Search PubMed⌕ Search

Biomedical subjects

M R Green

Publications and source records attributed to M R Green.

At least 55 records · Page 3Linked to original sources
PubMed2000

Future randomized trials for non small-cell lung cancer.

Combination chemotherapy is the standard of care for management of previously untreated, good performance status patients with advanced non small-cell lung cancer. Most of the regimens in use worldwide are platinum-based doublets. Recent data from the Eastern Cooperative Oncology Group suggest that multiple different platinum-based regimens produce similar response rates and overall survival when used as first-line treatment. In upcoming randomized trials designed to explore possible improvements in therapy, three different strategies are being evaluated. One involves head-to-head comparisons of new, often non-platinum-based doublet combinations with standard platinum-based, two-drug regimens. A second emphasizes the possible benefits of combinations using three cytotoxic agents compared to a two-drug standard. The third is focused on adding a new molecular targeting agent, such as an anti growth factor, growth factor receptor antibody, or an intracellular signal transduction inhibitor, to a standard combination of two cytotoxic drugs. This paper reviews some of the randomized phase III trials exemplifying each of these approaches to therapy for patients with advanced non small-cell lung cancer.

Journal Article↗
PubMed1999

Functional recognition of the 3' splice site AG by the splicing factor U2AF35.

In metazoans, spliceosome assembly is initiated through recognition of the 5' splice site by U1 snRNP and the polypyrimidine tract by the U2 small nuclear ribonucleoprotein particle (snRNP) auxiliary factor, U2AF. U2AF is a heterodimer comprising a large subunit, U2AF65, and a small subunit, U2AF35. U2AF65 directly contacts the polypyrimidine tract and is required for splicing in vitro. In comparison, the role of U2AF35 has been puzzling: U2AF35 is highly conserved and is required for viability, but can be dispensed with for splicing in vitro. Here we use site-specific crosslinking to show that very early during spliceosome assembly U2AF35 directly contacts the 3' splice site. Mutational analysis and in vitro genetic selection indicate that U2AF35 has a sequence-specific RNA-binding activity that recognizes the 3'-splice-site consensus, AG/G. We show that for introns with weak polypyrimidine tracts, the U2AF35-3'-splice-site interaction is critical for U2AF binding and splicing. Our results demonstrate a new biochemical activity of U2AF35, identify the factor that initially recognizes the 3' splice site, and explain why the AG dinucleotide is required for the first step of splicing for some but not all introns.

Adenine Nucleotides↗
PubMed1999

A novel nuclear export activity in HIV-1 matrix protein required for viral replication.

An important aspect of the pathophysiology of human immunodeficiency virus type-1 (HIV-1) infection is the ability of the virus to replicate in non-dividing cells. HIV-1 matrix (MA), the amino-terminal domain of the Pr55 gag polyprotein (Pr55), bears a nuclear localization signal that promotes localization of the viral preintegration complex to the nucleus of non-dividing cells following virus entry. However, late during infection, MA, as part of Pr55, directs unspliced viral RNA to the plasma membrane, the site of virus assembly. How MA can mediate these two opposing targeting functions is not understood. Here we demonstrate that MA has a previously undescribed nuclear export activity. Although MA lacks the canonical leucine-rich nuclear export signal, nuclear export is mediated through the conserved Crm1p pathway and functions in both mammalian cells and yeast. A mutation that disrupts the MA nuclear export signal (MA-M4) mislocalizes Pr55 and genomic viral RNA to the nucleus, thereby severely impairing viral replication. Furthermore, we show that MA-M4 can act in a dominant-negative fashion to mislocalize genomic viral RNA even in the presence of wild-type MA. We conclude that the MA nuclear export signal is required to counteract the MA nuclear localization signal, thus ensuring the cytoplasmic availability of the components required for virion assembly.

Biological Transport↗
PubMed1999

Edatrexate (10-ethyl-deaza-aminopterin) (NSC #626715) with or without leucovorin rescue for malignant mesothelioma. Sequential phase II trials by the cancer and leukemia group B.

BACKGROUND: The Cancer and Leukemia Group B (CALGB) conducted sequential Phase II multicenter trials to evaluate the activity of edatrexate alone (E) or with leucovorin rescue (EL) in patients with malignant pleural mesothelioma (CALGB Protocol 9131). METHODS: Twenty patients were accrued to the E portion of the study and received edatrexate, 80 mg/m(2), intravenously over 20-30 minutes weekly. After a protocol amendment precipitated by excessive toxic events with E, 40 patients were enrolled in the EL arm and received the same dose of edatrexate with leucovorin, 15 mg orally, every 6 hours for 4 doses beginning 24 hours after edatrexate. Eligibility criteria included a CALGB performance status of 0-2 and no prior chemotherapy. A central pathology review was performed. Of the 58 patients included in this analysis (20 receiving E and 38 receiving EL), 36 had epithelial cell type and 22 had mixed or sarcomatous cell types. There were 31 patients with measurable disease and 27 with evaluable disease. RESULTS: The overall response rate was 25% for E (95% confidence interval [95% CI], 9-49%) and 16% for EL (95% CI, 6-31%). There was a 5% complete response [CR] rate, a 10% partial response [PR] rate, and a 10% regression [R] rate for E and a 0% CR rate, a 3% PR rate, and a 13% R rate for EL. The median survival duration from study entry was 9.6 months and 6.6 months, respectively, for E and EL; 1-year survival was 50% and 32%, respectively, for E and EL. There were four early deaths with the E regimen (including two from neutropenic sepsis) and one early death with the EL regimen (from progressive disease). Principal toxicities included mu cositis, myelosuppression, and rash, which were less frequent with leucovorin rescue. CONCLUSIONS: Moderate antitumor activity has been observed with both regimens. Leucovorin rescue ameliorated the mucosal, hematologic, and dermatologic toxicities of edatrexate, but also may have reduced its efficacy.

Aminopterin↗
PubMed1999

Profound misregulation of muscle-specific gene expression in facioscapulohumeral muscular dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is a neuromuscular disorder characterized by an insidious onset and progressive course. The disease has a frequency of about 1 in 20,000 and is transmitted in an autosomal dominant fashion with almost complete penetrance. Deletion of an integral number of tandemly arrayed 3.3-kb repeat units (D4Z4) on chromosome 4q35 is associated with FSHD but otherwise the molecular basis of the disease and its pathophysiology remain obscure. Comparison of mRNA populations between appropriate cell types can facilitate identification of genes relevant to a particular biological or pathological process. In this report, we have compared mRNA populations of FSHD and normal muscle. Unexpectedly, the dystrophic muscle displayed profound alterations in gene expression characterized by severe underexpression or overexpression of specific mRNAs. Intriguingly, many of the deregulated mRNAs are muscle specific. Our results suggest that a global misregulation of gene expression is the underlying basis for FSHD, distinguishing it from other forms of muscular dystrophy. The experimental approach used here is applicable to any genetic disorder whose pathogenic mechanism is incompletely understood.

Base Sequence↗
PubMed1999

Solution structures of the first and second RNA-binding domains of human U2 small nuclear ribonucleoprotein particle auxiliary factor (U2AF(65)).

The large subunit of the human U2 small nuclear ribonucleoprotein particle auxiliary factor (hU2AF(65)) is an essential RNA-splicing factor required for the recognition of the polypyrimidine tract immediately upstream of the 3' splice site. In the present study, we determined the solution structures of two hU2AF(65) fragments, corresponding to the first and second RNA-binding domains (RBD1 and RBD2, respectively), by nuclear magnetic resonance spectroscopy. The tertiary structure of RBD2 is similar to that of typical RNA-binding domains with the beta1-alpha1-beta2-beta3-alpha2-beta4 topology. In contrast, the hU2AF(65) RBD1 structure has unique features: (i) the alpha1 helix is elongated by one turn toward the C-terminus; (ii) the loop between alpha1 and beta2 (the alpha1/beta2 loop) is much longer and has a defined conformation; (iii) the beta2 strand is (188)AVQIN(192), which was not predicted by sequence alignments; and (iv) the beta2/beta3 loop is much shorter. Chemical shift perturbation experiments showed that the U2AF-binding RNA fragments interact with the four beta-strands of RBD2 whereas, in contrast, they interact with beta1, beta3 and beta4, but not with beta2 or the alpha1/beta2 loop, of RBD1. The characteristic alpha1-beta2 structure of the hU2AF(65) RBD1 may interact with other proteins, such as UAP56.

Amino Acid Sequence↗
PubMed1999

Enhancement of TBP binding by activators and general transcription factors.

Eukaryotic transcriptional activators function, at least in part, by promoting assembly of the preinitiation complex, which comprises RNA polymerase II and its general transcription factors (GTFs). Activator-mediated stimulation of the assembly of the preinitiation complex has been studied in vitro but has been relatively refractory to in vivo analysis. Here we use a DNA-crosslinking/immunoprecipitation assay to study in living cells the first step in the assembly of the preinitiation complex, the interaction between the TATA-box-binding protein (TBP) and its binding site, the TATA box. Analysis of a variety of endogenous yeast genes, and of a series of activators of differing strength, reveals a general correlation between TBP binding and transcriptional activity. Using mutant yeast strains, we show that Mot1 prevents the binding of TBP to inactive promoters and that activator-mediated stimulation of TBP binding requires additional GTFs, including TFIIB and Srb4. Taken together, our results indicate that TBP binding in vivo is stringently controlled, and that the ability of activators to stimulate this step in the assembly of the preinitiation complex is a highly cooperative process involving multiple transcription factors.

Adenosine Triphosphatases↗
PubMed1999

The hepatitis B pX protein promotes dimerization and DNA binding of cellular basic region/leucine zipper proteins by targeting the conserved basic region.

The hepatitis B virus pX protein is a potent transcriptional activator of viral and cellular genes whose mechanism of action is poorly understood. Here we show that pX dramatically stimulates in vitro DNA binding of a variety of cellular proteins that contain basic region/leucine zipper (bZIP) DNA binding domains. The basis for increased DNA binding is a direct interaction between pX and the conserved bZIP basic region, which promotes bZIP dimerization and the increased concentration of the bZIP homodimer then drives the DNA binding reaction. Unexpectedly, we found that the DNA binding specificity of various pX-bZIP complexes differs from one another and from that of the bZIP itself. Thus, through recognition of the conserved basic region, pX promotes dimerization, increases DNA binding, and alters DNA recognition. These properties of pX are remarkably similar to those of the human T-cell lymphotrophic virus type I Tax protein. Although Tax and pX are not homologous, we show that the regions of the two proteins that stimulate bZIP binding contain apparent metal binding sites. Finally, consistent with this in vitro activity, we provide evidence that both Tax and pX activate transcription in vivo, at least in part, by facilitating occupancy of bZIPs on target promoters.

Amino Acid Sequence↗
PubMed1999

Pre-mRNA splicing of IgM exons M1 and M2 is directed by a juxtaposed splicing enhancer and inhibitor.

Splicing of certain pre-mRNA introns is dependent on an enhancer element, which is typically purine-rich. It is generally thought that enhancers increase the use of suboptimal splicing signals, and one specific proposal is that enhancers stabilize binding of U2AF65 to weak polypyrimidine (Py) tracts. Here, we test this model using an IgM pre-mRNA substrate, which contains a well-characterized enhancer. Although the enhancer was required for in vitro splicing, we found it had no effect on U2AF65 binding. Unexpectedly, replacement of the natural IgM Py tract, branchpoint, and 5' splice site with consensus splicing signals did not circumvent the enhancer requirement. These observations led us to identify a novel regulatory element within the IgM M2 exon that acts as a splicing inhibitor; removal of the inhibitor enabled splicing to occur in the absence of the enhancer. The IgM M2 splicing inhibitor is evolutionarily conserved, can inhibit the activity of an unrelated, constitutively spliced pre-mRNA, and acts by repressing splicing complex assembly. Interestingly, the inhibitor itself forms an ATP-dependent complex that contains U2 snRNP. We conclude that splicing of IgM exons M1 and M2 is directed by two juxtaposed regulatory elements-an enhancer and an inhibitor-and that a primary function of the enhancer is to counteract the inhibitor.

Base Sequence↗
PubMed1999

Is quality of life predictive of the survival of patients with advanced nonsmall cell lung carcinoma?

BACKGROUND: Several studies have recently reported on the importance of quality of life (QOL) in predicting the survival of patients with lung carcinoma. To confirm these reports, the relationship between survival and QOL, as measured by the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire and Duke-UNC Social Support Scale, was examined within a group of 206 patients with advanced nonsmall cell lung carcinoma treated in a randomized clinical trial conducted by the Cancer and Leukemia Group B (CALGB 8931). METHODS: Patients completed the EORTC instrument and the Duke-UNC Social Support Scale at baseline in the clinic. The Cox proportional hazards model was used to determine the incremental contribution QOL provided in predicting survival beyond the effect of known clinical prognostic variables. RESULTS: Clinical factors that were jointly predictive of poorer survival included low performance status, nonadenocarcinoma histology, presence of dyspnea, weight loss greater than 5%, albumin level less than 3.5 mg/dL, and adrenal metastases. Univariate analyses showed that patient-reported EORTC subscales describing increased pain, appetite loss, fatigue, lung carcinoma symptoms, poorer overall QOL, and poorer physical functioning predicted significantly poorer survival. Multivariate analyses showed that, after adjustment for clinical factors, overall QOL was not a significant predictor of survival. Rather, the only EORTC subscale of prognostic importance was the pain subscale, in which a 40-point increase was associated with a 27% increase in the hazard rate. CONCLUSIONS: This study did not confirm the prognostic importance of overall QOL. Rather, after adjustment for significant clinical factors, a patient-provided pain report had the greatest prognostic importance.

Adult↗
PubMed1999

A novel member of the NF2/ERM/4.1 superfamily with growth suppressing properties in lung cancer.

A novel putative tumor suppressor gene and member of the NF2/ERM/ 4.1 superfamily was isolated using Differential Display PCR (DDPCR) on primary lung tumors. When reintroduced into nonexpressing non-small cell lung carcinoma cell lines, this gene, named DAL-1 (for Differentially expressed in Adenocarcinoma of the Lung), was shown to suppress growth. In addition, significantly reduced expression (>50%) of DAL-1 was measured in 39 primary non-small cell lung carcinoma tumors as compared with patient-matched normal lung tissue. Immunocytochemical staining with a polyclonal anti-DAL-1 antibody localized the protein to the plasma membrane, particularly at cell-cell contact points, a pattern reminiscent of other members of the protein 4.1 superfamily including ezrin and NF2. The data suggest DAL-1 is a novel membrane-associated protein with potential to play an important role in the origin and progression of lung cancer.

Amino Acid Sequence↗
PubMed1999

Lung cancer staging and treatment in multidisciplinary trials: Cancer and Leukemia Group B cooperative group approach. Thoracic Surgeons of CALGB.

BACKGROUND: Aggressive routine surgical staging is necessary to evaluate patients to be treated on cooperative oncology protocols. Less than 1% of lung cancer patients in the United States are currently being treated in a clinical trial. Only with results from large, prospective trials can the questions of neoadjuvant and adjuvant therapy be answered. METHODS: An outline describing the schema of preoperative patient evaluation, surgical staging, and the definition of surgical staging and resection procedures appropriate for patients considered for cooperative group protocol is presented. Current Cancer and Leukemia Group B (CALGB) protocols are used in the discussion as examples of this systematic approach. CONCLUSIONS: Over the next few years, it will be important to enter the maximum number of patients into combined modality studies to identify the role of neoadjuvant treatment in lung cancer. Entry of patients into protocols will also make their pathological specimens and clinical information available for basic science research related to treatment results. Adherence to a logical sequence of patient evaluation as outlined above will optimize patient care, as well as accrual to cooperative group studies.

Clinical Trials as Topic↗
PubMed1999

A human nuclear-localized chaperone that regulates dimerization, DNA binding, and transcriptional activity of bZIP proteins.

We have identified and cloned a human nuclear protein that dramatically increases DNA binding of transcription factors that contain a basic region-leucine zipper (bZIP) DNA binding domain. We show that this bZIP enhancing factor (BEF) functions as a molecular chaperone. BEF stimulates DNA binding by recognizing the unfolded leucine zipper and promoting the folding of bZIP monomers to dimers; the elevated concentration of the bZIP dimer then drives the DNA binding reaction. Antisense experiments indicate that BEF is required for efficient transcriptional activation by bZIP proteins in vivo. Our results reveal protein folding in the nucleus as a step at which sequence-specific DNA binding proteins can be regulated.

Amino Acid Sequence↗
PubMed1999

High-dose paclitaxel plus G-CSF for malignant mesothelioma: CALGB phase II study 9234.

BACKGROUND: New agents with activity in mesothelioma are sorely needed. The Cancer and Leukemia Group B (CALGB) therefore performed a phase II study of high-dose paclitaxel in patients with malignant mesothelioma who had no prior chemotherapy. PATIENTS AND METHODS: Thirty-five patients accrued to this multi-institutional phase II study of paclitaxel given as a 24-hour infusion at 250 mg/m2 every three weeks plus filgrastim (G-CSF) 300 mcg subcutaneously days 3-18. RESULTS: There were three (9%) regressions of evaluable disease. The median survival was five months (95% confidence interval (95% CI): 1.9-9.6 months), the one-year survival rate was 14% and the two-year survival rate was 6%. Toxicity was tolerable with one death from pneumonia (without neutropenia) on day 18 and a 23% rate of grade 4 granulocytopenia. CONCLUSIONS: The level of activity seen with paclitaxel is similar to that seen in other CALGB trials of the single agents carboplatin, trimetrexate and 5-azacytidine. Future studies of of paclitaxel (at lower doses) in combination with synergistic agents could be considered.

Adult↗
PubMed1999

Coordinate upregulation of tenascin C expression with degree of photodamage in human skin.

Tenascin C is a large extracellular matrix glycoprotein involved in morphogenesis and wound healing. The distribution and expression levels of tenascin were examined in photodamaged skin to investigate the hypothesis that photoaged skin displays characteristics of wound repair. In situ hybridization and semiquantitative immunohistochemistry were performed on paired skin biopsies from patients with varying levels of photodamage, using monoclonal antibodies and cRNA probes for tenascin and its large isoform. In sun-protected skin, tenascin protein was distributed adjacent to the dermoepidermal junction, usually sparsely and discontinuously; tenascin mRNA was detected in dermal fibroblasts and some keratinocytes. In photodamaged skin, tenascin protein was increased in proportion to the clinical level of photodamage (analysis of variance: P < 0.0001, n = 29). With increased photodamage, tenascin protein expression became continuous along the dermoepidermal junction, extending deeper into and sometimes throughout the papillary dermis; tenascin mRNA was detected throughout the epidermis. Large tenascin isoform protein and mRNA distribution mirrored that of pantenascin, suggesting that it may be the predominant species in photodamaged skin. There was no correlation between tenascin expression levels and age or sex, and no seasonal variation was noted. The results indicate that photodamaged skin demonstrates tenascin increases consistent with an early wound healing response. However, tenascin increases in photodamage appear to be permanent and may therefore interfere with effective repair of ultraviolet-induced damage. In conclusion, this study has shown that dermal tenascin expression increases in proportion to the degree of photodamage. In normal skin, the temporal and spatial patterns of tenascin expression during morphogenesis and tissue remodelling are crucial to their correct progression. In photoageing, the 'normal' control of tenascin expression seems to be abrogated.

Adult↗
PubMed1999

Effect of gel re-organization and tensional forces on alpha2beta1 integrin levels in dermal fibroblasts.

Mechanical forces are known to play an important role in regulating cell function in a wide range of biological systems. This is of particular relevance to dermal fibroblast function, given that the skin is known to be held under an intrinsic natural tension. To understand more about the generation of force by dermal fibroblasts and their ability to respond to changes in it, we have studied the role of the beta1 integrin receptors expressed by dermal fibroblasts in their ability to generate tensional forces within a collagen type I matrix and the effect of altered tensional force on integrin expression by dermal fibroblasts. Using a purpose-built culture force monitor, function-blocking antibodies directed towards the beta1 receptors dramatically reduced the tensional forces generated by dermal fibroblasts in a 3D collagen I matrix. However, the specific involvement of alpha1 or alpha2 subunits could not be demonstrated. Analysis of cellular response demonstrated that cells isolated from contracting collagen gels expressed fourfold higher levels of alpha2 mRNA than cells isolated from fully restrained gels. The levels of beta1 messenger RNA were relatively unaffected by reductions in force. Cells exposed to single reductions in force, however, did not exhibit alterations in either alpha1 or beta1 mRNA levels. We propose, therefore that alpha2beta1 integrin receptor levels in dermal fibroblasts are not altered in response to single reductions of gel tension, but do change following a continual change in force and associated matrix re-organization

Antigens, CD↗
PubMed1999

Eicosanoid and cytokine levels in acute skin irritation in response to tape stripping and capsaicin.

We assessed the effects of physical and chemical irritants on a profile of acute inflammatory mediators in normal human skin. Skin damage in both cases is accompanied by a flux of inflammatory processes and repair mechanisms, which remain imprecisely understood. We used 10 sequential cellotape strips or topical application of 0.075% capsaicin as skin irritants and characterized the subsequent production and/or release of inflammatory mediators in suction blister fluids from human skin in vivo. In tape stripped skin, levels of prostaglandin E2 and interleukin-1alpha were increased 3.4-fold and 3.3-fold, respectively (p<0.0001; p<0.02), levels of tumour necrosis factor-alpha were decreased 3.0-fold (p<0.01), whereas levels of interleukin-6 and leukotriene B4 in blister fluids remained relatively unchanged. For the capsaicin-treated skin, levels of mediators showed only minor differences when compared with matched controls. However, a correlation was observed between levels of prostaglandin E2 and interleukin-1alpha in capsaicin pre-treated blister fluids (r=0.58, p<0.01, n=19). These data are consistent with prostaglandin E2 and interleukin-1alpha playing key roles in acute skin responses to mild irritants.

Acute Disease↗