoners or individuals who were coerced or paid. RESULTS: The tandem therapy was completed safely in 12 of the 14 sessions, with no problems such as pressure upper and lower limit alarms or circuit coagulation. In 2 sessions, the tandem therapy had to be interrupted due to coagulation on the dialysis circuit side. Antibody titers were reduced by a median of 3-fold for both IgG and IgM. There was no acute antibody-associated rejection. CONCLUSIONS: In preoperative apheresis therapy for ABOi kidney transplantation, tandem therapy of pre-dilution OHDF and cTPE may be a useful treatment option that can be performed safely and results in sufficient reduction of antibody levels.

Dimerization-dependent serine protease activity of FAM111A prevents replication fork stalling at topoisomerase 1 cleavage complexes.

FAM111A, a serine protease, plays roles in DNA replication and antiviral defense. Missense mutations in the catalytic domain cause hyper-autocleavage and are associated with genetic disorders with developmental defects. Despite the enzyme's biological significance, the molecular architecture of the FAM111A serine protease domain (SPD) is unknown. Here, we show that FAM111A is a dimerization-dependent protease containing a narrow, recessed active site that cleaves substrates with a chymotrypsin-like specificity. X-ray crystal structures and mutagenesis studies reveal that FAM111A dimerizes via the N-terminal helix within the SPD. This dimerization induces an activation cascade from the dimerization sensor loop to the oxyanion hole through disorder-to-order transitions. Dimerization is essential for proteolytic activity in vitro and for facilitating DNA replication at DNA-protein crosslink obstacles in cells, while it is dispensable for autocleavage. These findings underscore the role of dimerization in FAM111A's function and highlight the distinction in its dimerization dependency between substrate cleavage and autocleavage.

Frailty and sarcopenia in older kidney transplant recipients: a cross-sectional study.

PURPOSE: The aging of the kidney transplant population is accelerating, and measures against geriatric syndromes including frailty and sarcopenia, which elevate the risk of needing long-term care and even death, are being considered important. Recently, both the frailty and sarcopenia criteria for Asians were revised based on various research reports and clinical experiences. The purpose of this study is twofold: firstly, to investigate the prevalence of frailty based on the revised Japanese version of the Cardiovascular Health Study (J-CHS) criteria and the Kihon Checklist (KCL) and that of sarcopenia based on the Asian Working Group for Sarcopenia (AWGS) 2019 as well as the relationship between frailty and sarcopenia, and secondly, to determine the concurrent validity of the KCL with the revised J-CHScriteria in older kidney transplant recipients. METHODS: This study was a single-center cross-sectional investigation carried out on older kidney transplant recipients who visited our hospital from August 2017 to February 2019. The diagnosis of frailty was assessed using the revised J-CHS criteria and the KCL. The diagnosis of sarcopenia was made by low skeletal muscle mass and either low physical performance or low muscle strength based on the AWGS 2019. To examine the relationship between frailty and sarcopenia, categorical variables were compared using chi-squared test and continuous variables Mann-Whitney U test. Spearman's correlation analysis was used to investigate the correlation between the KCL score and the revised J-CHS score. The concurrent validity of the KCL for estimating frailty based on the revised J-CHS criteria was evaluated using the receiver operating characteristics (ROC) curve analysis. RESULTS: A total of 100 older kidney transplant recipients were enrolled in this study. The median age was 67, 63 (63%) were males, and the median time after transplant was 95 months. The prevalence of frailty based on the revised J-CHS criteria and the KCL, and sarcopenia based on the AWGS 2019 was 15%, and 19%, and 16% respectively. Sarcopenia was significantly associated with frailty based on the KCL (p = 0.016), while not with frailty based on the revised J-CHS criteria (p = 0.11). The KCL score significantly correlated with the revised J-CHS score (p < 0.001). The area under the ROC curve was 0.91. CONCLUSION: Frailty and sarcopenia are interrelated complex geriatric syndromes that are risk factors for adverse health outcomes. In older kidney transplant recipients, frailty and sarcopenia were highly prevalent and frequently co-existed. Furthermore, the KCL was verified as a useful tool for frailty screening in these patient. Easy identification of patients with frailty, which is reversible, can help clinicians institute appropriate corrective measures for kidney transplant recipients to improve transplant outcomes.

A Case of Bariatric Surgery for a Japanese Kidney Transplant Recipient With Diabetes Mellitus: A Case Report.

The patient, a 54-year-old woman, underwent a living donor kidney transplant at Osaka City University Hospital 7 years before the bariatric surgery. Her comorbidities were diabetes, sleep apnea, and severe obesity (weight 103 kg, body mass index [BMI] 36 kg/m2), and her diabetes was poorly controlled with an HbA1c of 8.5%. On admission, she weighed 99 kg, BMI was 34 kg/m2, Serum creatinine (S-Cre) was 1.54 mg/dL, and HbA1c was 7.1%. A laparoscopic sleeve gastrectomy was performed, and her weight decreased without complications during the perioperative period. She was discharged on postoperative day 28. Two months after surgery, her weight was 87 kg, BMI 30 kg/m2, S-Cre 1.34 mg/dL, HbA1c 6.7 %, renal function improved, urine protein decreased, and insulin dosage decreased dramatically. We report this valuable case because there are no reports of bariatric surgery in Japanese renal transplant recipients.

Functions and evolution of FAM111 serine proteases.

Proteolysis plays fundamental and regulatory roles in diverse cellular processes. The serine protease FAM111A (FAM111 trypsin-like peptidase A) emerged recently as a protease involved in two seemingly distinct processes: DNA replication and antiviral defense. FAM111A localizes to nascent DNA and plays a role at the DNA replication fork. At the fork, FAM111A is hypothesized to promote DNA replication at DNA-protein crosslinks (DPCs) and protein obstacles. On the other hand, FAM111A has also been identified as a host restriction factor for mutants of SV40 and orthopoxviruses. FAM111A also has a paralog, FAM111B, a serine protease with unknown cellular functions. Furthermore, heterozygous missense mutations in FAM111A and FAM111B cause distinct genetic disorders. In this review, we discuss possible models that could explain how FAM111A can function as a protease in both DNA replication and antiviral defense. We also review the consequences of FAM111A and FAM111B mutations and explore possible mechanisms underlying the diseases. Additionally, we propose a possible explanation for what drove the evolution of FAM111 proteins and discuss why some species have two FAM111 proteases. Altogether, studies of FAM111 proteases in DNA repair, antiviral defense, and genetic diseases will help us elucidate their functions and the regulatory mechanisms.

Laparoscopic ureteroneocystostomy for iatrogenic ureterovaginal fistula after modified radical hysterectomy: A case report.

An unique laparoscopic ureteroneocystostomy technique was performed to treat an iatrogenic ureterovaginal fistula that was formed in a 69-year-old woman following open modified radical hysterectomy for endometrial cancer. Severe adhesions between the distal ureter and the surrounding tissues, including the iliac artery, were observed. Owing to difficulties in identifying the distal ureter, the proximal ureter was identified and dissected downward to free the ureter, thereby allowing anastomosis. This report shows that laparoscopic ureteroneocystostomy for ureterovaginal fistula repair may prove useful owing to its minimally invasive and broad approach.

Novel Technique for Hand-Assisted Laparoscopic Nephrectomy for Advanced Renal Cell Carcinoma with Renal Vein and Inferior Vena Cava Thrombi: Three Case Reports.

Introduction: The treatment of thrombi in the renal vein (RV) and inferior vena cava (IVC) requires advanced laparoscopic experience. We present three cases of hand-assisted laparoscopic nephrectomy (HALN) using a novel technique for treating advanced renal cell carcinoma (RCC) with thrombi in the RV and IVC. Case Presentation. Three patients with RCC with RV or IVC thrombus below level I underwent HALN. Two patients had right RCC with RV and IVC thrombi. One patient had left RCC with an RV thrombus. We hooked a vessel loop to the end of the thrombus and pulled it up manually to make space for vascular processing. The RV was narrowed and dissected using Hem-o-lok clips or an Endo GIA stapler. Conclusion: In carefully selected cases, renal vascular processing could be easily and safely performed using a vessel loop in HALN with thrombectomy.

Clinical outcome of ABO-incompatible living unrelated donor kidney transplantation.

BACKGROUND: ABO-incompatible living unrelated donor kidney transplantation is an immunologically high-risk procedure, but few reports have been made on the outcomes of these transplants. PATIENTS AND METHODS: We analyzed 12 kidney transplants using ABO-incompatible living-unrelated donors performed at our institution between January 1999 and December 2007, focusing on the immunosuppressive protocols, complications and graft survivals. RESULTS: Patient and graft survival rates were 100%. One patient experienced antibody-mediated rejection and intractable acute cellular rejection, one had antibody-mediated rejection and one had acute cellular rejection, but their grafts survived after intensive immunosuppressive treatment. There were no severe complications among the recipients. CONCLUSIONS: In ABO-incompatible living unrelated donor kidney transplantation, severe rejections may occur due to ABO incompatibility and poor histocompatibility. Therefore, appropriate desensitization, immunosuppression and recipient care are needed for a successful transplant. Recent significant improvements in outcomes indicate that it has become a viable treatment option, given the lack of available donor organs.

MYC regulates ribosome biogenesis and mitochondrial gene expression programs through its interaction with host cell factor-1.

The oncoprotein transcription factor MYC is a major driver of malignancy and a highly validated but challenging target for the development of anticancer therapies. Novel strategies to inhibit MYC may come from understanding the co-factors it uses to drive pro-tumorigenic gene expression programs, providing their role in MYC activity is understood. Here we interrogate how one MYC co-factor, host cell factor (HCF)-1, contributes to MYC activity in a human Burkitt lymphoma setting. We identify genes connected to mitochondrial function and ribosome biogenesis as direct MYC/HCF-1 targets and demonstrate how modulation of the MYC-HCF-1 interaction influences cell growth, metabolite profiles, global gene expression patterns, and tumor growth in vivo. This work defines HCF-1 as a critical MYC co-factor, places the MYC-HCF-1 interaction in biological context, and highlights HCF-1 as a focal point for development of novel anti-MYC therapies.

Tumours form when cells lose control of their growth. Usually, cells produce signals that control how much and how often they divide. But if these signals become faulty, cells may grow too quickly or multiply too often. For example, a group of proteins known as MYC proteins activate growth genes in a cell, but too much of these proteins causes cells to grow uncontrollably. With one third of all cancer deaths linked to excess MYC proteins, these molecules could be key targets for anti-cancer drugs. However, current treatments fail to target these proteins. One option for treating cancers linked to MYC proteins could be to target proteins that work alongside MYC proteins, such as the protein HCF-1, which can attach to MYC proteins. To test if HCF-1 could be a potential drug target, Popay et al. first studied how HCF-1 and MYC proteins interacted using specific cancer cells grown in the laboratory. This revealed that when the two proteins connected, they activated genes that trigger rapid cell growth. When these cancer cells were then injected into mice, tumours quickly grew. However, when the MYC and HCF-1 attachments in the cancer cells were disrupted, the tumours shrunk. This suggests that if anti-cancer drugs were able to target HCF-1 proteins, they could potentially reduce or even reverse the growth of tumours. While further research is needed to identify drug candidates, these findings reveal a promising target for treating tumours that stem from over-abundant MYC proteins.

The deubiquitinating enzyme BAP1 regulates cell growth via interaction with HCF-1.

The deubiquitinating enzyme BRCA1-associated protein 1 (BAP1) possesses growth inhibitory activity and functions as a tumor suppressor. In this study we report that BAP1 also plays positive roles in cell proliferation. BAP1 depletion by RNAi inhibits cell proliferation as does overexpression of a dominant negative mutant of BAP1. Mass spectrometry analyses of copurified proteins revealed that BAP1 is associated with factors involved in chromatin modulation and transcriptional regulation. We show that the interaction with host cell factor-1 (HCF-1), a cell-cycle regulator composed of HCF-1N and HCF-1C, is critical for the BAP1-mediated growth regulation. We found that HCF-1N is modified with Lys-48-linked polyubiquitin chains on its Kelch domain. The HCF-1 binding motif of BAP1 is required for interaction with HCF-1N and mediates deubiquitination of HCF-1N by BAP1. The importance of the BAP1-HCF-1 interaction is underscored by the fact that growth suppression by the dominant negative BAP1 mutant is entirely dependent on the HCF-1 binding motif. These results suggest that BAP1 regulates cell proliferation by deubiquitinating HCF-1.