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N Courtis

Publications and source records attributed to N Courtis.

13 recordsLinked to original sources
PubMed2000

Polyadenylate polymerase enzymatic activity in mammary tumor cytosols: A new independent prognostic marker in primary breast cancer.

Polyadenylate polymerase (PAP) is one of the enzymes involved in the formation of the polyadenylate tail of the 3' end of mRNA. High levels of PAP activity were associated with rapidly proliferating cells. Here we evaluate the prognostic value of PAP activity in breast cancer patients. PAP specific activity values were measured by a highly sensitive assay in the tumor cytosols of 228 women with primary breast cancer. The median follow-up period was 58 months. PAP specific activity values ranged from 2.1-39.4 units/mg protein in the breast tumor cytosols, and the activity was correlated with the level of expression of the antigen. An optimal cutoff value of 5.5 units/mg extracted protein was first defined by statistical analysis. PAP status was then compared with other established prognostic factors in terms of relapse-free survival (RFS) and overall survival (OS). PAP activity levels had a tendency to increase with tumor-node-metastasis (TNM) stage and were higher in node-positive patients. Evaluation of the prognostic value of PAP was performed using univariate and multivariate analyses. Univariate analysis showed that PAP-positive patients had a less favorable prognosis for both RFS (relative risk (RR) = 2.35; P < 0.001] and OS (RR = 3.15; P < 0.001). PAP significantly added to the prognostic power for RFS (RR = 2.51; P = 0.0012) and OS (RR = 4.21; P < 0.001) in multivariate analysis, whereas patient age, tumor size, and nodal and ER status remained independent factors for predicting survival. When only node-negative patients were examined, PAP was found to be an independent factor for predicting RFS (RR = 3.68; P = 0.0032) and OS (RR = 4.81; P < 0.001). PAP did not appear to have a prognostic significance for node-positive patients. PAP is a new prognostic factor for early recurrence and death in breast cancer patients. Our results suggest that PAP may be used as an independent unfavorable prognostic factor in node-negative breast cancer patients because there were no significant associations between PAP and the other prognostic indicators evaluated in this group of patients.

Adult↗
PubMed1999

The polyadenylation inhibitor cordycepin (3'dA) causes a decline in c-MYC mRNA levels without affecting c-MYC protein levels.

Study of the distribution of the poly(A) tail length of c-myc mRNA in several cell lines revealed a distinct, prevailing population with short poly(A) tails, derived through sequential deadenylation. To elucidate the possible in vivo function of this distinct short tailed c-myc mRNA population, the polyadenylation inhibitor cordycepin was used. This resulted in a decline in steady state c-myc mRNA levels with the remaining messenger mostly oligoadenylated. However, c-MYC proteins did not follow the reduction of the c-myc mRNA. On the other hand, in cells exposed to physiological agents known to downregulate c-myc expression, the reduction of mRNA steady state levels, was reflected upon c-MYC protein levels. The dissociation between c-myc mRNA and protein levels caused by cordycepin was not due to the stabilization of the c-MYC proteins and was not an indiscriminate effect since in the presence of cordycepin, c-fos mRNA and protein levels concomitantly declined. Our data indicate that under these conditions, a long poly(A) tail is not instrumental for c-myc mRNA translation and furthermore, the discrepancy in the steady state of c-myc mRNA level: c-MYC protein ratio between control cells and cells treated with cordycepin indicates that c-myc mRNA is subjected to translational control.

Deoxyadenosines↗
PubMed1998

Poly(A)polymerase activity levels in breast tumour cytosols.

The enzyme poly(A) polymerase (PAP) catalyses the polyadenylation of mRNA and its activity levels vary within the cell cycle. The levels of activity of this enzyme were measured in the cytosol of breast tumours from 62 untreated patients and compared to clinical prognostic parameters as well as other biological markers. The enzyme levels measured ranged from 3 to 46 units/mg protein. A statistically significant association was observed between high PAP activity values and the TNM stage of the disease as well as node invasiveness. Furthermore, there was a positive correlation between PAP activity values and c-erbB-2 overexpression but not with its amplification. No significant correlation was observed with c-myc amplification or overexpression and cathepsin D levels. A direct relationship between steroid receptor content and PAP activity levels, which was more prominent in the case of the progesterone receptor, was observed. However, also on the basis of previous data PAP activity may prove to be indicative of aggressive disease. Furthermore, measurements of PAP activity may contribute to the definition of the biological profile of tumour cells.

Biomarkers, Tumor↗
PubMed1996

In vivo generation of 3' and 5' truncated species in the process of c-myc mRNA decay.

It has been demonstrated that the half-life of c-myc mRNA is modulated in response to physiological agents. The elucidation of the decay process and the identification of the critical steps in the in vivo c-myc mRNA degradation pathway can be approached by following the fate of c-myc mRNA under the influence of such factors. IFN-alpha was the factor used to modulate c-myc mRNA half-life in HeLa 1C5 cells, a stable clone derived from HeLa cells. This cell line carries multiple copies of the c-myc gene, under the control of the dexamethasone inducible mouse mammary tumor virus-long terminal repeat (MMTV-LTR). Exposure of HeLa 1C5 cells to IFN-alpha resulted in a further 2-fold increase over the dexamethasone-induced c-myc mRNA. However, the c-myc mRNA in IFN-alpha treated cells was less stable than that in the control cells. RNase H mapping of the 3' untranslated region of c-myc mRNA revealed, in addition to the full length mRNA, three smaller fragments. These fragments were proven to be truncated, non-adenylated c-myc mRNA species generated in vivo. Exposure of HeLa 1C5 cells to Interferon-alpha before induction with dexamethasone resulted in the enhanced presence of these intermediates. RNase H analysis of c-myc mRNA after actinomycin D chase revealed that deadenylation led to the formation of a relatively more stable oligoadenylated c-myc mRNA population which did not appear to be precursor to the truncated intermediates. The detection of truncated 3' end c-myc mRNA adenylated fragments as well, implies that the c-myc mRNA degradation process may follow an alternative pathway possibly involving endonucleolytic cleavage.

Animals↗
PubMed1989

Patterns of adenosine deaminase, ecto-5'-nucleotidase, poly(A)polymerase and surface light chain expression in chronic lymphocytic leukemias.

The levels of activity of three enzymes have been measured in the circulating malignant lymphocytes of 47 patients with B chronic lymphocytic leukemia (CLL). These were the purine degradative enzymes, adenosine deaminase (ADA) and ecto-5'-nucleotidase (5'NT) and the enzyme responsible for the polyadenylation of mRNA, poly(A) polymerase. The patterns of activity of the above enzymes and the expression of surface immunoglobulin light chains were examined. A heterogeneity in the specific activity of the enzymes was observed which could not be attributed to variations of the percentage of B lymphocytes. A positive correlation was found between ADA and poly(A)polymerase activity (r = 0.383, p less than 0.01). Furthermore, the expression of immunoglobulin light chain phenotype was inversely related to 5'NT specific activity; CLL cases in which less than 20% of the cells expressed lambda chain phenotype, presented 5'NT specific activity of 16.7 +/- 3.3 (S.E.) nmol/h/10(6) cells, whereas in CLL cases with more than 20% of the cells expressing this phenotype the enzyme specific activity was 4.8 +/- 1.6 (S.E.) nmol/h/10(6) cells (p less than 0.02). These findings suggest that the simultaneous determination of enzymatic activities and immunological markers, might be useful in defining subsets in CLL and the subsequent clinical treatment.

5'-Nucleotidase↗
PubMed1988

Relation between the activity of poly(A)polymerase and the levels of protein synthesis in the lymphocytes of patients with chronic lymphocytic leukemia.

The activity levels of the enzyme poly(A)polymerase and the levels of protein synthesis primed by endogenous messenger RNA (mRNA) as well as polyuridylic acid, poly(U) directed polyphenylalanine synthesis, were determined in lymphocytic extracts from 17 patients with chronic lymphocytic leukemia of the B cell type. The enzyme activity values have not been found to correlate with the poly(U)-protein synthesis, whereas a positive linear correlation has been established between the activity levels of poly(A)polymerase and the endogenous mRNA-primed protein synthesis (r = 0.735, p less than 0.01). This difference between exogenously and endogenously primed protein synthesis in concern with poly(A)polymerase is discussed.

Humans↗
PubMed1987

A colorimetric assay for the determination of 5'-nucleotidase activity.

A rapid, simple, quantitative and sensitive assay for the determination of 5'-nucleotidase has been developed. The method can be applied to both soluble and membrane bound forms of the leukocyte enzyme. Enzyme activity is determined by colorimetric estimation of NH3 released from adenosine, the product of 5'-nucleotidase activity in the presence of adenosine deaminase. The assay may be performed in microtitre plates and read with an automatic multiscan spectrophotometer. Thus it can be applied to a large number of samples for routine medical and research purposes.

5'-Nucleotidase↗
PubMed1984

Polyadenylic acid polymerase activity in normal and leukemic human leukocytes.

Soluble polyadenylic acid [poly(A)] polymerase and poly(A) nucleases content of normal human blood lymphocytes and leukemic blood cell populations was determined. Blood lymphocytes from seven normal individuals were used as controls. Leukemic cells were obtained from 69 patients with various types of acute and chronic leukemias. Chronic lymphocytic leukemias presented poly(A) polymerase values with a mean of 9 +/- 4 (S.D.). Although most of the chronic lymphocytic leukemia cases presented poly(A) polymerase activities similar to those of normal lymphocytes (3 +/- 3), a small number fell into the specific activity values of acute leukemias, which were significantly higher and covered a wider range. The mean values for acute myeloblastic, acute monoblastic, and acute lymphoblastic leukemias were 53 +/- 50, 21 +/- 8, and 29 +/- 14, respectively. A statistically significant difference was found between chronic and acute leukemias (p less than 0.01). The observed differences in poly(A) polymerase levels of acute lymphoblastic leukemia versus chronic lymphocytic leukemia persisted after fractionation of the crude extracts and, furthermore, they could not be attributed to differences in the levels of poly(A)-degrading enzymes [poly(A) endo- and exonucleases]. Fractionation of leukemic extracts on Sephadex G-75 revealed two molecular forms of poly(A) polymerase activity.

Humans↗
PubMedDate not supplied

K562 cell sensitization to 5-fluorouracil- or interferon-alpha-induced apoptosis via cordycepin (3'-deoxyadenosine): fine control of cell apoptosis via poly(A) polymerase upregulation.

K562 cells represent a classical model for the study of drug resistance. Induction of apoptosis is accompanied by concomitant distinct modulations of poly(A) polymerase (PAP) and other proteins involved in mRNA maturation. Recent data suggest the involvement of mRNA stability in the induction of specific apoptosis pathways. In this study we used a specific polyadenylation inhibitor, cordycepin (3-deoxyadenosine), to investigate the involvement of polyadenylation in K562 cell apoptosis and drug resistance. The combination of cordycepin with either 5-fluorouracil or interferon-alpha sensitized chemoresistant K562 cells to apoptosis. This sensitization was followed by distinct PAP modulations before and after the appearance of characteristic apoptosis pointers (DNA laddering, DAPI staining, mitochondrial transmembrane potential). PAP modulations appeared essential for K562 sensitization. mRNA polyadenylation therefore seemed to be involved not only in apoptosis but also in drug resistance. Polyadenylation inhibition by cordycepin under certain conditions sensitized chemoresistant K562 cells to apoptosis and thus polyadenylation could prove to be a fine target for overcoming drug resistance.

Apoptosis↗