Oncogenic activation of the Ron tyrosine kinase (Macrophage Stimulating Protein receptor) relies on substitutions of two highly conserved residues in the catalytic domain (D1232V and M1254T), which ...result in ligand-independent activation of the receptor, in vivo tumorigenesis and metastasis. We show here that the Y/F conversion of the Y1317 residue in the kinase domain impairs tumorigenic and metastatic properties of Ron activated by the MEN2B-like mutation (RonM1254T), but not by other two oncogenic substitutions. Furthermore, RonM1254T lacking the multifunctional docking site retains transforming and metastatic activity. These data reveal that the transforming activity of RonM1254T mutant is dependent on Y1317 phosphorylation, suggesting a shift in intramolecular substrate specificity. Consistently, a shift of RonM1254T kinase substrate specificity was observed by in vitro peptide phosphorylation assays and in vivo receptor auto-phosphorylation. The Y1317 phosphorylation elicits by itself activation of PI-3K/Akt and MAPK signalling pathways. Our data indicate that the accomplishment of the full oncogenic phenotype of RonM1254T requires the phosphorylation both of the canonical C-terminal docking site and of the unique Y1317 residue in the tyrosine kinase domain.
Human malignant mesothelioma (HMM), which is strongly related to asbestos exposure, exhibits high resistance to many anticancer drugs. Asbestos fibre deposition in the lung may cause hypoxia and iron ...chelation at the fibre surface. Hypoxia-inducible factor (HIF)-1alpha, which is upregulated by a decreased availability of oxygen and iron, controls the expression of membrane transporters, such as P-glycoprotein (Pgp), which actively extrude the anticancer drugs. The present study aimed to assess whether asbestos may play a role in the induction of doxorubicin resistance in HMM cells through the activation of HIF-1alpha and an increased expression of Pgp. After 24-h incubation with crocidolite asbestos or with the iron chelator dexrazoxane, or under hypoxia, HMM cells were tested for HIF-1alpha activation, Pgp expression, accumulation of doxorubicin and sensitivity to its toxic effect. Crocidolite, dexrazoxane and hypoxia caused HIF-1alpha activation, Pgp overexpression and increased resistance to doxorubicin accumulation and toxicity. These effects were prevented by the co-incubation with the cell-permeating iron salt ferric nitrilotriacetate, which caused an increase of intracellular iron bioavailability, measured as increased activity of the iron regulatory protein-1. Crocidolite, dexrazoxane and hypoxia induce doxorubicin resistance in human malignant mesothelioma cells by increasing hypoxia-inducible factor-1alpha activity, through an iron-sensitive mechanism.
CDC25Mm is a mouse guanine nucleotide exchange factor specific for Ras, exclusively expressed in the brain. We used a reporter gene containing a Ras-responsive fos-promoter in order to gain ...information on the role played by this exchange factor in signal transduction. Transient expression of CDC25Mm in CHO cells activates Ras. Moreover serum, but not insulin, can upregulate the response mediated by CDC25Mm and this modulation requires that the CDC25Mm maintains its N-terminal region. NIH3T3 fibroblasts, stably overexpressing this exchange factor, show a partially transformed phenotype, suggesting that the Ras-dependent pathway is constitutively active. In these cells serum and lysophosphatidic acid (LPA) stimulate Ras activity above the basal level while PDGF does not. Both serum and LPA-induced Ras activations in CDC25Mm overexpressing cells can be completely inhibited by pertussis toxin. Moreover, these responses are strongly reduced by coexpression of a truncated version of CDC25Mm lacking the C-terminal catalytic portion. This construct behaves in a dominant negative manner suggesting that it may compete with CDC25Mm by sequestering in an unproductive way signalling components activated by these factors. The data presented indicate that CDC25Mm does not participate in connecting tyrosine kinase receptors with Ras, while it could mediate Ras activation induced by pertussis toxin sensitive Gi-coupled receptors.
During a study on the biology of the pandalid shrimps from North Tyrrhenian Sea (western Mediterranean) the bopyrid parasite Pseudione affinis G.O. Sars was found inhabiting the branchial chamber of ...Plesionika martia A. Milne Edwards. 14 shrimps, on 1501 examined individuals, were found with branchial gall, but only 10 individuals harboured mature isopods since the others had "lost" the host. No shrimp harboured more than one female. A pattern of seasonal infection was not evident. The size of the female P. martia ranged from 13.9 to 22.7 mm of carapace length, while those of the males from 13.8 to 20.6 mm. The size of the female P. affinis ranged from. 9.3 to 13.5 mm of total length, that of the male from 2.7 to 3.5 mm. A positive correlation between the size of the parasite and that of the shrimps was found. The gills appeared splayed and flattened but without any sign of damage. The morphology of the abdominal pleopods of infested shrimps was similar to that of the healthy individuals. In males the production of spermatozoa was limited, in females the ovaries were resting. The collection of an ovigerous female P. martia with branchial gall, but without host parasite, however, demonstrates that as soon as the shrimps "lose" the parasite their gonads may return functional also if they produce less eggs than the healthy individuals. Further the degree of fullness of the infested shrimp foreguts as well as the type of prey were similar to that of the healthy individuals, thus suggesting that the growth rate and the principal functions of the host are not heavily affected by the presence of parasites.
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