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PubMed1998

Upregulation of functional ryanodine receptors during in vitro aging of human diploid fibroblasts.

We demonstrate for the first time that cellular aging in vitro is accompanied by a dramatic elevation in the levels of ryanodine receptor-bearing Ca2+ channels. These channels normally reside within microsomal membranes and gate Ca2+ release from intracellular stores. We therefore measured cytosolic Ca2+ levels in 'young' (30 mean population doublings, MPDs) and 'senescent' (53 to 58 MPDs) human diploid fibroblasts (HDFs). Application of the known ryanodine receptor modulators, caffeine or cyclic adenosine diphosphate-ribose (cADPr), triggered cytosolic Ca2+ signals in both young and senescent cells. The signal magnitude however was significantly greater in senescent compared with young HDFs. In parallel, incubation with a highly specific anti-ryanodine receptor antiserum resulted in specific immunofluorescence only in senescent HDFs. We envisage that elevated levels of functional ryanodine receptors may underlie the defective Ca2+ handling and cellular degeneration that occurs with aging.

Adenosine Diphosphate Ribose↗

PubMed1996

Heterogeneity in radiosensitivity of human diploid fibroblasts from keloids and normal skins.

Colony-forming ability was employed in evaluating the susceptibility to in vitro gamma ionizing radiation in human diploid skin fibroblasts (HDF). Twelve pairs of HDF, each composed of fibroblasts from excised keloid lesion and local normal skin tissue as its control, were studied in patients with clinically persistent keloids. Parameters of radiosensitivity, both D0 and D10, and growth kinetics were examined. The radiosensitivity in three of the 12 keloids (25%) were demonstrated significantly increased than their counterpart controls, even though no difference in growth kinetics in between. Moreover, a broad range in the radiosensitivity of fibroblast cells was demonstrated and it is suggested that there is a great heterogeneity of cellular response to radiation in HDF.

Aged↗

PubMed1993

Effect of the tumor promoter phorbol 12-myristate 13-acetate (PMA) on proliferation of young and senescent WI-38 human diploid fibroblasts.

The effects of the tumor promoter phorbol 12-myristate 13-acetate (PMA) on the proliferation, protein kinase C activity (PKC), and c-fos gene expression were examined in cultures of young and senescent (90-95% lifespan completed) WI-38 human diploid fibroblasts. We observed that, following stimulation with medium containing 10% fetal bovine serum (FBS), the translocation of PKC from the cytosol to the particulate compartment was less efficient in senescent WI-38 cells than in young cells. However, when PMA was added to the medium, the intracellular distribution of PKC activity in old cells became nearly identical to that observed in young cells. The inducibility of c-fos mRNA by serum addition, which is a protein kinase C-dependent event, was significantly amplified in the presence of PMA. Moreover, the duration of peak c-fos expression, after stimulation by FBS and PMA, increased in senescent cells as compared to young cells. Our results reveal that the normal signal transduction pathway is altered in senescent, slowly proliferating human fibroblasts and that it can be partially restored in the presence of the tumor promoter PMA.

Cell Division↗

PubMed1993

Selective loss of CDC2 and CDK2 induction by tumor necrosis factor-alpha in senescent human diploid fibroblasts.

Normal human diploid fibroblasts undergo a finite number of doublings in culture. This process of senescence is accompanied by a loss in the ability to respond to proliferative stimuli and is therefore distinct from the quiescent state induced by nutrient deprivation. We have studied changes in gene expression induced in these cells following exposure to the cytokine, tumor necrosis factor-alpha (TNF). We observed that TNF induced CDC2 and CDK2 expression in early-passage quiescent WI-38 fibroblasts. However, as cells approached senescence, their ability to induce CDC2 and CDK2, as well as stimulate DNA synthesis in response to TNF, progressively declined, with minimal to absent induction in senescent cells. This occurred despite the TNF-dependent induction of such proliferation-independent genes as manganese superoxide dismutase and interleukin-6 in senescent and quiescent cells. Serum was similarly unable to induce CDC2 or CDK2 expression in senescent cells. These results demonstrate that senescent cells are selectively deficient in TNF-mediated induction of CDC2 and CDK2, genes crucial to DNA synthesis and mitosis.

CDC2 Protein Kinase↗

PubMed1994

Retardation of the senescence of cultured human diploid fibroblasts by carnosine.

We have examined the effects of the naturally occurring dipeptide carnosine (beta-alanyl-L-histidine) on the growth, morphology, and lifespan of cultured human diploid fibroblasts. With human foreskin cells, HFF-1, and fetal lung cells, MRC-5, we have shown that carnosine at high concentrations (20-50 mM) in standard medium retards senescence and rejuvenates senescent cultures. These late-passage cultures preserve a nonsenescent morphology in the presence of carnosine, in comparison to the senescent morphology first described by Hayflick and Moorhead. Transfer of these late-passage cells in medium containing carnosine to unsupplemented normal medium results in the appearance of the senescent phenotype. The serial subculture of cells in the presence of carnosine does not prevent the Hayflick limit to growth, although the lifespan in population doublings as well as chronological age is often increased. This effect is obscured by the normal variability of human fibroblast lifespans, which we have confirmed. Transfer of cells approaching senescence in normal medium to medium supplemented with carnosine rejuvenates the cells but the extension in lifespan is variable. Neither D-carnosine, (beta-alanyl-D-histidine), homocarnosine, anserine, nor beta-alanine had the same effects as carnosine on human fibroblasts. Carnosine is an antioxidant, but it is more likely that it preserves cellular integrity by its effects on protein metabolism.

Carnosine↗

PubMed1994

Platelet-derived growth factor-BB stimulates synthesis of the integrin alpha 2-subunit in human diploid fibroblasts.

Platelet-derived growth factor (PDGF)-BB stimulates fibroblast-mediated contraction of collagen gels, as well as migration of fibroblasts through collagen-coated membranes. In the present study we examined effects of PDGF-BB stimulation on the synthesis of collagen-binding beta 1 integrins by human diploid fibroblasts (AG 1518). PDGF-BB stimulation led to an increase in the rare of integrin alpha 2-subunit synthesis. In contrast, synthesis of the integrin alpha 1- or alpha 3-subunits were not affected by PDGF-BB stimulation. Furthermore, levels of alpha 2-subunit mRNA relative to levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA increased after PDGF-BB stimulation. The latter finding is compatible with PDGF-BB stimulating transcription of the alpha 2-subunit gene. PDGF-BB stimulation did not influence the relation between levels of integrin beta 1-subunit mRNA and GAPDH mRNA. In addition, the rate of synthesis or post-translational processing of the integrin beta 1-subunit were not, or only marginally, affected by PDGF-BB stimulation. It is likely that the motility response elicited in fibroblasts by PDGF-BB involves such alterations in the synthesis of the alpha 2-subunit of the alpha 2 beta 1 collagen-binding integrin.

Becaplermin↗

PubMed1995

Overexpression of cyclin D1 blocks proliferation of normal diploid fibroblasts.

Human cyclin D1 forms complexes with several Cdks, with proliferating cell nuclear antigen, and with a recently discovered 21-kDa inhibitor of Cdk activity. Substrates for cyclin D1/Cdks have not been identified in vivo, but it has been proposed that the D class of cyclins might play a role in regulating the activity of the retinoblastoma gene product p105Rb. Here we report that normal human diploid fibroblasts that endogenously or ectopically express high levels of cyclin D1 are unable to enter S phase in response to normally mitogenic stimuli. Fibroblasts that have reached the end of their in vitro life span (senescent cells) express five-fold higher levels of cyclin D1 protein than low-passage cells and individual cells in mass culture that fail to initiate DNA synthesis in response to serum addition have severalfold higher levels of this cyclin than proliferation-competent cells. These observations provide evidence that cyclin D1 is involved with the regulation of cell proliferation by more than one mechanism.

Base Sequence↗

PubMed1995

The effect of low oxygen tension on the in vitro-replicative life span of human diploid fibroblast cells and their transformed derivatives.

Human diploid fibroblasts (HDF) IMR90, starting at various population doubling levels (PDL), were serially cultured under four different oxygen conditions; the conventional atmospheric 20% O2 condition and three lower oxygen conditions (1, 6, and 12% O2). All cultures from different PDLs showed that a longer replicative life span was achieved under the lower oxygen conditions. When the starting culture PDL was between 33 and 62, the increased life span rate was constant (average 22%) at 1% O2, but the rate decreased when the starting PDL was higher. The growth advantage under the 1% O2 condition was also observed in the very late passages of cultures to some extent, but terminal cultures with senescent cells were not stimulated by the low oxygen condition. When cultures at an extended PDL under the 1% O2 condition were shifted back to the 20% O2 condition, the cells rapidly senesced. HDF from a subject with Werner syndrome, a premature aging disease, which are known to have reduced replicative potential in vitro, also showed 43% increase in life span under the lowest oxygen conditions. When SV40 large T-transformed IMR90 cells at preimmortal stages were tested, no significant growth differences were observed under different oxygen conditions, and all the cultures died out at a similar PDL. These results suggest: (1) The atmospheric 20% oxygen tension hastens HDF senescence. (2) Young cells are more resistant to oxygen tension than old cells. (3) SV40 large T transformation abolishes the oxygen effect on cellular aging.

Cell Division↗

PubMed1995

Increased p53 protein associated with aging in human diploid fibroblasts.

Molecular changes associated with cellular aging in a strain of human diploid fibroblasts, IMR-90, were addressed by analyzing the expression of the tumor suppressor protein, p53. In all studies, IMR-90 cultures were characterized as "young" or "near-senescent" based on morphology, rate of population doubling, capacity for DNA synthesis, and presence of established markers for senescence. When p53 was immunoprecipitated by monoclonal antibodies and detected by Western immunoblot analysis, more protein per cell was detected in the near-senescent cultures. A greater than 10-fold increase in p53 protein was measured with the PAb 1801 (N-terminal-specific) anti-p53 antibody, whereas PAb 122 (C-terminal-specific) measured a 5-fold increase. Although near-senescent cultures demonstrated a higher level of p53 than young cells, these cultures had similar charges and molecular weight p53 isoforms when analyzed by two-dimensional Western blots. When p53 RNA was compared to total RNA there was a decrease in p53 RNA with age, but on a per cell basis p53 RNA was elevated. These results provide evidence for transcriptional regulation of p53 during aging and support the hypothesis that elevated levels of p53 protein may play a role in cellular senescence.

Cell Cycle↗

PubMed1996

Altered expression of the twist gene in young versus senescent human diploid fibroblasts.

We have recently reported the cloning and characterization of the human twist gene (H-twist), which encodes an evolutionarily conserved helix-loop-helix transcription factor. In several species, twist has been shown to play a role in mesoderm differentiation. We now report on the differential expression of H-twist as a function of in vitro life span in human diploid fibroblasts. H-twist was found to be expressed at a relatively high level in quiescent young cells. Addition of fresh serum to young G0 cultures results in a rapid repression of H-twist mRNA expression. This repression depends on the presence of growth factors, specifically EGF, and requires protein synthesis. mRNA stability studies using either actinomycin D or alpha-amanitin indicate a similar decay rate of H-twist mRNA in both young and senescent cells, suggesting that the differential expression of H-twist in young versus old is not primarily regulated at the level of mRNA turnover.

Cell Line↗

PubMed2001

Occurrence of a diploid type and a new first intermediate host of a human lung fluke, Paragonimus westermani, in Korea.

The biology, chromosome number, and karyotype of a lung fluke, Paragonimus westermani (Kerbert, 1878) collected in Haenam, Haenam-gun Chollanam-do, Korea were analyzed. We compared the size of metacercariae from Haenam with those taken from a crayfish collected at Youngam, Youngam-gun, Chollanam-do, Korea. The mean length of P. westermani metacercariae from Haenam was 300.3 microm and that from Youngam was 362.0 microm. Adult worms were recovered from the lungs of experimentally infected dogs. The mean egg sizes obtained from adult flukes were 72.1 x 46.8 microm from Haenam and 93.5 x 54.2 microm from Youngam. Semisulcospira tegulata collected in the Youngam area were found to be infected with cercariae of P. westermani, one of the snail-borne human lung fluke trematodes in Korea. Of 4218 snails studied, 5 (0.12%) harbored P. westrermani larvae. This is the first report of S. tegulata serving as the initial intermediate host of P. westermani. The chromosome numbers of P. westermani from Haenam and Youngam were 2n = 22 and 3n = 33. The diploid type of P. westermani has not been previously reported in Korea.

Animals↗

PubMed1998

Microscopic and Ultrastructural Examination of Vegetative Incompatibility in Partial Diploids Heterozygous at het Loci in Neurospora crassa

Vegetative (or heterokaryon) incompatibility is often characterized by cell death after anastomosis. In Neurospora crassa, partial diploid strains heterozygous for a single heterokaryon incompatibility (het) gene are viable, but grow at a significantly inhibited rate. Strains heterozygous for het-6 or het-c were examined microscopically for evidence of cell death; approximately 15% of cells randomly distributed within such colonies were dead or dying. Electron microscopy revealed extensive organelle degradation and plasmolysis. Ultimately, the cytoplasm fragmented into small membrane-bound bodies. Hyphal regrowth into dying cells from adjacent healthy cells was common. Ultrastructure and cell size measurements indicated no differences in death processes between incompatibility caused by het-6 and het-c. Linear growth rate was the only measured parameter which correlated with the observed macroscopic differences in colony morphology between het genes. The ultrastructural changes in dying cells were consistent with descriptions of apoptosis in plants and animals. However, designating vegetative incompatibility as apoptosis is premature without further study. Copyright 1998 Academic Press.

Journal Article↗

PubMed1996

CUMC-6, a new diploid human cell line derived from a squamous carcinoma of the uterine cervix.

A new cell line, CUMC-6, has been derived from an invasive nonkeratinizing squamous cell carcinoma of the uterine cervix in a 31-year-old patient. It has been maintained in long-term culture for 61 months, and passaged over 300 times. Monolayer-cultured cells were polygonal in shape, showing a pavement-like arrangement and a tendency to pile up without contact inhibition. The epithelial nature of the cultured CUMC-6 cells was confirmed by transmission electron microscopy which demonstrated the presence of desmosomes and tonofilaments. The subcutaneous injection of cultured cells into nude mice gave rise to fast-growing tumors. The transplanted tumor showed similar histological features, but poor differentiation compared to the original tumor. Cultured CUMC-6 cells produced human chorionic gonadotropin beta-subunit (beta-HCG) and alpha-fetoprotein (AFP). Cytosol estrogen and progesterone receptors were not measured in this cell line. The results of isozyme analyses were distinct from the HeLa cell line. Repeated chromosome analysis from passage 6 to 300 revealed that most metaphases of this cell line contained diploid number of chromosomes. The structural abnormality consistently observed in this cell line was the elongation of short arm of chromosome 1. The G- or R-banded pattern of this chromosome suggested inv dup (1) (1pter-->1p34[symbol: see text] 1p21-->1p34[symbol: see text] 1p34-->1qter). Human leukocyte antigen (HLA) typing of CUMC-6 cells indicated the presence of DR12 and DQw3. Analysis of the DNA extracted from the CUMC-6 cells showed the presence of human papillomavirus (HPV) type 16 and 18 DNAs. The results of oncogene analyses using Southern blotting technique revealed amplification and rearrangement of oncogene c-myc and no amplification of oncogene L-myc. Using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique, we have screened CUMC-6 cells for p53 mutation in exons 4 to 9. No mobility shift was observed in this cell line. These results suggest that chromosome 1 abnormality, oncogene alteration, and HPV infection work together in cervical tumorigenesis.

Animals↗

PubMed1993

An exact algebraic theory of genetic drift in finite diploid populations with random mating.

We study random mating in a finite diploid monoecious population with two alleles at one locus. We take into account selection and a constant probability of self-mating. The generations are assumed discrete (non-overlapping). An exact algebraic theory of genetic drift is developed by the technique of transition probability matrices. The theory works on the genotype level (Hedrick, 1970), but also allows the population size to vary from generation to generation. Thus, it gives an exact statistical description of bottleneck processes, as an inhomogeneous Markov chain. Numerical Monte Carlo simulations are performed and give full agreement with the present algebraic theory. The decay rates for heterozygosity agree with the asymptotic theory by Wright (1931).

Animals↗

PubMed1993

A note on the reduction of the dynamics of multilocus diploid genetic systems with multiplicative fitness.

The dynamics of any diploid multilocus genetic system with two alleles and uniform dynamics per locus can be deduced from that of the corresponding single-locus system by trinomial sampling to produce the frequencies of the different mutant classes, provided that fitness is multiplicative, and there is linkage equilibrium (allowing for physical linkage, however). The component processes that can be considered are mutation, gene conversion, gamete production (with recombination) and random mating, and selection. If mutations occur according to Bernoulli trials, outcrossing sexual systems have a genetic load exactly deducible from that of the single-locus system.

Animals↗

PubMed2000

Bridging the gap: human diploid cell strains and the origin of AIDS.

Recent descriptions of the first human and chimpanzee cases of human immunodeficiency virus type 1 (HIV-1)-related retroviral infections dating from 1959 have stirred interest in the origin of AIDS. Although the theory of a chimpanzee origin of HIV-1 with cross-species transfer to man has now gained popularity, a more likely scenario is that chimps and humans were infected by an HIV-1 precursor virus derived from a contaminated poliovaccine. The reason for the rapidity and ease of cross-species transfer of this precursor virus has not been elucidated. We hypothesize that the poliovaccine was passaged in a human diploid cell strain. This simple manipulation allowed the retrovirus to adapt to human tissues and may have spawned the AIDS pandemic.

Acquired Immunodeficiency Syndrome↗

PubMed2000

Fundamental theorem of natural selection and frequency-dependent selection: analysis of the matrix game diploid model.

Following Ewens' interpretation about Fisher's fundamental theorem of natural selection, the matrix game model for diploid populations undergoing non-overlapping, discrete generations is investigated. The total genetic variance is decomposed and it is shown that the partial change in the mean fitness, which is equal to the additive genetic variance over the mean fitness, can be thought of as a change due only to the partial changes in the phenotypic frequencies.

Animals↗

PubMed2000

Phylogeny, duplication, and intraspecific variation of Adh sequences in New World diploid cottons (Gossypium l., malvaceae).

The 13 "D-genome"cotton species are a monophyletic assemblage of morphologically diverse diploids that inhabit arid to semiarid regions in Mexico, with 1 disjunct species each in Peru and the Galapagos Islands and 1 species whose range extends northward into Arizona. While these species lack commercially significant fiber (i. e., cotton), they are important in that they represent one of the parental genomes of the cultivated tetraploid cottons. To assess phylogenetic relationships among these species, we sequenced and analyzed a region of a nuclear-encoded alcohol dehydrogenase gene (AdhA). Phylogenetic analysis resulted in a topology that is generally consistent with current taxonomic alignment of the species, although the phylogeny based on AdhA sequences conflicts with those inferred from cpDNA and ITS data sets, most notably in the position of the anomalous species Gossypium gossypioides. In one lineage, we detected both gene duplication and sequence polymorphisms that transcend species boundaries; sequences in this lineage formed a monophyletic clade, yet no taxon within the clade contained a monophyletic collection of sequences. Potential explanations for this latter phenomenon, including gene duplication, gene flow, and lineage sorting, are discussed.

Alcohol Dehydrogenase↗