The human F box protein beta-Trcp associates with the Cul1/Skp1 complex and regulates the stability of beta-catenin

Ubiquitin-conjugation targets numerous cellular regulators for proteasome-mediated degradation. Thus, the identification of ubiquitin ligases and their physiological substrates is crucially important, especially for those cases in which aberrant levels of regulatory proteins (e.g., beta-catenin, p27) result from a deregulated ubiquitination pathway. In yeast, the proteolysis of several G1 regulators is controlled by ubiquitin ligases (or SCFs) formed by three subunits: Skp1, Cul A (Cdc53), and one of many F-box proteins. Specific F-box proteins (Fbps) recruit different substrates to the SCF. Although many Fbps have been identified in mammals, their specific substrates and the existence of multiple SCFs have not yet been reported. We have found that one human Fbp, beta-Trcp (beta-Transducin repeat containing protein), does indeed form a novel SCF with human Skp1 and Cul1. Consistent with recent reports indicating that Xenopus and Drosophila beta-Trcp homologs act as negative regulators of the Wnt/beta-catenin signaling pathway, we report here that human beta-Trcp interacts with beta-catenin in vivo. Furthermore, beta-catenin is specifically stabilized in vivo by the expression of a dominant negative beta-Trcp. These results indicate that the Cul1/Skp1/beta-Trcp complex forms a ubiquitin ligase that mediates the degradation of beta-catenin.

Castleman's disease

Castleman's disease (CD) is a rare atypical lymphoproliferative disorder whose morphology, soon after the original presentation of Castleman et al., has been definitely subdivided in a hyaline vascular (HV) and plasma cell (PC) histopathological pattern, with intermediate variants. The former occurs much more frequently than the latter and is usually localized to the mediastinum or pulmonary hilum. The latter involves lymph nodes separately or in aggregations and often displays multicentricity with systemic symptoms including autoimmune phenomena and aggressive course. Infections are the most frequent causes of patient demise in these cases, followed by malignancies such as Kaposi's sarcoma, malignant lymphoma or epithelial neoplasia. Increase of follicular dendritic reticulum cells (FDRC), often dysplastic, in the germinal center (GC) and marginal zone (MZ), broad MZ expansion with prominence of immunophenotypically aberrant B cells (Ki B3-negative, CD5-positive), possible predominance of paracortical plasma cells often with clusters of clonal l-light chain restricted plasma cells, increase of paracortical plasmacytoid monocytes, represent common hallmarks of CD. However, small hyalinized and hypervascular GCs with hypervascular interfollicular stroma and sinus effacement are common features of the HV variant, whereas hyperplastic GCs with plasma cell aggregates in lymph node paracortex and partially spared sinuses are characteristic features of the PC variant. The frequent concomitance of the HV and PC types at separate sites, together with transient morphological patterns from one type to the other and from the localized to multicentric form during the course of the disease, along with B and T cell impaired functions, with frequent development of autoantibodies, have suggested that CD is a single disorder related to immune dysregulation. A key event in the pathogenesis of CD has been recently suggested to be an abnormal production of a B cell growth factor, such as IL-6, leading to lymphoproliferation and plasma cell differentiation and being involved in the oncogenesis of plasmacytoma. In this event, Kaposi's sarcoma associated virus (HHV-8), which has been found in many cases of CD, especially in the multicentric form, could play a crucial role both in producing IL-6 and releasing angiogenic factors. A possible differentiation block may lead to the development of a malignant lymphoma. Kaposi's sarcoma or other malignant neoplasias can be supposed to be consequences of the immunodeficiency typical of CD.

Binding of the cysteine proteinases papain and cathepsin B-like to coated laminin: use of synthetic peptides from laminin and from the laminin binding region of the beta 1 integrin subunit to characterize the binding site

Cysteine proteinases of the papain superfamily, i.e., papain and cathepsin B-like proteinase, were found to be able to bind to laminin-coated wells. When papain and cathepsin B-like proteinase were used, saturable binding curves were found. The characterization of the binding site was carried out using synthetic peptides which corresponded to the most relevant functional sites of laminin and an octapeptide from the laminin binding region of the beta1 integrin subunit. In binding experiments, the decapeptide RNIAEIIKDI and the pentapeptide YIGSR were able to displace papain and cathepsin B-like proteinase from coated laminin. Nevertheless, the integrin beta1 peptide DLYYLMDL was the most powerful in the same experimental system. From these results, the C-terminal region of this cross-shaped protein, i.e., the end of the long arm, and the region including the YIGSR sequence of the short arm of the beta chain would be the cysteine proteinase binding site. This binding site is probably the result of the network organization of laminin which brings two regions, separated on a single laminin molecule, into proximity. In previous work, digestion of basement membranes has been found to be associated with the binding of cysteine proteinases to these supramolecular structures [N. Guinec, V. Dalet-Fumeron, and M. Pagano (1992) FEBS Lett. 308, 305-308]. The present report demonstrates that laminin is the cysteine proteinase binding protein of basement membranes. This property of laminin could be associated with tumor invasion and other tissue remodeling processes linked to proteolysis of basement membranes and extracellular matrices.

Down-regulation of p27 is associated with development of colorectal adenocarcinoma metastases

The cyclin-dependent kinase inhibitor p27 is a negative regulator of the cell cycle and a potential tumor suppressor gene. Because we had previously demonstrated that loss of p27 protein is associated with aggressive behavior in colorectal adenocarcinomas, we used immunohistochemistry and in situ hybridization to evaluate the potential role of alterations in p27 expression in primary and metastatic colorectal adenocarcinomas. Parallel immunostaining was performed for Ki-67 and p53. We evaluated 13 cases of metachronous and 23 cases of synchronous primary and metastatic colorectal tumor pairs. In the synchronous subgroup (Stage IV tumors), 57% of the primary tumor and metastases pairs did not express p27 protein and the remainder were low expressors. In the metachronous subgroup, 54% of the primary tumors were low expressors and the remainder high expressors of p27 protein. There was a significant reduction in the expression of p27 in the metachronous metastases (mean positive cells: 14.5%) when compared to the corresponding primary tumors (mean positive cells: 41.8%), P = 0.0023. All the primary and metastatic tumors in the metachronous subgroup showed high levels of p27 mRNA expression. There was no association between loss of p27 and either Ki-67 count or p53 expression. Because p27 is known to be up-regulated when epithelial cells are grown in suspension, the down-regulation of p27 in circulating tumor cells may confer the ability to grow in an environment of altered extracellular matrix or intercellular adhesion properties, two situations which may facilitate metastases.

Prevalence of the Rhizobium etli-like allele in genes coding for 16S rRNA among the indigenous rhizobial populations found associated with wild beans from the Southern Andes in Argentina

A collection of rhizobial isolates from nodules of wild beans, Phaseolus vulgaris var. aborigineus, found growing in virgin lands in 17 geographically separate sites in northwest Argentina was characterized on the basis of host range, growth, hybridization to a nifH probe, analysis of genes coding for 16S rRNA (16S rDNA), DNA fingerprinting, and plasmid profiles. Nodules in field-collected wild bean plants were largely dominated by rhizobia carrying the 16S rDNA allele of Rhizobium etli. A similar prevalence of the R. etli allele was observed among rhizobia trapped from nearby soil. Intragroup diversity of wild bean isolates with either R. etli-like or Rhizobium leguminosarum bv. phaseoli-like alleles was generally found across northwest Argentina. The predominance of the R. etli allele suggests that in this center of origin of P. vulgaris the coevolution of Rhizobium spp. and primitive beans has resulted in this preferential symbiotic association.

The synthesis and utilization of 2,4-dinitrophenyl-labeled irreversible peptidyl diazomethyl ketone inhibitors

Biotinylated diazomethyl ketones have been much used to detect cysteine proteases on Western blots, but high background may occur due to the presence of endogenously biotinylated proteins. In order to overcome this problem, we have examined the potential utility of a peptidyl diazomethyl ketone labeled with a 2,4-dinitrophenyl (DNP) group as a potential inhibitor and disclosing agent of cathepsin B/L-like proteases. This DNP-labeled peptide, DNP-Ahx-Gly-Phe-Ala-CHN2, was used to detect a 30-kDa cathepsin L-like protease, produced by Fasciola hepatica, on Western blots with high sensitivity and relatively low background staining. The DNP-labeled diazomethyl ketone was also found to be a good inhibitor for bovine cathepsin B, human cathepsin L, and a novel F. hepatica cathepsin L-like protease, when assayed fluorimetrically, displaying second-order rate constants (ki/Ki) of 7.93 x 10(2), 2.16 x 10(2), and 3.73 x 10(2) M-1 s-1, respectively.

Expression of collagenase/gelatinase activity from basement-membrane fibronectin--isolation after limited proteolysis of a bovine lens capsule and molecular definition of this thiol-dependent zinc metalloproteinase

We have isolated the collagenase/gelatinase activity of fibronectin from a bovine lens capsule hydrolysate, using heparin-agarose, gelatin-agarose, immunopurification with polyclonal antibodies directed against bovine plasma fibronectin, and immunopurification with a monoclonal antibody directed against the extra-domain A of cellular fibronectin. The expression of collagenase/gelatinase activity by the purified fibronectin fragment was dependent on the incubation time at 37 degrees C and the addition of gelatin to the purified sample. Under these conditions, the purified fibronectin fragment exhibited collagenase/gelatinase activity, as measured by means of gelatin zymography and the intramolecularly quenched fluorogenic substrate of collagenases (7-methoxycoumarin-4-yl)-acetylprolylleucylglycylleucyl-[3-(2,4-di nitrophenyl)-L-2,3-diaminopropionyl]-alanylarginylamide. This activity was due to proteins of 47 kDa and 37 kDa, as indicated by the gelatin-zymography pattern. When the processing was analyzed, by means of SDS/PAGE under reducing conditions, purified starting material of 66 kDa and 55 kDa was observed, and molecular masses of 45, 30 and 27 kDa were found for the processed samples. Under these conditions, the processing was more significant when a substrate, i.e the fluorogenic peptide or gelatin, was added to the processing mixture. An inhibition-profile study showed a zinc-dependent collagenase activity. Using the 45-kDa chymotryptic fragment from human plasma fibronectin, which contains the collagen-binding site, the same results were obtained. These results allow us to define a thiol-dependent zinc metalloproteinase expressed after limited proteolysis of both basement membrane and plasma fibronectins. This proteinase contains a collagen-binding domain, a zinc-binding sequence, and a cysteine involved in catalysis. This enzyme is a member of the thimet family of zinc metalloproteinases.

Loss or altered subcellular localization of p27 in Barrett's associated adenocarcinoma

The cyclin-dependent kinase inhibitor p27 is a negative regulator of the cell division cycle. It is expressed at the highest levels during the quiescent (G0) and prereplicative (G1) phases, and its degradation is required for entry into the S phase. Because lack of p27 is associated with aggressive behavior in a variety of tumors of epithelial and lymphoid origin, we used immunohistochemistry and in situ hybridization to evaluate the expression of p27 in metaplastic and dysplastic Barrett's epithelium and to assess its prognostic significance in Barrett's associated adenocarcinoma (BAA) of the esophagus. In metaplastic Barrett's epithelium, p27 protein and mRNA were restricted to the superficial third of glands in all cases and extended to the lower third in 4 cases. In contrast, expression of p27 message and protein was both increased and full-thickness, in the 23 cases with high-grade dysplasia adjacent to BAA and in carcinoma in situ. Although all invasive carcinomas had elevated levels of p27 mRNA, 45 (83%) of 54 invasive carcinomas had low p27 protein levels (<50% positive tumor cells). Low p27 protein correlated with higher histological grade (P < 0.0001), depth of invasion (P = 0.0120), presence of lymph node metastasis (P = 0.05), and survival (P = 0.0197). In addition to the nuclear staining, cytoplasmic staining of p27 was noted in 11 of 23 (48%) of cases of dysplasia and in 14 of 54 (26%) adenocarcinomas and confirmed, in a subset of cases, by subcellular fractionation of protein lysates obtained from fresh tumor tissues. Cytoplasmic localization of p27 was also associated with decreased survival (P = 0.0239). Loss of p27 conferred poor prognosis independently of proliferative index, as assessed by Ki-67 (MIB-1) immunostaining, which was not significantly different in survivors versus nonsurvivors. These results show that: (a) distribution of p27 message and protein parallel one another in metaplastic and dysplastic Barrett's epithelium, suggesting transcriptional regulation of the gene in the nonneoplastic setting; (b) p27 is inactivated in the majority of BAA as a result of either post-transcriptional modification or altered subcellular localization; and (c) loss of the cell cycle inhibitor p27 is associated with parameters of aggressive behavior and unfavorable outcome in BAA.

Prediction and cross-validation of neural networks versus logistic regression: using hepatic disorders as an example

The authors developed and cross-validated prediction models for newly diagnosed cases of liver disorders by using logistic regression and neural networks. Computerized files of health care encounters from the Fallon Community Health Plan were used to identify 1,674 subjects who had had liver-related health services between July 1, 1992, and June 30, 1993. A total of 219 subjects were confirmed by review of medical records as incident cases. The 1,674 subjects were randomly and evenly divided into training and test sets. The training set was used to derive prediction algorithms based solely on the automated data; the test set was used for cross-validation. The area under the Receiver Operating Characteristic curve for a neural network model was significantly larger than that for logistic regression in the training set (p = 0.04). However, the performance was statistically equivalent in the test set (p = 0.45). Despite its superior performance in the training set, the generalizability of the neural network model is limited. Logistic regression may therefore be preferred over neural network on the basis of its established advantages. More generalizable modeling techniques for neural networks may be necessary before they are practical for medical research.

Activation of protein kinase C triggers its ubiquitination and degradation

Treatment of cells with tumor-promoting phorbol esters results in the activation but then depletion of phorbol ester-responsive protein kinase C (PKC) isoforms. The ubiquitin-proteasome pathway has been implicated in regulating the levels of many cellular proteins, including those involved in cell cycle control. We report here that in 3Y1 rat fibroblasts, proteasome inhibitors prevent the depletion of PKC isoforms alpha, delta, and epsilon in response to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Proteasome inhibitors also blocked the tumor-promoting effects of TPA on 3Y1 cells overexpressing c-Src, which results from the depletion of PKC delta. Consistent with the involvement of the ubiquitin-proteasome pathway in the degradation of PKC isoforms, ubiquitinated PKC alpha, delta, and epsilon were detected within 30 min of TPA treatment. Diacylglycerol, the physiological activator of PKC, also stimulated ubiquitination and degradation of PKC, suggesting that ubiquitination is a physiological response to PKC activation. Compounds that inhibit activation of PKC prevented both TPA- and diacylglycerol-induced PKC depletion and ubiquitination. Moreover, a kinase-dead ATP-binding mutant of PKC alpha could not be depleted by TPA treatment. These data are consistent with a suicide model whereby activation of PKC triggers its own degradation via the ubiquitin-proteasome pathway.

Ubiquitin-dependent degradation of cyclin B is accelerated in polyploid megakaryocytes

During the endomitotic cell cycle of megakaryocytic cell lines, the levels of cyclin B1 and the activity of cyclin B1-dependent Cdc2 kinase, although detectable, are reduced as compared with megakaryocytes undergoing a mitotic cell cycle. The levels of cyclin A, however, are comparable during both cell cycles. The expression of cyclin B1 mRNA is also equivalent in proliferating and polyploidizing cells. In the current study, we found that the rate of cyclin B1 protein degradation is enhanced in polyploidizing megakaryocytes. This finding has led us to further investigate whether the ubiquitin-proteosome pathway responsible for cyclin B degradation is accelerated in these cells. Our data indicate that polyploidizing megakaryocytic cell lines nad primary bone marrow cells treated with the megakaryocyte proliferation- and ploidy-promoting factor, the c-Mpl ligand, display increased activities of the ubiquitin-proteosome pathway, which degrades cyclin B, as compared with proliferating megakaryocytic cell lines or diploid bone marrow cells, respectively. This degradation has all the hallmarks of a ubiquitin pathway, including the dependence on ATP, the appearance of high molecular weight conjugated forms of cyclin B, and inhibition of the proteolytic process by a mutated form of the ubiquitin-conjugating enzyme Ubc4. Our studies also indicate that the ability to degrade cyclin A is equivalent in both the mitotic and endomitotic cell cycles. The increased potential of polyploid megakaryocytes to degrade cyclin B may be part of the cellular programming that leads to aborted mitosis.

Hunger in children in the United States: potential behavioral and emotional correlates

OBJECTIVE

Results from a recent series of surveys from 9 states and the District of Columbia by the Community Childhood Hunger Identification Project (CCHIP) provide an estimate that 4 million American children experience prolonged periodic food insufficiency and hunger each year, 8% of the children under the age of 12 in this country. The same studies show that an additional 10 million children are at risk for hunger. The current study examined the relationship between hunger as defined by the CCHIP measure (food insufficiency attributable to constrained resources) and variables reflecting the psychosocial functioning of low-income, school-aged children.

METHODS

The study group included 328 parents and children from a CCHIP study of families with at least 1 child under the age of 12 years living in the city of Pittsburgh and the surrounding Allegheny County. A two-stage area probability sampling design with standard cluster techniques was used. All parents whose child was between the ages of 6 and 12 years at the time of interview were asked to complete a Pediatric Symptom Checklist, a brief parent-report questionnaire that assesses children's emotional and behavioral symptoms. Hunger status was defined by parent responses to the standard 8 food-insufficiency questions from the CCHIP survey that are used to classify households and children as "hungry," "at-risk for hunger," or "not hungry."

RESULTS

In an area probability sample of low-income families, those defined as hungry on the CCHIP measure were significantly more likely to have clinical levels of psychosocial dysfunction on the Pediatric Symptom Checklist than children defined as at-risk for hunger or not hungry. Analysis of individual items and factor scores on the Pediatric Symptom Checklist showed that virtually all behavioral, emotional, and academic problems were more prevalent in hungry children, but that aggression and anxiety had the strongest degree of association with experiences of hunger.

CONCLUSION

Children from families that report multiple experiences of food insufficiency and hunger are more likely to show behavioral, emotional, and academic problems on a standardized measure of psychosocial dysfunction than children from the same low-income communities whose families do not report experiences of hunger. Although causality cannot be determined from a cross-sectional design, the strength of these findings suggests the importance of greater awareness on the part of health care providers and public health officials of the role of food insufficiency and hunger in the lives of poor children.

Estimation of the prevalence of injection drug use in greater Boston in 1993

This article is a report on different methods of estimation of the number of injection drug users (IDUs) in the Boston standard metropolitan statistical area (SMSA) in 1993. Because the sharing of needles is a means of transmission for HIV, an estimate of the prevalence of injection drug use is essential for acquired immunodeficiency syndrome (AIDS) prevention programs. The data for this study come from the Massachusetts Department of Public Health Bureau of Substance Abuse, the Massachusetts AIDS Surveillance Unit, the Drug Abuse Warning Network (DAWN), the National Household Survey on Drug Abuse: Population Estimates 1993, and the Massachusetts State Police Crime Reporting Unit. The estimates in this study can be assessed with regard to the different time frames that are involved, noting that some estimates are useful only to establish upper or lower bounds. The estimate that best meshes with the findings of this report is that there were between 13,500-16,500 injection drug users in greater Boston and 45,000-60,000 IDUs in Massachusetts in 1993.

Cell cycle regulation by the ubiquitin pathway

In the past 2 years, two ubiquitin-dependent proteolytic pathways have been established as important players in the regulation of the cell division cycle. In S. cerevisiae, the entry into S phase requires ubiquitin-mediated degradation of a cdk inhibitor, p40Sic1, in a pathway that involves the E2 enzyme Cdc34. Recent studies reviewed herein show that the Cdc34 pathway targets phosphorylated substrates. A second pathway that regulates chromosome segregation and mitotic exit by degrading anaphase inhibitors and mitotic cyclins involves a different E2 and a large molecular weight E3 complex, called the anaphase-promoting complex or cyclosome. This pathway targets substrates containing one or more destruction box motif.

Prognostic role of the cyclin-dependent kinase inhibitor p27 in non-small cell lung cancer

Despite its potential role as a tumor suppressor, p27 gene, a member of the Cip/Kip family of cyclin-dependent kinase inhibitor genes, has never been found mutated in human tumors. We investigated p27 protein expression in a series of 108 non-small cell lung cancers (57.4% stage 1, 16.7% stage 2, and 25.9% stage 3) to determine whether the lack or altered expression of this protein correlates with neoplastic transformation and/or progression. We performed immunohistochemistry and Western blot analysis of each specimen. We found that tumors expressing low to undetectable levels of p27 contained high p27 degradation activity. When we evaluated the outcome of the patients in relationship to p27 expression, we found p27 to be a prognostic factor correlating with the overall survival times (P = 0.0012). The possibility of a simple assay, such as the immunohistochemical analysis of p27 expression on routinely formalin-fixed, paraffin-embedded specimens, has considerable value for the prognosis of patients who undergo surgical resection. In addition, confirmation of the involvement of the proteasome-mediated proteolysis in p27 degradation should stimulate new strategies of nonsurgical treatments of non-small cell lung cancer.

Viral load and disease progression in infants infected with human immunodeficiency virus type 1. Women and Infants Transmission Study Group

BACKGROUND

There are only limited data on human immunodeficiency virus type 1 (HIV-1) RNA in perinatally infected infants. Understanding the dynamics of HIV-1 infection and its relation to disease progression may help identify opportunities for effective antiviral treatment in infected infants.

METHODS

We obtained plasma samples from 106 HIV-infected infants at birth; at 1, 2, 4, 6, 9, 12, 15, and 18 months of age; and subsequently every 6 months. HIV-1 RNA was assayed by means of a reverse-transcription polymerase chain reaction. The infants were born between 1990 and 1993, and only 21 percent of the infants' mothers received any treatment with zidovudine during pregnancy.

RESULTS

Plasma HIV-1 RNA levels increased rapidly after birth, peaked at 1 to 2 months of age (median values at 1 and 2 months, 318,000 and 256,000 copies per milliliter, respectively), and then slowly declined to a median of 34,000 copies per milliliter at 24 months. Newborns with a first positive HIV-1 culture within 48 hours after birth had significantly higher HIV-1 RNA levels, although only during the first two months of life, than those with a first positive culture seven or more days after birth. Infants with a rapid progression of disease had higher peak HIV-1 RNA levels in the first two months of life than those without rapid progression (median value, 724,000 vs. 219,000 copies per milliliter; P=0.006), as well as a higher geometric mean value during the first year of life (median value, 330,000 vs. 158,000 copies per milliliter, P=0.001).

CONCLUSIONS

In perinatally infected infants, HIV-1 RNA levels are high and decline only slowly during the first two years of life. Infants with very high viral loads in the first months of life are at increased risk for a rapid progression of disease, which suggests that early treatment with antiretroviral agents may be indicated for these infants.