Biomedical subjects
Publications and source records attributed to G Thomas.
The activation of p70s6k is accompanied by a complex series of phosphorylation events. In this review we propose a model of activation which divides p70s6k into four functional modules that cooperate in leading to full enzyme activity. In the light of the model, we suggest how candidate effectors of p70s6k activation might function by directing the phosphorylation of specific sites.
Treatment of mammalian cells with the immunosuppressant rapamycin, a bacterial macrolide, selectively suppresses mitogen-induced translation of an essential class of mRNAs which contain an oligopyrimidine tract at their transcriptional start (5'TOP), most notably mRNAs encoding ribosomal proteins and elongation factors. In parallel, rapamycin blocks mitogen-induced p70 ribosomal protein S6 kinase (p70s6k) phosphorylation and activation. Utilizing chimeric mRNA constructs containing either a wild-type or disrupted 5'TOP, we demonstrate that an intact polypyrimidine tract is required for rapamycin to elicit an inhibitory effect on the translation of these transcripts. In turn, a dominant-interfering p70s6k, which selectively prevents p70s6k activation by blocking phosphorylation of the rapamycin-sensitive sites, suppresses the translation of the chimeric mRNA containing the wild-type but not the disrupted 5'TOP. Conversion of the principal rapamycin-sensitive p70s6k phosphorylation site, T389, to an acidic residue confers rapamycin resistance on the kinase and negates the inhibitory effects of the macrolide on 5'TOP mRNA translation in cells expressing this mutant. The results demonstrate that the rapamycin block of mitogen-induced 5'TOP mRNA translation is mediated through inhibition of p70s6k activation.
Although the occurrence of loss of genetic material in hepatocellular carcinoma (HCC) has been documented both by cytogenetic analysis and by monitoring of allelic losses, a global overview of the extent and frequency of deletion occurring throughout the genome is not yet available. To contribute to this information, DNAs extracted from flow-sorted aneuploid nuclei from HCC and matched normal DNAs were typed for 275 microsatellite loci that were distributed along the autosomes. An average of 190 (69%) informative loci per case were generated on 48 HCC. Complete loss of heterozygozity in the tumor DNA was observed for 15.6% of the typed loci. The chromosome segments that were most frequently affected by deletion were: 8p (60%), 17p (48%), 1p (44%), 4q (42%), 16p (40%), 16q (39%), 6q (35%), 9p (30%), and 13q (29%). On average, 8 of the 39 chromosome segments studied per tumor carried at least one locus that demonstrated loss of heterozygosity (ie., the fractional allelic loss was 0.21). Groups of concerted nonsyntenic losses were observed for 16p and 1p and for 16p and 4q. The location of putative tumor suppressor genes on the most frequently deleted regions was confirmed and, in some cases, refined.
beta-Amyloid (A beta) toxicity has a critical role in the pathology of Alzheimer's disease (AD) but its function in the neurodegenerative process is not clearly established. Recently, we demonstrated a novel action of beta-amyloid on peripheral blood vessels: endothelial dysfunction through reactive oxygen species. Here we report the direct effect of A beta on cerebrovascular endothelium. Following treatment with A beta 1-40, bovine cerebral arteries showed characteristic features of endothelial dysfunction such as increased contraction to vasoconstrictor and diminished relaxation to endothelium-dependent vasodilators. Electron microscopy revealed significant damage to the endothelium by A beta. Pretreatment with the antioxidant superoxide dismutase (SOD) and PBN (n-tert-butyl-alpha-phenylnitrone) antagonized the effects of A beta. Endothelial damage induced by A beta could produce ischemic and inflammatory changes contributing to the pathology of AD.
Activation of furin requires autoproteolytic cleavage of its 83-amino acid propeptide at the consensus furin site, Arg-Thr-Lys-Arg107/. This RER-localized cleavage is necessary, but not sufficient, for enzyme activation. Rather, full activation of furin requires exposure to, and correct routing within, the TGN/endosomal system. Here, we identify the steps in addition to the initial propeptide cleavage necessary for activation of furin. Exposure of membrane preparations containing an inactive RER-localized soluble furin construct to either: (i) an acidic and calcium-containing environment characteristic of the TGN; or (ii) mild trypsinization at neutral pH, resulted in the activation of the endoprotease. Taken together, these results suggest that the pH drop facilitates the removal of a furin inhibitor. Consistent with these findings, following cleavage in the RER, the furin propeptide remains associated with the enzyme and functions as a potent inhibitor of the endoprotease. Co-immunoprecipitation studies coupled with analysis by mass spectrometry show that release of the propeptide at acidic pH, and hence activation of furin, requires a second cleavage within the autoinhibitory domain at a site containing a P6 arginine (-Arg70-Gly-Val-Thr-Lys-Arg75/-). The significance of this cleavage in regulating the compartment-specific activation of furin, and the relationship of the furin activation pathway to those of other serine endoproteases are discussed.
As a result of chromosome translocations, the EWS gene is fused to a variety of transcription factors in human solid neoplasia. In Ewing tumors EWS can be fused to four different members of the ETS family, namely FLI-1, ERG, ETV1 and E1AF. We have identified a new member of the ETS family, called FEV, which is fused to EWS in a subset of Ewing tumors. FEV encodes a 238 amino acid protein which contains an ETS DNA binding domain closely related to that of FLI-1 and ERG. However, the N-terminal portion of FEV is only 42 amino acids long which suggests that FEV is lacking important transcription regulatory domains contained in FLI-1 and ERG N-terminal parts. The C-terminal end of FEV is rich in alanine residues which may indicate that FEV is a transcription repressor. The FEV gene is encoded by three exons and is located on chromosome 2. FEV expression was only detected in adult prostate and small intestine but not in other adult nor in fetal tissues, thus indicating that FEV has a restricted expression pattern. Following a scheme similar to previously described translocations in Ewing tumors, a t(2;22) chromosome translocation fuses the N-terminal domain of EWS to the ETS DNA binding domain of FEV.
Reactive oxygen species modulate major cellular functions by mechanisms which are still poorly understood. Recently, H2O2 has been reported to stimulate the activity of the mitogen-activated protein kinases (MAPKs) ERK and JNK, and the expression of the proto-oncogenes c-fos and c-jun. As their expression is enhanced by H2O2 in astrocytes, we studied whether these MAPKs were stimulated by H2O2 in primary cultured astrocytes. The result was positive, a maximum of stimulation being reached with 200 microM H2O2 (0.3 pmol H2O2/cell) for both ERK and JNK. ERK was previously reported to stimulate cytosolic phospholipase A2 phosphorylation and activity. H2O2 stimulated the release of arachidonic acid in astrocytes, as already reported in other cell types. We found also that cPLA2 phosphorylation was increased by H2O2. Moreover, the stimulation by H2O2 of ERK and JNK was decreased by phospholipase A2 activity inhibitors. When astrocytes were incubated first with eicosatetraynoic acid, a structural analogue competing in arachidonic acid metabolism, the stimulation of JNK by H2O was also inhibited, suggesting the involvement of arachidonic acid metabolites. Cyclooxygenase or cytochrome P450 monooxygenase inhibitors failed in decreasing the MAPK stimulation by H2O2, whereas lipoxygenase inhibitors completely abolished that of JNK. Mitogenicity has been reported to be stimulated by H2O2 in other cell types. Although ERK was strongly and durably stimulated by 200 microM H2O2 in astrocytes, at the same extent as by mitogenic growth factors, basal thymidine incorporation rate was decreased by more than 80% after 12-15 h. Moreover, the stimulation of thymidine incorporation induced by basic fibroblast growth factor was transiently abolished by H2O2. Furthermore, H2O2 likely induced the expression of CL100/PAC1/MKP-1, a dual specificity phosphatase which has been implicated in ERK and JNK inactivation in the nucleus. Finally, the prior treatment of astrocytes with MK886, a 5-lipoxygenase-activating protein inhibitor, prevented JNK from stimulation, but did not prevent thymidine incorporation from inhibition, both induced by H2O2. These results strongly suggest an involvement of arachidonic acid and/or its metabolites in the stimulation of both ERK and JNK following the oxidative stress evoked by H2O2, which induced a cell cycle arrest probably independent of the stimulation of JNK.
Instability of microsatellites is a hallmark of the DNA replication error phenotype (RER+) due to the inactivation of mismatch repair genes. In humans, microsatellite instability has first been described in colorectal tumors developing in either hereditary nonpolyposis colorectal cancer or sporadic patients. Colorectal tumorigenesis in RER+ and RER- tumors is probably due to distinct mechanisms, and RER+ tumors have a better prognosis than RER- tumors. The study of the RER status of a tumor may thus be important in the future to determine biological prognosis factors and investigate therapeutical strategies. The RER status of 134 primary tumors and 26 cell lines derived from colorectal cancers was established by PCR amplification and analysis of a minimum of 32 microsatellite loci. This characterization allowed us to unambiguously classify 35 primary tumors and 7 cell lines as RER+. Typing of a single poly(A) tract, BAT-26, was sufficient to confirm the RER status of 159 of these 160 tumors and cell lines. Moreover, in DNA from unaffected individuals, normal tissues of a subset of the RER+ patients, and all RER- tumors or cell lines, BAT-26 was quasi-monomorphic, showing only minor size variations. BAT-26 alleles showing shortening from 4 to 15 bp were observed in all but 1 of the RER+ tumors and cell lines. The size difference between the range of normal large alleles and unstable small alleles was sufficient to be detected by electrophoresis on conventional polyacrylamide gels stained with ethidium bromide. We thus propose a simple, low-cost, and rapid method to screen for the RER status of colorectal cancer primary tumors and cell lines, even in the absence of matching normal DNA and, in most cases, without the need for radioactivity. This method could easily be set up in routine laboratories.
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In order to determine the efficacy and toxicity of the gonadotrophin-releasing hormone agonist Leuprolide in the management of patients with recurrent or metastatic endometrial cancer, we performed a phase II study. Patients were included if there was clinical or radiological documentation of bidimensionally measurable recurrent or metastatic endometrial cancer that was deemed incurable. Treatment was 7.5 mg i.m. every 28 days, and was to continue for at least 2 courses until evidence of disease progression, patient requested withdrawal, or unacceptable toxicity. Twenty-five patients received Leuprolide for recurrent or metastatic endometrial cancer. The median age at study entry was 62 years, and the median time from initial diagnosis to first course of Leuprolide was 25 months. Six patients had received no systemic or radiotherapy prior to study entry, and 2 of these had not previously undergone hysterectomy. Fifteen patients received prior pelvic radiotherapy and 3 patients received prior whole abdominal radiotherapy. Nine of the 25 patients had received prior progestational agents, and 2 had received prior systemic chemotherapy. There were no responders, 8 patients had stable disease for a median 5 months (range 1-8), 14 patients progressed on therapy, and 3 patients were not evaluable for response due to receiving only 1 treatment. One patient experienced a grade 3 toxicity that was possibly attributable to Leuprolide (deep venous thrombosis). The median survival from study entry was 6 months. Twelve patients received progesterone after discontinuing this study, and none responded. Leuprolide does not appear to be a clinically active agent in the treatment of recurrent or metastatic endometrial cancer.
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BACKGROUND: Patients with malignant pleural mesothelioma (MPM) usually die of progressive local disease. This report describes the results of a Phase III trial comparing maximum debulking surgery and postoperative cisplatin, interferon alpha-2b, and tamoxifen (CIT) immunochemotherapy with and without intraoperative photodynamic therapy (PDT) to determine (1) whether such a multimodal approach can be performed with minimum morbidity and mortality in malignant pleural mesothelioma (MPM), and (2) whether first-generation (i.e., 630-nm laser light, Photofrin II) intrapleural PDT impacts on local recurrence of survival. METHODS: From July 1993 to June 1996, 63 patients with localized MPM were randomized to either PDT or no PDT. The tumors of 15 patients could not be debulked to 5 mm. Patients assigned to PDT (n = 25) and no PDT (n = 23) were similar with respect to age, sex, tumor volume, and histology. RESULTS: The type of resection (11 pleurectomies and 14 pneumonectomies vs. 12 pleurectomies and 11 pneumonectomies), length postoperative stay, and ICU time were comparable (PDT vs. no PDT). There was one operative death (hemorrhage), and each group had two bronchopleural fistulas. Postoperative staging divided patients into the following categories: stage I: PDT, 2, no PDT, 2; stage II: PDT, 2, no PDT, 2; stage III, PDT, 21; no PDT, 17; stage IV, PDT, 0; no PDT, 2. Comparable numbers of CIT cycles were delivered. Median survival for the 15 non-debulked patients was 7.2 months, compared to 14 months for the 48 patients on protocol. There were no differences in median survival (14.4 vs. 14.1 months) or median progression-free time (8.5 vs. 7.7 months), and sites of first recurrence were similar. CONCLUSIONS: Aggressive multimodal therapy can be delivered for patients with higher stage MPM. First-generation PDT does not prolong survival or increase local control for MPM.
The scientific value of multicenter studies is still questionable, as there are no methods available that allow to determine whether in fact identical items are recorded in the same way in different centers. Subjective classifications (for example according to the New York Heart Association (NYHA)), definitions of items, documentation habits and procedures may not be comparable in different hospitals. For that reason the concept of a "virtual patient" for calibration of database systems was developed as a new methodological approach. The "virtual patients" describes a computer program that includes and uses multimedia-tools to represent an exactly defined patient. A sound card enables a patient to talk and to represent intracardial and intrapulmonary sounds. Additional information including echocardiographic sequences, perioperative video sequences, x-ray analysis, angiograms, etc. is represented in the program. Thus during the perioperative course of a patient the complete relevant pre-, intra- and postoperative information regarding the patient is provided. Any physician participating in a multicenter study is asked to record the data of this virtual patient and to store it in a database system using the sheets applied in a multicenter study. As the patient is exactly defined (virtual patient) incorrect classifications and incomplete recordings, etc. can easily be detected and discussed. The virtual patient is a tool that allows calibration of database systems by direct comparison of the documentation technique between different physicians and different hospitals participating in multicenter studies. It is thus a multimedia-instrument to support standardization and quality assurance of database systems.
The "Dorsalorgan" of pentastomids is an embryonic gland. With respect to a general revision of the glandular equipment of pentastomids and its synonyms the term embryonic gland, first mentioned by Esslinger in 1968, or glandula embryonalis (original) appears to be most suitable. Thus, this terminology may no longer lead to confusion of these glands with dorsal organs of other arthropods. The ultrastructure of the embryonic gland and its role within the development of the embryonic envelopes of the pentastomid genus Raillietiella is described herein for the first time. The embryonic gland is composed of numerous secretory cells, which are arranged concentrically around a bottle-shaped cavity. The cells of the neck region produce an extracellular supporting layer to stabilize the collar. The basal cells are characterized by numerous microvilli, secreting mucus into the cavity. The product of the embryonic gland is secreted between the zona radiata externa/interna and the blastoderm cuticle, respectively. The embryonic gland disintegrates before larval hatching.
The ultrastructure of accessory genital glands in Raillietiella sp. is described and their function is discussed. In females we assume that they reactivate sperm, which are stored in the receptacula seminis after copulation. In males we think they are primer-pheromone glands, which inject secretions into the female during copulation and stimulate the development of the female genital system. This study presents a revised nomenclature, which allows for the comparison of former results.
Hypodermal gland cells in Raillietiella sp. represent a new cell type in pentastomids. They were discovered in infective larvae (intermediate host) and in juvenile raillietiellids (final host) during molting. The ultrastructural development of hypodermal gland cells is described in this report. We think that hypodermal gland cells are class 1 gland cells, which form temporary cilia during molting. Their possible function as releaser-pheromone gland cells is discussed.
The EWS gene has been identified as being systematically translocated in Ewing's sarcoma. In order to ascertain the basis of a marked interethnic difference in the incidence of Ewing's sarcoma, intron 6 of EWS, which is located near the translocation breakpoint region (EWSR1), was characterized. Sequence analysis of the entire intron 6 region revealed a very high density of Alu elements. Most of these Alu sequences could be classified in previously described subfamilies, facilitating delineation of an evolutionary model that involves successive retroposition events. According to this model, the EWS intron 6 region progressively expanded until about 5 million years ago. More recently (10(5) years ago), in part of the human population, the size of this region decreased by over 50% as the result of a homeologous recombination between two Alu sequences, which removed 2480 bp. This rare allele has only been observed in individuals of African origin, a population that is characterized by the lowest incidence of Ewing's sarcoma.