Evaluation of cytotoxic treatment of patients with osteosarcoma by an in vitro chemoresistance assay

During the previous two decades several assays have been developed aiming to select the most effective chemotherapy regimen for each individual, avoiding the possible toxicity of ineffective drugs. In order to evaluate cytotoxic treatment for patients with osteosarcoma, we applied an in vitro chemoresistance assay by culturing tumour cells and determining their in vitro survival rates after exposure to various chemotherapeutic drugs. The conditions of the assay were optimised in two established osteosarcoma cell lines (KHOS and U2-OS), as compared with data derived after treatment of primary normal adult osteoblasts. Chemotherapeutic drugs (cisplatin, adriamycin or methotrexate or combinations) concentrations were chosen in a range that has been reported to induce tumour cell death in the plasma patients' The method applied successfully in 6 cell cultures originated from biopsies of 7 patients with osteosarcoma and the in vitro response to chemotherapeutic drugs was correlated with the clinical outcome. Such analysis revealed both positive and negative correlation of the in vitro data to the patients clinical responses. Therefore, this study indicated that, although in vitro chemoresistance is a valuable assay, additional analysis and implications of other factors are required for a general evaluation of cytotoxic treatment for patients with osteosarcoma.

Fibroblast cultures from healthy centenarians have an active proteasome

Healthy centenarians represent the best example of successful ageing. Various studies have shown that centenarians have escaped the major age-associated diseases, they have several well-conserved immune parameters and at least one gene allele has been identified and linked with their increased longevity. During ageing there is an accumulation of oxidised proteins, a phenomenon that has been related to an impaired function of the 20S proteasome in aged cells. We have, therefore, analysed the expression and the proteolytic activity of the proteasome in centenarian cells. Four fibroblast cultures derived from healthy centenarians were studied and compared with cultures derived from adult donors of different ages. Analysis of several proteasome subunits RNA expression levels, determination of one peptidase activity and identification of oxidised proteins in these samples revealed that centenarian cultures have a functional proteasome. In addition, it was found that the centenarian cultures exhibit characteristics similar to the younger rather than the older control donors derived cultures in all three assays. These data indicate that centenarian cells may be different from elderly donors cells, thus opening up new dimensions for the identification and characterisation of factors that are linked with longevity.

Aging and longevity. A paradigm of complementation between homeostatic mechanisms and genetic control?

Aging is a universal and inevitable phenomenon that affects nearly all animal species. It can be considered the product of an interaction between genetic, environmental, and lifestyle factors, which in turn influence longevity that varies between and within species. It has been proposed not only that the aging process is under genetic control, but that it can also be considered a result of the failure of homeostasis due to the accumulation of damage. This review article discusses these issues, focusing on the function of genes that associate with aging and longevity, as well as on the molecular mechanisms that control cell survival and maintenance during aging.

Genetics of aging: lessons from centenarians

Aging is a universal phenomenon that affects nearly all animal species. It can be considered as the product of an interaction between genetic, environmental and lifestyle factors, which in turn influence longevity that varies between and within species. Several studies have been focused in healthy centenarians, because these exceptional individuals represent the best example of successful aging. These studies have shown that centenarians have escaped the major age-associated diseases, they have well conserved several immune parameters, and at least one gene allele has been identified and linked with longevity. In parallel, studies at cellular level have identified several genes that influence, positively or negatively, normal replicative in vitro life-span. The ability of these genes to regulate aging in vitro, in conjunction with the telomeres shortening hypothesis have raised the intriguing question of the existence of a molecular clock that counts and thus may modulates human aging and longevity. This review article will discuss these issues, focusing in the nature of the genetic factors that associate with these phenomena.

Induction of replicative senescence biomarkers by sublethal oxidative stresses in normal human fibroblast

We tested the long-term effects of sublethal oxidative stresses on replicative senescence. WI-38 human diploid fibroblasts (HDFs) at early cumulative population doublings (CPDs) were exposed to five stresses with 30 microM tert-butylhydroperoxide (t-BHP). After at least 2 d of recovery, the cells developed biomarkers of replicative senescence: loss of replicative potential, increase in senescence-associated beta-galactosidase activity, overexpression of p21(Waf-1/SDI-1/Cip1), and inability to hyperphosphorylate pRb. The level of mRNAs overexpressed in senescent WI-38 or IMR-90 HDFs increased after five stresses with 30 microM t-BHP or a single stress under 450 microM H(2)O(2). These corresponding genes include fibronectin, osteonectin, alpha1(I)-procollagen, apolipoprotein J, SM22, SS9, and GTP-alpha binding protein. The common 4977 bp mitochondrial DNA deletion was detected in WI-38 HDFs at late CPDs and at early CPDs after t-BHP stresses. In conclusion, sublethal oxidative stresses lead HDFs to a state close to replicative senescence.

Different functions are required for initiation and maintenance of immortalization of rat embryo fibroblasts by SV40 large T antigen

We have used two different, but complementary assays to characterize functions of SV40 T antigen that are necessary for its ability to immortalize rat embryo fibroblasts. In accordance with previous work, we found that several functions were required. These include activities that map to the p53 binding domain and the amino terminal 176 amino acids which contain the J domain as well as the CR1 and CR2 domain required for binding and sequestering the RB family of pocket proteins. Moreover, we found that even though activities dependent only upon the amino terminus were sufficient for immortalization they were unable to maintain it. This suggests that immortalization by these amino terminal functions requires either additional events or immortalization of a subset of cells within the heterogeneous rat embryo fibroblast population. We further found that an activity dependent upon amino acids 17 - 27 which remove a portion of the CR1 domain and the predicted alpha-1 helix of the J domain was not necessary to maintain growth but was required for direct immortalization suggesting that at least one of the functions required initially was not required to maintain the immortal state. This represents the first demonstration that some of the functions required for maintenance of the immortal state differ from those required for initiation of immortalization.

Telomere length in fibroblasts and blood cells from healthy centenarians

Several lines of evidence indicate that telomere shortening during in vitro aging of human somatic cells plays a causal role in cellular senescence. A critical telomere length seems to be associated with the replicative block characterizing senescent cells. In this paper we analyzed the mean length of the terminal restriction fragments (TRF) in fibroblast strains from 4 healthy centenarians, that is, in cells aged in vivo, and from 11 individuals of different ages. No correlation between mean TRF length and donor age was found. As expected, telomere shortening was detected during in vitro propagation of centenarian fibroblasts, suggesting that in fibroblasts aged in vivo telomeres can be far from reaching a critical length. Accordingly, chromosome analysis did not show the presence of telomeric associations in early passage centenarian fibroblasts. In blood cells from various individuals, the expected inverse correlation between mean TRF length and donor age was found. In particular, a substantial difference (about 2 kb) between telomere length in the two cell types was observed in the same centenarian. Expression analysis of three senescence-induced genes, i.e., fibronectin, apolipoprotein J, and p21, revealed for only the fibronectin expression levels a clear positive correlation with donor age. Our results suggest that (1) telomere shortening could play a different role in the aging of different cell types and (2) the characteristics of fibroblasts aged in vitro might not be representative of what occurs in vivo.

Expression of the growth arrest specific genes in rat embryonic fibroblasts undergoing senescence

Replicative senescence is an in vitro biological phenomenon that results the irreversible growth arrest of mammalian cells. In contrast, cellular quiescence is reversible upon the addition of mitogens or replating. Quiescence is associated with the expression of a particular gene family--the growth arrest specific (GAS) genes. I have determined whether gas genes expression also associates with senescence, as well as whether serum stimulation of senescent cells has the same inhibiting effect as in quiescent cells. Analysis of RNA of cultures of rat embryonic fibroblasts suggests that gas-1 and gas-6 gene expression is associated with the irreversible growth arrest of senescence. However, serum was found to have a different effect upon gas-1 and gas-6 expression in quiescent and senescent cells, because its stimulation of quiescent cells results in a dramatic decrease of their RNA levels, but it had no effect in senescent cells. Finally, analysis of the data is raising the possibility that the gas-1 and gas-6 genes expression may also be associated with conditions of cellular stress.

Cloning and identification of genes that associate with mammalian replicative senescence

Cellular senescence and limited proliferative capacity of normal diploid cells has a dominant phenotype over immortality of cancerous cells, suggesting its regulation by the expression of a set of genes. In order to isolate the genes that associate with senescence, we have employed a clonal system of conditional SV40 T antigen rat embryo fibroblast cell lines which undergo senescence upon T antigen inactivation. Construction of cDNA libraries from two conditional cell lines and application of differential screening and subtractive hybridization techniques have resulted in the cloning of eight senescence-induced genes (SGP-2/Apo J, alpha 1-procollagen, osteonectin, fibronectin, SM22, cytochrome C oxidase, GTP-alpha, and a novel gene) and a senescence-repressed gene (FRS-2). Three of these genes encode for extracellular matrix proteins, others are involved in the calcium-dependent signal transduction pathways, while the SGP-2/Apo J gene may have a cellular protective function. RNA analysis has shown that the senescence-associated genes are overexpressed in both normal rat embryonic fibroblasts and human osteoblasts cell cultures undergoing aging in vitro. In comparison, the expression of these genes in a rat fibroblast immortalized cell line (208F cells) was down-regulated after both its partial and its full transformation by ras oncogenes. Thus, cloning of senescence-associated genes opens up new ways to elucidate and/or to modulate aging and cancer.

Molecular links between cellular mortality and immortality (review)

Normal diploid cells cultivated in vitro exhibit limited division potential while undergoing ageing during serial passaging. In contrast, cells that have been genetically transformed appear to have lost the regulatory mechanisms of limited growth potential and may continue to divide indefinitely. While cellular mortality is characterised by a progressive cessation of cell growth manifested in cell culture by senescence, immortalisation is the escape from senescence as a result of multiple mechanisms involving the inactivation of tumour suppressor genes, the elevated expression of oncogenes, as well as other genetic and epigenetic changes. The mechanisms governing mortality and immortality are fundamentally linked. The physiological and biochemical features which characterise cellular mortality are examined, herein in the search for markers and timing mechanisms of mortality. The genetic elements involved in the control of mortality and immortality are also discussed, and the fundamental similarities between the molecular and genetic aspects which govern the determination of the phenotypes manifesting the two processes are underlined.

Rat embryo fibroblasts immortalized with simian virus 40 large T antigen undergo senescence upon its inactivation

Introduction of simian virus 40 T antigen into rodent fibroblasts gives rise to cells that can proliferate indefinitely but are dependent upon it for maintenance of their growth once the normal mitotic life span has elapsed. Inactivation of T antigen in these immortalized cells causes rapid and irreversible cessation of growth. To determine whether this growth arrest is associated with entry into senescence, we have undertaken a genetic and biological analysis of conditionally immortal (tsa) cell lines derived by immortalizing rat embryo fibroblasts with the thermolabile tsA58 T antigen. This analysis has identified the following parallels between the tsa cells after inactivation of T antigen and senescent rat embryo fibroblasts: (i) growth arrest is irreversible; (ii) it occurs in G1 as well as G2; (iii) the G1 block can be partially overcome by stimulation with 20% fetal calf serum, but the G2 block cannot be overcome; (iv) 20% fetal calf serum induces c-fos, but c-myc is unaltered; and (v) fibronectin and p21(Waf1/Cip1/Sdi1) are upregulated upon growth arrest. These results suggest that T-antigen-immortalized fibroblasts are committed to undergo senescence but are prevented from undergoing this process by T antigen. Inactivation of T antigen removes this block and results in senescence of the cells. Thus, these cell lines may represent a powerful system for study of the molecular basis of entry into senescence.

The role of cdc2, cdc25 and cyclin A genes in the maintenance of immortalization and growth arrest in a rat embryonic fibroblast conditional cell line

Immortalization of rodent cells by oncogenes is a complex biological process which involves the abnormal regulation of genes who control cellular proliferation. The role of the cell cycle control genes cdc2, cdc25 and cyclin A in the maintenance of immortalization and in growth arrest was examined in the tsa14, a SV40 T antigen rat embryonic fibroblast conditional for growth cell line. Analysis of RNA expression showed minimal levels of cdc2 mRNA in both proliferating and growth-arrested tsa14 cells. In contrast, cyclin A mRNA was found downregulated in growth-arrested tsa14 cells, as well as in senescent primary rat embryonic fibroblasts (REFS). The ability of cdc2, or cdc25, or cyclin A genes to maintain the tsa14 immortal phenotype was also examined by electroporations of these genes into the tsa14 cells. Clones over-expressing the electroporated cdc2, or cdc25, or cyclin A, or combinations of these genes growth arrested at the non-permissive conditions similar to controls, thereby suggesting that the expression of these genes alone is insufficient for tsa14 maintenance of immortalization.

The conformation of tRNA genes. Chemical modification studies

It has been suggested that eukaryotic tRNA genes might adopt a higher order stem and loop structure to facilitate transcription by interaction of their variably spaced intragenic promoter blocks. Using sodium bisulphite, which reacts specifically with cytosine residues in single-stranded nucleic acids, no deamination of C in the TTCGAA sequence of the 3' ICR of a tRNA(Leu) gene could be detected under conditions which caused 60% deamination of cytosine residues within the loop region of a synthetic cruciform cloned in the same negatively supercoiled plasmid vector. We conclude that, under these conditions, such structures occur in tRNA genes very rarely, if at all.

Abnormalities of retinoblastoma gene structure in human lung tumors

The retinoblastoma (Rb) gene is associated with the pathogenesis of several types of human cancer, including retinoblastoma, osteosarcoma, soft tissue sarcomas, and lung, breast and bladder carcinomas. Loss of heterozygosity is a common mode in allelic inactivation of Rb and other tumor-suppressor genes. We investigated DNA from 15 human lung tumors for loss of heterozygosity of the Rb locus using a polymerase chain reaction (PCR) based restriction fragment length polymorphism assay. Of informative cases we found loss of heterozygosity in 2 out of 3 squamous cell carcinomas and 1 out of 2 adenocarcinomas of the lung. We also found structural rearrangements in two out of fourteen Hind III digested lung tumors examined at the 5' region of the human Rb gene using Southern blot hybridization analysis. Since these two tumors were classified as stage III it is possible that the alteration of Rb gene is involved in the progression of this type of cancer. Using specific primers for exons 15, 16, 21 and 22 of the Rb gene, we carried out amplification of these exons by polymerase chain reaction. None of these tumors showed a deletion of exons 15, 16, 21 and 22.

Oncogenes in cellular immortalisation and differentiation (review)

Oncogenes have been shown to be able to overcome the limited proliferative capacity of normal mammalian cells in culture enforcing them to an immortalised phenotype, which in turn may act as a primary step in tumourigenesis. The oncogenes which display such immortalisation activity have the common feature of nuclear localisation, while the oncogenes which are capable of transforming cells are mainly cytoplasmic. Oncogenes from both families have been shown to interfere with the differentiation processes of several cell types. There is evidence that some of these proto-oncogenes may function as regulators of normal cell differentiation, and when immortalisation occurs this is a process of blocking the cell from achieving a differentiated state. This article focuses on the ability of some oncogenes with different functions, such as myc and ras, to override the limited cellular proliferative capacity and their effects on differentiation; finally it examines the recent implications that some onco-suppressor genes are actively participating in cellular differentiation processes.

The role of the 5'-flanking sequence of a human tRNA(Glu) gene in modulation of its transcriptional activity in vitro

The role of a tRNA-like structure within the 5'-flanking sequence of a human tRNA(Glu) gene in the modulation of its transcription in vitro by HeLa cell extracts has been investigated using several deletion mutants of a recombinant of the gene which lacked part or all of the tRNA-like structure. The transcriptional efficiency of four mutants was the same as that of the wild-type recombinant, two mutants had decreased transcriptional efficiency, one was more efficient, and one, lacking part of the 5' intragenic control region, was inactive. Correlation of the transcriptional efficiencies with the position and the size of the 5'-flanking sequence that was deleted indicated that the tRNA-like structure may be deleted without loss of transcriptional efficiency. Current models for the modulation of tRNA gene transcription by the 5'-flanking sequence are assessed in the light of the results obtained, and a potential model is presented.

Human tRNAGlu genes: their copy number and organisation

The tRNAGlu gene copy number, determined by genomic blot analysis of human placental DNA, is approximately thirteen. These studies, using several probes and DNA digested with several restriction enzymes singly or in combination, show that most of these tRNAGlu genes are flanked by DNA of very similar sequence for at least 5 kb. This conclusion is supported by the close similarity of the restriction maps of two lambda Charon-4A recombinants of human genomic DNA containing two different tRNAGlu genes.