The Saccharomyces cerevisiae ETH1 gene, an inducible homolog of exonuclease III that provides resistance to DNA-damaging agents and limits spontaneous mutagenesis.
The recently sequenced Saccharomyces cerevisiae genome was searched for a gene with homology to the gene encoding the major human AP endonuclease, a component of the highly conserved DNA base excision repair pathway. An open reading frame was found to encode a putative protein (34% identical to the Schizosaccharomyces pombe eth1(+) [open reading frame SPBC3D6.10] gene product) with a 347-residue segment homologous to the exonuclease III family of AP endonucleases. Synthesis of mRNA from ETH1 in wild-type cells was induced sixfold relative to that in untreated cells after exposure to the alkylating agent methyl methanesulfonate (MMS). To investigate the function of ETH1, deletions of the open reading frame were made in a wild-type strain and a strain deficient in the known yeast AP endonuclease encoded by APN1. eth1 strains were not more sensitive to killing by MMS, hydrogen peroxide, or phleomycin D1, whereas apn1 strains were approximately 3-fold more sensitive to MMS and approximately 10-fold more sensitive to hydrogen peroxide than was the wild type. Double-mutant strains (apn1 eth1) were approximately 15-fold more sensitive to MMS and approximately 2- to 3-fold more sensitive to hydrogen peroxide and phleomycin D1 than were apn1 strains. Elimination of ETH1 in apn1 strains also increased spontaneous mutation rates 9- or 31-fold compared to the wild type as determined by reversion to adenine or lysine prototrophy, respectively. Transformation of apn1 eth1 cells with an expression vector containing ETH1 reversed the hypersensitivity to MMS and limited the rate of spontaneous mutagenesis. Expression of ETH1 in a dut-1 xthA3 Escherichia coli strain demonstrated that the gene product functionally complements the missing AP endonuclease activity. Thus, in apn1 cells where the major AP endonuclease activity is missing, ETH1 offers an alternate capacity for repair of spontaneous or induced damage to DNA that is normally repaired by Apn1 protein. (+info)
Differential regulation of p21waf-1/cip-1 and Mdm2 by etoposide: etoposide inhibits the p53-Mdm2 autoregulatory feedback loop.
The Mdm2 protein is frequently overexpressed in human non-seminomatous germ cell tumours and transitional carcinoma of the bladder where it may contribute to tolerance of wtp53. Mdm2 forms an autoregulatory feedback loop with p53; the Mdm2 gene is responsive to transactivation by p53 and once synthesized the Mdm2 protein terminates the p53 response. We show here that the topoisomerase poison etoposide, like ultra violet irradiation, inhibits Mdm2 synthesis. Cytotoxic concentrations of etoposide (IC90 for > 3 h) result in inhibition of Mdm2 induction at both the RNA and protein level. Rapid apoptosis ensues. Global transcription is not inhibited: p21waf-1/cip1 and GADD45 expression increase in a dose dependent manner. Inhibition of Mdm2 synthesis depends on the continuous presence of etoposide, suggesting the DNA damage may prevent transcription. Downregulation of Mdm2 transcript occurs in cells expressing HPV16-E6 suggesting that inhibition of Mdm2 transcription is p53-independent. When cells are -treated with a pulse (1 h) of etoposide and reincubated in drug free medium, Mdm2 synthesis commences immediately after damage is repaired (3 h) and the p53 response is attenuated. Induction of apoptosis and loss of clonogenicity are 3-5-fold lower under pulse treatment conditions. This is the first observation of inhibition of Mdm2 transcription following treatment with topoisomerase (topo II) poisons, a feature that may be useful in tumour types where p53 is tolerated by overexpression of Mdm2. (+info)
The integrin alpha v beta 6 binds and activates latent TGF beta 1: a mechanism for regulating pulmonary inflammation and fibrosis.
Transforming growth factor beta (TGF beta) family members are secreted in inactive complexes with a latency-associated peptide (LAP), a protein derived from the N-terminal region of the TGF beta gene product. Extracellular activation of these complexes is a critical but incompletely understood step in regulation of TGF beta function in vivo. We show that TGF beta 1 LAP is a ligand for the integrin alpha v beta 6 and that alpha v beta 6-expressing cells induce spatially restricted activation of TGF beta 1. This finding explains why mice lacking this integrin develop exaggerated inflammation and, as we show, are protected from pulmonary fibrosis. These data identify a novel mechanism for locally regulating TGF beta 1 function in vivo by regulating expression of the alpha v beta 6 integrin. (+info)
Testicular cancer: an oncological success story.
Testicular cancer has become a model for a curable neoplasm. Our studies with cisplatin combination chemotherapy allow us to conclude that: (a) short-duration intensive induction therapy with the most active agents in optimal dosage is more important than maintenance therapy; (b) modest dose escalation increases toxicity without improving therapeutic efficacy; (c) it is possible to develop curative salvage therapy for refractory germ cell tumors; and (d) preclinical models predicting synergism, such as vinblastine + bleomycin or cisplatin + etoposide have clinical relevance. Finally, testicular cancer has also become a model for new drug development. Cisplatin was approved by the Food and Drug Administration for testis and ovarian cancer, and etoposide and ifosfamide were approved for refractory germ cell tumors. The success of these studies confirms the importance of the continued search for new investigational drugs in all solid tumors. (+info)
Can we cure indolent lymphomas?
The current consensus is that indolent lymphomas are incurable disorders. There are some indications that these malignancies are potentially curable. Indeed, not all indolent lymphomas are currently incurable. For example, patients with Ann Arbor stage I-II indolent lymphomas can experience long-term disease-free survival and probable cure. Also, from the available literature data, it seems that the achievement of a molecular complete remission is a desirable objective. Patients who achieve a persistently negative PCR state seldom relapse, whereas the opposite is true for persistently positive cases. In view of its excellent correlation with disease-free survival when examined serially in multiple blood or marrow samples, the PCR technique has the potential of providing a tumor marker that can be used as an early end point for clinical trials. By serving as an early surrogate end point, PCR could play an important role in expediting the development of new treatment strategies. Whether IFN is capable of increasing the molecular complete remission rate as measured by PCR is not known. However, it is clear that from the clinical standpoint, IFN has been able to increase 2-fold the length of remission in patients with advanced indolent lymphomas. In at least two studies, this has been associated with prolongation of survival. More intensive regimens such as alternating triple therapy, when used in combination with IFN, seem to have improved the quality of remissions as judged by the PCR assay. Finally, the site where the bcl-2 breakpoint occurs seems to have clinical significance. Those follicular lymphomas with germ-line bcl-2, in our experience, have behaved more aggressively than the others, and their failure-free survival seems different from the usual indolent lymphomas and more closely resembles the large cell lymphomas. Although the biological significance of this observation is not yet understood, this group might actually constitute a prognostically different subset with a more aggressive and perhaps more curable lymphoma. Whether the plateau observed in their failure-free survival curve will be maintained with more follow-up and whether they might be a curable subset remain to be determined. (+info)
Effects of pirfenidone on procollagen gene expression at the transcriptional level in bleomycin hamster model of lung fibrosis.
A time course study was carried out to elucidate the mechanisms for antifibrotic effect of pirfenidone (PD). Hamsters were intratracheally (i.t.) instilled with saline (SA) or bleomycin (BL) (7.5 units/kg/5 ml). The animals were fed a diet containing 0.5% PD or the same control diet (CD) without the drug 2 days before and throughout the study. The animals were sacrificed at various times after instillation. The lung hydroxyproline level in BL + CD groups was gradually increased and peaked at 21 days to 181% of the SA + CD control. The BL + PD-treated groups showed a gradual decrease in their lung collagen content, showing a maximum reduction of 40% at day 21. The lung malondialdehyde levels of the BL + CD groups were increased by several-fold of the corresponding SA + CD groups at various times. The lung prolyl hydroxylase (PH) activities in the BL + CD groups were also increased by several-fold of the corresponding SA + CD groups at these time points. The hamsters in the BL + PD showed a gradual decrease in the lung malondialdehyde levels from 10 to 21days compared with their corresponding BL + CD groups. Treatment with PD also reduced the lung PH activities in the BL + PD groups compared with the corresponding BL + CD groups. However, PD failed to manifest any direct inhibitory effect on PH activity in vitro. BL treatment increased the lung procollagen I and III gene expressions in the BL + CD groups by several-fold at varying times compared with the corresponding SA + CD, and treatment with PD in the BL + PD groups significantly down-regulated the BL-induced overexpression of these genes. Studies evaluating the regulation of these genes at the transcriptional level revealed PD significantly reduced the transcription of PC I at 14 days. Our results indicate that the antifibrotic effect of PD was partly due to suppression of the BL-induced inflammatory events and partly due to down-regulation of BL-induced overexpression of lung procollagen I and III genes. (+info)
T cell independence of bleomycin-induced pulmonary fibrosis.
The role of T cells and cytokines in bleomycin (BLM)-induced fibrosis was evaluated in susceptible and resistant strains of normal and SCID mice. Histology and hydroxyproline analysis showed that BLM induced pulmonary fibrosis in C57BL/6 and (C57BL/6 x BALB/c)F1 mice, whereas BALB/c mice were resistant to the disease. To test whether lymphocytes were required for the induction of BLM-induced pulmonary fibrosis, SCID mice were injected intratracheally with BLM and evaluated for the development of pulmonary inflammation and fibrosis. Similar morphological changes and increases in hydroxyproline were observed in both C57BL/6 SCID and (C57BL/6 x CB.17)F1 SCID animals compared to those seen in wild-type C57BL/6 and (C57BL/6 x BALB/c)F1 mice. In contrast, CB.17 SCID mice, which are genetically similar to BALB/c mice, were resistant to disease induction. Analysis of the cellular infiltrate in BLM-treated C57Bl/6 SCID mice confirmed a lack of T cells in the lungs of SCID mice and demonstrated a pronounced accumulation of eosinophils in areas of developing pulmonary fibrosis. NK cells were significantly elevated in untreated SCID mice and did not increase further after BLM treatment. Analysis of selected cytokines 1 day after initiation of BLM-induced pulmonary fibrosis indicated that the levels of TNF-alpha and IFN-gamma appeared to segregate with fibrosis in both the SCID and wild-type mice. The data demonstrate that T cells are not required for the induction of fibrosis by BLM and suggest that responses by non-lymphoid cells may be sufficient for the induction of fibrosis. (+info)
Follicular large cell lymphoma: an aggressive lymphoma that often presents with favorable prognostic features.
It is debated whether follicular large cell lymphoma (FLCL) has a clinical behavior that is distinct from indolent follicular lymphomas, and whether there is a subset of patients who can be potentially cured. We report here our experience with 100 FLCL patients treated at our institution since 1984 with three successive programs. We evaluated the predictive value of pretreatment clinical features, including two risk models, the Tumor Score System and the International Prognostic Index (IPI). With a median follow-up of 67 months, the 5-year survival is 72% and the failure-free survival (FFS) is 67%, with a possible plateau in the FFS curve, particularly for patients with stage I-III disease. Features associated with shorter survival included age >/=60, elevated lactic dehydrogenase (LDH) or beta-2-microglobulin (beta2M), advanced stage, and bone marrow involvement. Stage III patients had significantly better survival than stage IV patients (P <.05). By the IPI and Tumor Score System, 80% of the patients were in the lower risk groups; both systems stratified patients into prognostic groups. Patients with FLCL have clinical features and response to treatment similar to that reported for diffuse large cell lymphoma. Prognostic risk systems for aggressive lymphomas are useful for FLCL. A meaningful fraction of patients may possibly be cured when treated as aggressive lymphomas. (+info)