Defective potassium currents in ataxia telangiectasia fibroblasts

Similarities exist between the progressive cerebellar ataxia in ataxia telangiectasia (AT) patients and a number of neurodegenerative diseases in both mouse and man involving specific mutations in ion channels and/or ion channel activity. These relationships led us to investigate the possibility of defective ion channel activity in AT cells. We examined changes in the membrane potential of AT fibroblasts in response to extracellular cation addition and found that the ability of AT fibroblasts to depolarize in response to increasing concentrations of extracellular K⁺ is significantly reduced when compared with control fibroblasts. Electrophysiological measurements performed with a number of AT cell lines, as well as two matched sets of primary AT fibroblast cultures, reveal that outward rectifier K⁺ currents are largely absent in AT fibroblasts in comparison with control cells. These K⁺ current defects can be corrected in AT fibroblasts transfected with the full-length ATM cDNA. These data implicate, for the first time, a role for ATM in the regulation of K⁺ channel activity and membrane potential.     

Phosphorylation of SMC1 is a critical downstream event in the ATM-NBS1-BRCA1 pathway

The ATM protein kinase is activated by intermolecular autophosphorylation in response to DNA damage and initiates cellular signaling pathways that facilitate cell survival and reduce chromosomal breakage. Here, we show that NBS1 and BRCA1 are required for the recruitment of previously activated ATM to the sites of DNA breaks after ionizing irradiation, and that this recruitment is required for the phosphorylation of SMC1 by ATM. To explore the functional importance of SMC1 phosphorylation, murine cells were generated, in which the two damage-induced phosphorylation sites in SMC1 are mutated. Although these cells demonstrate normal phosphorylation and focus formation of ATM, NBS1, and BRCA1 proteins after IR, they exhibit a defective S-phase checkpoint, decreased survival, and increased chromosomal aberrations after DNA damage. These observations suggest that many of the abnormal stress responses seen in cells lacking ATM, NBS1, or BRCA1 result from a failure of ATM migration to sites of DNA breaks and a resultant lack of SMC1 phosphorylation.     

Cytoprotective effects of hematopoietic growth factors on primary human acute myeloid leukemias are not mediated through changes in BCL-2, bax, or p21WAF1/CIP1

BACKGROUND: Hematopoietic growth factors (HGF) can suppress chemotherapy-induced programmed cell death (apoptosis) in hematopoietic cells. Although HGF can modulate the expression of apoptosis-regulatory genes, including bcl-2, bax, and p21WAF1/CIP1 in cell lines, few data address whether HGF regulate the expression of these proteins in primary acute myeloid leukemia (AML). MATERIALS AND METHODS: We evaluated the expression of bcl-2, bax, and p21WAF1/CIP1 in primary samples from patients with AML in the presence and absence of HGF. The potential association of HGF-induced changes in the levels of these proteins with inhibition of chemotherapy-induced apoptosis was further investigated. RESULTS: While a combination of steel factor (SF) and PIXY321 inhibited etoposide-induced apoptosis in 8/11 primary AML samples studied, Bcl-2 and bax protein levels were unaffected by exposure to HGF and/or etoposide. In contrast, HGF enhanced basal and etoposide-induced p21WAF1/CIP1 protein levels in 9/11 and 7/11 of the cases, respectively. In several cases, inhibition of apoptosis by HGF was seen without up-regulation of p21WAF1/CIP1 levels, suggesting that modulation of p21WAF1/CIP1 is not required for HGF-mediated inhibition of apoptosis. CONCLUSIONS: These data indicate that HGF-mediated inhibition of chemotherapy-induced apoptosis in primary AML samples is not mediated through changes in Bcl-2, bax, and p21WAF1/CIP1 protein levels.     

Human papillomavirus 16 E6 expression disrupts the p53-mediated cellular response to DNA damage.

Infection with certain types of human papillomaviruses (HPV) is highly associated with carcinomas of the human uterine cervix. However, HPV infection alone does not appear to be sufficient for the process of malignant transformation, suggesting the requirement of additional cellular events. After DNA damage, normal mammalian cells exhibit G1 cell-cycle arrest and inhibition of replicative DNA synthesis. This mechanism, which requires wild-type p53, presumably allows cells to undertake DNA repair and avoid the fixation of mutations. We directly tested whether the normal response of cervical epithelial cells to DNA damage may be undermined by interactions between the E6 protein expressed by oncogenic HPV types and wild-type p53. We treated primary keratinocytes with the DNA-damaging agent actinomycin D and demonstrated inhibition of replicative DNA synthesis and a significant increase in p53 protein levels. In contrast, inhibition of DNA synthesis and increases in p53 protein did not occur after actinomycin D treatment of keratinocytes immortalized with HPV16 E6/E7 or in cervical carcinoma cell lines containing HPV16, HPV18, or mutant p53 alone. To test the effects of E6 alone on the cellular response to DNA damage, HPV16 E6 was expressed in the carcinoma cell line RKO, resulting in undetectable baseline levels of p53 protein and loss of the G1 arrest that normally occurs in these cells after DNA damage. These findings demonstrate that oncogenic E6 can disrupt an important cellular response to DNA damage mediated by p53 and may contribute to the subsequent accumulation of genetic changes associated with cervical tumorigenesis.     

Mitochondrial dysfunction in ataxia-telangiectasia

Ataxia-telangiectasia mutated (ATM) plays a central role in DNA damage responses, and its loss leads to development of T-cell malignancies. Here, we show that ATM loss also leads to intrinsic mitochondrial abnormalities in thymocytes, including elevated reactive oxygen species, increased aberrant mitochondria, high cellular respiratory capacity, and decreased mitophagy. A fraction of ATM protein is localized in mitochondria, and it is rapidly activated by mitochondrial dysfunction. Unexpectedly, allelic loss of the autophagy regulator Beclin-1 significantly delayed tumor development in ATM-null mice. This effect was not associated with rescue of DNA damage signaling but rather with a significant reversal of the mitochondrial abnormalities. These data support a model in which ATM plays direct roles in modulating mitochondrial homeostasis and suggest that mitochondrial dysfunction and associated increases in mitochondrial reactive oxygen species contribute to the cancer-prone phenotype observed in organisms lacking ATM. Thus, ataxia-telangiectasia should be considered, at least in part, as a mitochondrial disease.     

Digital radiography of the gastrointestinal tract

The gastrointestinal tract lends itself quite well to digital imaging. Since fluoroscopy is already employed, the images can easily be obtained in digital format and several manufacturers have now developed systems for commercial use. Because of the type of pathology as well as the inherent subject contrast, it would appear the resolution requirements for digital imaging of the gastrointestinal tract are less than in other organ systems. The necessary resolution level is already technically available and feasible without significant cost. Digital imaging also holds promise of at least a modest reduction in radiation dose to the patient, as well as a reduction in costs, although these factors are operator dependent. However, digital imaging provides a latitude in performing the examination that is not available with screenfilm systems. Finally, there is promise that by acquiring gastrointestinal images in digital format, manipulation of the images may help increase diagnostic accuracy by improving both technical and perceptive components of diagnosis. Not only will simple image manipulation be helpful but there is even potential for computer-assisted evaluation of gastrointestinal images.     

Involvement of the cohesin protein, Smc1, in Atm-dependent and independent responses to DNA damage

Structural maintenance of chromosomes (SMC) proteins play important roles in sister chromatid cohesion, chromosome condensation, sex-chromosome dosage compensation, and DNA recombination and repair. Protein complexes containing heterodimers of the Smc1 and Smc3 proteins have been implicated specifically in both sister chromatid cohesion and DNA recombination. Here, we show that the protein kinase, Atm, which belongs to a family of phosphatidylinositol 3-kinases that regulate cell cycle checkpoints and DNA recombination and repair, phosphorylates Smc1 protein after ionizing irradiation. Atm phosphorylates Smc1 on serines 957 and 966 in vitro and in vivo, and expression of an Smc1 protein mutated at these phosphorylation sites abrogates the ionizing irradiation-induced S phase cell cycle checkpoint. Optimal phosphorylation of these sites in Smc1 after ionizing irradiation also requires the presence of the Atm substrates Nbs1 and Brca1. These same sites in Smc1 are phosphorylated after treatment with UV irradiation or hydroxyurea in an Atm-independent manner, thus demonstrating that another kinase must be involved in responses to these cellular stresses. Yeast containing hypomorphic mutations in SMC1 and human cells overexpressing Smc1 mutated at both of these phosphorylation sites exhibit decreased survival following ionizing irradiation. These results demonstrate that Smc1 participates in cellular responses to DNA damage and link Smc1 to the Atm signal transduction pathway.     

Ueber einige allgemein als familiär bekannte Nervenkrankheiten

Ohne ZusammenfassungDie neueste, während der Korrektur erschienene Literatur, z. B. Scharnke, Ueber myotone Dystrophie", konnte nicht mehr berücksichtigt werden.     

Ueber die Beziehungen von Hirnrindenschädigung und Erhöhung der Krampfprädisposition

Ohne Zusammenfassung

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