Generation of a BAC transgenic mouse strain that expresses CreERT and a fluorescent protein under the transcriptional control of the Fzd5 locus

BACKGROUND

The expression of FZD5 distinguishes immature human mesenchymal stem/stromal cells (MSC) in cultures, and the function of FZD5 is crucial for maintaining the proliferation and multilineage differentiation capacity of human MSC. We herein investigated whether Fzd5 expression also marks undifferentiated MSC in animals.

METHODS

We generated a transgenic mouse strain (Fzd5-CreERT-tFP635) that expresses CreERT and the fluorescent protein, TurboFP635 (tFP635), under the transcriptional control of the Fzd5 gene using the BAC transgenic technique, and identified cells expressing tFP635 by flow cytometry. We also conducted lineage tracing with this strain.

RESULTS

In the bone marrow of transgenic mice, tFP635 was preferentially expressed in MSC, Leptin receptor-expressing MSC (LepR⁺MSCs), and some Pdgfrα⁺ Sca1⁺ MSC (PαS). Inducible lineage tracing using the Fzd5-CreERT-tFP635; CAG-CAT-EGFP strain at the adult stage showed that Fzd5-expressing cells and their descendants labeled with GFP were progressively dominant in LepR⁺MSC and PαS, and GFP⁺ cells persisted for 1 year after the activation of CreERT. Adipocyte progenitor cells (APCs), osteoblast progenitor cells (OPCs), and Cd51⁺ stromal cells were also labeled with GFP.

CONCLUSIONS

Our transgenic mouse marks two different types of MSC, LepR⁺MSC and PαS.

Cholix toxin, an eukaryotic elongation factor 2 ADP-ribosyltransferase, interacts with Prohibitins and induces apoptosis with mitochondrial dysfunction in human hepatocytes

Vibrio cholerae produced-Cholix toxin (Cholix) is a cytotoxin that ADP-ribosylates eukaryotic elongation factor 2, inhibiting protein synthesis, and inducing apoptosis. Here, we identified prohibitin (PHB) 1 and 2 as novel Cholix-interacting membrane proteins in immortalised human hepatocytes and HepG2 cells by Cholix immunoprecipitation assays. The expression level of PHB1 was decreased by Cholix after a 12hr incubation. Cholix-induced poly (ADP-ribose) polymerase (PARP) cleavage was significantly enhanced in PHB (PHB1 or PHB2) knockdown cells. In contrast, transiently overexpressed PHB in hepatocytes attenuated Cholix-induced Bax/Bak conformational changes and PARP cleavage. In addition, Cholix-induced reactive oxygen species production and accumulation of fragmented mitochondria were enhanced in PHB-knockdown cells. Furthermore, Cholix induced activation of Rho-associated coiled coil-containing protein kinase 1 (ROCK1), which was enhanced in PHB-knockdown cells, followed by actin filament depolymerisation and accumulation of tubulin in the blebbing cells. Inhibition of ROCK1 by siRNA or its inhibitor suppressed Cholix-induced PARP cleavage and reactive oxygen species generation. Our findings identify PHB as a new protein that interacts with Cholix and is involved in Cholix-induced mitochondrial dysfunction and cytoskeletal rearrangement by ROCK1 activation during apoptosis.

Correlation Between Splenectomy and Portal Vein Complications in Living Donor Liver Transplantation

OBJECTIVES

In adults undergoing living donor liver transplantation (LDLT), the transplanted livers are partial grafts, and the portal venous pressure is higher than that observed with whole liver grafts. In patients undergoing LDLT concomitant with splenomegaly, portal venous flow is often diverted to collateral vessels, leading to a high risk of portal vein thrombosis. In such cases, occlusion of the collateral veins is important; however, complete occlusion of all collaterals without blocking the blood flow through the splenic artery causes portal hypertension and liver failure. We aimed to examine the effect of performing a splenectomy concomitant with LDLT to reduce portal vein complications.

METHODS

Between 1991 and 2017, we performed 170 LDLT operations, including 83 in adults. For this cohort study, adult cases were divided into 2 groups. Group I was those who underwent LDLT without splenectomy (n = 60); Group II was those who underwent LDLT with splenectomy for the reduction of portal hypertension (n = 23). We investigated the incident rates of complications, including blood loss, lethal portal vein thrombosis (intrahepatic thrombosis), acute rejection, and so on. We also investigated the survival rates in both groups.

RESULTS

The incident rate of lethal portal vein thrombosis in Group II was significantly lower than that observed in Group I (4.4% vs 21.7%, respectively, P = .0363). There were no statistically significant differences observed between the groups with respect to blood loss, survival rates, and other such parameters.

CONCLUSION

LDLT concomitant with splenectomy might effectively reduce the occurrence of portal vein complications in adults.

Effect of Middle Hepatic Vein Tributaries Preserving Technique Until Just Before Graft Retrieval on Donors' Surgical Outcomes in Living Donor Liver Transplantation

BACKGROUND

The technique of preserving the major tributaries of the middle hepatic vein (MHV) (V5 and V8) until just before graft retrieval is beneficial to minimize congestion time of the graft. However, it remains unclear whether this technique exerts a burden on donors in terms of operative time, blood loss, and postoperative hepatic dysfunction. In this study we investigated adverse effects of the MHV tributaries preserving technique until immediately before graft retrieval on donors' surgical outcomes.

METHODS

Data from 71 donors who underwent right hepatectomy without MHV for a liver transplantation at our hospital from January 2002 to August 2016 were retrospectively reviewed. Donors were divided into 3 groups as follows: group 1 (n = 12), no MHV tributary reconstruction; group 2 (n = 33), single MHV tributary reconstruction; group 3 (n = 26), 2 or 3 MHV tributaries reconstruction. Donor operation time, blood loss, proportion of the remnant liver, maximum postoperative total bilirubin, aspartate aminotransferase, alanine transaminase, minimum platelets, prothrombin time, albumin level, number of days in hospital from surgery to discharge, and surgical complications were compared.

RESULTS

Compared with groups 2 and 3, group 1 exhibited shorter average operational time and less average blood loss, but the difference was not significant. Comparisons of all other factors indicated no significant differences.

CONCLUSION

The technique of preserving the major tributaries of the MHV until just immediately before graft retrieval does not appear to impose an apparent burden on donors.

Cytoprotective Effects of Mesenchymal Stem Cells During Liver Transplantation from Donors After Cardiac Death in Rats

BACKGROUND

Liver transplantation from donors after cardiac death (DCD) might increase the pool of available organs. Recently, some investigators reported the potential use of mesenchymal stem cells (MSCs) to improve the outcome of liver transplantation from DCD. The aim of this study was to evaluate the cytoprotective effects and safety of MSC transplantation on liver grafts from DCD.

METHODS

Rats were divided into 4 groups (n = 5) as follows: 1. the heart-beating group, in which liver grafts were retrieved from heart-beating donors; 2. the DCD group, in which liver grafts were retrieved from DCD that had experienced apnea-induced agonal conditions; 3. the MSC-1 group, and 4. the MSC-2 group, in which liver grafts were retrieved as with the DCD group, but were infused MSCs (2.0 × 10⁵ or 1.0 × 10⁶, respectively). The retrieved livers were perfused with oxygenated Krebs-Henseleit bicarbonate buffer (37°C) through the portal vein for 2 hours after 6 hours of cold preservation. Perfusate, bile, and liver tissues were then investigated.

RESULTS

Bile production in the MSC-2 group was significantly improved compared with that in the DCD group. Based on histologic findings, narrowing of the sinusoidal space in the both MSC groups was improved compared with that in the DCD group.

CONCLUSIONS

MSCs could protect the function of liver grafts from warm ischemia-reperfusion injury and improve the viability of DCD liver grafts. In addition, we found that the infusion of 1.0 × 10⁶ MSCs does not obstruct the hepatic sinusoids of grafts from DCD.

A Case of Successful Simultaneous Pancreas-Kidney Transplantation Using the Injured Pancreas Graft

OBJECTIVE

Graft injuries sometimes occur and may cause complications such as the leakage of pancreatic secretions, which is often lethal. We report our experience of a case of successful simultaneous pancreas-kidney transplantation using injured pancreas graft.

PATIENTS AND METHODS

The recipient was a 57-year-old woman with type 1 diabetes mellitus, and the donor was a 30-year-old man with a brain injury. In the donation, the pancreas parenchyma, splenic artery, and gastroduodenal artery were injured iatrogenically. We therefore reconstructed these arteries using vessel grafts and then performed simultaneous pancreas-kidney transplantation.

RESULTS

Five days after transplantation, we noted a high titer of amylase in the ascites; therefore, we performed an urgent laparotomy. The origin of the amylase was the injured pancreatic parenchyma, and continued washing and drainage were carried out. We reconstructed the duodenojejunostomy using the Roux-en-Y technique to separate the passage of food from the pancreas graft to prevent injury to other organs due to exposure to pancreatic secretions. Thereafter, we inserted a decompression tube into the anastomosis thorough the blind end of the jejunum. Finally, we inserted 3 drainage tubes for lavage. Following this procedure, the patient recovered gradually and no longer required hemodialysis and insulin therapy. She was discharged from our hospital 56 days after transplantation.

CONCLUSION

The restoration of the injured graft was possible by management of pancreatic secretions and use of the donor's vessel grafts. Shortage of donors is a problem throughout the world; thus, it is important to use injured grafts for transplantation if possible.

Histone lysine methyltransferase G9a is a novel epigenetic target for the treatment of hepatocellular carcinoma

Histone H3 lysine 9 dimethylation (H3K9me2) is mainly regulated by the histone lysine methyltransferase G9a and is associated with the repression of transcription. However, both the role of G9a and the significance of H3K9me2 in hepatocellular carcinoma (HCC) cells remain unclear. In this study, we conducted loss-of-function assay of G9a using short-hairpin RNA and pharmacological interference. Knockdown of G9a reduced H3K9me2 levels and impaired both HCC cell growth and sphere formation. However, transforming growth factor β1-induced epithelial mesenchymal transition (EMT) was not suppressed by G9a knockdown. Combined analyses of chromatin immunoprecipitation followed by sequencing and RNA-sequencing led to successful identification of 96 candidate epigenetic targets of G9a. Pharmacological inhibition of G9a by BIX-01294 resulted in both cell growth inhibition and induction of apoptosis in HCC cells. Intraperitoneal administration of BIX-01294 suppressed the growth of xenograft tumors generated by implantation of HCC cells in non-obese diabetic/severe combined immunodeficient mice. Immunohistochemical analyses revealed high levels of G9a and H3K9me2 in 36 (66.7%) and 35 (64.8%) primary HCC tissues, respectively. G9a expression levels were significantly positively correlated with H3K9me2 levels in tumor tissues. In contrast, in non-tumor tissues, G9a and H3K9me2 were only observed in biliary epithelial cells and periportal hepatocytes. In conclusion, G9a inhibition impairs anchorage-dependent and -independent cell growth, but not EMT in HCC cells. Our data indicate that pharmacological interference of G9a might be a novel epigenetic approach for the treatment of HCC.

Relationship Between Bile Duct Reconstruction and Complications in Living Donor Liver Transplantation

OBJECTIVES

In living donor liver transplantation (LDLT), the recipient bile duct is thin and short. Bile duct complications often occur in LDLT, with persistent long-term adverse effects. Recently, we began to perform microsurgical reconstruction of the bile duct. The purpose of this study was to investigate the relationship between bile duct reconstruction methods and complications in LDLT.

METHODS

From 1991 to 2014, we performed 161 LDLTs (pediatric:adult = 90:71; left lobe:right lobe = 95:66). In this study, we retrospectively investigated the initial bile duct complications in LDLT and performed univariate and multivariate analyses to identify the independent risk factors for complications.

RESULTS

The most frequent complication was biliary stricture (9.9%), followed by biliary leakage (6.8%). On univariate and multiple logistic regression analysis, the independent risk factors for biliary stricture were bile leakage (P = .0103) and recurrent cholangitis (P = .0077). However, there were no risk factors for biliary leakage on univariate analysis in our study. The reconstruction methods (hepaticojejunostomy or duct-to-duct anastomosis) and reconstruction technique (with or without microsurgery) were not risk factors for biliary stricture and leakage.

CONCLUSION

In this study, the most frequent complication of LDLT was biliary stricture. The independent risk factors for biliary stricture were biliary leakage and recurrent cholangitis. Duct-to-duct anastomosis and microsurgical reconstruction of the bile duct were not risk factors for biliary stricture and leakage.

The Significance of Screening for HLA Antibodies in the Long-Term Follow-up of Pediatric Liver Transplant Recipients

BACKGROUND

Post-transplant donor-specific anti-HLA antibodies (DSA) reportedly have detrimental effects on the outcomes of organ transplantation. However, the prevalence of post-transplant DSA in the long term after pediatric liver transplantation remains unclear, and the significance of post-transplant DSA is unknown. The aim of this cross-sectional study was to determine the prevalence of and characteristics of patients with post-transplant DSA.

MATERIALS AND METHODS

Of the 84 pediatric liver transplant recipients who were followed up in the outpatient department of our institution, 34 patients with available HLA typing data were included after they or their parent(s) provided informed consent for DSA evaluations. Luminex single-antigen bead assays were performed, and a mean fluorescence intensity of ≥1000 was used as the cut-off for a positive reaction.

RESULTS

No class I DSA were detected, whereas class II DSA were detected in 11 patients (32%). There were no differences in age at transplantation, immunosuppressive drugs, or follow-up period between the DSA-positive and DSA-negative patients. The rate of positive pre-transplant complement-dependent cytotoxicity crossmatch was higher with class II DSA than without, although the difference was not statistically significant.

CONCLUSIONS

The utility of screening for class I DSA was insignificant in the long-term follow-up of pediatric liver transplant recipients. The prevalence of class II DSA was relatively high; therefore, screening for class II DSA might be justified, although a follow-up survey of the association between post-transplant class II DSA and the long-term clinical course needs to be conducted.

Jmjd2/Kdm4 demethylases are required for expression of Il3ra and survival of acute myeloid leukemia cells

Agger et al. show that Jmjd2/Kdm4 activities are required for MLL-AF9 translocated AML. Expression of the interleukin 3 receptor α (Il3ra) subunit is dependent on Jmjd2/Kdm4 through a mechanism involving removal of H3K9me3 from the promoter of the Il3ra gene.

Acute myeloid leukemias (AMLs) with a rearrangement of the mixed-linage leukemia (MLL) gene are aggressive hematopoietic malignancies. Here, we explored the feasibility of using the H3K9- and H3K36-specific demethylases Jmjd2/Kdm4 as putative drug targets in MLL-AF9 translocated leukemia. Using Jmjd2a, Jmjd2b, and Jmjd2c conditional triple-knockout mice, we show that Jmjd2/Kdm4 activities are required for MLL-AF9 translocated AML in vivo and in vitro. We demonstrate that expression of the interleukin 3 receptor α (Il3ra also known as Cd123) subunit is dependent on Jmjd2/Kdm4 through a mechanism involving removal of H3K9me3 from the promoter of the Il3ra gene. Importantly, ectopic expression of Il3ra in Jmjd2/Kdm4 knockout cells alleviates the requirement of Jmjd2/Kdm4 for the survival of AML cells, showing that Il3ra is a critical downstream target of Jmjd2/Kdm4 in leukemia. These results suggest that the JMJD2/KDM4 proteins are promising drug targets for the treatment of AML.

Successful Case of Somatostatin Analog Stopping Gastrointestinal Bleeding, One of the Most Frequent Complications After Simultaneous Pancreas-kidney Transplantation: A Case Report

OBJECT

Pancreas transplantation has the highest surgical complication rate of all routinely performed organ transplantation procedures. The complications are not only caused by the pancreas itself but also occur due to issues with the transplant recipient. We report the case of a patient who experienced massive gastrointestinal bleeding after simultaneous pancreas-kidney transplantation (SPK), which was stopped successfully using somatostatin analog.

PATIENTS AND METHODS

The patient was a 45-year-old woman with diabetes mellitus type 1 who underwent SPK with enteric drainage. She had melena 5 days after SPK.

RESULTS

At first, we suspected that the melena was caused by the transplanted duodenum because of rejection and ischemic changes. The patient experienced severe bleeding 9 days after SPK. We quickly performed open surgery and inserted an endoscope from the recipient's ileum to investigate the transplanted duodenum. However, no bleeding source was found, including in the transplanted duodenum and the recipient's ileum end. We determined that the bleeding source was the recipient's ascending colon. We attempted to perform endovascular treatment but could not detect the source of the bleeding; therefore, we used somatostatin analog to let the blood vessels shrink and reduce pancreatic output. Thereafter, the function of the transplanted pancreas and kidney gradually recovered, and the recipient was discharged 154 days after SPK.

CONCLUSION

Gastrointestinal bleeding is a lethal complication and has several different causes, such as mucosal rejection, ischemic changes, and exocrine output of the pancreas graft. Somatostatin analog is one of the most acceptable treatments for patients who have gastrointestinal bleeding after SPK.

SWI/SNF Subunits SMARCA4, SMARCD2 and DPF2 Collaborate in MLL-Rearranged Leukaemia Maintenance

Alterations in chromatin structure caused by deregulated epigenetic mechanisms collaborate with underlying genetic lesions to promote cancer. SMARCA4/BRG1, a core component of the SWI/SNF ATP-dependent chromatin-remodelling complex, has been implicated by its mutational spectrum as exerting a tumour-suppressor function in many solid tumours; recently however, it has been reported to sustain leukaemogenic transformation in MLL-rearranged leukaemia in mice. Here we further explore the role of SMARCA4 and the two SWI/SNF subunits SMARCD2/BAF60B and DPF2/BAF45D in leukaemia. We observed the selective requirement for these proteins for leukaemic cell expansion and self-renewal in-vitro as well as in leukaemia. Gene expression profiling in human cells of each of these three factors suggests that they have overlapping functions in leukaemia. The gene expression changes induced by loss of the three proteins demonstrate that they are required for the expression of haematopoietic stem cell associated genes but in contrast to previous results obtained in mouse cells, the three proteins are not required for the expression of c-MYC regulated genes.

Haploinsufficiency of the c-myc transcriptional repressor FIR, as a dominant negative-alternative splicing model, promoted p53-dependent T-cell acute lymphoblastic leukemia progression by activating Notch1

FUSE-binding protein (FBP)-interacting repressor (FIR) is a c-myc transcriptional suppressor. A splice variant of FIR that lacks exon 2 in the transcriptional repressor domain (FIRΔexon2) upregulates c-myc transcription by inactivating wild-type FIR. The ratio of FIRΔexon2/FIR mRNA was increased in human colorectal cancer and hepatocellular carcinoma tissues. Because FIRΔexon2 is considered to be a dominant negative regulator of FIR, FIR heterozygous knockout (FIR⁺/⁻) C57BL6 mice were generated. FIR complete knockout (FIR⁻/⁻) was embryonic lethal before E9.5; therefore, it is essential for embryogenesis. This strongly suggests that insufficiency of FIR is crucial for carcinogenesis. FIR⁺/⁻ mice exhibited prominent c-myc mRNA upregulation, particularly in the peripheral blood (PB), without any significant pathogenic phenotype. Furthermore, elevated FIRΔexon2/FIR mRNA expression was detected in human leukemia samples and cell lines. Because the single knockout of TP53 generates thymic lymphoma, FIR⁺/⁻TP53⁻/⁻ generated T-cell type acute lymphocytic/lymphoblastic leukemia (T-ALL) with increased organ or bone marrow invasion with poor prognosis. RNA-sequencing analysis of sorted thymic lymphoma cells revealed that the Notch signaling pathway was activated significantly in FIR⁺/⁻TP53⁻/⁻ compared with that in FIR⁺/⁺TP53⁻/⁻ mice. Notch1 mRNA expression in sorted thymic lymphoma cells was confirmed using qRT-PCR. In addition, flow cytometry revealed that c-myc mRNA was negatively correlated with FIR but positively correlated with Notch1 in sorted T-ALL/thymic lymphoma cells. Moreover, the knockdown of TP53 or c-myc using siRNA decreased Notch1 expression in cancer cells. In addition, an adenovirus vector encoding FIRΔexon2 cDNA increased bleomycin-induced DNA damage. Taken together, these data suggest that the altered expression of FIRΔexon2 increased Notch1 at least partially by activating c-Myc via a TP53-independent pathway. In conclusion, the alternative splicing of FIR, which generates FIRΔexon2, may contribute to both colorectal carcinogenesis and leukemogenesis.

Donors' quality of life evaluated by short form-36 analysis after living donor liver transplantation in a single-center experience

BACKGROUND AND PURPOSE

The purpose of this study was to compare the quality of life of donors using the Short Form 36 (SF-36) analysis between the left and right graft periods of living donor liver transplantation.

PATIENTS AND METHODS

In the left graft period (July 1991 to July 2003), 68 donors were eligible for analysis and 76 were eligible in the right graft period (August 2003 to October 2010). Nine right lobe grafts were included in the left graft period, and 52 right lobe grafts were included in the right graft period. We investigated the risks of donation and evaluated the following: blood loss, operation time, postoperative liver function, and duration of hospitalization. We also assessed quality of life in donors, who were mailed a structured questionnaire and the SF-36.

RESULTS

Ten of the 68 donors in the left graft period and 12 of the 76 in the right graft period had postoperative complications. Most postoperative complications were treated without surgical procedures. There was no donor death in our series. Forty-eight donors in the left graft period and 36 in the right graft period responded to our investigation. Compared with published Japanese norms in SF-36, our donors scored similar or higher than the general population in both groups. Two donors in the left graft period and one in the right graft period regretted their decisions to donate. All donors returned to normalcy.

CONCLUSIONS

These results suggested that the donors' quality of life was guaranteed in terms of the SF-36 investigation regardless of the donation period in our series.

The TIF1β-HP1 system maintains transcriptional integrity of hematopoietic stem cells

TIF1β is a transcriptional corepressor that recruits repressive chromatin modifiers to target genes. Its biological function and physiological targets in somatic stem cells remain largely unknown. Here, we show that TIF1β is essential for the maintenance of hematopoietic stem cells (HSCs). Deletion of Tif1b in mice induced active cycling and apoptosis of HSCs and promoted egression of HSCs from the bone marrow, leading to rapid depletion of HSCs. Strikingly, Tif1b-deficient HSCs showed a strong trend of ectopic expression of nonhematopoietic genes. Levels of heterochromatin protein 1 (HP1α, β and γ) proteins, which form a complex with TIF1β, were significantly reduced in the absence of TIF1β and depletion of HP1 recapitulated a part of the phenotypes of Tif1b-deficient HSCs. These results demonstrate that the TIF1β-HP1 system functions as a critical repressive machinery that targets genes not normally activated in the hematopoietic compartment, thereby maintaining the transcriptional signature specific to HSCs.

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Deletion of Tif1b in mice causes rapid depletion of HSCs

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Loss of TIF1β leads to reduction in HP1 proteins in HSCs

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The TIF1β-HP1 system represses nonhematopoietic genes in HSCs

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The TIF1β-HP1 system helps maintain the transcriptional integrity of HSCs

Disulfiram eradicates tumor-initiating hepatocellular carcinoma cells in ROS-p38 MAPK pathway-dependent and -independent manners

Tumor-initiating cells (TICs) play a central role in tumor development, metastasis, and recurrence. In the present study, we investigated the effect of disulfiram (DSF), an inhibitor of aldehyde dehydrogenase, toward tumor-initiating hepatocellular carcinoma (HCC) cells. DSF treatment suppressed the anchorage-independent sphere formation of both HCC cells. Flow cytometric analyses showed that DSF but not 5-fluorouracil (5-FU) drastically reduces the number of tumor-initiating HCC cells. The sphere formation assays of epithelial cell adhesion molecule (EpCAM)⁺ HCC cells co-treated with p38-specific inhibitor revealed that DSF suppresses self-renewal capability mainly through the activation of reactive oxygen species (ROS)-p38 MAPK pathway. Microarray experiments also revealed the enrichment of the gene set involved in p38 MAPK signaling in EpCAM⁺ cells treated with DSF but not 5-FU. In addition, DSF appeared to downregulate Glypican 3 (GPC3) in a manner independent of ROS-p38 MAPK pathway. GPC3 was co-expressed with EpCAM in HCC cell lines and primary HCC cells and GPC3-knockdown reduced the number of EpCAM⁺ cells by compromising their self-renewal capability and inducing the apoptosis. These results indicate that DSF impaired the tumorigenicity of tumor-initiating HCC cells through activation of ROS-p38 pathway and in part through the downregulation of GPC3. DSF might be a promising therapeutic agent for the eradication of tumor-initiating HCC cells.

Concurrent loss of Ezh2 and Tet2 cooperates in the pathogenesis of myelodysplastic disorders

Deletion of Ezh2 results in transcriptional repression of developmental regulator genes, derepression of oncogenic polycomb targets, and induction of MDS/MPN-like disease in mice that is exacerbated by concurrent deletion of Tet2.

Polycomb group (PcG) proteins are essential regulators of hematopoietic stem cells. Recent extensive mutation analyses of the myeloid malignancies have revealed that inactivating somatic mutations in PcG genes such as EZH2 and ASXL1 occur frequently in patients with myelodysplastic disorders including myelodysplastic syndromes (MDSs) and MDS/myeloproliferative neoplasm (MPN) overlap disorders (MDS/MPN). In our patient cohort, EZH2 mutations were also found and often coincided with tet methylcytosine dioxygenase 2 (TET2) mutations. Consistent with these findings, deletion of Ezh2 alone was enough to induce MDS/MPN-like diseases in mice. Furthermore, concurrent depletion of Ezh2 and Tet2 established more advanced myelodysplasia and markedly accelerated the development of myelodysplastic disorders including both MDS and MDS/MPN. Comprehensive genome-wide analyses in hematopoietic progenitor cells revealed that upon deletion of Ezh2, key developmental regulator genes were kept transcriptionally repressed, suggesting compensation by Ezh1, whereas a cohort of oncogenic direct and indirect polycomb targets became derepressed. Our findings provide the first evidence of the tumor suppressor function of EZH2 in myeloid malignancies and highlight the cooperative effect of concurrent gene mutations in the pathogenesis of myelodysplastic disorders.

The optimal timing for preparation of recipient superficial femoral veins to minimize intraoperative blood loss in living donor liver transplantation

AIMS

Intraoperative blood loss (IBL) usually predominates during the dissection of the native liver. A right-lobe living donor liver transplantation (LDLT) sometimes requires an additional procedure to obtain an autologous vein from the recipient for the vascular reconstruction. These procedure can sometime contribute to progressive coagulopathy causing unexpected bleeding. Therefore, we analyzed our cases to determine the optimal timing for vascular preparation from the patient in terms of IBL.

METHODS

Among 67 patients included in the study, 30 did not require an additional procedure to obtain the venous graft (group A), and 37 LDLT employed a superficial femoral vein (SFV). Of these, 13 had undergone removal of SFV after the hilar dissection and liver mobilization from retrohepatic area while preserving the inferior vena cava (group B), and 24 removal of the SFV immediately after hilar dissection without liver mobilization from the retrohepatic space (group C).

RESULTS

A significant difference existed only in the scores of the Model for End-stage Liver Disease. Although the median IBL for group C was similar to that for group A, the median IBL for group B was significantly higher than that for other 2 groups. The median duration from skin incision to graft implantation for group B was significantly longer than that for groups A and group C, because of the additional hemostatic procedures in the retrohepatic space including the leg site.

CONCLUSIONS

The timing for removal of SFV in LDLT patients affects IBL associated with consumptive coagulopathy and prolongs operative time. Based on our experience, we concluded that SFV preparation should be performed before liver mobilization from the retrohepatic area to minimize IBL.

A patient with hepatic artery thrombosis after living-donor liver transplantation survived the great East Japan earthquake 3 days after reoperation: a case report

BACKGROUND

On March 11, 2011, our hospital was severely damaged by the Great East Japan Earthquake. We report the rare case of a 5-month-old patient with hepatic artery thrombosis (HAT) after living donor liver transplantation (LDLT), who survived the earthquake that occurred 3 days after the reoperation; we were able to save this patient without abilities to perform blood tests or computed tomography (CT) for 4 days.

METHODS

This female infant with biliary atresia underwent LDLT 5 months after birth and developed peritonitis owing to perforation of the small intestine 7 days later. Her blood pressure decreased and she developed HAT. We performed emergency reconstruction of the hepatic artery and repair of the small intestine, and 3 days after surgery, the Great East Japan Earthquake occurred.

RESULTS

We could not perform blood tests or CT scans because the water supply was damaged. Gas supply lines were also damaged and sterilization was not possible; surgical tools were limited. However, emergency power was available, so we performed ultrasonography every 6 hours and predicted liver function from intrahepatic blood flow and monitored for Glisson's capsule edema. The blood examination system recovered 14 days after LDLT, and we confirmed improvement of liver function. The patient was extubated 37 days after LDLT and discharged on postoperative day 67.

CONCLUSIONS

Portable ultrasonography was useful in evaluating intrahepatic blood flow and Glisson's capsule edema. Furthermore, it was effective during a disaster because it required no water or gas.

Aldehyde dehydrogenase 1 is associated with recurrence-free survival but not stem cell-like properties in hepatocellular carcinoma

AIM

  It has been reported that aldehyde dehydrogenase 1 A1 (ALDH1) could be not only a normal stem cell marker but also a cancer stem cell marker. ALDH1 expression could be a predictor of poor prognosis in a wide range of cancers. However, the role of ALDH1 in hepatocellular carcinoma (HCC) remains unclear.

METHOD

  We conducted loss-of-function assays for ALDH1 by using short-hairpin RNA in HCC cells and evaluated the correlation between ALDH1 expression and clinicopathological features based on immunohistochemical assessment of 49 primary HCC tissues.

RESULTS

  Neither cell proliferation nor the anchorage-independent sphere formation ability of HCC cells were altered after ALDH1 knockdown. Flow cytometric analyses revealed that ALDH1 knockdown showed no remarkable change in the proportion of epithelial cell adhesion molecule (EpCAM)(+) tumor-initiating cells. Although non-tumor tissues in primary HCC samples diffusely and homogenously expressed ALDH1 at low levels, tumor tissues contained cells with high levels of ALDH1 expression at varying frequencies. Primary HCC samples were categorized as ALDH1-high or ALDH1-low based on the percentage of ALDH1-overexpressing cells. ALDH1-high HCC was characterized by low serum levels of α-fetoprotein (P < 0.01) and well-differentiated pathology (P = 0.03). Multivariate analysis showed that high ALDH1 expression was a favorable prognostic factor in recurrence-free survival of HCC (P = 0.02).

CONCLUSION

  Our findings show that ALDH1 expression has little association with stem cell-like features in HCC cells. ALDH1 might function as a differentiation marker rather than a stem cell marker in HCC.

The relationship between recurrences and immunosuppression on living donor liver transplantation for hepatocellular carcinoma

OBJECTIVES

Living donor liver transplantation (LDLT) offers timely transplantation for patients with hepatocellular carcinoma (HCC). If ABO-incompatible LDLT is feasible, the needs for pretransplantation treatments may be eliminated. It is known that negative impacts of immunosuppression are limited among LDLT for HCC, however, we believe that excessive immunosuppression is one of the risk factors for recurrence. We compared the impacts of immunosuppression for LDLT with hepatectomy outcomes for HCC.

METHODS

From 1991 to 2010, we performed 144 LDLTs including 14 patients with HCC. Seven met the Milan criteria. Immunosuppressive therapies were based on tacrolimus plus methylprednisolone plus CD25 antibody. For ABO-incompatible cases, we also used mycophenolate mofetil and rituximab. Five cases underwent strong imunosuppressive therapy (steroid pulse or rituximab) within 180 days. In addition, we performed hepatectomy for 180 HCC cases from 1997 to 2010.

RESULTS

Overall survival rates of the LDLT cohort and hepatectomy groups were similar, but disease-free 5-year survival rates (DFS) of the LDLT cohort were significantly better than those of the hepatectomy group (total = 54.4% versus 27.4%, within the Milan criteria cases, 71.4% versus 33.8%). Thus, the negative impact of immunosuppression on recurrence was less than the benefit of a whole liver resection. Among strongly immunosuppressed cases, 5-years DFS rates were significantly worse than among other immunosuppressed cases (20.0% versus 76.2%). Upon univariate analysis, the factors associated with HCC recurrence were alpha-fetoprotein levels and steroid doses within 180 days, but multivariate analysis did not show a predictor for recurrence.

CONCLUSION

Patients who are strongly immunosuppressed may have several negative impacts for recurrences. More careful indications must be selected for ABO-incompatible cases.

Bmi1 confers resistance to oxidative stress on hematopoietic stem cells

Background

The polycomb-group (PcG) proteins function as general regulators of stem cells. We previously reported that retrovirus-mediated overexpression of Bmi1, a gene encoding a core component of polycomb repressive complex (PRC) 1, maintained self-renewing hematopoietic stem cells (HSCs) during long-term culture. However, the effects of overexpression of Bmi1 on HSCs in vivo remained to be precisely addressed.

Methodology/Principal findings

In this study, we generated a mouse line where Bmi1 can be conditionally overexpressed under the control of the endogenous Rosa26 promoter in a hematopoietic cell-specific fashion (Tie2-Cre;R26Stop^FLBmi1). Although overexpression of Bmi1 did not significantly affect steady state hematopoiesis, it promoted expansion of functional HSCs during ex vivo culture and efficiently protected HSCs against loss of self-renewal capacity during serial transplantation. Overexpression of Bmi1 had no effect on DNA damage response triggered by ionizing radiation. In contrast, Tie2-Cre;R26Stop^FLBmi1 HSCs under oxidative stress maintained a multipotent state and generally tolerated oxidative stress better than the control. Unexpectedly, overexpression of Bmi1 had no impact on the level of intracellular reactive oxygen species (ROS).

Conclusions/Significance

Our findings demonstrate that overexpression of Bmi1 confers resistance to stresses, particularly oxidative stress, onto HSCs. This thereby enhances their regenerative capacity and suggests that Bmi1 is located downstream of ROS signaling and negatively regulated by it.

Emx2 is a dose-dependent negative regulator of Sox2 telencephalic enhancers

The transcription factor Sox2 is essential for neural stem cells (NSC) maintenance in the hippocampus and in vitro. The transcription factor Emx2 is also critical for hippocampal development and NSC self-renewal. Searching for ‘modifier’ genes affecting the Sox2 deficiency phenotype in mouse, we observed that loss of one Emx2 allele substantially increased the telencephalic β-geo (LacZ) expression of a transgene driven by the 5′ or 3′ Sox2 enhancer. Reciprocally, Emx2 overexpression in NSC cultures inhibited the activity of the same transgene. In vivo, loss of one Emx2 allele increased Sox2 levels in the medial telencephalic wall, including the hippocampal primordium. In hypomorphic Sox2 mutants, retaining a single ‘weak’ Sox2 allele, Emx2 deficiency substantially rescued hippocampal radial glia stem cells and neurogenesis, indicating that Emx2 functionally interacts with Sox2 at the stem cell level. Electrophoresis mobility shift assays and transfection indicated that Emx2 represses the activities of both Sox2 enhancers. Emx2 bound to overlapping Emx2/POU-binding sites, preventing binding of the POU transcriptional activator Brn2. Additionally, Emx2 directly interacted with Brn2 without binding to DNA. These data imply that Emx2 may perform part of its functions by negatively modulating Sox2 in specific brain areas, thus controlling important aspects of NSC function in development.

Lethal myelofibrosis induced by Bmi1-deficient hematopoietic cells unveils a tumor suppressor function of the polycomb group genes

Polycomb-group (PcG) proteins form the multiprotein polycomb repressive complexes (PRC) 1 and 2, and function as transcriptional repressors through histone modifications. They maintain the proliferative capacity of hematopoietic stem and progenitor cells by repressing the transcription of tumor suppressor genes, namely Ink4a and Arf, and thus have been characterized as oncogenes. However, the identification of inactivating mutations in the PcG gene, EZH2, unveiled a tumor suppressor function in myeloid malignancies, including primary myelofibrosis (PMF). Here, we show that loss of another PcG gene, Bmi1, causes pathological hematopoiesis similar to PMF. In a mouse model, loss of Bmi1 in Ink4a-Arf(-/-) hematopoietic cells induced abnormal megakaryocytopoiesis accompanied by marked extramedullary hematopoiesis, which eventually resulted in lethal myelofibrosis. Absence of Bmi1 caused derepression of a cohort of genes, including Hmga2, which is an oncogene overexpressed in PMF. Chromatin immunoprecipitation assays revealed that Bmi1 directly represses the transcription of Hmga2. Overexpression of Hmga2 in hematopoietic stem cells induced a myeloproliferative state with enhanced megakaryocytopoiesis in mice, implicating Hmga2 in the development of pathological hematopoiesis in the absence of Bmi1. Our findings provide the first genetic evidence of a tumor suppressor function of Bmi1 and uncover the role of PcG proteins in restricting growth by silencing oncogenes.

3-Deazaneplanocin A is a promising therapeutic agent for the eradication of tumor-initiating hepatocellular carcinoma cells

Recent advances in stem cell biology have identified tumor-initiating cells (TICs) in a variety of cancers including hepatocellular carcinoma (HCC). Polycomb group gene products such as BMI1 and EZH2 have been characterized as general self-renewal regulators in a wide range of normal stem cells and TICs. We previously reported that Ezh2 tightly regulates the self-renewal and differentiation of murine hepatic stem/progenitor cells. However, the role of EZH2 in tumor-initiating HCC cells remains unclear. In this study, we conducted loss-of-function assay of EZH2 using short-hairpin RNA and pharmacological inhibition of EZH2 by an S-adenosylhomocysteine hydrolase inhibitor, 3-deazaneplanocin A (DZNep). Both EZH2-knockdown and DZNep treatment impaired cell growth and anchorage-independent sphere formation of HCC cells in culture. Flow cytometric analyses revealed that the two approaches decreased the number of epithelial cell adhesion molecule (EpCAM)(+) tumor-initiating cells. Administration of 5-fluorouracil (5-FU) or DZNep suppressed the tumors by implanted HCC cells in non-obese diabetic/severe combined immunodeficient mice. Of note, however, DZNep but not 5-FU predominantly reduced the number of EpCAM(+) cells and diminished the self-renewal capability of these cells as judged by sphere formation assays. Our findings reveal that tumor-initiating HCC cells are highly dependent on EZH2 for their tumorigenic activity. Although further analyses of TICs from primary HCC would be necessary, pharmacological interference with EZH2 might be a promising therapeutic approach to targeting tumor-initiating HCC cells.

Direct activation of STAT5 by ETV6-LYN fusion protein promotes induction of myeloproliferative neoplasm with myelofibrosis

Myeloproliferative neoplasms (MPN), a group of haematopoietic stem cell (HSC) disorders, are often accompanied by myelofibrosis. We previously identified the fusion of the ETV6 gene to the LYN gene (ETV6-LYN) in idiopathic myelofibrosis with ins(12;8)(p13;q11q21). The introduction of ETV6-LYN into HSCs resulted in fatal MPN with massive myelofibrosis in mice, implicating the rearranged LYN kinase in the pathogenesis of MPN with myelofibrosis. However, the signalling molecules directly downstream from and activated by ETV6-LYN remain unknown. In this study, we demonstrated that the direct activation of STAT5 by ETV6-LYN is crucial for the development of MPN. ETV6-LYN was constitutively active as a kinase through autophosphorylation. ETV6-LYN, but not its kinase-dead mutant, supported cytokine-free proliferation of haematopoietic cells. STAT5 was activated in a JAK2-independent manner in ETV6-LYN-expressing cells. ETV6-LYN interacted with STAT5 and directly activated STAT5 both in vitro and in vivo. Of note, ETV6-LYN did not support the formation of colonies by Stat5-deficient HSCs under cytokine-free conditions and the capacity of ETV6-LYN to induce MPN with myelofibrosis was profoundly attenuated in a Stat5-null background. These findings define STAT5 as a direct target of ETV6-LYN and unveil the LYN-STAT5 axis as a novel pathway to augment proliferative signals in MPN and leukaemia.

Forced expression of the histone demethylase Fbxl10 maintains self-renewing hematopoietic stem cells

OBJECTIVE

The methylation status of histones changes dramatically depending on cellular context and defines cell type-specific gene expression profiles. Histone demethylases have recently been implicated in this process. However, it is unknown how histone demethylases function in the maintenance of self-renewing hematopoietic stem cells (HSCs).

MATERIALS AND METHODS

We profiled the expression of histone demethylase genes in mouse hematopoietic cells and listed genes preferentially expressed in HSCs. We analyzed the impact of a selected gene by transducing CD34(-)c-Kit(+)Sca-1(+)lineage marker(-) (CD34(-)KSL) HSCs using retroviral system followed by in vitro methylcellulose colony assays and in vivo competitive repopulation assays.

RESULTS

We found that F-box and leucine-rich repeat protein 10 (Fbxl10, also known as Jhdm1b or Kdm2b), is highly expressed in CD34(-)KSL HSCs. Fbxl10 encodes a demethylase specific to the histone H3 mono/di-methylated at lysine 36 (H3K36me1/me2) and forms complexes with polycomb-group proteins, essential regulators of HSCs. Forced expression of Fbxl10 in HSCs expanded numbers of colony-forming cells with multilineage differentiation potential in culture and prevented exhaustion of the long-term repopulating potential of HSCs following serial transplantation. Fbxl10 tightly repressed the expression of cyclin-dependent kinase inhibitor genes, including Ink4a, Ink4b, and Ink4c, through direct binding to their promoters and gene bodies and demethylation at H3K36. Increased levels of mono-ubiquitylation of H2A at target loci also suggested the collaboration of Fbxl10 with polycomb-group proteins.

CONCLUSIONS

Our findings implicate Fbxl10 in the maintenance of self-renewal capacity of HSCs, thus highlight a role of histone demethylation for the first time in the epigenetic regulation of HSCs.

Bmi1 promotes hepatic stem cell expansion and tumorigenicity in both Ink4a/Arf-dependent and -independent manners in mice

We previously reported that forced expression of Bmi1 (B lymphoma Moloney murine leukemia virus insertion region 1 homolog) in murine hepatic stem/progenitor cells purified from fetal liver enhances their self-renewal and drives cancer initiation. In the present study, we examined the contribution of the Ink4a/Arf tumor suppressor gene locus, one of the major targets of Bmi1, to stem cell expansion and cancer initiation. Bmi1(-/-) Delta-like protein (Dlk)(+) hepatic stem/progenitor cells showed de-repression of the Ink4a/Arf locus and displayed impaired growth activity. In contrast, Ink4a/Arf(-/-) Dlk(+) cells gave rise to considerably larger colonies containing a greater number of bipotent cells than wild-type Dlk(+) cells. Although Ink4a/Arf(-/-) Dlk(+) cells did not initiate tumors in recipient nonobese diabetic/severe combined immunodeficiency mice, enforced expression of Bmi1 in Ink4a/Arf(-/-) Dlk(+) cells further augmented their self-renewal capacity and resulted in tumor formation in vivo. Microarray analyses successfully identified five down-regulated genes as candidate downstream targets for Bmi1 in hepatic stem/progenitor cells. Of these genes, enforced expression of sex determining region Y-box 17 (Sox17) in Dlk(+) cells strongly suppressed colony propagation and tumor growth.

CONCLUSION

These results indicate that repression of targets of Bmi1 other than the Ink4a/Arf locus plays a crucial role in the oncogenic transformation of hepatic stem/progenitor cells. Functional analyses of Bmi1 target genes would be of importance to elucidate the molecular machinery underlying hepatic stem cell system and explore therapeutic approaches for the eradication of liver cancer stem cells.

Role of SoxB1 transcription factors in development

SoxB1 factors, which include Sox1, 2, and 3, share more than 90% amino acid identity in their DNA binding HMG box and participate in diverse developmental events. They are known to exert cell-type-specific functions in concert with other transcription factors on Sox factor-dependent regulatory enhancers. Due to the high degree of sequence similarity both within and outside the HMG box, SoxB1 members show almost identical biological activities. As a result, they exhibit strong functional redundancy in regions where SoxB1 members are coexpressed, such as neural stem/progenitor cells in the developing central nervous system.

Quality of life and problems affecting recipients more than 10 years after living donor liver transplantation

BACKGROUND

We initiated living donor liver transplantation (LDLT) in 1991, allowing us to examine issues related to long-term survival. The aim of this study was to review the long-term outcomes of LDLT in children.

PATIENTS AND METHODS

We performed 116 LDLT from 1991 to present, including 17 recipients who survived >10 years. They were evaluated for growth, immunosuppressive therapy, complications, and quality of life (QOL).

RESULTS

The average age at LDLT was 5.4 years (range, 6 months to 17 years), with a present average age of 17.2 years (range, 11-28 years). At the time of LDLT, 6 recipients had growth retardation with body weights low for age by 2 standard deviations (SD). However, 4 of 6 recipients who underwent LDLT before age of 2 years caught up, reaching average heights and body weights for their ages. Among 6 recipients who were diagnosed with acute rejections by biopsy >5 years after LDLT, 5 improved after steroid pulse therapy. One recipient with a steroid-resistant acute rejection was administered deoxyspergualin after steroids. Chronic rejection was not observed in this series. One recipient has not required immunosuppressive therapy for >4 years with a good present condition.

CONCLUSION

The majority of LDLT recipients achieved a good QOL during long-term survival; they are pursuing normal studies.

The use of recipient superficial femoral vein as a venous graft for portal vein reconstruction in right lobe living donor liver transplantation

In living donor liver transplantation (LDLT), portal vein thrombosis (PVT) in the recipient is frequently regarded as a contraindication. To reconstruct the PV of a right-lobe liver graft (RLG) using an interposition or jump graft from the splenomesenteric junction, various vein grafts and technical modifications have been introduced. The internal jugular, external iliac, or great saphenous veins have been utilized in such reconstructive procedures. However, the superficial femoral vein (SFV) is preferable to the autologous vein grafts in terms of caliber, wall thickness, and length. We employed the recipient SFV to reconstruct PVT among 40 adult LDLT using RLG. Thirty-three were reconstructed by single end-to-end anastomosis with the right or left recipient PV. Three patients were transplanted with a RLG using 2 separated PVs reconstructed by double anastomoses with both the right and left PVs of the recipient. The remaining 4 patients required venous grafting for portal reconstruction. We used the recipient SFV as an interposition or jump graft from the splenomesenteric junction to the graft PV. There were 2 cases of anastomotic PV stenosis; 1 in portal reconstruction without a venous graft and the other with a SFV graft. Both were treated successfully by balloon angioplasty. The recipient SFV is an excellent size match for the PV reconstruction as a long interposition or jump conduit when the venous system from the deceased donor is not available. The indication for LDLT in patients with complete PVT should be carefully decided before transplantation in terms of portal reconstruction.

Distinct expression of polycomb group proteins EZH2 and BMI1 in hepatocellular carcinoma

Polycomb gene products play a crucial role in the development of highly malignant phenotypes and aggressive cancer progression in a variety of cancers; however, their role in hepatocellular carcinoma remains unclear. First, we analyzed the impact of EZH2 and BMI1 modulation on cell growth of HepG2 cells. 3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assays revealed marked growth inhibition after EZH2 or BMI1 knockdown. In addition, simultaneous knockdown of these 2 genes further augmented cell growth inhibitory effects. Next, we conducted immunohistochemical assessment of 86 hepatocellular carcinoma surgical specimens, evaluating the correlation between EZH2 and BMI1 protein expression and clinicopathologic features. High-level EZH2 and BMI1 expression was detected in 57 (66.3%) and 52 tumor tissues (60.5%), respectively. Among these, 48 tumor tissues (55.8%) showed colocalization of EZH2 and BMI1 in almost all tumor cells. The cumulative recurrence rate, but not survival rate, was significantly higher in patients positive for EZH2 (P = .029) and BMI1 (P = .039) than in their negative counterparts, as determined by Kaplan-Meier analysis. These data indicate that EZH2 and BMI1 may cooperate in initiation and progression of hepatocellular carcinoma.

Phasic characteristics of inspiratory crackles of bacterial and atypical pneumonia

BACKGROUND

No known physical findings are available to differentiate between bacterial pneumonia (BP) and atypical pneumonia (AP) in patients with community-acquired pneumonia (CAP).

OBJECTIVE

To evaluate the possible differences in phasic characteristics of inspiratory crackles between BP and AP in patients with CAP.

METHODS

Retrospective chart reviews were conducted to obtain phasic characteristics of inspiratory crackles (early, early-to-mid, late and pan-inspiratory crackles) in AP and BP groups in a community teaching hospital in Japan (n = 183).

RESULTS

100 patients with BP and 83 patients with AP were evaluated. Patients with BP were significantly more likely to present with pan-inspiratory crackles (49 (49.0) vs 5 (6.0); p<0.0001), whereas patients with AP were more likely to present with late inspiratory crackles (28 (33.7) vs 9 (9.0); p<0.0001) (mean (SD)). Among pneumonia patients with audible crackles, the sensitivity and specificity of pan-inspiratory crackles for BP were 83.1% and 85.7%, respectively, and the sensitivity and specificity of late inspiratory crackles for AP were 80.0% and 84.7%, respectively.

DISCUSSION

In patients with CAP and audible crackles, phasic characteristics of inspiratory crackles may be used to distinguish AP from BP. Prospective studies are needed to confirm these findings.

The polycomb gene product BMI1 contributes to the maintenance of tumor-initiating side population cells in hepatocellular carcinoma

Side population (SP) cell analysis and sorting have been successfully applied to hepatocellular carcinoma (HCC) cell lines to identify a minor cell population with cancer stem cell properties. However, the molecular mechanisms operating in SP cells remain unclear. The polycomb gene product BMI1 plays a central role in the self-renewal of somatic stem cells in a variety of tissues and organs and seems to be implicated in tumor development. In this study, we determined the critical role of BMI1 in the maintenance of cancer stem cells with the SP phenotype in HCC cell lines. BMI1 was preferentially expressed in SP cells in Huh7 and PLC/PRF/5 HCC cells compared with the corresponding non-SP cells. Lentiviral knockdown of BMI1 considerably decreased the number of SP cells in both Huh7 and PLC/PRF/5 cells. Long-term culture of purified SP cells resulted in a drastic reduction in the SP subpopulation upon the BMI1 knockdown, indicating that BMI1 is required for the self-renewal of SP cells in culture. More importantly, the BMI1 knockdown abolished the tumor-initiating ability of SP cells in nonobese diabetic/severe combined immunodeficiency mice. Derepression of the INK4A and ARF genes that are major targets for BMI1 was not necessarily associated with impaired self-renewal of SP cells caused by BMI1 knockdown. In conclusion, our findings define an important role for BMI1 in the maintenance of tumor-initiating SP cells in HCC. BMI1 might be a novel therapeutic target for the eradication of cancer stem cells in HCC.