Typical esthetic outcomes using 5 different modalities to treat MIH affected teeth: a case series

Therapeutic options for incisors affected by Molar Incisor Hypomineralization range from very conservative procedures to those considered to be more invasive. Clinicians must select the appropriate approach, considering the outcomes of the procedures. This case series presents clinical outcomes of five female patients with aesthetic complaints associated with the Molar Incisor Hipomineralization. Macroabrasion, microabrasion and dental vital bleaching were used as combination techniques in three cases. Resin infiltration was indicated for a specific case, considering the oncoming orthodontic treatment. Composite restoration was performed in one patient with posteruptive enamel breakdown. Clinicians must select the appropriate approach according to an individualized evaluation of each case, considering factors such as the patient's expectations, dental age, psychosocial period, the severity of the condition, presence of sensitivity and the presumed aesthetic result of the selected treatment. The advantages and disadvantages of the techniques are presented.

Las opciones terapéuticas para los incisivos afectados por hipomineralización incisivo molar van desde procedimientos muy conservadores hasta los considerados más invasivos. Los clínicos deben seleccionar el enfoque adecuado, teniendo en cuenta los resultados de los procedimientos. Esta serie de casos presenta los resultados clínicos de cinco pacientes femeninas con quejas estéticas asociadas a la Hipomineralización Incisivo Molar. En tres casos se utilizaron la macroabrasión, la microabrasión y el blanqueamiento dental vital como técnicas combinadas. La infiltración de resina fue indicada para un caso específico, considerando el tratamiento de ortodoncia próximo. Se realizó una restauración con composite en un paciente con rotura posteruptiva del esmalte. Los clínicos deben seleccionar el abordaje adecuado de acuerdo con una evaluación individualizada de cada caso, considerando factores como las expectativas del paciente, la edad dental, el período psicosocial, la gravedad de la afección, la presencia de sensibilidad y el resultado estético presumible del tratamiento seleccionado. Se presentan las ventajas e inconvenientes de las técnicas.

Cisplatin-induced cell death increases the degradation of the MRE11-RAD50-NBS1 complex through the autophagy/lysosomal pathway.

Cisplatin and other platinum-based anticancer agents are among the most widely used chemotherapy drugs in the treatment of different types of cancer. However, it is common to find patients who respond well to treatment at first but later relapse due to the appearance of resistance to cisplatin. Among the mechanisms responsible for this phenomenon is the increase in DNA damage repair. Here, we elucidate the effect of cisplatin on the MRN (MRE11-RAD50-NBS1) DNA damage sensor complex. We found that the tumor suppressor FBXW7 is a key factor in controlling the turnover of the MRN complex by inducing its degradation through lysosomes. Inhibition of lysosomal enzymes allowed the detection of the association of FBXW7-dependent ubiquitylated MRN with LC3 and the autophagy adaptor p62/SQSTM1 and the localization of MRN in lysosomes. Furthermore, cisplatin-induced cell death increased MRN degradation, suggesting that this complex is one of the targets that favor cell death. These findings open the possibility of using the induction of the degradation of the MRN complex after genotoxic damage as a potential therapeutic strategy to eliminate tumor cells.

Blanqueamiento dental en niños y adolescentes ¿El epílogo de un mito? Revisión de la Literatura / Clareamento dentário em crianças e adolescentes. O epílogo de um mito? Revisão da literatura / Teeth bleaching in children and adolescents. The epilogue of a myth? Literature Review

En torno al blanqueamiento dental existen muchas afirmaciones con poco soporte científico, tales como: los blanqueamientos son ácidos, dañan el esmalte, se utilizan férulas, hay restricción en dieta y en la gestación, con límite mínimo de edad para su uso, entre otros. Para la odontología es de suma importancia que toda afirmación se realice responsablemente con una evidencia científica para entregar lo mejor de cada tratamiento a los pacientes. Objetivo: Conocer las posibles indicaciones del blanqueamiento dental en niños y adolescentes, modalidades, los efectos sobre los tejidos blandos y duros, así como sus efectos secundarios, la hipersensibilidad dentinaria, su tratamiento farmacológico y su impacto psicosocial. Material y métodos: se realizó una búsqueda electrónica de los siguientes buscadores: PubMed, LILACS, SCIELO, Cochrane Library y SCOPUS, limitando la búsqueda entre los años 1998 y 2020 utilizando los términos relacionados a la investigación. Se incluyeron 71 artículos que cumplieron con los criterios de inclusión. Resultados: la mayoría de los autores recomiendan el uso de sistemas de blanqueamiento dental de acuerdo con parámetros establecidos.

Regarding teeth bleaching, there are many statements with little scientific support, such as: whitening is acidic, damages the enamel, guards are used, there is a restriction in diet and pregnancy, with a minimum age limit for its use, between others. For dentistry it is of utmost importance that all statements are made in a responsible manner with scientific evidence to provide the best of each treatment to patients. Objective: to know the possible indications for teeth bleaching in children and adolescents, the modalities, the effects on soft and hard tissues, as well as its side effects, dental hypersensitivity, its pharmacological treatment and its psychosocial impact. Material and methods: An electronic search of the following databases was performed: PubMed, LILACS, SCIELO, Cochrane Library and SCOPUS, limiting the search between 1998 and 2020 using the terms related to the research. Seventy-one articles that met the inclusion criteria were included. Results: Most authors recommend the use of teeth whitening systems according to established parameters

No que diz respeito ao clareamento dos dentes, existem muitas afirmações com pouco apoio científico todas as declarações sejam feitas de maneira responsável com evidências científicas para oferecer o melhor de cada tratamento aos pacientes. Objetivo: Conhecer as possíveis indicações para clareamento dental em crianças e adolescentes, modalidades, efeitos sobre os tecidos moles e duros, bem como seus efeitos colaterais, hipersensibilidade dentária, tratamento farmacológico e impacto psicossocial. Material e métodos: Foi realizada uma busca eletrônica nos seguintes mecanismos de busca: PubMed, LILACS, SCIELO, Cochrane Library e SCOPUS, limitando a busca entre 1998 e 2020, utilizando os termos relacionados à pesquisa. Setenta e um artigos que atenderam aos critérios de inclusão foram incluídos. Resultados: A maioria dos autores recomenda o uso de sistemas de clareamento dental de acordo com os parâmetros estabelecidos

p53 and FBXW7: Sometimes Two Guardians Are Worse than One.

Too much of a good thing can become a bad thing. An example is FBXW7, a well-known tumor suppressor that may also contribute to tumorigenesis. Here, we reflect on the results of three laboratories describing the role of FBXW7 in the degradation of p53 and the possible implications of this finding in tumor cell development. We also speculate about the function of FBXW7 as a key player in the cell fate after DNA damage and how this could be exploited in the treatment of cancer disease.

SCF(FBXW7)-mediated degradation of p53 promotes cell recovery after UV-induced DNA damage.

Eukaryotic cells have developed sophisticated mechanisms to ensure the integrity of the genome and prevent the transmission of altered genetic information to daughter cells. If this control system fails, accumulation of mutations would increase risk of diseases such as cancer. Ubiquitylation, an essential process for protein degradation and signal transduction, is critical for ensuring genome integrity as well as almost all cellular functions. Here, we investigated the role of the SKP1-Cullin-1-F-box protein (SCF)-[F-box and tryptophan-aspartic acid (WD) repeat domain containing 7 (FBXW7)] ubiquitin ligase in cell proliferation by searching for targets implicated in this process. We identified a hitherto-unknown FBXW7-interacting protein, p53, which is phosphorylated by glycogen synthase kinase 3 at serine 33 and then ubiquitylated by SCF(FBXW7) and degraded. This ubiquitylation is carried out in normally growing cells but primarily after DNA damage. Specifically, we found that SCF(FBXW7)-specific targeting of p53 is crucial for the recovery of cell proliferation after UV-induced DNA damage. Furthermore, we observed that amplification of FBXW7 in wild-type p53 tumors reduced the survival of patients with breast cancer. These results provide a rationale for using SCF(FBXW7) inhibitors in the treatment of this subset of tumors.-Galindo-Moreno, M., Giráldez, S., Limón-Mortés, M. C., Belmonte-Fernández, A., Reed, S. I., Sáez, C., Japón, M. Á., Tortolero, M., Romero, F. SCF(FBXW7)-mediated degradation of p53 promotes cell recovery after UV-induced DNA damage.

Obatoclax and Paclitaxel Synergistically Induce Apoptosis and Overcome Paclitaxel Resistance in Urothelial Cancer Cells.

Paclitaxel is a treatment option for advanced or metastatic bladder cancer after the failure of first-line cisplatin and gemcitabine, although resistance limits its clinical benefits. Mcl-1 is an anti-apoptotic protein that promotes resistance to paclitaxel in different tumors. Obatoclax, a BH3 mimetic of the Bcl-2 family of proteins, antagonizes Mcl-1 and hence may reverse paclitaxel resistance in Mcl-1-overexpressing tumors. In this study, paclitaxel-sensitive 5637 and -resistant HT1197 bladder cancer cells were treated with paclitaxel, obatoclax, or combinations of both. Apoptosis, cell cycle, and autophagy were measured by Western blot, flow cytometry, and fluorescence microscopy. Moreover, Mcl-1 expression was analyzed by immunohistochemistry in bladder carcinoma tissues. Our results confirmed that paclitaxel alone induced Mcl-1 downregulation and apoptosis in 5637, but not in HT1197 cells; however, combinations of obatoclax and paclitaxel sensitized HT1197 cells to the treatment. In obatoclax-treated 5637 and obatoclax + paclitaxel-treated HT1197 cells, the blockade of the autophagic flux correlated with apoptosis and was associated with caspase-dependent cleavage of beclin-1. Obatoclax alone delayed the cell cycle in 5637, but not in HT1197 cells, whereas combinations of both retarded the cell cycle and reduced mitotic slippage. In conclusion, obatoclax sensitizes HT1197 cells to paclitaxel-induced apoptosis through the blockade of the autophagic flux and effects on the cell cycle. Furthermore, Mcl-1 is overexpressed in many invasive bladder carcinomas, and it is related to tumor progression, so Mcl-1 expression may be of predictive value in bladder cancer.

Both p62/SQSTM1-HDAC6-dependent autophagy and the aggresome pathway mediate CDK1 degradation in human breast cancer.

Cyclin-dependent kinase 1 (CDK1) is the central mammalian regulator of cell proliferation and a promising therapeutic target for breast cancer. In fact, CDK1 inhibition downregulates survival and induces apoptosis. Due to its essential role, CDK1 expression and activity are strictly controlled at various levels. We previously described that CDK1 stability is also regulated and that SCF(ßTrCP) ubiquitinates CDK1, which is degraded via the lysosomal pathway. In addition, in breast tumors from patients, we found a negative correlation between CDK1 accumulation and ßTrCP levels, and a positive correlation with the degree of tumor malignancy. This prompted us to study the molecular mechanism involved in CDK1 clearance. In this report, we determine that both chemotherapeutic agents and proteolytic stress induce CDK1 degradation in human breast cancer MCF7 cells through p62/HDAC6-mediated selective autophagy. On the one hand, CDK1 binds to p62/SQSTM1-LC3 and, on the other hand, it interacts with HDAC6. Both complexes are dependent on the presence of an intact ßTrCP-binding motif on CDK1. Furthermore, we also show that CDK1 is recruited to aggresomes in response to proteasome inhibition for an extended period. We propose CDK1 clearance as a potential predictive biomarker of antitumor treatment efficacy.

G1/S phase progression is regulated by PLK1 degradation through the CDK1/ßTrCP axis.

Polo-like kinase 1 (PLK1) is a serine/threonine kinase involved in several stages of the cell cycle, including the entry and exit from mitosis, and cytokinesis. Furthermore, it has an essential role in the regulation of DNA replication. Together with cyclin A, PLK1 also promotes CDH1 phosphorylation to trigger its ubiquitination and degradation, allowing cell cycle progression. The PLK1 levels in different type of tumors are very high compared to normal tissues, which is consistent with its role in promoting proliferation. Therefore, several PLK1 inhibitors have been developed and tested for the treatment of cancer. Here, we further analyzed PLK1 degradation and found that cytoplasmic PLK1 is ubiquitinated and subsequently degraded by the SCFßTrCP/proteasome. This procedure is triggered when heat shock protein (HSP) 90 is inhibited with geldanamycin, which results in misfolding of PLK1. We also identified CDK1 as the major kinase involved in this degradation. Our work shows for the first time that HSP90 inhibition arrests cell cycle progression at the G1/S transition. This novel mechanism inhibits CDH1 degradation through CDK1-dependent PLK1 destruction by the SCFßTrCP/proteasome. In these conditions, CDH1 substrates do not accumulate and cell cycle arrests, providing a novel pathway for regulation of the cell cycle at the G1-to-S boundary.-Giráldez, S., Galindo-Moreno, M., Limón-Mortés, M. C., Rivas, A. C., Herrero-Ruiz, J., Mora-Santos, M., Sáez, C., Japón, M. Á., Tortolero, M., Romero, F. G1/S phase progression is regulated by PLK1 degradation through the CDK1/ßTrCP axis.

Loss of FBXW7 and accumulation of MCL1 and PLK1 promote paclitaxel resistance in breast cancer.

FBXW7 is a component of SCF (complex of SKP1, CUL1 and F-box-protein)-type ubiquitin ligases that targets several oncoproteins for ubiquitination and degradation by the proteasome. FBXW7 regulates cellular apoptosis by targeting MCL1 for ubiquitination. Recently, we identified PLK1 as a new substrate of FBXW7 modulating the intra-S-phase DNA-damage checkpoint. Taxanes are frequently used in breast cancer treatments, but the acquisition of resistance makes these treatments ineffective. We investigated the role of FBXW7 and their substrates MCL1 and PLK1 in regulating the apoptotic response to paclitaxel treatment in breast cancer cells and their expression in breast cancer tissues. Paclitaxel-sensitive MDA-MB-468 and a paclitaxel-resistant MDA-MB-468R subclone were used to study the role of FBXW7 and substrates in paclitaxel-induced apoptosis. Forced expression of FBXW7 or downregulation of MCL1 or PLK1 restored sensitivity to paclitaxel in MDA-MB-468R cells. By contrary, FBXW7-silenced MDA-MB-468 cells became resistant to paclitaxel. The expression of FBXW7 and substrates were studied in 296 invasive carcinomas by immunohistochemistry and disease-free survival was analyzed in a subset of patients treated with paclitaxel. In breast cancer tissues, loss of FBXW7 correlated with adverse prognosis markers and loss of FBXW7 and MCL1 or PLK1 accumulation were associated with diminished disease-free survival in paclitaxel-treated patients. We conclude that FBXW7 regulates the response to paclitaxel by targeting MCL1 and PLK1 in breast cancer cells and thus targeting these substrates may be a valuable adjunct for paclitaxel treatment. Also, FBXW7, MCL1 and PLK1 may be relevant predictive markers of tumor progression and response to paclitaxel treatment.

ßTrCP controls the lysosome-mediated degradation of CDK1, whose accumulation correlates with tumor malignancy.

In mammals, cell cycle progression is controlled by cyclin-dependent kinases, among which CDK1 plays important roles in the regulation of the G2/M transition, G1 progression and G1/S transition. CDK1 is highly regulated by its association to cyclins, phosphorylation and dephosphorylation, changes in subcellular localization, and by direct binding of CDK inhibitor proteins. CDK1 steady-state protein levels are held constant throughout the cell cycle by a coordinated regulation of protein synthesis and degradation. We show that CDK1 is ubiquitinated by the E3 ubiquitin ligase SCFßTrCP and degraded by the lysosome. Furthermore, we found that DNA damage not only triggers the stabilization of inhibitory phosphorylation sites on CDK1 and repression of CDK1 gene expression, but also regulates ßTrCP-induced CDK1 degradation in a cell type-dependent manner. Specifically, treatment with the chemotherapeutic agent doxorubicin in certain cell lines provokes CDK1 degradation and induces apoptosis, whereas in others it inhibits destruction of the protein. These observations raise the possibility that different tumor types, depending on their pathogenic spectrum mutations, may display different sensitivity to ßTrCP-induced CDK1 degradation after DNA damage. Finally, we found that CDK1 accumulation in patients' tumors shows a negative correlation with ßTrCP and a positive correlation with the degree of tumor malignancy.

Prostate cancer cell response to paclitaxel is affected by abnormally expressed securin PTTG1.

PTTG1 protein, the human securin, has a central role in sister chromatid separation during mitosis, and its altered expression has been reported in many tumor types. Paclitaxel is a widely used chemotherapeutic drug, whose mechanism of action is related to its ability to arrest cells in mitosis and the subsequent induction of the intrinsic apoptotic pathway. By using two prostate cancer cell lines with different responses to paclitaxel treatment, we have identified two situations in which PTTG1 influences cell fate differentially. In slippage-prone PC3 cells, both PTTG1 downregulation and overexpression induce an increase in mitotic cells that is associated with diminished apoptosis after paclitaxel treatment. In LNCaP cells, however, PTTG1 downregulation prevents mitotic entry and, subsequently, inhibits mitosis-associated, paclitaxel-induced apoptosis. In contrast, PTTG1 overexpression induces an increase in mitotic cells and apoptosis after paclitaxel treatment. We have also identified a role for Mcl-1 protein in preventing apoptosis during mitosis in PC3 cells, as simultaneous PTTG1 and Mcl-1 silencing enhances mitosis-associated apoptosis after paclitaxel treatment. The finding that a more efficient mitotic arrest alone in PC3 cells is not enough to increase apoptosis was also confirmed with the observation that a selected paclitaxel-resistant PC3 cell line showed an apoptosis-resistant phenotype associated with increased mitosis upon paclitaxel treatment. These findings could contribute to identify putative responsive and nonresponsive cells and help us to approach incomplete responses to paclitaxel in the clinical setting.

SCF(FBXW7α) modulates the intra-S-phase DNA-damage checkpoint by regulating Polo like kinase-1 stability.

The intra-S-checkpoint is essential to control cell progression through S phase under normal conditions and in response to replication stress. When DNA lesions are detected, replication fork progression is blocked allowing time for repair to avoid genomic instability and the risk of cancer. DNA replication initiates at many origins of replication in eukaryotic cells, where a series of proteins form pre-replicative complexes (pre-RCs) that are activated to become pre-initiation complexes and ensure a single round of replication in each cell cycle. PLK1 plays an important role in the regulation of DNA replication, contributing to the regulation of pre-RCs formation by phosphorylating several proteins, under both normal and stress conditions. Here we report that PLK1 is ubiquitinated and degraded by SCFFBXW7α/proteasome. Moreover, we identified a new Cdc4 phosphodegron in PLK1, conserved from yeast to humans, whose mutation prevents PLK1 destruction. We established that endogenous SCFFBXW7α degrades PLK1 in the G1 and S phases of an unperturbed cell cycle and in S phase following UV irradiation. Furthermore, we showed that FBXW7α overexpression or UV irradiation prevented the loading of proteins onto chromatin to form pre-RCs and, accordingly, reduced cell proliferation. We conclude that PLK1 degradation mediated by SCFFBXW7α modulates the intra-S-phase checkpoint.

A single mutation in Securin induces chromosomal instability and enhances cell invasion.

Pituitary tumour transforming gene (pttg1) encodes Securin, a protein involved in the inhibition of sister chromatid separation binding to Separase until the onset of anaphase. Separase is a cysteine-protease that degrades cohesin to segregate the sister chromatids to opposite poles of the cell. The amount of Securin is strongly regulated because it should allow Separase activation when it is degraded by the anaphase promoting complex/cyclosome, should arrest the cell cycle after DNA damage, when it is degraded through SKP1-CUL1-ßTrCP ubiquitin ligase, and its overexpression induces tumour formation and correlates with metastasis in multiple tumours. Securin is a phosphoprotein that contains 32 potentially phosphorylatable residues. We mutated and analysed most of them, and found a single mutant, hSecT60A, that showed enhanced oncogenic properties. Our fluorescence activated cell sorting analysis, fluorescence in situ hybridisation assays, tumour cell migration and invasion experiments and gene expression by microarrays analysis clearly involved hSecT60A in chromosomal instability and cell invasion. These results show, for the first time, that a single mutation in pttg1 is sufficient to trigger the oncogenic properties of Securin. The finding of this point mutation in patients might be used as an effective strategy for early detection of cancer.

Glycogen synthase kinase-3beta (GSK3beta) negatively regulates PTTG1/human securin protein stability, and GSK3beta inactivation correlates with securin accumulation in breast tumors.

PTTG1, also known as securin, is an inactivating partner of separase, the major effector for chromosome segregation during mitosis. At the metaphase-to-anaphase transition, securin is targeted for proteasomal destruction by the anaphase-promoting complex or cyclosome, allowing activation of separase. In addition, securin is overexpressed in metastatic or genomically instable tumors, suggesting a relevant role for securin in tumor progression. Stability of securin is regulated by phosphorylation; some phosphorylated forms are degraded out of mitosis, by the action of the SKP1-CUL1-F-box protein (SCF) complex. The kinases targeting securin for proteolysis have not been identified, and mechanistic insight into the cause of securin accumulation in human cancers is lacking. Here, we demonstrate that glycogen synthase kinase-3ß (GSK3ß) phosphorylates securin to promote its proteolysis via SCF(ßTrCP) E3 ubiquitin ligase. Importantly, a strong correlation between securin accumulation and GSK3ß inactivation was observed in breast cancer tissues, indicating that GSK3ß inactivation may account for securin accumulation in breast cancers.

Expression of pituitary tumor-transforming gene 1 (PTTG1)/securin in hepatitis B virus (HBV)-associated liver diseases: evidence for an HBV X protein-mediated inhibition of PTTG1 ubiquitination and degradation.

Chronic infection with hepatitis B virus (HBV) is strongly associated with hepatocellular carcinoma (HCC), and the viral HBx protein plays a crucial role in the pathogenesis of liver tumors. Because the protooncogene pituitary tumor-transforming gene 1 (PTTG1) is overexpressed in HCC, we investigated the regulation of this protein by HBx. We analyzed PTTG1 expression levels in liver biopsies from patients chronically infected with HBV, presenting different disease stages, and from HBx transgenic mice. PTTG1 was undetectable in biopsies from chronic hepatitis B patients or from normal mouse livers. In contrast, hyperplastic livers from transgenic mice and biopsies from patients with cirrhosis, presented PTTG1 expression which was found mainly in HBx-expressing hepatocytes. PTTG1 staining was further increased in HCC specimens. Experiments in vitro revealed that HBx induced a marked accumulation of PTTG1 protein without affecting its messenger RNA levels. HBx expression promoted the inhibition of PTTG1 ubiquitination, which in turn impaired its degradation by the proteasome. Glutathione S-transferase pull-down and co-immunoprecipitation experiments demonstrated that the interaction between PTTG1 and the Skp1-Cul1-F-box ubiquitin ligase complex (SCF) was partially disrupted, possibly through a mechanism involving protein-protein interactions of HBx with PTTG1 and/or SCF. Furthermore, confocal analysis revealed that HBx colocalized with PTTG1 and Cul1. We propose that HBx promotes an abnormal accumulation of PTTG1, which may provide new insights into the molecular mechanisms of HBV-related pathogenesis of progressive liver disease leading to HCC development.

Taste discrimination after separate pre-exposure and test sessions.

The effect of previous exposure on discrimination of two flavored solutions sharing a common taste was investigated in a pilot experiment. These solutions were at the limit of discrimination and the pre-exposure and test phases took place on different days. The results showed that mere pre-exposure (i.e., in absence of feedback) facilitates subsequent discrimination of same or different pairs of solutions. This result is in some aspects opposite to those reported recently by Dwyer and colleagues. This discrepancy is discussed analyzing the procedural differences observed between these studies.

UV-induced degradation of securin is mediated by SKP1-CUL1-beta TrCP E3 ubiquitin ligase.

Securin is a chaperone protein with bifunctional properties. It binds to separase to inhibit premature sister chromatid separation until the onset of anaphase, and it also takes part in cell-cycle arrest after UV irradiation. At metaphase-to-anaphase transition, securin is targeted for proteasomal destruction by the anaphase-promoting complex or cyclosome (APC/C), allowing activation of separase. However, although securin is reported to undergo proteasome-dependent degradation after UV irradiation, the ubiquitin ligase responsible for securin ubiquitylation has not been well characterized. In this study, we show that UV radiation induced a marked reduction of securin in both the nucleus and cytoplasm. Moreover, we show that GSK-3beta inhibitors prevent securin degradation, and that CUL1 and betaTrCP are involved in this depletion. We also confirmed that SKP1-CUL1-betaTrCP (SCF(betaTrCP)) ubiquitylates securin in vivo, and identified a conserved and unconventional betaTrCP recognition motif (DDAYPE) in the securin primary amino acid sequence of humans, nonhuman primates and rodents. Furthermore, downregulation of betaTrCP caused an accumulation of securin in non-irradiated cells. We conclude that SCF(betaTrCP) is the E3 ubiquitin ligase responsible for securin degradation after UV irradiation, and that it is involved in securin turnover in nonstressed cells.

Protein phosphatase 2A stabilizes human securin, whose phosphorylated forms are degraded via the SCF ubiquitin ligase.

Sister chromatid segregation is triggered at the metaphase-to-anaphase transition by the activation of the protease separase. For most of the cell cycle, separase activity is kept in check by its association with the inhibitory chaperone securin. Activation of separase occurs at anaphase onset, when securin is targeted for destruction by the anaphase-promoting complex or cyclosome E3 ubiquitin protein ligase. This results in the release of the cohesins from chromosomes, which in turn allows the segregation of sister chromatids to opposite spindle poles. Here we show that human securin (hSecurin) forms a complex with enzymatically active protein phosphatase 2A (PP2A) and that it is a substrate of the phosphatase, both in vitro and in vivo. Treatment of cells with okadaic acid, a potent inhibitor of PP2A, results in various hyperphosphorylated forms of hSecurin which are extremely unstable, due to the action of the Skp1/Cul1/F-box protein complex ubiquitin ligase. We propose that PP2A regulates hSecurin levels by counteracting its phosphorylation, which promotes its degradation. Misregulation of this process may lead to the formation of tumors, in which overproduction of hSecurin is often observed.

Prognostic significance of human pituitary tumor-transforming gene immunohistochemical expression in differentiated thyroid cancer.

CONTEXT: Human securin pituitary tumor-transforming gene (hPTTG) is overexpressed in a variety of primary neoplasias, including differentiated thyroid cancer (DTC). OBJECTIVE: The objective of this study was to examine the immunohistochemical expression of hPTTG in DTC and its association with known prognostic factors. DESIGN: hPTTG expression was analyzed by immunostaining on paraffin-embedded tissues. Clinical data were used to determine any associations between the expression of hPTTG and prognostic variables of DTC. A median follow-up of 43 months allowed us to analyze the persistence of disease and the response to radioiodine therapy. SETTING: The study was conducted at a tertiary university hospital. PATIENTS: Ninety-five patients undergoing surgical resection for DTC (n = 60) or benign nodular thyroid disease (n = 35) were studied. MAIN OUTCOME MEASURE: The main outcome measure was the association between hPTTG expression and prognostic factors in DTC. RESULTS: Among DTC cases, 21 (35%) had low and 39 (65%) had high hPTTG immunostaining. Adjacent nonneoplastic thyroid tissue was largely unstained. Among benign nodular thyroid disease cases, immunostaining was detected focally in eight (22.8%). A significant association was found between hPTTG expression and the presence of nodal (P < 0.01) or distant metastases (P < 0.05). A significant association with TNM was also found, because 83.3% of advanced TNM stages showed elevated hPTTG (P < 0.05). The association between hPTTG overexpression and decreased radioiodine uptake during follow-up was also significant (P < 0.05). The expression levels of hPTTG were confirmed as an independent prognostic factor for persistent disease (relative risk, 3.0; 95% confidence interval, 1.1-8.7; P < 0.05). CONCLUSIONS: Immunohistochemical analysis of hPTTG is of potential value in the determination of tumor aggressiveness in DTC.

Securin is a target of the UV response pathway in mammalian cells.

All eukaryotic cells possess elaborate mechanisms to protect genome integrity and ensure survival after DNA damage, ceasing proliferation and granting time for DNA repair. Securin is an inhibitory protein that is bound to a protease called Separase to inhibit sister chromatid separation until the onset of anaphase. At the metaphase-to-anaphase transition, Securin is degraded by the anaphase-promoting complex or cyclosome, and Separase contributes to the release of cohesins from the chromosome, allowing for the segregation of sister chromatids to opposite spindle poles. Here we provide evidence that human Securin (hSecurin) has a novel role in cell cycle arrest after exposure to UV light or ionizing radiation. In fact, irradiation downregulated the level of hSecurin protein, accelerating its degradation via the proteasome and reducing hSecurin mRNA translation, but the presence of hSecurin is necessary for cell proliferation arrest following UV treatment. Moreover, an alteration of UV-induced hSecurin downregulation could lead directly to the accumulation of DNA damage and the subsequent development of malignant tumors.