Biomedical subjects

A Maity

Publications and source records attributed to A Maity.

25 records · Page 2Linked to original sources

PubMed1994

Alternate polyadenylation in rodent cells results in two differentially expressed cyclin B1 mRNAs.

Cyclin B1 is required for the G2/M transition. In HeLa cells, the level of both its protein and mRNA varies dramatically through the cell cycle. In this study we examine the expression of cyclin B1 mRNA in Chinese hamster ovary cells and 3.7, a transformed rat embryo fibroblast line. In contrast to HeLa cells in which a single transcript is seen, both of these lines express two distinct transcripts of approximately 1.4 and 2.7 kbp in length which appear to be made using different polyadenylation sites. In CHO cells, the level of the upper band varies modestly through the cell cycle while the lower band remains almost constant. In contrast to HeLa cells, CHO cells in G1 express a significant amount of cyclin B1 mRNA. In synchronized 3.7 cells, the level of both transcripts is very low in G1 and rises in parallel as cells progress through S and G2, but the longer transcript disappears faster as cells reenter G1.

Animals↗

PubMed1994

The effects of radiation on the expression of a newly cloned and characterized rat cyclin B mRNA.

PURPOSE: To evaluate the hypothesis that the radiation induced G2 delay in the cell cycle is associated with radiation induced effects on cyclin B expression in a rodent cell system. METHODS AND MATERIALS: Two rodent, rat and Chinese hamster, cyclin B cDNAs were cloned and characterized. The two rodent species were 85% and 86% identical, respectively, when compared to the human cyclin B, indicating that they are the rodent homologous of cyclin B. 3.7 cells (rat embryo cells transformed by H-ras and v-myc) were synchronized and then irradiated. Flow cytometry and Northern blots were performed to evaluate the effects of radiation on cyclin expression in relation to phase of the cell cycle. RESULTS: Examination of the rodent cyclin B sequences revealed only two regions with significant divergence to the human sequence, one in the lysine rich region adjacent to the cyclin destruction box, which is the putative site for ubiquitination, and one at the C terminal end. Although many of the amino acids diverged in the lysine rich region, the positions of the lysines themselves were virtually invariant suggesting their potential importance in ubiquitination. Both rodent species were also noted to have a PEST-like sequence which occurs in the human, but not in non-mammalian cyclins cloned to date and could also potentially contribute to rapid destruction. The rat and Chinese hamster mRNAs contain much longer 3' untranslated regions than the published human sequence with multiple AUUUA and AUUU motifs which are seen in other mRNAs with rapid turnover times. This feature has not been previously found in cyclin mRNAs. In addition we have found that in the 3' region of the rodent cDNAs we find two potential polyadenylation sites suggesting that this gene may have several transcripts. Our studies suggest that multiple mechanisms of control of mammalian cyclin B destruction exist, both at the mRNA and protein level. Evidence is also provided that the levels of rat cyclin B mRNA peaks during G2/M. Irradiation is shown to induce a G2 delay in synchronized 3.7 cells, compared to unirradiated controls, and the delay is temporally related to decreased levels of cyclin B mRNA expression. Since the G2 delay induced by ionizing radiation may contribute to the ability of cells to survive irradiation, cyclin B expression may be a key component in the determination of sensitivity or resistance to radiation therapy. CONCLUSION: The isolation and characterization of two rodent cyclin B's confirm that multiple mechanisms of control of mammalian cyclin B destruction exist. Our studies show that rat cyclin B expression is influenced by radiation and is temporally related to the delay in the G2 phase induced by radiation.

Amino Acid Sequence↗

PubMed1994

The molecular basis for cell cycle delays following ionizing radiation: a review.

Exposure of a wide variety of cells to ionizing (X- or gamma-) irradiation results in a division delay which may have several components including a G1 block, a G2 arrest or an S phase delay. The G1 arrest is absent in many cell lines, and the S phase delay is typically seen following relatively high doses (> 5 Gy). In contrast, the G2 arrest is seen in virtually all eukaryotic cells and occurs following high and low doses, even under 1 Gy. The mechanism underlying the G2 arrest may involve suppression of cyclin B1 mRNA and/or protein in some cell lines and tyrosine phosphorylation of p34cdc2 in others. Similar mechanisms are likely to be operative in the G2 arrest induced by various chemotherapeutic agents including nitrogen mustard and etoposide. The upstream signal transduction pathways involved in the G2 arrest following ionizing radiation remain obscure in mammalian cells; however, in the budding yeast the rad9 gene and in the fission yeast the chk1/rad27 gene are involved. There is evidence indicating that shortening of the G2 arrest results in decreased survival which has led to the hypothesis that during this block, cells repair damaged DNA following exposure to genotoxic agents. In cell lines examined to date, wildtype p53 is required for the G1 arrest following ionizing radiation. The gadd45 gene may also have a role in this arrest. Elimination of the G1 arrest leads to no change in survival following radiation in some cell lines and increased radioresistance in others. It has been suggested that this induction of radioresistance in certain cell lines is due to loss of the ability to undergo apoptosis. Relatively little is known about the mechanism underlying the S phase delay. This delay is due to a depression in the rate of DNA synthesis and has both a slow and a fast component. In some cells the S phase delay can be abolished by staurosporine, suggesting involvement of a protein kinase. Understanding the molecular mechanisms behind these delays may lead to improvement in the efficacy of radiotherapy and/or chemotherapy if they can be exploited to decrease repair or increase apoptosis following exposure to those agents.

Animals↗

PubMed1994

Increased expression of cyclin B1 mRNA coincides with diminished G2-phase arrest in irradiated HeLa cells treated with staurosporine or caffeine.

The irradiation of cells results in delayed progression through the G2 phase of the cell cycle. Treatment of irradiated HeLa cells with caffeine greatly reduces the G2-phase delay, while caffeine does not alter progression of cells through the cell cycle in unirradiated cells. In this report we demonstrate that treatment of HeLa cells with the kinase inhibitor staurosporine, but not with the inhibitor H7, also results in a reduction of the G2-phase arrest after irradiation. Cell cycle progression in unirradiated cells is unaffected by 4.4 nM (2 ng/ml) staurosporine, which releases the radiation-induced G2-phase arrest. In HeLa cells, the G2-phase delay after irradiation in S phase is accompanied by decreased expression of cyclin B1 mRNA. Coincident with the reduction in G2-phase delay, we observed an increase in cyclin B1 mRNA accumulation in irradiated, staurosporine-treated cells compared to cells treated with irradiation alone. Caffeine treatment of irradiated HeLa cells also resulted in an elevation in the levels of cyclin B1 message. These results support the hypothesis that diminished cyclin B1 mRNA levels influence G2-phase arrest to some degree. The findings that both staurosporine and caffeine treatments reverse the depression in cyclin B1 expression suggest that these two compounds may act on a common pathway of cell cycle control in response to radiation injury.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1992

Mediastinal masses in children with Hodgkin's disease. An analysis of the Children's Hospital of Philadelphia and the Hospital of the University of Pennsylvania experience.

From 1970 to 1988, 121 patients younger than 18 years of age who had newly diagnosed Hodgkin's disease were treated at the Children's Hospital of Philadelphia (CHOP) and the Hospital of the University of Pennsylvania (HUP), Philadelphia, Pennsylvania. Fifty-five of 79 children with mediastinal masses (MM) had pretreatment chest radiographs from which a mediastinal mass ratio (MMR) could be calculated. Within a range of MMR values, 0.25 was the best prognosticator for event-free survival (EFS) for all patients. In those treated with radiation therapy (RT) alone, the intrathoracic relapse rate was zero of five patients with small MM (MMR less than 0.25) versus five of eight patients with large MM (P = 0.09). For combined-modality therapy (CMT), there were intrathoracic relapses in zero of four patients with small MM versus 5 of 32 patients with large MM (P = 0.8). For CMT, the intrathoracic relapse rates for those receiving more than 3500 cGy versus less than 2500 cGy were 0 of 4 patients and 5 of 27 patients, respectively (P = 0.8). The intrathoracic relapse rate in children with large MM was significantly lower for CMT than for RT (5 of 32 patients versus 5 of 8 patients) (P = 0.02). The authors concluded that in pediatric Hodgkin's disease, a MM with a MMR greater than or equal to 0.25 may be associated with poor intrathoracic control after RT alone. Despite this, children with large MM treated with RT alone had an excellent overall survival rate.

Adolescent↗

PubMed1992

Comparison of high-dose and low-dose radiation with and without chemotherapy for children with Hodgkin's disease: an analysis of the experience at the Children's Hospital of Philadelphia and the Hospital of the University of Pennsylvania.

PURPOSE: In an effort to minimize complications related to high-dose radiotherapy (RT), children with Hodgkin's disease are often treated with low-dose RT (less than 25 Gy) plus chemotherapy. We performed a retrospective study comparing the results in these children with those from children treated with higher doses of RT (30 to 40 Gy) with or without chemotherapy. PATIENTS AND METHODS: From 1970 to 1988, 121 patients younger than 18 years of age with newly diagnosed Hodgkin's disease were treated at the Children's Hospital of Philadelphia (CHOP) and the Hospital of the University of Pennsylvania (HUP). Before 1977, most children underwent laparotomy and received high-dose RT with or without chemotherapy. Since then, high-dose RT alone has been reserved for pathologic stage IA and IIA postpubertal children without large mediastinal masses. In general, most postpubertal children with stage IIB through IVB disease or large mediastinal masses and all prepubertal children have received low-dose RT plus chemotherapy without laparotomy. RESULTS: The 10-year actuarial survival for all children was 86%, and the event-free survival (EFS) was 67% (median follow-up, 6.6 years). For 58 children treated with low-dose RT plus chemotherapy, 10-year survival and EFS (median follow-up, 6.8 years) were 88% and 67%, respectively. The corresponding figures for 10-year survival and EFS in 48 children treated with high-dose RT with or without chemotherapy were 88% and 66%, respectively. In children receiving combined modality therapy, the in-field failure rate was 7% for sites given between 17.5 and 22.5 Gy and 2% for sites given more than 32.5 Gy. In children receiving RT alone, the failure rate was 5% for sites given more than 32.5 Gy. CONCLUSION: We conclude that low-dose RT plus chemotherapy has yielded results comparable to those with higher doses of RT with or without chemotherapy.

Adolescent↗

PubMedDate not supplied

Hypoxia and VEGF mRNA expression in human tumors.

High expression of circulating plasma vascular endothelial growth factor (VEGF) in patients with cancer is an indicator of poor treatment response. Similarly, hypoxia in tumors, as measured by oxygen needle electrodes, has been found to predict for tumor-treatment failure. These two predictors may be related because hypoxia is a potent stimulator of VEGF expression in vitro. However, the demonstration of a relationship between hypoxia and VEGF in human tumors has, to date, been indirect or even negative. The purpose of this study was to test whether this unexpected result was caused by factors unique to human tumors, or whether the prior results could have been influenced by the known complexities of VEGF regulation. Therefore, we undertook a direct assessment of VEGF induction in human tumors using in situ hybridization and compared its distribution with that of hypoxia, as measured by the distribution of adducts of the hypoxia marker EF5. The distribution of both markers was assessed in relationship to the distribution of blood vessels, as measured by antibodies to CD31. Our hypothesis was that VEGF mRNA and hypoxia would colocalize, assuming that detectability of the former was not limiting. Four squamous cell carcinomas, three sarcomas and one glioblastoma multiforme were studied. When VEGF mRNA signal was detectable, its maxima colocalized with regional maxima of EF5 binding. The strongest levels of both signals were sometimes adjacent to regions of tissue necrosis. However, we were unable to predict absolute levels of EF5 binding based on absolute levels of VEGF mRNA. Conversely, for all tumors studied, regions with relatively low levels of EF5 binding had relatively low or undetectable VEGF mRNA. We found moderate EF5 binding in some keratinized cells but VEGF mRNA was not expressed by these differentiated cells. The paradigm that hypoxia and VEGF expression are linked in human tumors is supported by the data presented herein. A better understanding of the biology behind VEGF expression, including its modulation by hypoxia, is important for optimizing its use as a prognostic indicator and/or modulating its presence with biologic therapies.

Biomarkers↗