Activation of oncogenic transcription factor AP-1 in T cells infected with human T cell leukemia virus type 1

Human T cell leukemia virus type 1 (HTLV-1) Tax protein transforms primary human T cells in vitro. We previously showed that Tax induces the expression of various family members of the transcription factor AP-1 such as c-Jun, JunD, c-Fos, and Fra-1 at the mRNA level in T cells. In this study, we have examined the ability of Tax to activate transcription through the AP-1-binding site (AP-1 site). A transient transfection study showed that Tax can activate transcription through the AP-1-binding site in a human T cell line, whereas any combination of AP-1 proteins did so much less than Tax, indicating that the activation of the AP-1 site by Tax may require a mechanism other than the induction of AP-1 mRNA. Fresh peripheral blood leukemia cells of all surveyed ATL patients displayed constitutive AP-1 DNA-binding activity, whereas no normal individuals did. However, the HTLV-1 genes, including tax, are not significantly expressed in fresh leukemia cells from ATL patients. Our present results suggest that activation of AP-1 occurs through Tax-dependent and -independent mechanisms in HTLV-1-infected T cells, which may play some roles in dysregulated phenotypes of HTLV-1-infected cells.

Activation of HIF1alpha ubiquitination by a reconstituted von Hippel-Lindau (VHL) tumor suppressor complex

Mutations in the VHL tumor suppressor gene result in constitutive expression of many hypoxia-inducible genes, at least in part because of increases in the cellular level of hypoxia-inducible transcription factor HIF1alpha, which in normal cells is rapidly ubiquitinated and degraded by the proteasome under normoxic conditions. The recent observation that the VHL protein is a subunit of an Skp1-Cul1/Cdc53-F-box (SCF)-like E3 ubiquitin ligase raised the possibility that VHL may be directly responsible for regulating cellular levels of HIF1alpha by targeting it for ubiquitination and proteolysis. In this report, we test this hypothesis directly. We report development of methods for production of the purified recombinant VHL complex and present direct biochemical evidence that it can function with an E1 ubiquitin-activating enzyme and E2 ubiquitin-conjugating enzyme to activate HIF1alpha ubiquitination in vitro. Our findings provide new insight into the function of the VHL tumor suppressor protein, and they provide a foundation for future investigations of the mechanisms underlying VHL regulation of oxygen-dependent gene expression.

[Three cases of measles-associated interstitial pneumonia]

It has been reported that measles-associated pneumonia is easily complicated with fatal respiratory failure. During the 6 months from January to June 1998, we treated three young patients with measles-associated pneumonia who had previously been healthy. Their chest X-ray and CT examinations revealed mainly interstitial and partially alveolar pneumonia surrounding extensive areas of bronchiolitis. In one patient, respiratory failure was present, and arterial blood gas analysis showed severe hypoxemia. Therefore, this patient was treated with a mechanical ventilator, which dramatically improved the condition. The other two patients received steroid-pulse therapy and improved rapidly. We believed that in measles-associated pneumonia, steroid pulse therapy is to be recommended for the severely ill patient. According to a report by the Japanese Ministry of Health and Welfare, measles-like disease was widespread in Japan in 1991 and occasionally encountered in 1996. But in Yamanashi Prefecture, the disease was prevalent in 1991, 1994 and 1998. The number of patients in our hospital had reflected the prevalence in the prefecture. It is suggested that the measles is a disease of regional prevalence.

[A study of recovery factor about drug addiction recovery center "DARC"]

This study examines the effectiveness of the 'DARC' (Drug Addiction Rehabilitation Center) and its program in treating patients with drug dependence. DARC is the only rehabilitation facility group managed by recovered drug users in Japan. It uses the 'Twelve Step Program' as part of its recovery regime. Through structured questionnaires, the changes of participants' and ex-participants' everyday behavior, their acceptance of spirituality, attitude toward drugs, self-esteem, their coping skills and loneliness were examined. The results revealed: a.. Negative partial correlation between loneliness and everyday behavior. b.. Negative partial correlation between loneliness and positive/effective coping skills. c.. Positive partial correlation between acceptance of 'spirituality' and attitude toward drugs. d.. Positive partial correlation between acceptance of 'spirituality' and positive/effective coping skills. These results suggest that the acceptance of 'spirituality' and decreasing loneliness are important factors in the recovery from drug dependence.

Familial Parkinson disease gene product, parkin, is a ubiquitin-protein ligase

Autosomal recessive juvenile parkinsonism (AR-JP), one of the most common familial forms of Parkinson disease, is characterized by selective dopaminergic neural cell death and the absence of the Lewy body, a cytoplasmic inclusion body consisting of aggregates of abnormally accumulated proteins. We previously cloned PARK2, mutations of which cause AR-JP (ref. 2), but the function of the gene product, parkin, remains unknown. We report here that parkin is involved in protein degradation as a ubiquitin-protein ligase collaborating with the ubiquitin-conjugating enzyme UbcH7, and that mutant parkins from AR-JP patients show loss of the ubiquitin-protein ligase activity. Our findings indicate that accumulation of proteins that have yet to be identified causes a selective neural cell death without formation of Lewy bodies. Our findings should enhance the exploration of the molecular mechanisms of neurodegeneration in Parkinson disease as well as in other neurodegenerative diseases that are characterized by involvement of abnormal protein ubiquitination, including Alzheimer disease, other tauopathies, CAG triplet repeat disorders and amyotrophic lateral sclerosis.

Synthesis and bioactivities of novel piperidylpyrimidine derivatives: inhibitors of tumor necrosis factor-alpha production

New piperidylpyrimidine derivatives, including quinazolines, were prepared, and their abilities to inhibit TNF-alpha production evaluated. Some compounds showed potent inhibitory activity in mouse macrophages stimulated with LPS. The synthesis and structure activity relationships of these compounds are described.

Constitutive activation of transcription factor AP-1 in primary adult T-cell leukemia cells

Human T-cell leukemia virus type-I (HTLV-I) is the etiologic agent of adult T-cell leukemia (ATL). This study examined the status of the oncogenic transcription factor AP-1 in leukemic cells freshly isolated from patients with ATL. Leukemic cells from peripheral blood of all patients with ATL exhibited constitutive AP-1 DNA binding activity, whereas mononuclear cells from normal individuals did not. In agreement with previous studies, HTLV-I transforming protein, Tax, was found to stimulate the DNA binding activity of AP-1 in a T-cell line. However, HTLV-I genes, including Tax, were not significantly expressed in leukemic cells freshly obtained from patients with ATL. Moreover, all T-cell lines derived from leukemic cells of patients with ATL also displayed constitutive AP-1 DNA binding activity, but expressed little Tax protein. Thus, leukemic cells of patients with ATL appear to have Tax-independent mechanisms that induce AP-1 activity, both in vivo and in vitro. In antibody supershift experiments, AP-1 in fresh leukemic cells and ATL-derived cell lines were found to contain JunD. Consistently, all primary ATL cells and ATL-derived cell lines expressed high levels of JunD messenger RNA. Our results suggest that AP-1 is activated in leukemic cells of patients with ATL through a Tax-independent mechanism and this may play a role in the deregulated phenotypes of ATL leukemic cells. (Blood. 2000;95:3915-3921)

Time to recover from atrial hormonal, mechanical, and electrical dysfunction after successful electrical cardioversion of persistent atrial fibrillation

Although transient atrial dysfunction has been reported after electrical cardioversion of atrial fibrillation (AF), the difference in the time to recover from the atrial hormonal, mechanical, and electrical dysfunction has not been described. Thus, we evaluated the time course of recovery from atrial hormonal, mechanical, and electrical dysfunction after cardioversion in patients with nonvalvular AF. We attempted electrical cardioversion in 87 consecutive patients with nonvalvular AF that had persisted for > or =6 months, and in 24 patients (28%) with maintained sinus rhythm for > or =6 months. To evaluate atrial hormonal, mechanical, and electrical dysfunction in these 24 patients, we measured plasma concentration of atrial natriuretic peptide, the atrial peak velocity in transmitral flow, and the ratio of peak systolic-to-diastolic pulmonary venous flow (S/D ratio) using echocardiography, and the duration and the root mean voltage for the terminal 20 ms (LP20) of the filtered P wave using P-wave signal-averaged electrocardiography. Atrial natriuretic peptide rapidly returned to baseline within 1 day after cardioversion, and maintained these levels for 6 months. Atrial peak velocity in transmitral flow and S/D ratio were significantly increased at 2 weeks, and continued to increase until 1 month, and then reached a plateau. The duration and LP20 began to recover only 6 months after cardioversion. One to 3 years after conversion, the duration and LP20 had nearly reached a plateau, but the latter value remained below normal. In patients with nonvalvular AF of prolonged duration, recovery from atrial electrical dysfunction after sinus conversion took much longer than that from either atrial hormonal or mechanical dysfunction.

SCF(beta)(-TrCP) ubiquitin ligase-mediated processing of NF-kappaB p105 requires phosphorylation of its C-terminus by IkappaB kinase

Processing of the p105 precursor to form the active subunit p50 of the NF-kappaB transcription factor is a unique case in which the ubiquitin system is involved in limited processing rather than in complete destruction of the target substrate. A glycine-rich region along with a downstream acidic domain have been demonstrated to be essential for processing. Here we demonstrate that following IkappaB kinase (IkappaK)-mediated phosphorylation, the C-terminal domain of p105 (residues 918-934) serves as a recognition motif for the SCF(beta)(-TrCP) ubiquitin ligase. Expression of IkappaKbeta dramatically increases processing of wild-type p105, but not of p105-Delta918-934. Dominant-negative beta-TrCP inhibits IkappaK-dependent processing. Furthermore, the ligase and wild-type p105 but not p105-Delta918-934 associate physically following phosphorylation. In vitro, SCF(beta)(-TrCP) specifically conjugates and promotes processing of phosphorylated p105. Importantly, the TrCP recognition motif in p105 is different from that described for IkappaBs, beta-catenin and human immunodeficiency virus type 1 Vpu. Since p105-Delta918-934 is also conjugated and processed, it appears that p105 can be recognized under different physiological conditions by two different ligases, targeting two distinct recognition motifs.

Differential interaction of plakoglobin and beta-catenin with the ubiquitin-proteasome system

Beta-catenin and plakoglobin are closely related armadillo family proteins with shared and distinct properties; Both are associated with cadherins in actin-containing adherens junctions. Plakoglobin is also found in desmosomes where it anchors intermediate filaments to the desmosomal plaques. Beta-catenin, on the other hand, is a component of the Wnt signaling pathway, which is involved in embryonic morphogenesis and tumorigenesis. A key step in the regulation of this pathway involves modulation of beta-catenin stability. A multiprotein complex, regulated by Wnt, directs the phosphorylation of beta-catenin and its degradation by the ubiquitin-proteasome system. Plakoglobin can also associate with members of this complex, but inhibition of proteasomal degradation has little effect on its levels while dramatically increasing the levels of beta-catenin. Beta-TrCP, an F-box protein of the SCF E3 ubiquitin ligase complex, was recently shown to play a role in the turnover of beta-catenin. To elucidate the basis for the apparent differences in the turnover of beta-catenin and plakoglobin we compared the handling of these two proteins by the ubiquitin-proteasome system. We show here that a deletion mutant of beta-TrCP, lacking the F-box, can stabilize the endogenous beta-catenin leading to its nuclear translocation and induction of beta-catenin/LEF-1-directed transcription, without affecting the levels of plakoglobin. However, when plakoglobin was overexpressed, it readily associated with beta-TrCP, efficiently competed with beta-catenin for binding to beta-TrCP and became polyubiquitinated. Fractionation studies revealed that about 85% of plakoglobin in 293 cells, is Triton X-100-insoluble compared to 50% of beta-catenin. These results suggest that while both plakoglobin and beta-catenin can comparably interact with beta-TrCP and the ubiquitination system, the sequestration of plakoglobin by the membrane-cytoskeleton system renders it inaccessible to the proteolytic machinery and stabilizes it.

An autopsy case with clinically and molecular genetically diagnosed Huntington's disease with only minimal non-specific neuropathological findings

An autopsy case with clinically and molecular genetically diagnosed Huntington's disease (HD) accompanied with minimal non-specific neuropathological features was reported. When the patient was 45 years old, he had faulty memory, mood swing, personality change and agitation. Neurological and psychiatric examinations revealed choreoathetoid movements in limbs and trunk, generalized hyperreflexia and mental deterioration. However, cerebellar ataxia and muscle rigidity were not disclosed. Neuroimaging study did not show a definite atrophy of heads of caudate nuclei. Neuroacanthocytosis and Wilson's disease were ruled out by the peripheral blood examination and serum Cu and ceruloplasmin examination. At the age of 55 he died of pneumonia. Post-mortem examination revealed minimal non-specific neuropathological features for HD (Vonsattel's grade 0), that is, no visible fibrillary gliosis in the striatum, and few neuronal loss and only proliferation of astrocytes (astrocytosis) in the striatum. Molecular-genetic study the patient's brain tissues and his youngest son's blood was performed. These studies revealed 40 CAG repeats in the patient, 56 CAG repeats in his youngest son. These results suggest they may be HD. Vonsattel et al. [ 1998] insist that grade 0 comprises 1% of all HD brains, and grade 1 comprises 4% of all HD brains. But we could not find any reports in which the clinical and neuropathological features were described in detail on the cases with clinically and molecular genetically diagnosed HD without specific pathological findings. Therefore, we present in detail the clinical and neuropathological features of such case.

Fulminant hepatitis B following bone marrow transplantation in an HBsAg-negative, HBsAb-positive recipient; reactivation of dormant virus during the immunosuppressive period

It is widely accepted that seroconversion of HBsAg to HBsAb indicates clearance of hepatitis B virus. We describe a 50-year-old man with chronic myelocytic leukemia who developed lethal hepatitis B 22 months after allo-BMT. He had been negative for HBsAg and positive for HBsAb before BMT. Hepatitis B virus latently existing in the liver cells before BMT proliferated during the immunosuppressed period causing fatal hepatitis. Recipients with positive HBsAb should be considered to have the potential for active hepatitis B to emerge after BMT. Bone Marrow Transplantation (2000) 25, 105-108.

Ubiquitin ligase activity and tyrosine phosphorylation underlie suppression of growth factor signaling by c-Cbl/Sli-1

Receptor desensitization is accomplished by accelerated endocytosis and degradation of ligand-receptor complexes. An in vitro reconstituted system indicates that Cbl adaptor proteins directly control downregulation of the receptor for the epidermal growth factor (EGFR) by recruiting ubiquitin-activating and -conjugating enzymes. We infer a sequential process initiated by autophosphorylation of EGFR at a previously identified lysosome-targeting motif that subsequently recruits Cbl. This is followed by tyrosine phosphorylation of c-Cbl at a site flanking its RING finger, which enables receptor ubiquitination and degradation. Whereas all three members of the Cbl family can enhance ubiquitination, two oncogenic Cbl variants, whose RING fingers are defective and phosphorylation sites are missing, are unable to desensitize EGFR. Our study identifies Cbl proteins as components of the ubiquitin ligation machinery and implies that they similarly suppress many other signaling pathways.

A single-chain antibody fragment specific for the Plasmodium berghei ookinete protein Pbs21 confers transmission blockade in the mosquito midgut

Mouse monoclonal antibody 13.1 (mAb 13.1) directed against Pbs21, a 21-kDa sexual-stage surface protein of Plasmodium berghei, is known to inhibit oocyst development from gametocytes and ookinetes in the mosquito midgut. To examine the properties and potential uses of a single-chain antibody fragment (scFv) for blocking transmission of malaria parasites to mosquitoes, we have cloned and sequenced the genes encoding variable regions of the immunoglobulin heavy and light chains (V(H) and V(L)) of mAb 13.1. The V(H) and V(L) genes were assembled as an scFv gene, and expressed in a baculovirus expression system. Following purification of 13.1 scFv, Western blotting and inhibition ELISA assays confirmed that 13.1 scFv retained the binding specificity of the parent mAb 13.1 for Pbs21. Furthermore, 13.1 scFv bound to the surface of P. berghei ookinetes, and blocked oocyst development in the mosquito midgut by at least 93%, as assessed by oocyst counts in mosquitoes. We suggest that the 13.1 scFv gene could be useful not only in studying the mechanism of transmission blockade, but also in generating, by mosquito germline transformation, a model system to evaluate the production of mosquitoes refractory to malaria.

Stabilization of iron regulatory protein 2, IRP2, by aluminum

Iron regulatory protein 2 (IRP2) is one of the central regulators of iron homeostasis. IRP2 regulates expression of molecules involved in iron metabolism by binding to iron responsive elements (IREs) in the transcripts of those molecules in iron depletion. IRP2 is regulated by the accelerated degradation initiated by the iron-catalyzed oxidation. Here we report that aluminum antagonizes the iron-induced decrease in IRE binding activity of IRP2. Aluminum also inhibits iron-induced oxidation of IRP2 in vitro. These results suggest that aluminum stabilizes IRP2 by interfering with the iron-catalyzed oxidation, which results in perturbation of iron metabolism.

Quantitation and isomeric structure analysis of free oligosaccharides present in the cytosol fraction of mouse liver: detection of a free disialobiantennary oligosaccharide and glucosylated oligomannosides

The amounts and isomeric structures of free oligosaccharides derived from N-linked sugar chains present in the cytosol fraction of perfused mouse liver were analyzed by tagging the reducing end with 2-aminopyridine followed by 2-dimensional HPLC mapping with standard sugar chains. Sixteen pyridylaminated (PA-) oligomannosides terminating with a PA-GlcNAc residue (GN1-type), three glucose-containing oligomannosides, and four oligomannosides terminating with a PA-di-N-acetylchitobiose (GN2-type) were detected. The total contents of the GN1- and GN2-type oligomannosides were 3. 4 and 0.5 nmol, respectively, per gram of wet tissue. Maltooligosaccharides (dimer to pentamer) were also detected, the total content of which was 13 nmol per gram of wet tissue. Besides these oligosaccharides, a PA-disialobiantennary sugar chain-the sole complex-type sugar chain-was also detected. All the oligomannosides identified had partial structures of Glc(3)Man(9)GlNAc(2)-p-p-dolichol, revealing that they were metabolic degradation products. Manalpha1-2Manalpha1-2Manalpha1-3(Manalpha1-6)++ +Manbeta1-4GlcNAc (M5B') was the major oligomannoside, suggesting that cytosolic endo-beta-N-acetylglucosaminidase and neutral alpha-mannosidase participate in the degradation, because these enzymes have suitable substrate specificities for the production of M5B'. Degradation by these enzymes seems to be the main pathway by which oligomannosides are degraded in mouse cytosol; however, small amounts of Manalpha1-6(Manalpha1-3)Manalpha1-6(Manalpha1-3) Manbeta1-4(GlcNAc)1-2 and related oligomannosides together with parts of their structures were also detected, suggesting that there is another minor route by which cytosolic free oligomannosides are produced.

Identification of the von Hippel-lindau tumor-suppressor protein as part of an active E3 ubiquitin ligase complex

Mutations of von Hippel-Lindau disease (VHL) tumor-suppressor gene product (pVHL) are found in patients with dominant inherited VHL syndrome and in the vast majority of sporadic clear cell renal carcinomas. The function of the pVHL protein has not been clarified. pVHL has been shown to form a complex with elongin B and elongin C (VBC) and with cullin (CUL)-2. In light of the structural analogy of VBC-CUL-2 to SKP1-CUL-1-F-box ubiquitin ligases, the ubiquitin ligase activity of VBC-CUL-2 was examined in this study. We show that VBC-CUL-2 exhibits ubiquitin ligase activity, and we identified UbcH5a, b, and c, but not CDC34, as the ubiquitin-conjugating enzymes of the VBC-CUL-2 ubiquitin ligase. The protein Rbx1/ROC1 enhances ligase activity of VBC-CUL-2 as it does in the SKP1-CUL-1-F-box protein ligase complex. We also found that pVHL associates with two proteins, p100 and p220, which migrate at a similar molecular weight as two major bands in the ubiquitination assay. Furthermore, naturally occurring pVHL missense mutations, including mutants capable of forming a complex with elongin B-elongin C-CUL-2, fail to associate with p100 and p220 and cannot exhibit the E3 ligase activity. These results suggest that pVHL might be the substrate recognition subunit of the VBC-CUL-2 E3 ligase. This is also, to our knowledge, the first example of a human tumor-suppressor protein being directly involved in the ubiquitin conjugation system which leads to the targeted degradation of substrate proteins.

Allylthiamindisulfide and related compounds enhance thermogenesis with increasing noradrenaline and adrenaline secretion in rats

The effects of allylthiamindisulfide, an allyl derivative of thiamin, and related compounds on thermogenesis were investigated by measuring noradrenaline and adrenaline secretion and the temperatures of interscapular brown adipose tissue (IBAT) and rectum in rats. In Experiment 1, the effects of the administrations of allylthiamindisulfide and related compounds on noradrenaline and adrenaline secretion were evaluated as compared to thiamin in anesthetized rats. The administration of allylthiamindisulfide significantly increased the plasma concentrations of noradrenaline and adrenaline. These increases were dose dependent, while that of thiamin was not. Four synthetic compounds related to allylthiamindisulfide also increased the plasma adrenaline and noradrenaline concentrations. In Experiment 2, the effects of allylthiamindisulfide on thermogenesis were investigated by the direct measurement of temperatures in the IBAT and rectum in anesthetized rats, and compared to the effects induced by thiamin and diallyldisulfide. The temperatures in the IBAT and rectum were significantly increased by the administration of allylthiamindisulfide and diallyldisulfide, while there was no significant increase as the result of thiamin administration. These results suggest that allylthiamindisulfide and related compounds enhance thermogenesis by increasing noradrenaline and adrenaline secretion in rats.

[Clinical effect of arotinolol hydrochloride and its influence on renal function in elderly patients with essential hypertension]

Arotinolol hydrochloride with alpha-and beta-receptor blocking action, developed in Japan, is mainly used for the treatment of hypertension. The study population consisted of 42 outpatients with essential hypertension with a blood pressure greater or equal to 160/96 mmHg. 10 men and 32 women, with a mean age of 77.5 year. The patients received 10 mg arotinolol hydrochloride daily for 24 weeks which was taken orally twice a day. We evaluated the changes of blood pressure, heart rate and chief complaints of patients before and every 4 weeks during treatment and the renal function before, 12 weeks after and 24 weeks after, the administration of arotinolol hydrochloride. Blood pressure and heart rate decreased significantly after 4 weeks of treatment with arotinolol hydrochloride (p < 0.05). However, no significant changes were found in blood urea nitrogen, serum creatinine, serum albumin, beta2-microglobuline, NAG or creatinine clearance during the 24 weeks of treatment. These results indicate that arotinolol hydrochloride has antihypertensive effects without renal dysfunction in elderly patients with essential hypertension.

Development of a compact computed tomographic apparatus for dental use

OBJECTIVE

To describe a compact computed tomographic apparatus (Ortho-CT) for use in dental practice.

METHODS

Ortho-CT is a cone-beam-type of CT apparatus consisting of a multifunctional maxillofacial imaging machine (Scanora, Soredex, Helsinki, Finland) in which the film is replaced with an X-ray imaging intensifier (Hamamatsu Photonics, Hamamatsu, Japan). The region of image reconstruction is a cylinder 32 mm in height and 38 mm in diameter and the voxel is a 0.136-mm cube. Scanning is at 85 kV and 10 mA with a 1 mm Cu filter. The scan time is 17 s comparable with that required for rotational panoramic radiography. A single scan collects 512 sets of projection data through 360 degrees and the image is reconstructed by a personal computer. The time required for image reconstruction is about 10 min.

RESULTS

The resolution limit was about 2.0 lp mm-1 and the skin entrance dose 0.62 mGy. Excellent image quality was obtained with a tissue-equivalent skull phantom: roots, periodontal ligament space, lamina dura, and cancellous bone were clearly visualized.

CONCLUSION

Ortho-CT provides three-dimensional images of excellent quality for dental use at a low entrance dose.

Identification of the ubiquitin carrier proteins, E2s, involved in signal-induced conjugation and subsequent degradation of IkappaBalpha

The last step in the activation of the transcription factor NF-kappaB is signal-induced, ubiquitin- and proteasome-mediated degradation of the inhibitor IkappaBalpha. Although most of the components involved in the activation and degradation pathways have been identified, the ubiquitin carrier proteins (E2) have remained elusive. Here we show that the two highly homologous members of the UBCH5 family, UBCH5b and UBCH5c, and CDC34/UBC3, the mammalian homolog of yeast Cdc34/Ubc3, are the E2 enzymes involved in the process. The conjugation reaction they catalyze in vitro is specific, as they do not recognize the S32A,S36A mutant species of IkappaBalpha that cannot be phosphorylated and conjugated following an extracellular signal. Furthermore, the reaction is specifically inhibited by a doubly phosphorylated peptide that spans the ubiquitin ligase recognition domain of the inhibitor. Cys-to-Ala mutant species of the enzymes that cannot bind ubiquitin inhibit tumor necrosis factor alpha-induced degradation of the inhibitor in vivo. Not surprisingly, they have a similar effect in a cell-free system as well. Although it is clear that the E2 enzymes are not entirely specific to IkappaBalpha, they are also not involved in the conjugation and degradation of the bulk of cellular proteins, thus exhibiting some degree of specificity that is mediated probably via their association with a defined subset of ubiquitin-protein ligases. The mechanisms that underlie the involvement of two different E2 species in IkappaBalpha conjugation are not clear at present. It is possible that different conjugating machineries operate under different physiological conditions or in different cells.