Biomedical subjects

F della Ragione

Publications and source records attributed to F della Ragione.

5 recordsLinked to original sources

PubMed1996

P16INK4A gene homozygous deletions in human acute leukaemias with alterations of chromosome 9.

Acute leukaemias are characterized by nonrandom chromosomal aberrations which are often strictly related to the inactivation of tumour suppressor genes (TSGs). Alterations at the short arm of chromosome 9 have been reported in a remarkable percentage of acute lymphoblastic leukaemias (ALL) and have been suggested to cause the loss of activity of the putative TSG, p16INK4A (MTS1/CDKN2) gene. In order to evaluate the correlation between this gene inactivation and visible cytogenetic abnormalities, we have investigated p16INK4A homozygous gene deletions in 10 paediatric acute leukaemias of different cell lineages which demonstrated karyotype aberrations involving chromosome 9. Moreover, the dimension of the genetic alteration was evaluated by studying the loss of heterozygosity of two highly polymorphic markers of chromosome 9p, namely alpha-interferon (IFNA) and D9S104, and the deletion of 5'-methylthioadenosine phosphorylase (MTAPase) gene. Finally, the deletion of a gene belonging to p16INK4A family, the p18 gene, was analysed in these acute leukaemias. Our results demonstrated that: (1) the biallelic loss of p16INK4A gene is strictly related to a specific immunophenotype, namely ALL of T-cell lineage; (ii) no significant correlation exists between alterations at chromosome 9p level and the homozygous deletions of p16INK4A gene; and (iii) p18 gene was not deleted in the examined cases. These findings suggest a possible correlation between the T-lymphocyte phenotype and the expression of p16INK4A gene. Moreover, the absence of MTAPase activity seems to be a valuable marker of p16INK4A gene inactivation, thus indicating that the deleted chromosomal area on 9p21 very frequently involves the MTAPase gene.

Base Sequence↗

PubMed1996

Homozygous deletions of cyclin-dependent kinase inhibitor genes, p16(INK4A) and p18, in childhood T cell lineage acute lymphoblastic leukemias.

p16(INK4A) and p18 proteins are highly specific inhibitors of cyclin-dependent serine/threonine kinase activities required for the overcoming of the G1 checkpoint in the eukaryotic cell division cycle. The frequent cytogenetic aberrations occurring in several human neoplasms at the level of their codifying genes along with their molecular function strongly suggest that they might be important tumor suppressor genes. We looked for homozygous deletions of p16(INK4A) and p18 genes in 21 cases of childhood T cell lineage acute lymphoblastic leukemia (ALL). Twenty of 21 patients (95%) had homozygous deletions of p16(INK4A) gene while three out of 21 (14%) showed p18 gene biallelic deletion. Loss of heterozygosity studies were performed in 18 of the T cell ALL investigated by means of two highly polymorphic 9p21 markers. The results obtained demonstrated that genetic deletions of different extension occur on the short arms of the 9 chromosome pair. Karyotypic analyses, performed in 13 cases, failed to demonstrate 9p alterations in 12 samples, (92%) thus demonstrating that p16(INK4A) gene homozygous deletions are not restricted to cases with cytogenetically detectable 9p aberrations. The high incidence of p16(INK4A) gene deletions in pediatric T cell lineage ALL suggests that this genetic alteration could represent an early and key event in the development of such a malignancy but it should not have any prognostic value. Conversely, the inactivation of p18 gene, observed in a lower but significant number of cases, could participate in the progression of acute leukemias towards a more aggressive disease. Finally, our results may suggest that p16(INK4A) protein plays a key role in the control of proliferation and/or differentiation of human T lymphocytes.

Adolescent↗

PubMed1995

High frequency of homozygous deletions of CDK4I gene in childhood acute lymphoblastic leukaemia.

To determine the incidence of homozygous deletions of the newly identified tumour suppressor gene, CDK4I, molecular genomic DNA analyses by PCR technique were performed on primary neoplastic cells from 22 childhood acute leukaemias obtained at presentation. The blast cells derived in all the analysed cases from bone marrow. We found that none of acute myeloblastic leukaemias (four cases) showed the CDK4I alteration, whereas 6/13 (46%) common acute lymphoblastic leukaemias (ALLs) displayed homozygous deletions. Moreover, and even more important, all the blasts purified from ALLs derived from early lymphoid precursors (three early-T ALLs and two pre-B ALLs) showed the absence of CDK4I gene. When the entire coding sequence of the CDK4I gene from samples without homozygous deletions was analysed by the single-strand conformational polymorphism method, no point mutations were identified. These results demonstrate that CDK4I gene deletions are very frequent and probably early events in childhood acute leukaemias of lymphoid origin and especially in early-T and pre-B ALLs. Moreover, the molecular mechanism of the loss of function of the gene is correlated, at least in childhood ALLs, almost exclusively to deletions and not to point mutations.

Base Sequence↗

PubMed1983

Transport and metabolism of 5'-methylthioadenosine in human erythrocytes.

The transport and metabolism of 5'-deoxy-5'-S-methylthioadenosine have been studied in intact human erythrocytes. The sulfur nucleoside is rapidly accumulated into red cells and the extent of uptake largely exceeds the theoretical equilibrium between inner and outer compartment owing to its conversion into a non-permeable compound, namely 5-methylthioribose 1-phosphate. To characterize the nucleoside transport, phosphate-depleted erythrocytes, in which the methylthioadenosine metabolism is negligible, have been employed. The results indicate that: (i) the transport occurs via a facilitated-diffusion mechanism; (ii) the process is not energy-dependent and (iii) no specific cation is required. The kinetic analyses of both the transport and the metabolism show that the uptake of methylthioadenosine is a result of the tandem action of a transport step of high capacity (Vmax = 604 +/- 51 pmol/10(6) cells per min) and low affinity (Km = 3270 +/- 321 microM) followed by a metabolic step of low capacity (Vmax = 6.6 pmol/10(6) cells per min) and high affinity (Km = 30 microM). Furthermore, a substrate inhibition exerted by methylthioadenosine at high concentration (over 200 microM) on its specific phosphorylase is reported for the first time. Experiments performed with several analogs of the thioether indicate that the adenine amino group and the hydrophobic substituent at the 5'-position are critical for the transport carrier recognition. Adenine is the most powerful inhibitor of methylthioadenosine transport.

Adenosine↗

PubMed1982

Polyamine biosynthesis and interconversion in rodent tissues.

Polyamine levels in rodent tissues are regulated by the activities of three enzymes: ornithine decarboxylase, S-adenosylmethionine decarboxylase, and spermidine/spermine N1-acetyltransferase. These enzymes are present in the cell in very small amounts, have very short half-lives, and are highly inducible. Ornithine decarboxylase was purified to homogeneity (about 10,000-fold) from androgen-treated mouse kidneys, which have enzyme levels several hundred times higher than those in other fully induced mammalian tissues. This decarboxylase could be specifically labeled either in vitro or in vivo by reaction with radioactive alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor. Such covalent binding of alpha-difluoromethylornithine was used to titrate the number of molecules of the enzyme and to estimate its purity. It was also used for autoradiographic localization of the enzyme within tissues and to follow the degradation of the protein in vivo. S-Adenosylmethionine decarboxylase has been purified from rat liver and psoas muscle, and significant differences between the enzyme forms present in these tissues were observed. The rate-limiting enzyme in the interconversion of the polyamines, spermidine/spermine N1-acetyltransferase was purified more than 100,000-fold from carbon tetrachloride-induced rat liver. This acetylase acts on both spermine and spermidine to form N1-acetyl derivatives, which are then oxidized by polyamine oxidase forming spermidine and putrescine, respectively.

Acetyltransferases↗