AKT overactivation can suppress DNA repair via p70S6 kinase-dependent downregulation of MRE11

Deregulated AKT kinase activity due to PTEN deficiency in cancer cells contributes to oncogenesis by incompletely understood mechanisms. Here, we show that PTEN deletion in HCT116 and DLD1 colon carcinoma cells leads to suppression of CHK1 and CHK2 activation in response to irradiation, impaired G2 checkpoint proficiency and radiosensitization. These defects are associated with reduced expression of MRE11, RAD50 and NBS1, components of the apical MRE11/RAD50/NBS1 (MRN) DNA damage response complex. Consistent with reduced MRN complex function, PTEN-deficient cells fail to resect DNA double-strand breaks efficiently after irradiation and show greatly diminished proficiency for DNA repair via the error-free homologous recombination (HR) repair pathway. MRE11 is highly unstable in PTEN-deficient cells but stability can be significantly restored by inhibiting mTORC1 or p70S6 kinase (p70S6K), downstream kinases whose activities are stimulated by AKT, or by mutating a residue in MRE11 that we show is phosphorylated by p70S6K in vitro. In primary human fibroblasts, activated AKT suppresses MRN complex expression to escalate RAS-induced DNA damage and thereby reinforce oncogene-induced senescence. Taken together, our data demonstrate that deregulation of the PI3K-AKT/ mTORC1/ p70S6K pathways, an event frequently observed in cancer, exert profound effects on genome stability via MRE11 with potential implications for tumour initiation and therapy

Liver function disturbances in Guillain-Barre syndrome:A prospective longitudinal study in 100 patients

In 100 consecutive patients with Guillain-Barre syndrome, we assessed liver function on admission and at fixed intervals after either intravenous immunoglobulin (IgIV) or plasma-exchange (PE) treatment. On admission, 38% showed a plasma alanine aminotransferase elevation, gamma glutamyl transferase elevation, or both of more than 1.5 times the upper limit of normal. Ten of these patients had serologic evidence of recent cytomegalovirus infection. The remaining 28 patients were negative for other known causes of liver damage, including infection with Epstein-Barr virus or hepatitis A, B, and C; alcohol abuse; hepatotoxic drugs; recent surgery; and concurrent liver disease. In a hospital control group of 100 consecutive patients with subarachnoid hemorrhage, only 5 had unexplained liver function disturbances on admission (p <0.0001). In the IgIV-treated group, the percentage of patients with elevated liver function tests increased from 35% before to 69% shortly after treatment at 2 weeks postadmission (p <0.005). In the PE-treated group, this percentage decreased somewhat from 41% to 36% (not significant). There was also a significant rise in median plasma activity of the various liver enzymes in the IgIV group. At 1 month, however, significant difference had disappeared. At 3 and 6 months, the percentage of patients with liver function disturbances reached a significantly lower level in both treatment groups compared with the time of admission. We concluded that many patients with Guillain-Barre syndrome had mild liver function disturbances without obvious cause. In addition, IgIV treatment was associated with mild transient liver function disturbances through an unknown mechanism

Liver function disturbances in Guillain-Barre syndrome: A prospective longitudinal study in 100 patients

In 100 consecutive patients with Guillain-Barre syndrome, we assessed liver function on admission and at fixed intervals after either intravenous immunoglobulin (IgIV) or plasma-exchange (PE) treatment. On admission, 38% showed a plasma alanine aminotransferase elevation, gamma glutamyl transferase elevation, or both of more than 1.5 times the upper limit of normal. Ten of these patients had serologic evidence of recent cytomegalovirus infection. The remaining 28 patients were negative for other known causes of liver damage, including infection with Epstein-Barr virus or hepatitis A, B, and C; alcohol abuse; hepatotoxic drugs; recent surgery; and concurrent liver disease. In a hospital control group of 100 consecutive patients with subarachnoid hemorrhage, only 5 had unexplained liver function disturbances on admission (p <0.0001). In the IgIV-treated group, the percentage of patients with elevated liver function tests increased from 35% before to 69% shortly after treatment at 2 weeks postadmission (p <0.005). In the PE-treated group, this percentage decreased somewhat from 41% to 36% (not significant). There was also a significant rise in median plasma activity of the various liver enzymes in the IgIV group. At 1 month, however, significant difference had disappeared. At 3 and 6 months, the percentage of patients with liver function disturbances reached a significantly lower level in both treatment groups compared with the time of admission. We concluded that many patients with Guillain-Barre syndrome had mild liver function disturbances without obvious cause. In addition, IgIV treatment was associated with mild transient liver function disturbances through an unknown mechanism