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

BRAF(E600)-associated senescence-like cell cycle arrest of human naevi

Most normal mammalian cells have a finite lifespan(1), thought to constitute a protective mechanism against unlimited proliferation(2-4). This phenomenon, called senescence, is driven by telomere attrition, which triggers the induction of tumour suppressors including p16(INK4a) (ref. 5). In cultured cells, senescence can be elicited prematurely by oncogenes(6); however, whether such oncogene-induced senescence represents a physiological process has long been debated. Human naevi ( moles) are benign tumours of melanocytes that frequently harbour oncogenic mutations ( predominantly V600E, where valine is substituted for glutamic acid) in BRAF(7), a protein kinase and downstream effector of Ras. Nonetheless, naevi typically remain in a growth-arrested state for decades and only rarely progress into malignancy (melanoma)(8-10). This raises the question of whether naevi undergo BRAF(V600E)- induced senescence. Here we show that sustained BRAF(V600E) expression in human melanocytes induces cell cycle arrest, which is accompanied by the induction of both p16(INK4a) and senescence- associated acidic beta-galactosidase (SA-beta-Gal) activity, a commonly used senescence marker. Validating these results in vivo, congenital naevi are invariably positive for SA-beta-Gal, demonstrating the presence of this classical senescence-associated marker in a largely growth-arrested, neoplastic human lesion. In growth-arrested melanocytes, both in vitro and in situ, we observed a marked mosaic induction of p16(INK4a), suggesting that factors other than p16(INK4a) contribute to protection against BRAF(V600E)- driven proliferation. Naevi do not appear to suffer from telomere attrition, arguing in favour of an active oncogene-driven senescence process, rather than a loss of replicative potential. Thus, both in vitro and in vivo, BRAF(V600E)-expressing melanocytes display classical hallmarks of senescence, suggesting that oncogene-induced senescence represents a genuine protective physiological process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62941/1/nature03890.pd

Oncogene-Expressing Senescent Melanocytes Up-Regulate MHC Class II, a Candidate Melanoma Suppressor Function

Work in the lab of PDA was funded by CRUK program C10652/A16566, AI by Kay Kendall Leukemia Fund KKL1101, EM by the Medical research Council grants MR/K021095/1, MR/N023625/1

Retrofit Projects Through Pinch Technology

The pinch concept in heat recovery network design has become well-established in recent years. In ICI, the concept was reported to have saved an average of 30% on energy cost, coupled with capital cost savings in new plant designs. Payback times in retrofit applications were reported to be typically on the order of 12 months. Recent research has extended the concept for better consideration of capital cost trade-offs, of retrofit situations, and of changes to the chemical process itself. These new principles have been tried and tested in Union Carbide. Nine projects were completed within the first year, showing energy cost savings averaging 50% in new plant designs and payback times in retrofit applications typically on the order of six months or better. The paper explains the new concepts in outline and describes applications in Union Carbide. The applications are discussed in terms of technical features, economic benefits, and the 'technology transfer' task involved

Performance guarantees of jump neighborhoods on restricted related parallel machines

We study the performance of two popular jump neighborhoods on the classical scheduling problem of minimizing the makespan on related parallel machines under the additional restriction that jobs are only allowed to be scheduled on a subset of machines. In particular, we analyze the performance guarantee of local optima with respect to the jump and the lexicographical jump neighborhood

Local search performance guarantees for restricted related parallel machine scheduling

We consider the problem of minimizing the makespan on restricted related parallel machines. In restricted machine scheduling each job is only allowed to be scheduled on a subset of machines. We study the worst-case behavior of local search algorithms. In particular, we analyze the quality of local optima with respect to the jump, swap, push and lexicographical jump neighborhood