Identification of CDK4 as a target of c-MYC

The prototypic oncogene c-MYC encodes a transcription factor that can drive proliferation by promoting cell-cycle reentry. However, the mechanisms through which c-MYC achieves these effects have been unclear. Using serial analysis of gene expression, we have identified the cyclin-dependent kinase 4 (CDK4) gene as a transcriptional target of c-MYC. c-MYC induced a rapid increase in CDK4 mRNA levels through four highly conserved c-MYC binding sites within the CDK4 promoter. Cell-cycle progression is delayed in c-MYC-deficient RAT1 cells, and this delay was associated with a defect in CDK4 induction. Ectopic expression of CDK4 in these cells partially alleviated the growth defect. Thus, CDK4 provides a direct link between the oncogenic effects of c-MYC and cell-cycle regulation.

Cell-specific activation of nuclear factor-kappaB by the parasite Trypanosoma cruzi promotes resistance to intracellular infection

The transcription factor nuclear factor-kappaB (NF-kappaB) is central to the innate and acquired immune response to microbial pathogens, coordinating cellular responses to the presence of infection. Here we demonstrate a direct role for NF-kappaB activation in controlling intracellular infection in nonimmune cells. Trypanosoma cruzi is an intracellular parasite of mammalian cells with a marked preference for infection of myocytes. The molecular basis for this tissue tropism is unknown. Trypomastigotes, the infectious stage of T. cruzi, activate nuclear translocation and DNA binding of NF-kappaB p65 subunit and NF-kappaB-dependent gene expression in epithelial cells, endothelial cells, and fibroblasts. Inactivation of epithelial cell NF-kappaB signaling by inducible expression of the inhibitory mutant IkappaBaM significantly enhances parasite invasion. T. cruzi do not activate NF-kappaB in cells derived from skeletal, smooth, or cardiac muscle, despite the ability of these cells to respond to tumor necrosis factor-alpha with NF-kappaB activation. The in vitro infection level in these muscle-derived cells is more than double that seen in the other cell types tested. Therefore, the ability of T. cruzi to activate NF-kappaB correlates inversely with susceptibility to infection, suggesting that NF-kappaB activation is a determinant of the intracellular survival and tissue tropism of T. cruzi.

Air pollution and hospital admissions for respiratory and cardiovascular diseases in Hong Kong

OBJECTIVE

To investigate short term effects of concentrations of pollutants in ambient air on hospital admissions for cardiovascular and respiratory diseases in Hong Kong.

METHODS

Retrospective ecological study. A Poisson regression was performed of concentrations of daily air pollutant on daily counts of emergency hospital admissions in 12 major hospitals. The effects of time trend, season, and other cyclical factors, temperature, and humidity were accounted for. Autocorrelation and overdispersion were corrected. Daily concentrations of nitrogen dioxide (NO2), sulphur dioxide (SO2), ozone (O3), and particulate matter < 10 microns in aerodynamic diameter (PM10) were obtained from seven air monitoring stations in Hong Kong in 1994 and 1995. Relative risks (RR) of respiratory and cardiovascular disease admissions (for an increase of 10 micrograms/m3 in concentration of air pollutant) were calculated.

RESULTS

Significant associations were found between hospital admissions for all respiratory diseases, all cardiovascular diseases, chronic obstructive pulmonary diseases, and heart failure and the concentrations of all four pollutants. Admissions for asthma, pneumonia, and influenza were significantly associated with NO2, O3, and PM10. Relative risk (RR) for admissions for respiratory disease for the four pollutants ranged from 1.013 (for SO2) to 1.022 (for O3), and for admissions for cardiovascular disease, from 1.006 (for PM10) to 1.016 (for SO2). Those aged > or = 65 years were at higher risk. Significant positive interactions were detected between NO2, O3, and PM10, and between O3 and winter months.

CONCLUSIONS

Adverse health effects are evident at current ambient concentrations of air pollutants. Further reduction in air pollution is necessary to protect the health of the community, especially that of the high risk group.

Human cathepsin X: A cysteine protease with unique carboxypeptidase activity

Cathepsin X is a novel cysteine protease which was identified recently from the EST (expressed sequence tags) database. In a homology model of the mature cathepsin X, a unique three residue insertion between the Gln22 of the oxyanion hole and the active site Cys31 was found to be located in the primed region of the binding cleft as part of a surface loop corresponding to residues His23 to Tyr27, which we have termed the "mini-loop". From the model, it became apparent that this distinctive structural feature might confer exopeptidase activity to the enzyme. To verify this hypothesis, human procathepsin X was expressed in Pichia pastoris and converted to mature cathepsin X using small amounts of human cathepsin L. Cathepsin X was found to display excellent carboxypeptidase activity against the substrate Abz-FRF(4NO(2)), with a k(cat)/K(M) value of 1.23 x 10(5) M(-)(1) s(-)(1) at the optimal pH of 5.0. However, the activity of cathepsin X against the substrates Cbz-FR-MCA and Abz-AFRSAAQ-EDDnp was found to be extremely low, with k(cat)/K(M) values lower than 70 M(-)(1) s(-)(1). Therefore, cathepsin X displays a stricter exopeptidase activity than cathepsin B. No inhibition of cathepsin X by cystatin C could be detected up to a concentration of 4 microM of inhibitor. From a model of the protease complexed with Cbz-FRF, the bound carboxypeptidase substrate is predicted to establish a number of favorable contacts within the cathepsin X binding site, in particular with residues His23 and Tyr27 from the mini-loop. The presence of the mini-loop restricts the accessibility of cystatin C as well as of the endopeptidase and MCA substrates in the primed subsites of the protease. The marked structural and functional differences of cathepsin X relative to other members of the papain family of cysteine proteases will be of great value in designing specific inhibitors useful as research tools to investigate the physiological and potential pathological roles of this novel enzyme.

Highly Regio- and Stereoselective Intramolecular 1,3-Dipolar Cycloadditions of Norbornadiene-Tethered Nitrile Oxides

[reaction: see text] Intramolecular cycloadditions with high regio- and stereocontrol are important methods for the efficient assembly of complex molecular structures. Efficient routes to the synthesis of norbornadiene-tethered nitrile oxides have been developed, and their intramolecular 1,3-dipolar cycloadditions were studied. The cycloadditions occurred in good yields for a variety of substrates and were found to be highly regio- and stereoselective.

Interdependency of sequence and positional specificities for cysteine proteases of the papain family

The specificity of cysteine proteases is characterized by the nature of the amino acid sequence recognized by the enzymes (sequence specificity) as well as by the position of the scissile peptide bond (positional specificity, i.e., endopeptidase, aminopeptidase, or carboxypeptidase). In this paper, the interdependency of sequence and positional specificities for selected members of this class of enzymes has been investigated using fluorogenic substrates where both the position of the cleavable peptide bond and the nature of the sequence of residues in P2-P1 are varied. The results show that cathepsins K and L and papain, typically considered to act strictly as endopeptidases, can also display dipeptidyl carboxypeptidase activity against the substrate Abz-FRF(4NO2)A and dipeptidyl aminopeptidase activity against FR-MCA. In some cases the activity is even equal to or greater than that observed with cathepsin B and DPP-I (dipeptidyl peptidase I), which have been characterized previously as exopeptidases. In contrast, the exopeptidase activities of cathepsins K and L and papain are extremely low when the P2-P1 residues are A-A, indicating that, as observed for the normal endopeptidase activity, the exopeptidase activities rely heavily on interactions in subsite S2 (and possibly S1). However, cathepsin B and DPP-I are able to hydrolyze substrates through the exopeptidase route even in absence of preferred interactions in subsites S2 and S1. This is attributed to the presence in cathepsin B and DPP-I of specific structural elements which serve as an anchor for the C- or N-terminus of a substrate, thereby allowing favorable enzyme-substrate interaction independently of the P2-P1 sequence. As a consequence, the nature of the residue at position P2 of a substrate, which is usually the main factor determining the specificity for cysteine proteases of the papain family, does not have the same contribution for the exopeptidase activities of cathepsin B and DPP-I.

Synthesis of amidrazones using an engineered papain nitrile hydratase

To demonstrate the usefulness of an engineered papain nitrile hydratase as a biocatalyst, a peptide amidrazone was prepared by incubation of the nitrile MeOCO-Phe-Alanitrile with the Gln19Glu papain mutant in the presence of salicylic hydrazide as a nucleophile. The amidrazone results from nucleophilic attack by salicylic hydrazide at the imino carbon of the thioimidate adduct formed between the enzyme and the peptide nitrile substrate. Compared to wild-type enzyme, the engineered nitrile hydratase causes a better than 4000-fold increase in the rate of amidrazone formation and yields a product of much higher purity. The advantages over other nitrile-hydrolyzing enzymes and current limitations of the papain nitrile hydratase are discussed.

The Bennett lesion of the shoulder

In this article we review the imaging features and significance of the Bennett lesion of the shoulder. Standard radiographic, computed arthrotomographic, and MR findings in three baseball pitchers diagnosed with Bennett lesions of the shoulder are discussed. A crescent-shaped region of mineralization at the posteroinferior aspect of the glenoid rim, consistent with a Bennett lesion, arises at the insertion of the posterior joint capsule. The diagnosis of this lesion, typically in baseball pitchers, should raise suspicion for associated labral and rotator cuff abnormalities.

bic, a novel gene activated by proviral insertions in avian leukosis virus-induced lymphomas, is likely to function through its noncoding RNA

The bic locus is a common retroviral integration site in avian leukosis virus (ALV)-induced B-cell lymphomas originally identified by infection of chickens with ALVs of two different subgroups (Clurman and Hayward, Mol. Cell. Biol. 9:2657-2664, 1989). Based on its frequent association with c-myc activation and its preferential activation in metastatic tumors, the bic locus is thought to harbor a gene that can collaborate with c-myc in lymphomagenesis and presumably plays a role in late stages of tumor progression. In the present study, we have cloned and characterized two novel genes, bdw and bic, at the bic locus. bdw encoded a putative novel protein of 345 amino acids. However, its expression did not appear to be altered in tumor tissues, suggesting that it is not involved in oncogenesis. The bic gene consisted of two exons and was expressed as two spliced and alternatively polyadenylated transcripts at low levels in lymphoid/hematopoietic tissues. In tumors harboring bic integrations, proviruses drove bic gene expression by promoter insertion, resulting in high levels of expression of a chimeric RNA containing bic exon 2. Interestingly, bic lacked an extensive open reading frame, implying that it may function through its RNA. Computer analysis of RNA from small exon 2 of bic predicted extensive double-stranded structures, including a highly ordered RNA duplex between nucleotides 316 and 461. The possible role of bic in cell growth and differentiation is discussed in view of the emerging evidence that untranslated RNAs play a role in growth control.

Intraosseous ganglion of the patella

Osteolytic cystic lesions of the patella are rare lesions. A review of the literature revealed only one previously reported example. The pathogenesis and radiological and pathological features of intraosseous ganglion cysts are discussed. In addition, the differential diagnosis of lytic patellar lesions is discussed.

Multicenter, placebo-controlled study of fluoxetine in seasonal affective disorder

OBJECTIVE

The authors investigated the efficacy and safety of fluoxetine in the treatment of winter seasonal affective disorder.

METHOD

Sixty-eight outpatients who met the DSM-III-R criteria for recurrent major depressive episodes, seasonal (winter) pattern, were randomly assigned to 5 weeks of treatment with fluoxetine, 20 mg/day (N = 36), or placebo (N = 32). The outcome measures included the 29-item modified Hamilton Depression Rating Scale, administered by experienced clinicians, and the self-rated Beck Depression Inventory; adverse events and safety data were also recorded. Clinical response was defined as a greater than 50% reduction in depression score between baseline and study termination.

RESULTS

Both groups showed significant improvement. The fluoxetine group had lower depression scores at termination than the placebo group, but these differences did not achieve statistical significance. However, the rate of clinical response in the fluoxetine group (59%) was superior to that in the placebo group (34%). Post hoc analyses showed that the greatest fluoxetine responses were in the most markedly depressed patients and that overall response was greater for patients studied later in the season. Fluoxetine was well tolerated, and few subjects dropped out because of adverse events.

CONCLUSIONS

On the basis of clinical response rate, fluoxetine appears to be an effective, well-tolerated treatment for seasonal affective disorder. Because the differences between fluoxetine and placebo in the continuous outcome measures did not reach statistical significance, further studies with larger study groups and longer treatment periods are required to conclusively demonstrate efficacy of fluoxetine for seasonal affective disorder.

Secretion of yeast aspartic protease 3 is regulated by its carboxy-terminal tail: characterization of secreted YAP3p

Yeast aspartic protease 3 (YAP3p), a basic-residue specific proprotein processing enzyme, was shown to be a membrane-associated protease. The membrane association of YAP3p was demonstrated to be through a glycophosphatidylinositol anchor situated in the carboxy terminus of the enzyme. Carboxy-terminal truncation of YAP3p by 37 amino acids resulted in secretion of YAP3p into the growth medium. Western blot analysis after sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed two secreted forms of YAP3p with apparent molecular masses of approximately 180 and approximately 90 kDa. YAP3p has an isoelectric point of approximately 4.5 as determined by isoelectric focusing gel electrophoresis. Treatment of YAP3p with endoglycosidase H reduced the size of both forms of the protein to approximately 65 kDa, consistent with the presence of 10 potential N-linked glycosylation sites in the deduced amino acid sequence of this protein. Removal of the N-linked sugars did not affect the enzymatic activity of YAP3p. Analysis of the effect of temperature on the stability and the rate of enzymatic activity of YAP3p showed that the enzyme retained 100% of its activity when incubated for 1 h at 37 degrees C, while incubation at 50 degrees C for 1 h resulted in approximately 80% loss of activity. The dependence of activity on temperature demonstrated a calculated Q10 of 1.95.

A controlled comparison of flupenthixol decanoate injections and oral amitriptyline in depressed out-patients

Sixty-eight depressed out-patients were allocated to treatment with either oral amitriptyline (75-225 mg/day) or intramuscular flupenthixol decanoate (10-30 mg every 14 days) in flexible dosage for 12 weeks under double-blind procedures. Various observer- and self-rating scales were applied before and after 2, 4, 8 and 12 weeks of treatment. Twenty-four patients completed the course of amitriptyline and 20 the course of flupenthixol. All variables improved over time, but there were no significant differences between the two drugs. The Newcastle scores pre-treatment were not related to drug response suggesting that both drugs were similarly effective across a wide spectrum of depressive disorders. Patients on amitriptyline tended to complain of dry mouth; those on flupenthixol had a higher incidence of extrapyramidal signs, the majority receiving anti-parkinsonian drugs at some time during the treatment. Flupenthixol decanoate in low dose is a useful anti-depressant, but should be restricted to short courses of treatment, to patients refractory to other treatments, and to patients suspected of poor compliance.