Proteome-scale discovery of protein degradation and stabilization effectors

Targeted protein degradation and stabilization are promising therapeutic modalities because of their potency, versatility and their potential to expand the druggable target space1,2. However, only a few of the hundreds of E3 ligases and deubiquitinases in the human proteome have been harnessed for this purpose, which substantially limits the potential of the approach. Moreover, there may be other protein classes that could be exploited for protein stabilization or degradation3-5, but there are currently no methods that can identify such effector proteins in a scalable and unbiased manner. Here we established a synthetic proteome-scale platform to functionally identify human proteins that can promote the degradation or stabilization of a target protein in a proximity-dependent manner. Our results reveal that the human proteome contains a large cache of effectors of protein stability. The approach further enabled us to comprehensively compare the activities of human E3 ligases and deubiquitinases, identify and characterize non-canonical protein degraders and stabilizers and establish that effectors have vastly different activities against diverse targets. Notably, the top degraders were more potent against multiple therapeutically relevant targets than the currently used E3 ligases cereblon and VHL. Our study provides a functional catalogue of stability effectors for targeted protein degradation and stabilization and highlights the potential of induced proximity screens for the discovery of new proximity-dependent protein modulators.

Induction of oxidative stress biomarkers following whole-body irradiation in mice

Dose assessment is an important issue for radiation emergency medicine to determine appropriate clinical treatment. Hematopoietic tissues are extremely vulnerable to radiation exposure. A decrease in blood cell count following radiation exposure is the first quantitative bio-indicator using hematological techniques. We further examined induction of oxidative stress biomarkers in residual lymphocytes to identify new biomarkers for dosimetry. In vivo whole-body radiation to mice exposed to 5 Gy significantly induces DNA double-strand breaks, which were visualized by γ-H2AX in mouse blood cells. Mouse blood smears and peripheral blood mononuclear cells (PBMC) isolated from irradiated mice were used for immunostaining for oxidative biomarkers, parkin or Nrf2. Parkin is the E3 ubiquitin ligase, which is normally localized in the cytoplasm, is relocated to abnormal mitochondria with low membrane potential (ΔΨm), where it promotes clearance via mitophagy. Nrf2 transcription factor controls the major cellular antioxidant responses. Both markers of oxidative stress were more sensitive and persistent over time than nuclear DNA damage. In conclusion, parkin and Nrf2 are potential biomarkers for use in radiation dosimetry. Identification of several biological markers which show different kinetics for radiation response is essential for radiation dosimetry that allows the assessment of radiation injury and efficacy of clinical treatment in emergency radiation incidents. Radiation-induced oxidative damage is useful not only for radiation dose assessment but also for evaluation of radiation risks on humans.

Genetically Encoded Fluorescent Sensor for Poly-ADP-Ribose

Poly-(ADP-ribosyl)-ation (PARylation) is a reversible post-translational modification of proteins and DNA that plays an important role in various cellular processes such as DNA damage response, replication, transcription, and cell death. Here we designed a fully genetically encoded fluorescent sensor for poly-(ADP-ribose) (PAR) based on Förster resonance energy transfer (FRET). The WWE domain, which recognizes iso-ADP-ribose internal PAR-specific structural unit, was used as a PAR-targeting module. The sensor consisted of cyan Turquoise2 and yellow Venus fluorescent proteins, each in fusion with the WWE domain of RNF146 E3 ubiquitin ligase protein. This bipartite sensor named sPARroW (sensor for PARrelying on WWE) enabled monitoring of PAR accumulation and depletion in live mammalian cells in response to different stimuli, namely hydrogen peroxide treatment, UV irradiation and hyperthermia.

IFN-α2b inhibits the ethanol enriched-HBV cccDNA through blocking a positive feedback loop of HBx/MSL2/cccDNA/HBV/HBx in liver

Hepatitis B virus (HBV) is a major risk factor for liver diseases, in which HBV covalently closed circular DNA (cccDNA), as the genomic form that templates viral transcription, plays crucial roles in sustaining viral persistence. Clinically, the excessive ethanol intake accelerates the progression of liver diseases with HBV infection. Here, we supposed that ethanol might trigger HBV cccDNA in the liver. Interestingly, we observed that the ethanol remarkably elevated the levels of HBeAg, HBsAg, HBV DNA and cccDNA in HBV-expressing hepatoma cells. Mechanically, the ethanol increased the levels of HBx and MSL2 in vivo and in HBV-expressing HepG2 cells, but not in HBV-free HepG2 cells. Moreover, the down-regulation of MSL2 by small interference RNA could block the ethanol-promoted HBV cccDNA in HepG2.2.15 cells. As a commonly administered treatment for HBV, the effect of IFNα on ethanol-triggered HBV cccDNA remains poorly understood. Strikingly, we showed that the treatment with IFN-α2b inhibited the ethanol-promoted cccDNA through depressing MSL2 in the cells. Thus, we conclude that IFN-α2b inhibits the ethanol-enriched HBV cccDNA through blocking a positive feedback loop of HBx/MSL2/cccDNA/HBV/HBx. Our finding provides new insights into the mechanism by which IFN-α2b inhibits ethanol-enhanced HBV cccDNA. Therapeutically, IFNα may contribute to the cccDNA induced by ethanol in liver.

Molecular Analysis of Membrane Targeting by the C2 Domain of the E3 Ubiquitin Ligase Smurf1

SMAD ubiquitination regulatory factor 1 (Smurf1) is a Nedd4 family E3 ubiquitin ligase that regulates cell motility, polarity and TGFβ signaling. Smurf1 contains an N-terminal protein kinase C conserved 2 (C2) domain that targets cell membranes and is required for interactions with membrane-localized substrates such as RhoA. Here, we investigated the lipid-binding mechanism of Smurf1 C2, revealing a general affinity for anionic membranes in addition to a selective affinity for phosphoinositides (PIPs). We found that Smurf1 C2 localizes not only to the plasma membrane but also to negatively charged intracellular sites, acting as an anionic charge sensor and selective PIP-binding domain. Site-directed mutagenesis combined with docking/molecular dynamics simulations revealed that the Smurf1 C2 domain loop region primarily interacts with PIPs and cell membranes, as opposed to the β-surface cationic patch employed by other C2 domains. By depleting PIPs from the inner leaflet of the plasma membrane, we found that PIP binding is necessary for plasma membrane localization. Finally, we used a Smurf1 cellular ubiquitination assay to show that the amount of ubiquitin at the plasma membrane interface depends on the lipid-binding properties of Smurf1. This study shows the mechanism by which Smurf1 C2 targets membrane-based substrates and reveals a novel interaction for non-calcium-dependent C2 domains and membrane lipids.

WWP2 regulates proliferation of gastric cancer cells in a PTEN-dependent manner

WW domain containing E3 Ub-protein ligase 2 (WWP2) plays an important role in tumor progression as an E3 ligase of PTEN. Here, we investigated the role of WWP2 in gastric cancer (GC). We found that WWP2 is overexpressed in GC tissues, which is closely related to poor prognosis of GC patients. Using a WWP2-shRNA lentivirus expressing system, we established WWP2 stable-knockdown GC cell lines and found that knockdown of WWP2 inhibits the proliferation of GC cells both in vitro and in vivo. Also, WWP2 silencing induced the up-regulation of PTEN protein level and down-regulation of AKT phosphorylation level. We further investigated the role of PTEN in this regulating process by performing rescue assay and found that PTEN is essential for WWP2-mediated regulation of GC cells proliferation. Taken together, our results demonstrated that WWP2 promotes proliferation of GC cells by downregulating PTEN, which may provide new therapeutic targets for GC.

The E3 Ubiquitin Ligase TMEM129 Is a Tri-Spanning Transmembrane Protein

Misfolded proteins from the endoplasmic reticulum (ER) are transported back into the cytosol for degradation via the ubiquitin-proteasome system. The human cytomegalovirus protein US11 hijacks this ER-associated protein degradation (ERAD) pathway to downregulate human leukocyte antigen (HLA) class I molecules in virus-infected cells, thereby evading elimination by cytotoxic T-lymphocytes. Recently, we identified the E3 ubiquitin ligase transmembrane protein 129 (TMEM129) as a key player in this process, where interference with TMEM129 activity in human cells completely abrogates US11-mediated class I degradation. Here, we set out to further characterize TMEM129. We show that TMEM129 is a non-glycosylated protein containing a non-cleaved signal anchor sequence. By glycosylation scanning mutagenesis, we show that TMEM129 is a tri-spanning ER-membrane protein that adopts an N_exo–C_cyto orientation. This insertion in the ER membrane positions the C-terminal really interesting new gene (RING) domain of TMEM129 in the cytosol, making it available to catalyze ubiquitination reactions that are required for cytosolic degradation of secretory proteins.

The E3-ligase E6AP Represses Breast Cancer Metastasis via Regulation of ECT2-Rho Signaling

Metastatic disease is the major cause of breast cancer-related death and despite many advances, current therapies are rarely curative. Tumor cell migration and invasion require actin cytoskeletal reorganization to endow cells with capacity to disseminate and initiate the formation of secondary tumors. However, it is still unclear how these migratory cells colonize distant tissues to form macrometastases. The E6-associated protein, E6AP, acts both as an E3 ubiquitin-protein ligase and as a coactivator of steroid hormone receptors. We report that E6AP suppresses breast cancer invasiveness, colonization, and metastasis in mice, and in breast cancer patients, loss of E6AP associates with poor prognosis, particularly for basal breast cancer. E6AP regulates actin cytoskeletal remodeling via regulation of Rho GTPases, acting as a negative regulator of ECT2, a GEF required for activation of Rho GTPases. E6AP promotes ubiquitination and proteasomal degradation of ECT2 for which high expression predicts poor prognosis in breast cancer patients. We conclude that E6AP suppresses breast cancer metastasis by regulating actin cytoskeleton remodeling through the control of ECT2 and Rho GTPase activity. These findings establish E6AP as a novel suppressor of metastasis and provide a compelling rationale for inhibition of ECT2 as a therapeutic approach for patients with metastatic breast cancer. Cancer Res; 76(14); 4236-48. ©2016 AACR.

Morphological Alterations in Gastrocnemius and Soleus Muscles in Male and Female Mice in a Fibromyalgia Model

BACKGROUND

Fibromyalgia (FM) is a chronic musculoskeletal pain disorder, characterized by chronic widespread pain and bodily tenderness and is often accompanied by affective disturbances, however often with unknown etiology. According to recent reports, physical and psychological stress trigger FM. To develop new treatments for FM, experimental animal models for FM are needed to be development and characterized. Using a mouse model for FM including intermittent cold stress (ICS), we hypothesized that ICS leads to morphological alterations in skeletal muscles in mice.

METHODS

Male and female ICS mice were kept under alternating temperature (4 °C/room temperature [22 °C]); mice constantly kept at room temperature served as control. After scarification, gastrocnemius and soleus muscles were removed and snap-frozen in liquid nitrogen-cooled isopentane or fixed for electron microscopy.

RESULTS

In gastrocnemius/soleus muscles of male ICS mice, we found a 21.6% and 33.2% decrease of fiber cross sectional area (FCSA), which in soleus muscle concerns the loss of type IIa and IIx FCSA. This phenomenon was not seen in muscles of female ICS mice. However, this loss in male ICS mice was associated with an increase in gastrocnemius of the density of MIF+ (8.6%)-, MuRF+ (14.7%)-, Fbxo32+ (17.8%)-cells, a 12.1% loss of capillary contacts/muscle fiber as well as a 30.7% increase of damaged mitochondria in comparison with male control mice. Moreover, significant positive correlations exist among densities (n/mm(2)) of MIF+, MuRF+, Fbxo32+-cells in gastrocnemius/ soleus muscles of male ICS mice; these cell densities inversely correlate with FCSA especially in gastrocnemius muscle of male ICS mice.

CONCLUSION

The ICS-induced decrease of FCSA mainly concerns gastrocnemius muscle of male mice due to an increase of inflammatory and atrogenic cells. In soleus muscle of male ICS and soleus/gastrocnemius muscles of female ICS mice morphological alterations seem to occur not at all or delayed. The sex-specificity of findings, which is not easily reconciled with the epidemiology of FM (female predominance), implicate that gastrocnemius muscle of male ICS mice should preferentially be used for future investigations with FM. Moreover, we suggest to investigate morphological and/or molecular alterations at different time-points (up to two weeks) after ICS.

Mitophagy programs: mechanisms and physiological implications of mitochondrial targeting by autophagy

Mitochondria are an essential source of ATP for cellular function, but when damaged, mitochondria generate a plethora of stress signals, which lead to cellular dysfunction and eventually programmed cell death. Thus, a major component of maintaining cellular homeostasis is the recognition and removal of dysfunctional mitochondria through autophagy-mediated degradation, i.e., mitophagy. Mitophagy further constitutes a developmental program, and undergoes a high degree of crosstalk with apoptosis. Reduced mitochondrial quality control is linked to disease pathogenesis, suggesting the importance of process elucidation as a clinical target. Recent work has revealed multiple mitophagy programs that operate independently or undergo crosstalk, and require modulated autophagy receptor activities at outer membranes of mitochondria. Here, we review these mitophagy programs, focusing on pathway mechanisms which recognize and target mitochondria for sequestration by autophagosomes, as well as mechanisms controlling pathway activities. Furthermore, we provide an introduction to the currently available methods for detecting mitophagy.

NITROGEN LIMITATION ADAPTATION recruits PHOSPHATE2 to target the phosphate transporter PT2 for degradation during the regulation of Arabidopsis phosphate homeostasis

The NITROGEN LIMITATION ADAPTION (NLA) gene was initially shown to function in nitrogen limitation responses; however, recent work shows that the nla mutant hyperaccumulates Pi, phenocopying the Pi signaling mutant pho2. PHO2 encodes a putative E2 conjugase, UBC24. Here, we show that NLA is an E3 ligase that specifically requires UBC24 for polyubiquitination in Arabidopsis thaliana. Among five members of the Pht1 Pi-transporter family tested, NLA associates only with PT2 (Pht1;4). The NLA-UBC24 pair mediates polyubiquitination of PT2 but not PT1. Posttranslational decay of PT2 at high Pi is blocked in pho2 and inhibited by MG132, indicating the requirement of UBC24 and 26S proteasomes. Consistent with NLA/UBC24 function, induced NLA expression causes a UBC24-dependent decrease in PT2 levels. Confocal microscopy of fusion proteins revealed an NLA/PT2 interaction at the plasma membrane. Collectively, these results show that under Pi-replete conditions, NLA and UBC24 target the PT2 transporter for destruction. During the Pi deprivation response, NLA and PHO2 transcripts are cleaved by miR399 and miR827, respectively, and our results suggest that this downregulation relieves the posttranslational repression of PT2, allowing it to accumulate and participate in Pi uptake. Our work provides additional molecular details describing Pi signaling/homeostasis regulation by identifying NLA and UBC24 as partners and PT2 as one of their downstream targets.

High expression of P53-induced Ring-h2 protein is associated with poor prognosis in clear cell renal cell carcinoma

PURPOSE

This study was carried out to examine P53-induced Ring-h2 protein (Pirh2) expression and investigate its clinical and prognostic significance in patients with clear cell renal cell carcinoma (ccRCC).

METHODS

Pirh2 mRNA and protein expressions were detected by quantitative reverse-transcription polymerase chain reaction (Q-RT PCR) and Western blotting in 35 frozen renal cancer tissue specimens and 35 adjacent normal renal tissue specimens of the same patients. Pirh2 protein expression was assessed by immunohistochemical analysis in 92 paraffin-embedded specimens of human ccRCC and 30 specimens of adjacent normal renal tissue. Correlations between Pirh2 and clinicopathologic features and prognosis were analyzed statistically.

RESULTS

Pirh2 mRNA and protein levels in ccRCC samples were increased significantly as compared with the adjacent normal renal tissues (P < 0.001). Pirh2 mRNA overexpression correlated with high stage and grade of the renal cancer (P < 0.001 and P < 0.001 respectively). Pirh2 protein expression was negative in most normal renal tissue specimens (23/30) but positive in 52.2% (48/92) of ccRCC specimens (P = 0.006). Pirh2 protein expression correlated with tumor grade and stage (P < 0.001 and P < 0.001 respectively). The median follow-up interval was 42.0 months. Overexpression of Pirh2 protein in ccRCC was significantly associated with shorter overall survival and recurrence-free survival (P = 0.001 and P = 0.003, respectively). Multivariate analysis showed that Pirh2 expression was an independent prognostic factor for ccRCC patients (P = 0.037).

CONCLUSIONS

Pirh2 was up-regulated in ccRCC at both transcriptional and translational levels compared with normal renal tissues, suggesting that Pirh2 may be a potential prognostic marker for ccRCC.

Growth performance and nutrient composition of juvenile Nile tilapia (Oreochromis niloticus) fed Spirulina flakes, rice bran and mustard oil cake

INTRODUCTION

Tilapia (Oreochromis niloticus) is an important cultured fish that is widely distributed in Bangladesh. This study was conducted to improve the growth performance and nutrient contents of the fish using five different types of feeds.

METHODS

Tilapia fingerlings were fed two types of commercial fish feeds (Feed-1 and Feed-2), Spirulina flakes (Feed-3), Feed-2 mixed with Spirulina flakes (Feed-4) and manually mixed feed made from a mixture of mustard oil cake and rice bran (Feed-5). After 4 weeks of being fed with the diets, growth parameters and meat nutrient composition of the tilapia fingerlings were recorded.

RESULTS

Significant growth in length and weight was observed in juvenile tilapia fish fed with commercial Feed-1 only, while growth performance varied significantly among fingerlings fed other types of feeds. Body tissue calcium (92.8 mg/100 g), iron (1.29 mg/100 g) was higher in fishes fed with dry Spirulina flakes (Feed 3), while the highest amount of zinc (2.09 mg/100 g) was recorded in fishes fed Feed-5. Protein (13.32%) content was highest in fish fed Feed-2 mixed with Spirulina flakes (Feed-4).

CONCLUSION

Meat nutritional quality of tilapia can be improved by combining commercial feeds with Spirulina flakes, compared with feeding commercial feeds in isolation.

Assessing 'radiosensitivity' with kinetic profiles of γ-H2AX, 53BP1 and BRCA1 foci

BACKGROUND AND PURPOSE

DNA repair assays to identify radiosensitive patients have had limited clinical implementation due to long turn-around times or limited specificity. This study evaluates γ-H2AX-Irradiation Induced Foci (IRIF) kinetics as a more rapid surrogate for the 'gold standard' colony survival assay (CSA) using several known DNA repair disorders as reference models.

MATERIALS AND METHODS

Radiosensitive cells of known and unknown etiology were studied. γ-H2AX-IRIFs were quantified over 24 h, and the curves were fitted by combining logarithmic growth and exponential decay functions. Fitted values that differed from radionormal controls were considered aberrant and compared to CSA results.

RESULTS

We observed 87% agreement of IRIF data with the CSA for the 14 samples tested. Analysis of γ-H2AX-IRIF kinetics for known repair disorders indicated similarities between an RNF168(-/-) cell line and an RS cell of unknown etiology. These cell lines were further characterized by a reduction in BRCA1-IRIF formation and G2/M checkpoint activation.

CONCLUSIONS

γ-H2AX-IRIF kinetics showed high concordance with the CSA in RS populations demonstrating its potential as a more rapid surrogate assay. This method provides a means to globally identify defective DNA repair pathways in RS cells of unknown etiology through comparison with known DNA repair defects.

Morphological heterogeneity of oral salivary gland carcinomas: a clinicopathologic study of 41 cases with long term follow-up emphasizing the overlapping spectrum of adenoid cystic carcinoma and polymorphous low-grade adenocarcinoma

We analyzed 41 oral salivary gland carcinomas from consecutive 290 salivary gland carcinoma database (14%) with emphasis on the histological spectrum and clinical outcome of adenoid cystic carcinoma (ACC) and polymorphous low-grade adenocarcinoma (PLGA). The cohort included 14 ACCs, 14 mucoepidermoid carcinomas (MECs), 8 PLGAs, 3 adenocarcinomas, not otherwise specified and 2 acinic cell carcinomas. Mean age was 48, 58 and 61 yrs for ACC, MEC and PLGA, respectively. Eight patients (19.5%) died of tumor at a mean interval of 66.5 months. ACC and PLGA showed similar mean age, gender distribution, predominant palatal localization, nodal metastasis, perineural invasion and MIB-1 index. However, ACC tended to show higher tumor stage and residual tumor (R1/R2) more frequently than PLGA, but this was statistically not significant. ACC and PLGA showed overlapping architectural patterns. However, ACCs displayed well organized basal-luminal differentiation, highlighted by CK5/CK7 immunostaining. In contrast, PLGA showed a disorganized histological and immunohistological pattern. C-Kit expression (CD117) was common in ACC, generally mirroring that of CK7 and virtually lacking in PLGA. Kaplan-Meier analysis demonstrated a similar clinical course for ACC and PLGA with 5 years survivals of 87% and 80%, respectively. Fluorescence in situ hybridization (FISH) performed on all 290 salivary carcinomas confirmed the specificity of the translocation t (11; 19) for MEC and its absence in all other carcinomas including ACC and PLGA. Our results emphasize the diversity of oral salivary gland carcinomas and the overlapping clinicopathological features of ACC and PLGA.

Identification of distinctive patterns of USP19-mediated growth regulation in normal and malignant cells

We previously reported that the USP19 deubiquitinating enzyme positively regulates proliferation in fibroblasts by stabilizing KPC1, a ubiquitin ligase for p27(Kip1). To explore whether this role of USP19 extends to other cellular systems, we tested the effects of silencing of USP19 in several human prostate and breast models, including carcinoma cell lines. Depletion of USP19 inhibited proliferation in prostate cancer DU145, PC-3 and 22RV1 cells, which was similar to the pattern established in fibroblasts in that it was due to decreased progression from G1 to S phase and associated with a stabilization of the cyclin-dependent kinase inhibitor p27(Kip1). However, in contrast to previous findings in fibroblasts, the stabilization of p27(Kip1) upon USP19 depletion was not associated with changes in the levels of the KPC1 ligase. USP19 could also regulate the growth of immortalized MCF10A breast epithelial cells through a similar mechanism. This regulatory pattern was lost, though, in breast cancer MCF7 and MDA-MB-231 cells and in prostate carcinoma LNCaP cells. Of interest, the transformation of fibroblasts through overexpression of an oncogenic form of Ras disrupted the USP19-mediated regulation of cell growth and of levels of p27(Kip1) and KPC1. Thus, the cell context appears determinant for the ability of USP19 to regulate cell proliferation and p27(Kip1) levels. This may occur through both KPC1 dependent and independent mechanisms. Moreover, a complete loss of USP19 function on cell growth may arise as a result of oncogenic transformation of cells.

Grading ductal carcinoma in situ of the breast using an automated proliferation index

Tumor grade, size and margin status are the most significant factors in predicting the behavior of ductal carcinoma in-situ (DCIS). The inclusion of necrosis and nuclear grade in the grading of DCIS has demonstrated a fair but suboptimal agreement between pathologists. The grading of DCIS was studied and compared to the Van Nuys (VN) system, by using our newly proposed unifying "nuclear grade + proliferation index (N+P) grading system for invasive carcinomas. 162 DCIS tumors were studied including 49 VN I, 31 VN II, and 82 VN III cases. The VN and N+P systems were compared with each other and correlated with tumor size, ER, PR, p53, Her-2, EGFR, Bcl-2, p27 and p21 status. The two systems demonstrated similar frequencies for the different grades and an agreement with each other for all of the biomarkers studied. The greatest difference between the two systems was observed for those tumors initially classified as VN II (94% being down-graded to N+P I) and VN III (80% being down-graded to N+P II). These results suggest that the N+P system, combining nuclear grade with automated MIB-1 count, is a potentially valid and reproducible grading system for both non-invasive and invasive mammary carcinomas. It is automated, less subjective in assessing mitotic activity and necrosis and correlates with other prognostic biomarkers.

Hyalinizing trabecular tumor and papillary carcinoma of the thyroid

BACKGROUND

Hyalinizing trabecular tumor (HTT) is a rare thyroid neoplasm, which shares some histologic features with thyroid papillary carcinoma (TPC). Clinically, it is frequently misdiagnosed as papillary carcinoma, even for some experienced pathologists. The aim of this study was to investigate whether HTT is variant of TPC or HTT is an independent entity of thyroid neoplasm.

METHODS

The expression of CK19, galectin-3, HBME-1 and MIB-1 was detected by immunohistochemical staining in 12 cases of hyalinizing trabecular tumor and 20 cases of thyroid papillary carcinoma.

RESULTS

Two of the 12 HTT samples were positive or focally positive for CK19. Four of the 12 samples of HTT presented positive to galectin-3; 3 were stained strongly and the other one was focally positive. None of the 12 samples of HTT was positive for HBME-1. Five in 12 HTT samples were stained in nucleus for MIB-1. Almost all the 20 cases of thyroid papillary carcinoma were intensely stained for CK19, galectin-3 and HBME-1. Fifteen in 20 cases of thyroid papillary carcinoma showed nuclear staining for MIB-1.

CONCLUSIONS

HTT is an independent thyroid neoplasm, not a variant of TPC. This study could help in the differential diagnosis of HTT from TPC. CK19, galectin-3 and HBME-1 are adequate to identify HTT and TPC, but MIB-1 does not play an important role in discrimination between HTT and TPC.

[Effects of UO-126 on proliferation and fbw7 expression of HeLa cells]

AIM

To observe the effects of UO-126 on the expression of F-box and WD repeat domain-containing protein 7(FBW7)and on the proliferation of human cervical cancer cell lines (HeLa cells).

METHODS

HeLa cells were treated with different concentrations of UO-126, MTT assay was used to observe the proliferation of HeLa cells. Immunofluorescence showed the location and expression of FBW7 in HeLa cells. The mRNA and protein expression of FBW7 were detected by RT-PCR and Western blot before and after mitogen-activated protein kinases (MAPK)signal was blocked by UO-126 a MAPK inhibitor.

RESULTS

MTT results showed that the concentration range of MAPK signaling pathway inhibitor UO-126 inhibited the proliferation of HeLa cells in a concentration-and time-dependent manner(P<0.05). Immunofluorescence showed that the expression of positive FBW7 had increased after HeLa cells were treated with UO-126. RT-PCR and Western blot exhibited that the FBW7 mRNA and protein expression had significantly increased before and after HeLa cells were treated with UO-126(P<0.05).

CONCLUSION

UO-126 could inhibit HeLa cells proliferation, FBW7 lied downstream of MAPK signaling pathway.

CNI1/ATL31, a RING-type ubiquitin ligase that functions in the carbon/nitrogen response for growth phase transition in Arabidopsis seedlings

Plants are able to sense and respond to changes in the balance between carbon (C) and nitrogen (N) metabolite availability, known as the C/N response. During the transition to photoautotrophic growth following germination, growth of seedlings is arrested if a high external C/N ratio is detected. To clarify the mechanisms for C/N sensing and signaling during this transition period, we screened a large collection of FOX transgenic plants, overexpressing full-length cDNAs, for individuals able to continue post-germinative growth under severe C/N stress. One line, cni1-D (carbon/nitrogen insensitive 1-dominant), was shown to have a suppressed sensitivity to C/N conditions at both the physiological and molecular level. The CNI1 cDNA encoded a predicted RING-type ubiquitin ligase previously annotated as ATL31. Overexpression of ATL31 was confirmed to be responsible for the cni1-D phenotype, and a knock-out of this gene resulted in hypersensitivity to C/N conditions during post-germinative growth. The ATL31 protein was confirmed to contain ubiquitin ligase activity using an in vitro assay system. Moreover, removal of this ubiquitin ligase activity from the overexpressed protein resulted in the loss of the mutant phenotype. Taken together, these data demonstrated that CNI1/ATL31 activity is required for the plant C/N response during seedling growth transition.

[The immunohistochemical expression of cyclin B1 is associated with higher SUV in 18F-FDG-PET in non-small cell lung cancer patients. Initial results]

AIM

to study the expression of cyclin B1 and its possible relationship with the maximum SUV in FDG-PET and MIB1 expression in patients with NSCLC.

MATERIALS AND METHODS

49 patients (15 adenocarcinomas, 27 squamous cell carcinomas and 7 bronchoalveolar carcinomas) were included in this study; the immunohistochemical expression of cyclin B1 was determined using the tissue-array technique. Each PET was performed 60 minutes after the i.v. administration of 350-518 MBq of FDG on an Advance system (GE) in 2D acquisition mode.

RESULTS

cyclin B1 expression was detected in 40 out of 45 cases. The SUV values were higher (p=0.04) in the cyclin B1+ cases than in the negative cases (16.4+/-8.1 vs 10.9+/-6.2). Cyclin B1 expression and SUV values were not correlated with the clinical stage. The expression of cyclin B1+ correlated positively (p<0.0001) with that of MIB1. After univariate analysis, only the cellular proliferation was a prognostic factor (p=0.037).

CONCLUSIONS

our results suggest that there is a direct correlation between cyclin B1 expression and max-SUV values in the PET of NSCLC patients. When the association of cyclin B1 with positive MIB1 is also considered, our results support the role of cell proliferation in FDG uptake by the tumour.

Akt/protein kinase B overexpression as an accurate prognostic marker in adult diffuse astrocytoma

BACKGROUND

Akt/Protein kinase B (PKB) is a common downstream molecule of Ras signaling essential for cell survival. In an attempt to find a novel prognostic marker of diffuse astrocytoma, we performed an immunohistochemical analysis of Akt/PKB with regard to patient survival and regrowth patterns.

METHODS

Twenty-four adult patients with diffuse astrocytoma were similarly managed without early post-operative radiotherapy and followed up for a median period of 7.5 years. They were analysed by immunohistochemistry for Akt/PKB expression as well as p53 protein accumulation, epidermal growth factor receptor (EGFR) expression, and MIB-1 labeling index. The prognostic significance of each molecular covariate was tested by multivariate analysis using Cox's proportional hazard model including age, performance status, and extent of surgical resection.

FINDINGS

Akt/PKB overexpression significantly correlated with both shorter overall survival (OS) and progression-free survival (PFS) (p = 0.0110). All the Akt/PKB-positive patients with post-operative residual tumours experienced tumour recurrences, whereas only a small fraction of the Akt/PKB-negative individuals had recurrences (p = 0.0070). Invasive recurrence into surrounding brain occurred only in the Akt/PKB-overexpressed tumours. In contrast, MIB-1 labeling index correlated only with OS, while p53 protein accumulation correlated only with PFS. The Cox's proportional hazard model identified Akt/PKB overexpression as a significant prognostic factor for shorter PFS (p = 0.0117).

CONCLUSION

These results show that Akt/PKB overexpression would be suggestive of malignant progression and invasive regrowth of diffuse astrocytoma, and it can serve as a novel prognostic marker for this tumour.

Activity of telomerase in ovarian cancer cells. Clinical implications

Estimation of telomerase activity in cell nuclei of ovarian malignant tumours may provide an independent prognostic index. The test for telomerase activity in tumour cell nuclei may be accepted as a useful diagnostic test with application for differential diagnoses of benign ovarian tumours vs tumours of a borderline or malignant character.

Prognostic value of a proliferation index including MIB1 and argyrophilic nucleolar organizer regions proteins in node-negative breast cancer

OBJECTIVE

This study was designed to evaluate a cell proliferation marker, including the percentage of cycling cells (MIB1), and the duration of the cell cycle (assessed by argyrophilic nucleolar organizer regions proteins [AgNORs] measurement).

STUDY DESIGN

We included 90 patients with invasive node-negative breast cancer. None received chemotherapy. With the help of a double-staining technique, a proliferation index (PI) was determined by multiplying the percentage of MIB1-positive cells by the mean area of the AgNORs present in those MIB1-positive cells. PI was evaluated for its impact on overall survival (OS) and disease-free survival (DFS).

RESULTS

We demonstrated that PI was correlated to OS. For DFS, it conserved its high prognostic value only in univariate analysis. The global amount of AgNORs was more discriminative for DFS.

CONCLUSION

PI and AgNOR quantification supplied additional prognosis information in node-negative patients, and we propose to integrate them in further studies.

Interactions between the S-domain receptor kinases and AtPUB-ARM E3 ubiquitin ligases suggest a conserved signaling pathway in Arabidopsis

The Arabidopsis (Arabidopsis thaliana) genome encompasses multiple receptor kinase families with highly variable extracellular domains. Despite their large numbers, the various ligands and the downstream interacting partners for these kinases have been deciphered only for a few members. One such member, the S-receptor kinase, is known to mediate the self-incompatibility (SI) response in Brassica. S-receptor kinase has been shown to interact and phosphorylate a U-box/ARM-repeat-containing E3 ligase, ARC1, which, in turn, acts as a positive regulator of the SI response. In an effort to identify conserved signaling pathways in Arabidopsis, we performed yeast two-hybrid analyses of various S-domain receptor kinase family members with representative Arabidopsis plant U-box/ARM-repeat (AtPUB-ARM) E3 ligases. The kinase domains from S-domain receptor kinases were found to interact with ARM-repeat domains from AtPUB-ARM proteins. These kinase domains, along with M-locus protein kinase, a positive regulator of SI response, were also able to phosphorylate the ARM-repeat domains in in vitro phosphorylation assays. Subcellular localization patterns were investigated using transient expression assays in tobacco (Nicotiana tabacum) BY-2 cells and changes were detected in the presence of interacting kinases. Finally, potential links to the involvement of these interacting modules to the hormone abscisic acid (ABA) were investigated. Interestingly, AtPUB9 displayed redistribution to the plasma membrane of BY-2 cells when either treated with ABA or coexpressed with the active kinase domain of ARK1. As well, T-DNA insertion mutants for ARK1 and AtPUB9 lines were altered in their ABA sensitivity during germination and acted at or upstream of ABI3, indicating potential involvement of these proteins in ABA responses.

Arrest of cell proliferation in budding tumor cells ahead of the invading edge of colonic carcinomas. A preliminary report

BACKGROUND

Single or small groups of dedifferentiated tumor cells, referred to as tumor budding, may be found ahead of the defined invasive edge of colorectal carcinomas. Tumor budding is claimed to correlate with lymph node metastasis and local recurrence.

MATERIALS AND METHODS

Sections from six surgically removed invasive colonic carcinomas were stained with hematoxylin-eosin (H&E), MNF 116 (an epithelial marker) and for Ki-67 (a proliferation marker) and four specimens also for laminin-5 (a cell-locomotion marker).

RESULTS

In comparative fields, a mean of 86.2 tumor buds (range 60-132) were detected with MNF 116 immunostain, 5.8 tumor buds (mean, range 5-9) with H&E stain, 9.7 tumor buds (range 7-18) with Ki-67 immunostain and 9.3 tumor buds (range 8-12) with laminin-5.

CONCLUSION

The majority of the MNF 116-positive budding tumor cells ahead of the invading tumor front were not detected with H&E, or for Ki-67 or laminin-5. Host invasion by budding tumor cells might be activated only after the cell cycle has been switched off (G0).

A comparative analysis of lichen sclerosus of the vulva and lichen sclerosus that evolves to vulvar squamous cell carcinoma

OBJECTIVE

The aim of this study was to determine whether the premalignant change in lichen sclerosus (LS) could be identified with immunohistochemical analyses.

STUDY DESIGN

Eight cases of histologically diagnosed vulvar LS, which showed, after a period of 10 months-9 years, an evolution to carcinoma of the vulva that was histologically documented, were compared with 8 cases of vulvar LS, for which follow-up information was available for at least 9 years. The proliferative index and the expression of tumor suppressors p16 and p53 were analyzed.

RESULTS

The difference of MIB1 labeling index of evolving or unchanged LS cases was significant (P = .005). The difference in the p53 of evolving or unchanged LS cases shows a trend towards association (P = .08). Both LS cases (evolving or unchanged) did not show p16 positive staining.

CONCLUSION

The evaluation of MIB1 and p53 may identify those vulvar LS cases with a high likelihood of evolving into squamous cell carcinoma, which would need careful periodic checks or adjunctive biopsies. The study must be confirmed by a larger number of cases to substantiate this observation.

Proliferative index in astrocytic tumours

The accurate grading of astrocytic tumours is of prime importance because it is critical to the patient management and survival/outcome. Although internationally accepted WHO grading system of CNS tumours is based on histological features of H&E stained sections, yet there are cases where differentiation between grade II and grade III is difficult particularly when the biopsy is small. Proliferative index derived from MIB-1 immunostaining has been found to be useful in the distinction between various grades of malignancy. Formalin-fixed paraffin-embedded surgical specimens from 90 cases of astrocytic tumours, 30 each of low-grade astrocytoma (grade II), anaplastic astrocytoma (grade III), and glioblastoma multiforme (grade IV), were immunostained by standard indirect immunoperoxidase technique using MIB-1 monoclonal antibody. MIB-1 labeling index (MIB-1 LI) was calculated. The mean MIB-1 LI values of astrocytomas, anaplastic astrocytomas and glioblastomas were 1.75 +/- 1.5%, 8.74 +/- 6.2%, and 20.54 +/- 12.2% respectively and there was statistically significant difference between grade II and III (Unpaired "t" test, T value 5.907, p value < 0.001) and grade III and grade IV (T value 4.734, p value < 0.001). The statistical analysis also revealed that the mean MIB-1 LI increased with histological grade of malignancy (One way ANOVA test, p value < 0.001). This investigation further reinforces and corroborates the findings that MIB-1 LI is useful tool in assigning grading to the astrocytic tumours and hence in treatment modalities and should be used routinely.

Myoepithelial carcinoma of soft tissue: a case report

Myoepithelioma of soft tissue is a recently categorized entity and myoepithelial carcinoma is extremely rare. We describe a case of myoepithelial carcinoma of soft tissue in a 30-year-old male patient, who presented with a painless mass located at the back of left leg involving popliteal fossa that was present since childhood. A wide local excision was performed. The distinct histopathological features included infiltrative margins, cytologically moderate to severely atypical epithelioid/spindled cells with prominent nucleoli, 3-4 mitoses/10HPF, tumor necrosis and lymphovascular invasion. No heterologous elements were identified. The myoepithelial origin was confirmed by positive immunohistochemical staining for S100 protein, epithelial membrane antigen and smooth muscle actin. Mib-1 (Ki-67) proliferation index was 20-25%. These carcinomas have variable clinical presentation and can have an indolent course for several years. Recognition of myoepithelial carcinoma is clinically significant because compared to its benign counterpart, this has increased frequency of local recurrences and metastases that warrants a close clinical follow-up.

Parkin interacts with LIM Kinase 1 and reduces its cofilin-phosphorylation activity via ubiquitination

Mutations in the PARKIN (PARK2) gene have been found in the majority of early-onset familial Parkinson's disease (PD) patients with autosomal recessive juvenile parkinsonism (ARJP). Parkin protein functions as an ubiquitin (E3) ligase that targets specific proteins for degradation in the 26S proteasome. Here, based on a mass spectrometry analysis of the human dopaminergic neuroblastoma-derived cell line SH-SY5Y that over-expresses parkin, we found that parkin may suppress cofilin phosphorylation. LIM Kinase 1 (LIMK1) is the upstream protein that phosphorylates cofilin, an actin depolymerizing protein. Thus, we postulated a possible connection between parkin and LIMK1. Our studies in other cell lines, using co-transfection assays, demonstrated that LIMK1 and parkin bind each other. LIMK1 also interacted with previously known parkin interactors Hsp70 and CHIP. Parkin enhanced LIMK1-ubiquitination in the human neuroblastoma-derived BE(2)-M17 cell line, but not in the human embryonic kidney-derived HEK293 cell line. In fact, parkin-over-expression reduced the level of LIMK1-induced phosphocofilin in the BE(2)-M17 cells but not in the HEK293 cells. Additionally, in simian kidney-derived COS-7 cells, parkin-over-expression reduced LIMK1-induced actin filament accumulation. LIMK1 in cultured cells regulates parkin reversibly: LIMK1 did not phosphorylate parkin but LIMK1 overexpression reduced parkin self-ubiquitination in vitro and in HEK293 cells. Furthermore, in the cells co-transfected with parkin and p38, LIMK1 significantly decreased p38-ubiquitination by parkin. These findings demonstrate a cell-type dependent functional interaction between parkin and LIMK1 and provide new evidence that links parkin and LIMK1 in the pathogenesis of familial PD.

The Spectrum of Malignancy in Craniopharyngioma

Craniopharyngiomas are low-grade epithelial neoplasms occurring almost exclusively in the sellar/suprasellar region. Histologic malignancy is extremely rare; the literature consists mostly of isolated case reports. Herein, we report 3 patients with craniopharyngiomas exhibiting histologic malignancy, 2 of which received radiation therapy before its appearance. Hematoxylin and eosin-stained slides and selected immunohistochemical stains were reviewed in all cases. Microvessel density analysis was performed in case 2. The patients included 2 men and 1 woman, age 14, 31, and 58 years at presentation, respectively. All patients expired 3 months to 9 years after first resection and 3 to 9 months after identification of histologic malignancy. The latter developed after multiple recurrences and radiation therapy in 2 cases, but seemed to arise de novo in 1 case resembling odontogenic ghost cell carcinoma and lacking any definite low-grade craniopharyngioma precursor. The malignant component of the other 2 cases resembled squamous cell carcinoma and low-grade myoepithelial carcinoma, respectively. The MIB-1 labeling index was markedly increased in the malignant component in comparison with the low-grade precursor. Malignant transformation in craniopharyngiomas, although rare, does exist. It assumes varied histologic appearances, usually after multiple recurrences and radiation therapy, and has a near uniformly fatal outcome. De novo malignancy in odontogenic tumors of the sella is even more unusual, but also has an ominous prognosis.

A unifying concept of trophoblastic differentiation and malignancy defined by biomarker expression

Several trophoblast phenotypes, including cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast, emerge during gestation. To clarify the lineage relationship between these subtypes, we profiled p63 localization in developing and term placental tissue, as well as in trophoblastic tumors, using antibodies specific to full-length (TAp63) and one against all p63 isoforms (TAp63 and DeltaNp63). Localization of p63 was compared with that of biomarkers of proliferation and trophoblastic differentiation, including mib-1, inhibin, and MelCAM. In early gestation, p63 was localized principally to villous cytotrophoblast after contact with the villous mesenchyme, absent in the trophoblast columns, and early implantation trophoblast. In the maturing placenta, intraplacental perivillous fibrin correlated with the emergence of a p63-positive "transitional" (vacuolated) extravillous trophoblast from cytotrophoblast, which differentiated further into a "mature" p63-negative extravillous trophoblast. The same lineage pathway emerged from entrapped villi on the chorionic membrane. Virtually all p63 immunopositivity was attributed to dominant-negative p63. The immunophenotypic patterns seen in the immature and mature placenta permit the resolution of all trophoblastic phenotypes within 3 lineage pathways of cytotrophoblast differentiation, including cytotrophoblast-to-trophoblast column/implantation site, cytotrophoblast-to-syncytiotrophoblast, and cytotrophoblast-to-mature extravillous trophoblast. In the latter pathway, a transitional (vacuolated) p63-positive extravillous trophoblast emerges from and links cytotrophoblast to mature extravillous trophoblast in intraplacental fibrin, chorionic membrane, and basal plate. The placental trophoblast is thus resolved within this continuum of differentiation. Terms such as transitional and mature extravillous trophoblast are proposed to reflect the differentiation phases of this unique epithelium. p63 staining patterns in trophoblastic tumors reflect timing of neoplastic transformation during trophoblastic differentiation.

The Hectd1 ubiquitin ligase is required for development of the head mesenchyme and neural tube closure

Closure of the cranial neural tube depends on normal development of the head mesenchyme. Homozygous-mutant embryos for the ENU-induced open mind (opm) mutation exhibit exencephaly associated with defects in head mesenchyme development and dorsal-lateral hinge point formation. The head mesenchyme in opm mutant embryos is denser than in wildtype embryos and displays an abnormal cellular organization. Since cells that originate from both the cephalic paraxial mesoderm and the neural crest populate the head mesenchyme, we explored the origin of the abnormal head mesenchyme. opm mutant embryos show apparently normal development of neural crest-derived structures. Furthermore, the abnormal head mesenchyme in opm mutant embryos is not derived from the neural crest, but instead expresses molecular markers of cephalic mesoderm. We also report the identification of the opm mutation in the ubiquitously expressed Hectd1 E3 ubiquitin ligase. Two different Hectd1 alleles cause incompletely penetrant neural tube defects in heterozygous animals, indicating that Hectd1 function is required at a critical threshold for neural tube closure. This low penetrance of neural tube defects in embryos heterozygous for Hectd1 mutations suggests that Hectd1 should be considered as candidate susceptibility gene in human neural tube defects.

Low LATS2 mRNA level can predict favorable response to epirubicin plus cyclophosphamide, but not to docetaxel, in breast cancers

PURPOSE

Putative tumor suppressor genes LATS1 and LATS2 are implicated in the regulation of the cell cycle at the G2/M and G1/S phase, respectively. This study investigated possible correlations of intra-tumoral LATS1 and LATS2 mRNA levels with response to epirubicin plus cyclophosphamide (EC) or docetaxel (DOC) treatment.

METHODS

mRNA expression levels of LATS1 and LATS2 were determined by means of real-time PCR assay in 56 locally advanced breast cancers and 15 recurrent breast cancers treated with EC (n = 32) or DOC (n = 39).

RESULTS

Among the patients treated with EC, LATS2 mRNA levels of responders (0.72 +/- 0.11, mean +/- SE) were significantly (P < 0.05) lower than those of non-responders (1.62 +/- 0.44), and responders showed a tendency (P = 0.05) towards reduced LATS1 mRNA levels. Patients with low LATS2 mRNA levels (n = 16) showed a significantly (P < 0.05) higher response rate (75%) to EC treatment than those with high LATS2 mRNA levels (n = 16; response rate = 31%). Positive predictive value, negative predictive value, and diagnostic accuracy of LATS2 mRNA levels for prediction of response to EC were 75, 69, and 72%, respectively. On the other hand, neither LATS1 nor LATS2 mRNA levels were associated with response to DOC treatment.

CONCLUSION

These results suggest the possibility that intra-tumoral LATS2 mRNA levels may be clinically useful for the prediction of response to EC treatment by breast cancer patients. We speculate that disruption of the checkpoint function at the G1/S phase induced by down-regulation of LATS2 plays some part in the favorable response to EC.

Myocardial expression of Murf-1 and MAFbx after induction of chronic heart failure: Effect on myocardial contractility

OBJECTIVE

In chronic heart failure (CHF) the myocardial expression of the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha), which is thought to contribute to myocardial remodeling, was found to be increased. However, it is unknown whether the E3-ubiquitin ligases MAFbx and Murf-1 are involved in this remodeling process and whether their expression is regulated by TNF-alpha.

METHODS

Rats underwent ligation of the left coronary artery to induce CHF or were sham-operated. The expression of MAFbx/Murf-1 and troponin I was analyzed by RT-PCR and Western blotting in the non-infarcted area of the left ventricle. In cell culture experiments the potency of TNF-alpha to stimulate Murf-1/MAFbx expression, the intracellular signaling pathway, and the involvement of the E3-ligases for the impairment of contractility were assessed.

RESULTS

In CHF the myocardial expression of TNF-alpha was elevated 3.1-fold as compared to control. This was associated with a 4.5-fold and 2.7-fold increase in MAFbx and Murf-1 expression, respectively. A positive correlation between TNF-alpha and the expression of MAFbx or Murf-1 was evident. In neonatal rat cardiomyocytes, TNF-alpha induced the expression of MAFbx through p38MAPK-dependent pathways, whereas the induction of Murf-1 required the activation of the p42/44 MAPK pathway. Exposure of cardiomyocytes to TNF-alpha resulted in troponin I ubiquitinylation, subsequent degradation, and a decline in contractility. This was completely abrogated by siRNAs against Murf-1/MAFbx.

CONCLUSION

TNF-alpha, which is increasingly expressed in CHF, induces troponin I degradation through a MAFbx/Murf-1-dependent pathway. This was associated with an impairment of contractility and might be one mechanism involved in the adverse remodeling process in CHF.

A suite of tools and application notes for in vivo protein interaction assays using bioluminescence resonance energy transfer (BRET)

Bioluminescence resonance energy transfer (BRET) is a natural biophysical phenomenon that underlies an emerging technique to monitor protein-protein interactions in living cells in real time. Here, we present a series of technical advances to enhance the utility of the BRET assay in plants. A series of recombination cloning vectors was generated to accelerate the expression of proteins tagged with Renilla luciferase or yellow fluorescent protein under transient assay conditions and in stable transgenic plants. Working in stably transformed Arabidopsis or tobacco, we then detected BRET between three pairs of candidate interaction partners: dimerization of the E3 ubiquitin ligase COP1, interaction between COP1 and the B-box protein STH, and interaction between the light regulatory bZip transcription factors HY5 and HYH. A codon-optimized version of the Renilla luciferase gene resulted in improved expression in Arabidopsis. Renilla luciferase was active in a variety of subcellular organelles, including plastids, mitochondria, peroxisomes and Golgi stacks. In a survey of the Arabidopsis light signaling machinery as a model system, we estimated the likelihood that a known protein-protein interaction can be documented using BRET. Finally, we show that Renilla luciferase may serve as a reporter of protein stability in a cycloheximide chase assay.

E3 ubiquitin ligases as cancer targets and biomarkers

E3 ubiquitin ligases are a large family of proteins that are engaged in the regulation of the turnover and activity of many target proteins. Together with ubiquitin-activating enzyme E1 and ubiquitin-conjugating enzyme E2, E3 ubiquitin ligases catalyze the ubiquitination of a variety of biologically significant protein substrates for targeted degradation through the 26S proteasome, as well as for nonproteolytic regulation of their functions or subcellular localizations. E3 ubiquitin ligases, therefore, play an essential role in the regulation of many biologic processes. Increasing amounts of evidence strongly suggest that the abnormal regulation of some E3 ligases is involved in cancer development. Furthermore, some E3 ubiquitin ligases are frequently overexpressed in human cancers, which correlates well with increased chemoresistance and poor clinic prognosis. In this review, E3 ubiquitin ligases (such as murine double minute 2, inhibitor of apoptosis protein, and Skp1-Cullin-F-box protein) will be evaluated as potential cancer drug targets and prognostic biomarkers. Extensive study in this field would lead to a better understanding of the molecular mechanism by which E3 ligases regulate cellular processes and of how their deregulations contribute to carcinogenesis. This would eventually lead to the development of a novel class of anticancer drugs targeting specific E3 ubiquitin ligases, as well as the development of sensitive biomarkers for cancer treatment, diagnosis, and prognosis.

The BRCA1 E3 Ubiquitin Ligase Controls Centrosome Dynamics

The breast cancer specific tumor suppressor protein 1, BRCA1, mediates functions for all cells to grow. The puzzle of BRCA1 is that its loss is only associated with tumors in breast and ovarian epithelial cells. In this focused review, we highlight the data linking BRCA1 to the centrosome function, and we suggest that the specificity for breast tumors is due to a loss in restraint on centrosome function. Amplification of centrosome numbers secondary to loss of BRCA1 can drive the cell into the aneuploid state, thus, by this perspective loss of BRCA1 is a mutator phenotype.

PML contributes to a cellular mechanism of repression of herpes simplex virus type 1 infection that is inactivated by ICP0

Promyelocytic leukemia (PML) nuclear bodies (also known as ND10) are nuclear substructures that contain several proteins, including PML itself, Sp100, and hDaxx. PML has been implicated in many cellular processes, and ND10 are frequently associated with the replicating genomes of DNA viruses. During herpes simplex virus type 1 (HSV-1) infection, the viral regulatory protein ICP0 localizes to ND10 and induces the degradation of PML, thereby disrupting ND10 and dispersing their constituent proteins. ICP0-null mutant viruses are defective in PML degradation and ND10 disruption, and concomitantly they initiate productive infection very inefficiently. Although these data are consistent with a repressive role for PML and/or ND10 during HSV-1 infection, evidence in support of this hypothesis has been inconclusive. By use of short interfering RNA technology, we demonstrate that depletion of PML increases both gene expression and plaque formation by an ICP0-negative HSV-1 mutant, while having no effect on wild-type HSV-1. We conclude that PML contributes to a cellular antiviral repression mechanism that is countered by the activity of ICP0.

Localization of the coactivator Cdh1 and the cullin subunit Apc2 in a cryo-electron microscopy model of vertebrate APC/C

The anaphase-promoting complex/cyclosome (APC/C) is a ubiquitin ligase with essential functions in mitosis, meiosis, and G1 phase of the cell cycle. APC/C recognizes substrates via coactivator proteins such as Cdh1, and bound substrates are ubiquitinated by E2 enzymes that interact with a hetero-dimer of the RING subunit Apc11 and the cullin Apc2. We have obtained three-dimensional (3D) models of human and Xenopus APC/C by angular reconstitution and random conical tilt (RCT) analyses of negatively stained cryo-electron microscopy (cryo-EM) preparations, have determined the masses of these particles by scanning transmission electron microscopy (STEM), and have mapped the locations of Cdh1 and Apc2. These proteins are located on the same side of the asymmetric APC/C, implying that this is where substrates are ubiquitinated. We have further identified a large flexible domain in APC/C that adopts a different orientation upon Cdh1 binding. Cdh1 may thus activate APC/C both by recruiting substrates and by inducing conformational changes.

Metabolic acidosis has dual effects on sodium handling by rat kidney

Chronic metabolic acidosis (CMA) is associated with decreased NaCl reabsorption in the proximal tubule (PT). However, the effect of CMA on Na(+) transport in the distal tubule (DT) and collecting duct (CD) is poorly understood. Rats were placed in metabolic cages and had access to water (control), 0.28 M NH(4)Cl, or 0.28 M KCl solutions in a pair-feeding protocol for 5 days (5d). Metabolic acidosis developed within 24 h in NH(4)Cl-, but not in KCl-loaded rats. Interestingly, NH(4)Cl- but not KCl-loaded rats exhibited a significant natriuresis after 24 h of treatment. Urinary Na(+) excretion increased from 1.94 to 2.97 meq/24 h (P < 0.001) and returned to below baseline level (1.67 meq/l) after 5d of CMA. The protein abundance of the cortical Na-Cl cotransporter (NCC) remained unchanged at 24 h, but increased significantly (P < 0.01) after 5d of CMA. The protein abundance of alpha-, beta-, and gamma-subunits of the epithelial Na(+) channel (ENaC) in the cortex decreased sharply during the first 24 h and then returned to baseline levels after 5d of CMA. Interestingly, Sgk1 expression decreased after 24 h (-31%, P < 0.05) and then returned to baseline after 5d of CMA. Nedd4-2 expression was not altered during CMA. CMA enhanced serum aldosterone levels by 54% and increased the expression of aldosterone synthase in the adrenal gland by 134% after 5d of CMA. In conclusion, metabolic acidosis has dual effects on urinary Na(+) excretion. The early natriuresis results from decreased Na(+) reabsorption in the PT and Sgk1-related decreased ENaC activity in the DT and CD. Aldosterone-induced upregulation of NCC, Sgk1, and ENaC likely contributes to the antinatriuretic phase of metabolic acidosis. This adaptation prevents Na(+) wasting and volume depletion during chronic acid insult.

The DDB1-CUL4ADDB2 ubiquitin ligase is deficient in xeroderma pigmentosum group E and targets histone H2A at UV-damaged DNA sites

Xeroderma pigmentosum (XP) is a heritable human disorder characterized by defects in nucleotide excision repair (NER) and the development of skin cancer. Cells from XP group E (XP-E) patients have a defect in the UV-damaged DNA-binding protein complex (UV-DDB), involved in the damage recognition step of NER. UV-DDB comprises two subunits, products of the DDB1 and DDB2 genes, respectively. Mutations in the DDB2 gene account for the underlying defect in XP-E. The UV-DDB complex is a component of the newly identified cullin 4A-based ubiquitin E3 ligase, DDB1-CUL4A(DDB2). The E3 ubiquitin ligases recognize specific substrates and mediate their ubiquitination to regulate protein activity or target proteins for degradation by the proteasomal pathway. In this study, we have addressed the role of the UV-DDB-based E3 in NER and sought a physiological substrate. We demonstrate that monoubiquitinated histone H2A in native chromatin coimmunoprecipitates with the endogenous DDB1-CUL4A(DDB2) complex in response to UV irradiation. Further, mutations in DDB2 alter the formation and binding activity of the DDB1-CUL4A(DDB2) ligase, accompanied by impaired monoubiquitination of H2A after UV treatment of XP-E cells, compared with repair-proficient cells. This finding indicates that DDB2, as the substrate receptor of the DDB1-CUL4A-based ligase, specifically targets histone H2A for monoubiquitination in a photolesion-binding-dependent manner. Given that the loss of monoubiquitinated histone H2A at the sites of UV-damaged DNA is associated with decreased global genome repair in XP-E cells, this study suggests that histone modification, mediated by the XPE factor, facilitates the initiation of NER.

Recent advances in histopathology and immunohistochemistry of adrenocortical carcinoma

Discerning malignancy in resected adrenocortical neoplasms can pose diagnostic difficulty. Macroscopic examination is the first important step toward diagnosis and should include accurate measurement of weight and dimension of the specimens and description of the cut surface of the tumors. It is also important to sample the specimens for histological diagnosis near foci of hemorrhage and/or necrosis. Histological scoring systems evaluating multiple parameters, especially the criteria of Weiss, have been shown to be reliable in differential diagnosis between adrenocortical adenoma and carcinoma. A tumor is defined as adrenocortical carcinoma when three or more of the following criteria are met; (1) high nuclear grade, (2) mitotic rate six or more per 50 high power fields, (3) atypical mitosis, (4) clear cells less than 25%, (5) a diffuse architecture pattern in more than one-third of the tumor, (6) confluent necrosis, (7) venous invasion, (8) sinusoidal invasion, and (9) capsular invasion. The criteria are relatively straightforward and considered the most effective standard for diagnosis of adrenocortical malignancy. However, great care should be taken in applying the criteria to histological evaluation of two relatively rare and peculiar adrenocortical tumors, adrenocortical oncocytoma and pediatric adrenocortical neoplasms. At this juncture, ancillary biological or molecular markers are of little practical value in terms of differential diagnosis between adrenocortical adenoma and carcinoma but tumors with MIB1 or Ki-67 labeling index more than 2.5 may be considered malignant. Prognostic markers of adrenocortical carcinoma have not been established other than complete respectability of the tumor. There are also no surrogate markers for predicting response to therapy with Mitotane, an adrenolytic agent. It sometimes is important for surgical pathologists to differentiate adrenocortical carcinoma from metastatic malignancies of other sites. An immunohistochemical evaluation of adrenal 4 binding protein (Ad4BP) or SF-1, a transcription factor of all steroidogenesis, can aid in this differential diagnosis because nuclear immunoreactivity for this transcription factor is relatively specific to steroid producing cells.

14-3-3eta is a novel regulator of parkin ubiquitin ligase

Mutation of the parkin gene, which encodes an E3 ubiquitin-protein ligase, is the major cause of autosomal recessive juvenile parkinsonism (ARJP). Although various substrates for parkin have been identified, the mechanisms that regulate the ubiquitin ligase activity of parkin are poorly understood. Here we report that 14-3-3eta, a chaperone-like protein present abundantly in neurons, could bind to parkin and negatively regulate its ubiquitin ligase activity. Furthermore, 14-3-3eta could bind to the linker region of parkin but not parkin with ARJP-causing R42P, K161N, and T240R mutations. Intriguingly, alpha-synuclein (alpha-SN), another familial Parkinson's disease (PD) gene product, abrogated the 14-3-3eta-induced suppression of parkin activity. alpha-SN could bind tightly to 14-3-3eta and consequently sequester it from the parkin-14-3-3eta complex. PD-causing A30P and A53T mutants of alpha-SN could not bind 14-3-3eta, and failed to activate parkin. Our findings indicate that 14-3-3eta is a regulator that functionally links parkin and alpha-SN. The alpha-SN-positive and 14-3-3eta-negative control of parkin activity sheds new light on the pathophysiological roles of parkin.

Parkinson's disease: assays for the ubiquitin ligase activity of neural Parkin

The identification of monogenic variants of Parkinson's disease (PD) has provided novel insights into its unknown pathogenesis. As the first protein linked to autosomal-recessive forms of PD, Parkin became a welcome tool to explain biochemical and neuropathological observations that had suggested involvement of the ubiquitin-proteasome system (UPS) in PD. Based on cellular expression studies and biochemical in vitro experiments, several researchers ascribed an E3-type, E2-dependent ubiquitin protein ligase activity to wild-type (but not mutant) Parkin proteins. Although the individual components of the proposed Parkin ubiquitin ligase complex in the normal human brain remain to be identified and the E3 ligase effect of Parkin function has not yet been confirmed in an animal model, the scientific exploration of a protein with several links to the UPS has provided many leads in PD research. This chapter describes assays that the authors have used to examine the cellular and in vitro effects of neural Parkin.

Dual role of BRUCE as an antiapoptotic IAP and a chimeric E2/E3 ubiquitin ligase

Apoptotic cell death and survival is controlled by pro- and antiapoptotic proteins. Because these proteins act on each other, cell fate is dictated by the relative activity of pro- versus antiapoptotic proteins. Here we report that BRUCE, a conserved 528 kDa peripheral membrane protein of the trans-Golgi network, protects cells against apoptosis and functions as an inhibitor of apoptosis (IAP). By using wild-type and mutant forms we show that BRUCE inhibits caspase activity and apoptosis depending on its BIR domain. Upon apoptosis induction, BRUCE is antagonized by three mechanisms: first, through binding to Smac; second, by the protease HtrA2; and third, by caspase-mediated cleavage. In addition to its IAP activity BRUCE has the distinctive property of functioning as a chimeric E2/E3 ubiquitin ligase with Smac being a substrate. Our work suggests that, owing to its two activities and its localization, BRUCE may function as a specialized regulator of cell death pathways.

Decreased expression of e6-associated protein in breast and prostate carcinomas

The E6-associated protein (E6-AP) is a dual function protein. It acts as an E3 ubiquitin-protein ligase as well as a steroid hormone receptor coactivator. Considering the influence of steroid hormone receptors and their coactivators in the normal development and tumorigenesis of reproductive organs of both genders, we examined the roles of E6-AP in the tumorigenesis of breast and prostate tissues. We demonstrated that the expression of E6-AP protein is decreased in human invasive breast and prostate carcinomas compared with their adjacent normal tissues, and this down-regulation of E6-AP is accompanied by the up-regulation of estrogen receptor (ER)-alpha in breast and androgen receptor (AR) in prostate carcinomas. Furthermore, our in vivo data from E6-AP-knockout animals indicated that the expression levels of ERalpha and AR are increased in E6-AP-null mammary and prostate glands, respectively, when compared with that of normal control animals, suggesting that E6-AP modulates the protein levels of ERalpha in breast and AR in prostate glands.