The aggregation of mutant p53 produces prion-like properties in cancer

The tumor suppressor protein p53 loses its function in more than 50% of human malignant tumors. Recent studies have suggested that mutant p53 can form aggregates that are related to loss-of-function effects, negative dominance and gain-of-function effects and cancers with a worsened prognosis. In recent years, several degenerative diseases have been shown to have prion-like properties similar to mammalian prion proteins (PrPs). However, whereas prion diseases are rare, the incidence of these neurodegenerative pathologies is high. Malignant tumors involving mutated forms of the tumor suppressor p53 protein seem to have similar substrata. The aggregation of the entire p53 protein and three functional domains of p53 into amyloid oligomers and fibrils has been demonstrated. Amyloid aggregates of mutant p53 have been detected in breast cancer and malignant skin tumors. Most p53 mutations related to cancer development are found in the DNA-binding domain (p53C), which has been experimentally shown to form amyloid oligomers and fibrils. Several computation programs have corroborated the predicted propensity of p53C to form aggregates, and some of these programs suggest that p53C is more likely to form aggregates than the globular domain of PrP. Overall, studies imply that mutant p53 exerts a dominant-negative regulatory effect on wild-type (WT) p53 and exerts gain-of-function effects when co-aggregating with other proteins such as p63, p73 and acetyltransferase p300. We review here the prion-like behavior of oncogenic p53 mutants that provides an explanation for their dominant-negative and gain-of-function properties and for the high metastatic potential of cancers bearing p53 mutations. The inhibition of the aggregation of p53 into oligomeric and fibrillar amyloids appears to be a promising target for therapeutic intervention in malignant tumor diseases.     

Progress in understanding the <Emphasis Type="Italic">N-</Emphasis>demethylation of alkaloids by exploiting isotopic techniques

The reaction of N-demethylation plays an important role in the degradation of some alkaloids in a number of organisms. This review presents how our understanding of the N-demethylation of nicotine in plants has been improved through studies in cell cultures of Nicotiana plumbaginifolia and N. glutinosa using a variety of isotopic techniques. The overall aim is to understand how metabolism recycles the alkaloid skeleton, both in terms of the metabolic route(s) exploited and the reaction mechanisms of the enzymes involved. The former has been approached using high-resolution 2-dimensional NMR and GC-MS methods; the latter by determining kinetic isotope effects and modelling the potential reaction steps. It appears that the mechanism for nicotine demethylation in plants is similar to but has significant differences from that described for mammals and Pseudomonas bacteria. These differences are discussed.

Evolutionary divergence times in the Annonaceae: evidence of a late Miocene origin of Pseuduvaria in Sundaland with subsequent diversification in New Guinea

Background  

Phylogenetic analyses of the Annonaceae consistently identify four clades: a basal clade consisting of Anaxagorea, and a small 'ambavioid' clade that is sister to two main clades, the 'long branch clade' (LBC) and 'short branch clade' (SBC). Divergence times in the family have previously been estimated using non-parametric rate smoothing (NPRS) and penalized likelihood (PL). Here we use an uncorrelated lognormal (UCLD) relaxed molecular clock in BEAST to estimate diversification times of the main clades within the family with a focus on the Asian genus Pseuduvaria within the SBC. Two fossil calibration points are applied, including the first use of the recently discovered Annonaceae fossil Futabanthus. The taxonomy and morphology of Pseuduvaria have been well documented, although no previous dating or biogeographical studies have been undertaken. Ancestral areas at internal nodes within Pseuduvaria are determined using dispersal-vicariance analysis (DIVA) and weighted ancestral area analysis (WAAA).     

New genes of Xanthomonas citri subsp. citri involved in pathogenesis and adaptation revealed by a transposon-based mutant library

Background  

Citrus canker is a disease caused by the phytopathogens Xanthomonas citri subsp. citri, Xanthomonas fuscans subsp. aurantifolli and Xanthomonas alfalfae subsp. citrumelonis. The first of the three species, which causes citrus bacterial canker type A, is the most widely spread and severe, attacking all citrus species. In Brazil, this species is the most important, being found in practically all areas where citrus canker has been detected. Like most phytobacterioses, there is no efficient way to control citrus canker. Considering the importance of the disease worldwide, investigation is needed to accurately detect which genes are related to the pathogen-host adaptation process and which are associated with pathogenesis.     

Erk associates with and primes GSK-3beta for its inactivation resulting in upregulation of beta-catenin

Beta-catenin is upregulated in many human cancers and considered to be an oncogene. Hepatocellular carcinoma (HCC) is one of the most prevalent human malignancies, and individuals who are chronic hepatitis B virus (HBV) carriers have a greater than 100-fold increased relative risk of developing HCC. Here we report a mechanism by which HBV-X protein (HBX) upregulates beta-catenin. Erk, which is activated by HBX, associates with GSK-3beta through a docking motif ((291)FKFP) of GSK-3beta and phosphorylates GSK-3beta at the (43)Thr residue, which primes GSK-3beta for its subsequent phosphorylation at Ser9 by p90RSK, resulting in inactivation of GSK-3beta and upregulation of beta-catenin. This pathway is a general signal, as it was also observed in cell lines in which Erk-primed inactivation of GSK-3beta was regulated by IGF-1, TGF-beta, and receptor tyrosine kinase HER2, and is further supported by immunohistochemical staining in different human tumors, including cancers of the liver, breast, kidney, and stomach.     

Endosomal transport of ErbB-2: mechanism for nuclear entry of the cell surface receptor

The cell membrane receptor ErbB-2 migrates to the nucleus. However, the mechanism of its nuclear translocation is unclear. Here, we report a novel mechanism of its nuclear localization that involves interaction with the transport receptor importin beta1, nuclear pore protein Nup358, and a host of players in endocytic internalization. Knocking down importin beta1 using small interfering RNA oligonucleotides or inactivation of small GTPase Ran by RanQ69L, a dominant-negative mutant of Ran, causes a nuclear transport defect of ErbB-2. Mutation of a putative nuclear localization signal in ErbB-2 destroys its interaction with importin beta1 and arrests nuclear translocation, while inactivation of nuclear export receptor piles up ErbB-2 within the nucleus. Additionally, blocking of internalization by a dominant-negative mutant of dynamin halts its nuclear localization. Thus, the cell membrane-embedded ErbB-2, through endocytosis using the endocytic vesicle as a vehicle, importin beta1 as a driver and Nup358 as a traffic light, migrates from the cell surface to the nucleus. This novel mechanism explains how a receptor tyrosine kinase on the cell surface can be translocated into the nucleus. This pathway may serve as a general mechanism to allow direct communication between cell surface receptors and the nucleus, and our findings thus open a new era in understanding direct trafficking between the cell membrane and nucleus.     

Anchorage-independence as an index of proliferative potential and maturational age: a comparison of the growth of normal, primary explanted bovine granulosa cells in semisolid agar and in liquid culture

When seeded at low-density, normal primary explanted granulosa cells will grow to form clones of functionally differentiated cells in both semisolid agar and in liquid culture. The anchorage-independent clonogenic granulosa cell differs from the anchorage-dependent granulosa cells detected in clonal liquid culture in a number of properties. Basal cloning efficiency in liquid culture is up to 50-fold higher than in agar culture. In serum supplemented medium (20% fetal calf serum) cloning efficiency in liquid culture is unaltered in the presence of added epidermal growth factor (EGF), whereas, agar cloning efficiency is augmented six-fold when cells are incubated under identical conditions. Cells derived from primary anchorage-independent clones, when dispersed and replated, will generate secondary anchorage-independent clones and anchorage-dependent liquid clones. On the other hand, although cells derived from parallel primary anchorage-dependent clones will also generate secondary anchorage-dependent clones, generation of secondary anchorage-independent clones is not detectable. These findings suggest that the anchorage-independent clonal agar assay may be detecting a developmentally earlier granulosa cell subpopulation than is detectable in the liquid culture assay.