Lymphoblastoid lines and skin fibroblasts from patients with tuberous sclerosis are abnormally sensitive to ionizing radiation and to a radiomimetic chemical

mTOR inhibition attenuates chemosensitivity through the induction of chemotherapy resistant persisters

Chemotherapy can eradicate a majority of cancer cells. However, a small population of tumor cells often survives drug treatments through genetic and/or non-genetic mechanisms, leading to tumor recurrence. Here we report a reversible chemoresistance phenotype regulated by the mTOR pathway. Through a genome-wide CRISPR knockout library screen in pancreatic cancer cells treated with chemotherapeutic agents, we have identified the mTOR pathway as a prominent determinant of chemosensitivity. Pharmacological suppression of mTOR activity in cancer cells from diverse tissue origins leads to the persistence of a reversibly resistant population, which is otherwise eliminated by chemotherapeutic agents. Conversely, activation of the mTOR pathway increases chemosensitivity in vitro and in vivo and predicts better survival among various human cancers. Persister cells display a senescence phenotype. Inhibition of mTOR does not induce cellular senescence per se, but rather promotes the survival of senescent cells through regulation of autophagy and G2/M cell cycle arrest, as revealed by a small-molecule chemical library screen. Thus, mTOR plays a causal yet paradoxical role in regulating chemotherapeutic response; inhibition of the mTOR pathway, while suppressing tumor expansion, facilitates the development of a reversible drug-tolerant senescence state.

Radiobiological Characterization of Tuberous Sclerosis: a Delay in the Nucleo-Shuttling of ATM May Be Responsible for Radiosensitivity

The tuberous sclerosis complex (TSC) syndrome is associated with numerous cutaneous pathologies (notably on the face), epilepsy, intellectual disability and developmental retardation and, overall, high occurrence of benign tumors in several organs, like angiofibromas, giant cell astrocytomas, renal angiomyolipomas, and pulmonary lymphangioleiomyomatosis. TSC is caused by mutations of either of the hamartin or tuberin proteins that are mainly cytoplasmic. Some studies published in the 1980s reported that TSC is associated with radiosensitivity. However, its molecular basis in TSC cells is not documented enough. Here, we examined the functionality of the repair and signaling of radiation-induced DNA double-strand breaks (DSB) in fibroblasts derived from TSC patients. Quiescent TSC fibroblast cells elicited abnormally low rate of recognized DSB reflected by a low yield of nuclear foci formed by phosphorylated H2AX histones. Irradiated TSC cells also presented a delay in the nucleo-shuttling of the ATM kinase, potentially due to a specific binding of ATM to mutated TSC protein in cytoplasm. Lastly, TSC fibroblasts showed abnormally high MRE11 nuclease activity suggesting genomic instability. A combination of biphosphonates and statins complemented these impairments by facilitating the nucleoshuttling of ATM and increasing the yield of recognized DSB. Our results showed that TSC belongs to the group of syndromes associated with low but significant defect of DSB signaling and delay in the ATM nucleo-shuttling associated with radiosensitivity.

Cockayne syndrome and xeroderma pigmentosum

OBJECTIVES

To review genetic variants of Cockayne syndrome (CS) and xeroderma pigmentosum (XP), autosomal recessive disorders of DNA repair that affect the nervous system, and to illustrate them by the first case of xeroderma pigmentosum-Cockayne syndrome (XP-CS) complex to undergo neuropathologic examination.

METHODS

Published reports of clinical, pathologic, and molecular studies of CS, XP neurologic disease, and the XP-CS complex were reviewed, and a ninth case of XP-CS is summarized.

RESULTS

CS is a multisystem disorder that causes both profound growth failure of the soma and brain and progressive cachexia, retinal, cochlear, and neurologic degeneration, with a leukodystrophy and demyelinating neuropathy without an increase in cancer. XP presents as extreme photosensitivity of the skin and eyes with a 1000-fold increased frequency of cutaneous basal and squamous cell carcinomas and melanomas and a small increase in nervous system neoplasms. Some 20% of patients with XP incur progressive degeneration of previously normally developed neurons resulting in cortical, basal ganglia, cerebellar, and spinal atrophy, cochlear degeneration, and a mixed distal axonal neuropathy. Cultured cells from patients with CS or XP are hypersensitive to killing by ultraviolet (UV) radiation. Both CS and most XP cells have defective DNA nucleotide excision repair of actively transcribing genes; in addition, XP cells have defective repair of the global genome. There are two complementation groups in CS and seven in XP. Patients with the XP-CS complex fall into three XP complementation groups. Despite their XP genotype, six of nine individuals with the XP-CS complex, including the boy we followed up to his death at age 6, had the typical clinically and pathologically severe CS phenotype. Cultured skin and blood cells had extreme sensitivity to killing by UV radiation, DNA repair was severely deficient, post-UV unscheduled DNA synthesis was reduced to less than 5%, and post-UV plasmid mutation frequency was increased.

CONCLUSIONS

The paradoxical lack of parallelism of phenotype to genotype is unexplained in these disorders. Perhaps diverse mutations responsible for UV sensitivity and deficient DNA repair may also produce profound failure of brain and somatic growth, progressive cachexia and premature aging, and tissue-selective neurologic deterioration by their roles in regulation of transcription and repair of endogenous oxidative DNA damage.

Micronodular hyperplasia of type II pneumocytes--a new lung lesion associated with tuberous sclerosis

Open lung biopsy in a 38-year-old female with Pringle-Bourneville syndrome and recurrent pneumothorax revealed a micronodular pneumocyte II hyperplasia, a new entity probably associated with the tuberous sclerosis syndrome. The lesion caused an obstruction of the alveolar lymphatic vessels and alveolar ducts, resulting in an emphysema-like picture. This cystic dilation of alveoli and draining lymphatics followed by rupture caused the recurrent pneumothorax. The epithelial pneumocytic nature of the lesion was confirmed by immunohistochemistry and electronmicroscopy.

Bleomycin-induced chromosomal damage in tuberous sclerosis

To investigate the possible involvement of mutagen-induced chromosomal instability in tuberous sclerosis the blood lymphocytes obtained from eleven patients with this disease and eleven healthy controls of comparable age and sex were exposed to bleomycin in vitro during the late S and G2 phases of the cell cycle. Neither the spontaneous aberration yields nor the bleomycin-induced chromosomal sensitivity differed between the two groups. The chromosomal distribution of 578 and 478 induced breaks in patients and controls, respectively, was similar. Thus, bleomycin-induced G2 chromosomal hypersensitivity in lymphocytes of patients with tuberous sclerosis is not an intrinsic feature of this hereditary disease.

Cytogenetic studies in tuberous sclerosis

A cytogenetic study was performed with cultures derived from peripheral blood, unaffected skin, and angiofibromas of four patients suffering from the sporadic form of tuberous sclerosis (TSC). Increased frequencies of unstable chromosomal anomalies were found in lymphocytes and in fibroblasts from unaffected skin of the patients. The slight increase of the overall rate of unstable anomalies observed in angiofibroma-derived cultures above that of lymphocytes and skin fibroblasts, respectively, could almost entirely be attributed to a higher frequency of dicentric chromosomes. Of the 17 facial angiofibromas from which a total of 20 cell cultures were established, nine showed a normal karyotype, while eight exhibited stable chromosomal rearrangements, among which 19 clonal types could be identified. Unbalanced forms of various translocations caused partial trisomies of the long arms of chromosomes 1, 3, 7, 10, and 15. There was no clustering of breakpoints to a particular chromosomal region, nor was one particular chromosome preferentially involved. Frequencies and kinds of rearrangements varied between cultures derived from different angiofibromas from the same patient and between different culture charges from the same tumor. Tetraploidy was not generally more abundant in the angiofibroma-derived cultures, but there were a few culture charges with exceedingly high rates of tetraploid cells. The occurrence of premature centromere disjunction (PCD), either affecting all chromosomes or only part of them in angiofibroma-derived cultures, first described in TSC by Scappaticci et al. could be confirmed.

Sensitivity of cultured cells to gamma radiation in a patient exhibiting marked in vivo radiation sensitivity

An apparently normal 13-year-old girl developed multiple severe complications over several years after radiation therapy for Stage IIB Hodgkin's disease, including hypothyroidism, esophageal stenosis, restrictive lung and pericardial disease, extrahepatic biliary fibrosis, and sudden death presumed secondary to a myocardial infarction. Cultured skin fibroblast cells from the patient exhibited marked sensitivity to gamma radiation in vitro. The D0 of the radiation survival curve (the inverse of the straight line portion of the curve and that dose of radiation which theoretically leads to one lethal hit per cell) was 89 cGy, compared to a mean D0 for nine normal individuals of 155 cGy, and 85 cGy for two patients with the radiation sensitive disease ataxia-telangiectasia (AT). Profound clinical heterogeneity in response to cancer therapeutic agents may exist, with some individuals who show no signs or symptoms of DNA repair deficiency (for example, as is manifested by individuals with AT) exhibiting marked in vivo and in vitro sensitivity to certain DNA-damaging agents.

Chromosome abnormalities in tuberous sclerosis

In fibroblasts cultured from biopsies of the skin lesions of six patients with tuberous sclerosis (TS) there was a variable but consistent degree of karyotypic variation. Premature centromere disjunction (PCD) of all or part of the chromosomes, micronuclei, an increased incidence of breaks, dicentric chromosomes and the presence of polyploid metaphases were found in all cultures. The PCD was of the type encountered in Roberts syndrome and its frequency varied from 8% to 30%. In metaphases with PCD of one and of two chromosomes, the chromosome involved were identified, and chromosome 3 was involved 21 times among 59 chromosomes with PCD. Chromosome 3 tends to be preferentially involved in dicentric formation. In lymphocyte cultures from the same patients there were no metaphases with PCD, but there was a slight increase of breaks and the presence of dicentric chromosomes, also involving chromosome 3. Polyploid metaphases were increased in some of the cases. Karyotypic variation can be considered a cellular phenotypic characteristic of TS in fibroblasts cultured from the skin lesions, and its type indicates disturbances in the mechanics of centromere division and of chromosome distribution at cell division.

Enhancement of plasminogen activator activities by N-methyl-N'-nitro-N-nitrosoguanidine in tuberous sclerosis fibroblasts

The alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) enhanced the levels of plasminogen activator (PA) activity in fibroblast cells derived from the skin of patients with tuberous sclerosis. The enhanced enzyme levels were not correlated with those of cloning efficiency nor those of DNA synthesis after MNNG treatment. Enzyme enhancement was also observed in fibroblasts of ataxia telangiectasia and in human neoplastic glia cells, but not in fibroblasts of normal children. The PA induction test may be sufficiently sensitive for the detection of the cellular defects of tuberous sclerosis.

Patterns of crystallin expression during differentiation in vitro of several chick genotypes with different effects on lens cell growth rate

We have recently reported that chick lens cells during differentiation in long-term culture show a programme of change in crystallin expression which mimics events during lens development in vivo. The aim of the present work was to examine the stability of the programme by testing the response to genetic influences and exposure to a carcinogen. Five genetically distinct inbred strains of chick, differing in the intrinsic growth rates of lens epithelial cells in vitro, were used to study the effects of the rate of mitosis on crystallin expression, both during lens development and in long-term cell culture. The time of appearance of lentoids, their size and abundance and the rate of change in crystallin expression were all modified in a genotype-specific way, related to the rate of mitosis, but the programme of changes in crystallin expression was the same for all genotypes. Genetic differences were also found in the patterns of response to treatment of cultures during the logarithmic growth phase with a nitrosoguanidine compound known to affect cell differentiation in lens cultures and several other systems. The changes in crystallin expression and fibre differentiation were delayed, but cultures of the faster growing genotypes were least affected. With further culture, crystallin expression tended to recover to control values although levels of fibre differentiation and cell growth remained depressed. The results indicate that genetic differences in intrinsic growth rate moderate but do not change the programme of crystallin expression shown by lens epithelial cells in culture, and that this programme shows resistance to change.

Parkinson's disease and Alzheimer's disease: hypersensitivity to X rays in cultured cell lines

Fibroblast and/or lymphoblastoid lines from patients with several inherited primary neuronal degenerations are hypersensitive to DNA-damaging agents. Therefore, lymphoblastoid lines were irradiated from patients with sporadic Parkinson's disease (PD), Alzheimer's disease, and amyotrophic lateral sclerosis. The mean survival values of the eight Parkinson's disease and of the six Alzheimer's disease lines, but not of the five amyotrophic lateral sclerosis lines, were less than that of the 28 normal lines. Our results with Parkinson's disease and Alzheimer's disease cells can be explained by a genetic defect arising as a somatic mutation during embryogenesis, causing defective repair of the X-ray type of DNA damage. Such a DNA repair defect could cause an abnormal accumulation of spontaneously occurring DNA damage in Parkinson's disease and Alzheimer's disease neurons in vivo, resulting in their premature death.

Rapid rejoining of X-ray-induced DNA single-strand breaks in tuberous sclerosis fibroblasts

The formation and rejoining rates of X-ray-induced DNA single-strand breaks (SSBs) were examined in radiosensitive and non-radiosensitive fibroblast lines from patients with tuberous sclerosis (TS), and fibroblasts from normal individuals, using the sensitive and quantitative alkaline elution method. No difference was found between these cell lines in the frequency of DNA SSBs directly produced by X-irradiation at any dose up to 750 rad. Kinetic analysis of the rate of rejoining of DNA SSBs after X-irradiation at 500 rad indicated that the rate of rejoining involved at least two components, an initial fast component and a slower component. TS fibroblast lines, either radiosensitive or nonsensitive, were proficient as to DNA SSB repair, but they showed an increased rate of rejoining in the initial fast repair process, when compared to normal fibroblast lines. Although the molecular basis for the accelerated rejoining of DNA SSBs remains unknown, it is possible that the abnormality may be related to a basic defect in TS.

Hypersensitivity to ionizing radiation in cultured cells from Down syndrome patients

Down syndrome is caused by trisomy of chromosome 21 and is comprised of a constellation of abnormalities including neuropathological features that closely resemble those characterizing the neurodegeneration of Alzheimer disease. Because cultured cell lines from patients with Alzheimer disease and other neurodegenerations have a hypersensitivity to the lethal effects of DNA-damaging agents, we studied the response of Down syndrome lymphoblastoid lines to the lethal effects of ionizing and ultraviolet radiation. Lines from the four Down syndrome patients were more sensitive to X-rays than lines from 28 normal donors (P = 10(-4)), while survival of the Down syndrome lines after ultraviolet irradiation was not significantly different from normal. This hypersensitivity to X-rays, which may reflect defective repair of X-ray-induced DNA damage, represents the first abnormality common to cultured cells from both Down syndrome and Alzheimer disease patients.

Variable radiosensitivity in fibroblasts from patients with tuberous sclerosis

It has been reported that some of the cultured cell strains derived from patients with tuberous sclerosis (TS) showed hypersensitivity to gamma-rays or a radiomimetic chemical. Thirteen fibroblast cell strains from 11 patients with TS were examined for their sensitivity to x-rays as determined from their colony-forming ability. All strains derived from normal-appearing skin of patients, either sporadic or familial cases, showed sensitivity within the normal control range. Five cell strains originating from tumorous skin of 3 patients did not show hypersensitivity. It was concluded that the sensitivity to x-rays of cultured cells of TS is essentially normal. However, the mean D0 or D10 values of the strains from tumorous skin tended to be lower compared to those for normal skin of patients. In addition, we could confirm the hypersensitivity to x-rays in the cell strains of TS which had been shown to be hypersensitive to gamma-rays. These results appear to indicate that at least some of the cells of TS are liable to change to exhibit a hypersensitive trait in unknown acquired conditions.

Cell-culture studies on neurofibromatosis (von Recklinghausen's disease). III. Experiments on X-ray sensitivity

The X-ray sensitivity of strains of fibroblast-like cells derived from peripheral neurofibromas of ten patients with neurofibromatosis was compared with that of 12 strains of skin fibroblasts derived from healthy donors. Quantitative parameters of the dose-dependent reduction in colony-forming ability did not differ significantly between these two groups of strains. The cloning efficiencies of nonirradiated controls varied within the same range in strains derived from patients and from healthy donors.

Use of lymphoblastoid cell lines to evaluate the hypersensitivity to ultraviolet radiation in Cockayne syndrome

Cockayne syndrome (CS) is a rare autosomal recessive disease characterized by acute sun sensitivity, cachectic dwarfism, and neurologic and skeletal abnormalities. Cultured skin fibroblasts from patients with this disease are known to be hypersensitive to the lethal effects of 254-nm UV radiation. We have studied the sensitivity of 254-nm UV radiation of lymphoblastoid lines derived from 3 typical CS patients, 1 atypical CS patient who had a very late age of onset of clinical manifestations, 2 patients who had both xeroderma pigmentosum (XP) and typical CS, and 3 heterozygous parents of these patients. Post-UV survival was determined by the trypan-blue dye-exclusion method. The lymphoblastoid lines from the 3 typical CS patients, the atypical CS patient, and the 2 patients with both CS and XP had decreased post-UV viability in comparison with lines from normal donors. Lines from the heterozygous parents had normal post-UV viability. The post-UV viability of the typical CS lines was similar to that of a XP complementation group C line. The relative post-UV viability of lymphoblastoid lines from the typical CS patients was similar to the relative post-UV survival of their fibroblast lines. The lymphoblastoid line from the atypical CS patient had a post-UV viability similar to that of the typical CS patients. Thus, the relative hypersensitivity of CS patients' cells in vitro does not reflect the severity or age of onset of the patients' clinical manifestations. The lymphoblastoid lines from the 2 patients who had both CS and XP were significantly more sensitive to the UV radiation than those from patients with only CS. Our studies demonstrate that lymphoblastoid lines from patients with CS are appropriate and useful cell lines for the study of the inherited hypersensitivity to UV radiation.