Altered sensitivity of protein synthesis to paromomycin in extracts from aging human diploid fibroblasts

Age-related differences in the effects of paromomycin (Pm) on protein synthesis have been investigated in translation reactions with extracts derived from young and old human diploid fibroblasts. Translation products from reactions directed by endogenous or exogenous mRNA were analyzed by polyacrylamide gel electrophoresis and fluorography. The exogenous mRNA lacked codons for cysteine, and therefore cysteine incorporation into translation products represented translational error. This laboratory has previously used this assay to show that the basal translational error level in the absence of Pm increases in extracts from old fibroblasts. In this report, Pm stimulated the misincorporation of cysteine by 6-7 fold over cysteine misincorporation levels in the absence of Pm. This degree of Pm stimulation was similar in extracts from young and old fibroblasts. However, other results showed quantitative differences in the responses to Pm between young and old cell extracts. Old cell extracts were less sensitive to the stimulation of the rate of protein synthesis, and more sensitive to the inhibition of protein synthesis, by Pm. It is proposed that aging human diploid fibroblasts contain altered ribosomes which react differently with Pm.     

Secondary metabolic changes in fibroblasts from six patients with hereditary lactic acidosis

Studies on fibroblasts from patients with lactic acidosis of different causes showed secondary metabolic changes in pathways of glucose metabolism. These secondary changes may be important clues to the diagnosis of the many different types of hereditary lactic acidosis.     

Comparative use of glucose and fructose in cultured fibroblasts from patients with hereditary fructose intolerance

The utilization of fructose and glucose by fibroblast cultures obtained from patients with hereditary fructose intolerance (HFI) was studied in comparison with fibroblast controls. The cell growth, the time course ofd-glucose ord-fructose uptake and the consumption of fructose were similar for both HFI and control cells. Some results showed significant differences between these two cell types: HFI cells consumed less glucose, produced less lactate and contained less glycogen than control cells. Furthermore, significantly less [U-¹⁴C]d-glucose and [U-¹⁴C]d-fructose was incorporated into lipids in HFI cells than in control cells. The mechanisms responsible for these differences observed between the two cell types are not known.     

Human lysosomes can be purified from diploid skin fibroblasts by free-flow electrophoresis.

Human diploid fibroblasts underwent lysis when resuspended in isotonic sucrose. After preparation of a granular fraction by differential centrifugation, lysosomes were almost completely purified by free-flow electrophoresis. Electron micrographs of the final fraction of fibroblast lysosomes (about 25-fold purified) showed mostly secondary lysosomes having an appearance identical to those in intact cells. There was no indication that the purification steps selectd for any lysosomal subpopulation. The lysomal nature of the isolated organelles was confirmed by cytochemical staining for acid beta-glycerophosphatase. As judged by a 92% structure-linked latency of beta-N-acetylglucosaminidase in the final fraction, the structural integrity of the isolated lysosomes was unaffected by the purification procedure.     

Marrow fibroblasts from patients with myeloproliferative disorders show increased sensitivity to human serum mitogens

The growth of marrow fibroblasts from patients with myeloproliferative disorders (MPD) was investigated using platelet derived growth factor (PDGF) and human serum as mitogens in the presence of human plasma derived serum. The proliferation of fibroblasts in MPD patients was increased compared to normal individuals, especially in patients with chronic myelocytic leukaemia and essential thrombocythaemia. This increment of proliferation might be due to higher sensitivity of the fibroblasts to plasma derived serum than to PDGF, because the ratio of proliferation with PDGF to that without PDGF, when compared between patients and normals, remained unchanged. These results suggest that MPD fibroblasts are more sensitive to some factor(s) in plasma, and this fact could partially explain the pathogenesis of myelofibrosis in MPD patients.     

Normal glycine transport in cultured diploid fibroblasts from hyperglycinaemic subjects

The glycine uptake in cultured fibroblasts was studied in three children with non-ketotic hyperglycinaemia, one child with D-glyceric acidaemia and hyperglycinaemia and in six normal children, using an improved assay system giving individual protein correction. It was shown that all hyperglycinaemic children had normal uptake rates and kinetic characteristics similar to the controls.     

Oncogene v-src transforms and establishes embryonic rodent fibroblasts but not diploid human fibroblasts.

The conversion of cells from a normal phenotype to full malignancy apparently requires multiple genetic events. Efforts to reconstruct multistep tumorigenesis in cell culture have shown that two types of oncogenes (typified by HRAS and MYC) can cooperate to elicit complete transformation. Transformation of embryonic rodent cells by single oncogenes is reputed either not to occur or to require specialized circumstances. It has not been known how the large group of oncogenes that encode protein-tyrosine kinases might fit into this scheme. We now report that v-src, a prototype for the kinase oncogenes, can convert rat embryo fibroblasts to a fully transformed and tumorigenic phenotype when the gene is expressed vigorously. By contrast, v-src had no demonstrable effect on diploid human fibroblasts. Our results sustain the view that it is possible for at least some oncogenes to achieve a potency sufficient for unilateral tumorigenesis.     

Radiographic features of hereditary articular chondrocalcinosis. A comparative study with the sporadic type

To assess the radiological features of hereditary articular chondrocalcinosis, we performed a blind comparative study between 21 randomly selected patients with hereditary disease and 21 cases of sporadic pseudogout matched for age and sex. Each individual had AP projections of the hands, pelvis and knees. The films were evaluated for the presence of articular chondrocalcinosis and for the severity of the associated degenerative arthropathy. A grade of 0 to 3+ was assigned to each of the 4 variables of osteoarthritis: joint space narrowing, sclerosis, osteophytosis and subchondral cysts. The mean number of joints with chondrocalcinosis and its distribution was similar in both groups. In addition, no differences were found in the overall severity of the associated degenerative arthropathy. In both groups the disease was characterized by oligoarticular calcification and a mild degenerative arthropathy. These data along with data from other reported pedigrees, show that the radiological appearance in the hereditary type is frequently indistinguishable from that commonly observed in sporadic articular chondrocalcinosis.     

Altered insulin binding to monocytes and diploid fibroblasts from obese donors

Insulin binding was studied in fibroblasts and monocytes from nondiabetic subjects with a range of body mass indices (BMI). Binding was compared in fibroblasts from extremely obese subjects and normal weight subjects. The [125I] insulin displacement curve for the obese subjects was shifted to the right. Scatchard analysis suggested that cells from the obese group have an increased number of receptors with decreased affinity. Significant correlations were observed between the cell donor's BMI and the concentration of insulin required to inhibit half of the [125I]insulin specifically bound to fibroblasts (r = 0.8; P less than 0.005), the high affinity dissociation constant (r = 0.8; P less than 0.005), and the number of receptors (r = 0.6; P less than 0.05). Insulin binding to monocytes was measured for nondiabetic Pima Indian subjects with a range of BMI values. Scatchard analysis of the data indicated that the high affinity dissociation constant was positively correlated with BMI (r = 0.6; P less than 0.02). The number of receptors was also positively correlated with BMI (r = 0.6; P less than 0.05). The observation that both cultured cells and monocytes exhibit changes in insulin binding that correlate with the obesity of the cell source suggests that the insulin resistance of obesity may be partially a reflection of genetic differences at the site of the insulin receptor.     

Growth-regulated expression of D-type cyclin genes in human diploid fibroblasts.

The human CCND1 cyclin D1/PRAD1 gene was previously identified by a genetic screen for G1 cyclin function in Saccharomyces cerevisiae and also was identified as the putative BCL1 oncogene. However, its role in human cell proliferation is not known. To determine if expression of human D-type cyclin genes correlates with the state of cell growth, we examined the level of mRNAs for CCND1 and a related gene, CCND3, in normal human diploid fibroblasts (HDF). The levels of both mRNAs decrease upon serum depletion or at high cell densities. Following stimulation of quiescent fibroblasts with serum, the mRNA levels increase gradually to a peak at about 12 hr, prior to the onset of S phase. Induction of cyclin gene expression by serum is reduced concomitantly with the decline in FOS induction in aging HDFs, suggesting a possible relationship to the decrease in the proliferative response to mitogens during cellular senescence. Cycloheximide partially blocks the induction of CCND1 and CCND3 gene expression by serum, suggesting that both de novo protein synthesis-dependent and -independent pathways contribute to induction. Treatment of HDFs with defined growth factors suggests a correlation between CCND mRNA induction and DNA synthesis. However, induction of these genes is not sufficient for the transition from quiescence through G1 into S phase.     

Decreased accuracy of protein synthesis in extracts from aging human diploid fibroblasts

The accuracy of protein synthesis has been measured in extracts from human diploid fibroblasts of different ages. Extracts were supplied with purified mRNA for the coat protein of the cowpea variant of tobacco mosaic virus (CcTMV), which lacks codons for cysteine and methionine. The presence of 35S-cysteine in CcTMV coat protein synthesized during translation reactions therefore represents translational error. Translation reactions were performed with extracts from young fibroblasts (less than 50% of life span completed) and old fibroblasts (more than 90% of life span completed), and the translation products were purified by immunoprecipitation and analyzed by polyacrylamide gel electrophoresis. The error frequency increased from 4.2 x 10(-5) cysteines/amino acid in young cell extracts to 2.9 x 10(-4) cysteines/amino acid in old cell extracts. Cysteine incorporation was not due to nonspecific binding, and could be increased approximately sixfold by the addition of the misreading antibiotic, paromomycin. It is concluded that translational accuracy is not stable during aging in vitro, and it is proposed that this decrease in the fidelity of information transfer could be responsible for the variety of changes observed in aging cultured human cells.     

Nonhomologous chromatid exchange in hereditary and sporadic renal cell carcinomas.

For the development of renal cell carcinomas, it has been suggested that a germ-line or somatic mutation occurs on one of the homologous chromosomes 3p, and subsequently the other 3p segment is lost. We have examined the karyotype and/or the allelic combination on chromosomes 3 and 5 by restriction fragment length polymorphism analysis in normal kidney and tumor samples from 28 renal cell carcinomas that developed in two patients with von Hippel-Lindau disease; we then compared the results to those of sporadic tumors. An unbalanced translocation between chromosome 3p and 5q or other chromosomes was found to be the most common aberration. We developed a model of nonhomologous chromatid exchange involving breakpoint clusters at chromosomes 3p13, 3p11.2, 5q22, and 8q11.2. Subsequent chromatid segregation may result in net loss of the 3p segment either (i) in one step or (ii) after a nondisjunctional loss of the derivative chromosome carrying the 3p segment. This general mechanism could also be implicated to explain genetic changes occurring in other types of solid tumors.     

Microphotometric analysis of NADH-tetrazolium reductase deficiency in fibroblasts of patients with Leber hereditary optic neuropathy

We employed a microphotometric approach to examine whether a defect in the mitochondrial respiratory complex I expected in Leber hereditary optic neuropathy (LHON) as the consequence of a mtDNA (11778G>A) mutation in the ND4 gene coding for a subunit of the respiratory complex I can be detected at the single-cell level. Genetically stable fibroblast cell lines were established from skin biopsies of two members of a Chinese Indonesian family with LHON. The fibroblasts were homoplasmic for the 11778G>A mutation. The activity of the respiratory complex I was examined histochemically by staining for NADH-tetrazolium reductase. The histochemical staining showed a typical pattern with an apparent concentration of the activity around the nucleus, suggested as the reflection of the gradient in the thickness of the unsectioned fibroblast cells. Microphotometric quantification of the staining intensity showed that the activity is linear for at least 60min. The activity shows a discontinuity in its Arrhenius kinetics with a break point at 13.0–13.5°C (activation energy at 50–58 J/mol and 209–238 J/mol above and below the break temperature, respectively), indicating the membrane association of the NADH-tetrazolium reductase activity. Both patients showed lower fibroblast NADH-tetrazolium reductase activity, with a reduction of 30%. Our results demonstrate the utility of microphotometric analysis in the study of biochemical defects associated with mutations in the mtDNA.     

Growth of human diploid fibroblasts in the absence of glucose utilization.

Normal human diploid fibroblasts were able to undergo one to two cell divisions without glucose utilization in Eagle's minimum essential medium plus 10% dialyzed fetal calf serum if the medium was supplemented with hypoxanthine, thymidine, and uridine (supplemented medium termed HTU-MEM). Under these conditions, the added purine and pyrimidines were required for nucleic acid synthesis, as shown by the inability of Lesch-Nyhan fibroblasts to grow in HTU-MEM. Normal human diploid fibroblasts continued to produce lactate in HTU-MEM, but at a greatly reduced rate. Since cells grew in HTU-MEM without glucose utilization, the probable energy and carbon source was glutamine, which is present in relatively high concentration. Furthermore, the rate of glutamine utilization per cell division was 2-fold greater in HTU-MEM than in medium with 5.5 mM glucose. These results suggest that glutamine can be a major energy source for cells grown in vitro.     

Reduced ferrochelatase activity in fibroblasts from patients with porphyria variegata.

Ferrochelatase deficiency has been shown in both porphyria variegata (PV) and erythropoietic protoporphyria (EPP). It has been suggested that in PV there is a decrease in the enzyme, whereas in EPP the enzyme is unstable. In the present study ferrochelatase activity was measured in skin fibroblasts from three patients with PV and three normal subjects. The enzymatic activity in the patients with PV (17.5 +/- 4.5 pmoles heme formed per 10(7) fibroblasts per hour) was 50% of that of the control group (31.0 +/- 3.2 pmoles heme formed per 10(7) fibroblasts per hour). This supports the contention that the enzyme is deficient in PV and that an inactive ferrochelatase is the primary deficiency in this type of porphyria.     

Molecular mechanisms of oncogenic mutations in tumors from patients with bilateral and unilateral retinoblastoma.

The RB1 gene from 12 human retinoblastoma tumors has been analyzed exon-by-exon with the single-strand conformation polymorphism technique. Mutations were found in all tumors, and one-third of the tumors had independent mutations in both alleles neither of which were found in the germ line, confirming their true sporadic nature. In the remaining two-thirds of the tumors only one mutation was found, consistent with the loss-of-heterozygosity theory of tumorigenesis. Point mutations, the majority of which were C-->T transitions, were the most common abnormality and usually resulted in the conversion of an arginine codon to a stop codon. Small deletions were the second most common abnormality and most often created a downstream stop codon as the result of a reading frameshift. Deletions and point mutations also affected splice junctions. Direct repeats were present at the breakpoint junctions in the majority of deletions, supporting a slipped-mispairing mechanism. Point mutations generally produced DNA sequences which resulted in perfect homology with endogenous sequences which lay within 14 bp.     

Refractory nature of normal human diploid fibroblasts with respect to oncogene-mediated transformation

Human cells are known to be more refractory than rodent cells against oncogenic transformation in vitro. To date, the molecular mechanisms underlying such resistance remain largely unknown. The combination of simian virus 40 early region and H-Ras V12 has been effective for transformation of rat embryo fibroblasts, but not for human cells. However, the additional ectopic expression of the telomerase catalytic subunit (hTERT) was reported to be capable of causing transformation of normal human cells. In this study, however, we demonstrate that the combined expression of the above-mentioned three genetic elements is not always sufficient to transform normal human diploid fibroblasts (HDF). Although the expression and function of these introduced genetic elements were essentially the same, among four HDF, TIG-1 and TIG-3 were resistant to transformation. The other two (BJ and IMR-90) showed transformed phenotypes, but they were much restricted compared with rat embryo fibroblasts in expressing simian virus 40 early region and H-Ras V12. In correlation with these phenotypes, TIG-1 and TIG-3 remained diploid after the introduction of these genetic elements, whereas BJ and IMR-90 became highly aneuploid. These results strongly suggest that the lack of telomerase is not the sole reason for the refractory nature of HDF against transformation and that normal human cells have still undefined intrinsic mechanisms rendering them resistant to oncogenic transformation.