Macrocyclic piperazinones as potent dual inhibitors of farnesyltransferase and geranylgeranyltransferase-I

A series of macrocyclic piperazinone compounds with dual farnesyltransferase/geranylgeranyltransferase-I inhibitory activity was prepared. These compounds were found to be potent inhibitors of protein prenylation in cell culture. A hypothesis for the binding mode of compound 3o in FPTase is proposed.     

Nup358 integrates nuclear envelope breakdown with kinetochore assembly

Nuclear envelope breakdown (NEBD) and release of condensed chromosomes into the cytoplasm are key events in the early stages of mitosis in metazoans. NEBD involves the disassembly of all major structural elements of the nuclear envelope, including nuclear pore complexes (NPCs), and the dispersal of nuclear membrane components. The breakdown process is facilitated by microtubules of the mitotic spindle. After NEBD, engagement of spindle microtubules with chromosome-associated kinetochores leads to chromatid segregation. Several NPC subunits relocate to kinetochores after NEBD. siRNA-mediated depletion of one of these proteins, Nup358, reveals that it is essential for kinetochore function. In the absence of Nup358, chromosome congression and segregation are severely perturbed. At the same time, the assembly of other kinetochore components is strongly inhibited, leading to aberrant kinetochore structure. The implication is that Nup358 plays an essential role in integrating NEBD with kinetochore maturation and function. Mitotic arrest associated with Nup358 depletion further suggests that mitotic checkpoint complexes may remain active at nonkinetochore sites.     

Control of endothelial cell proliferation by calcium influx and arachidonic acid metabolism: a pharmacological approach

In physiological conditions, endothelial cell proliferation is strictly controlled by several growth factors, among which bFGF and VEGF are the most effective. Both bind to specific tyrosine kinase receptors and trigger intracellular signal cascades. In particular, bFGF stimulates the release of arachidonic acid (AA) and its metabolites in many types of endothelial cells in culture. In bovine aortic endothelial cells, it has been suggested that AA is released by the recruitment of cytosolic phospholipase A2 (cPLA2). AA metabolites are involved in the control of both endothelial cell motility (mostly via the cyclooxygenase pathway) and proliferation (via the lipoxygenase (LOX) cascade). On the other hand, evidence has been provided for a proliferative role of AA-induced calcium influx. By using a pharmacological approach, we have tried to elucidate the contribution to bovine aortic endothelial proliferation of the different pathways leading to production of AA and its metabolites. Two main informations were obtained by our experiments: first, AA release is not entirely due to cPLA2 involvement, but also to DAG lipase recruitment; second, cyclooxygenase derivatives play a role in the control of cell proliferation, and not only of motility. Moreover, by combining proliferation assays and single cell calcium measurements, we show that the blocking effect of carboxyamido-triazole (CAI), an inhibitor of tumor growth and angiogenesis acting on calcium influx-dependent pathways, including AA metabolism, is at least in part due to a direct effect on AA-induced calcium influx.     

Catalysis and electron transfer in protein crystals: the binary and ternary complexes of methylamine dehydrogenase with electron acceptors

Polarized absorption microspectrophotometry has been used to detect catalysis and intermolecular electron transfer in single crystals of two multiprotein complexes: (1) the binary complex between Paracoccus denitrificans methylamine dehydrogenase, which contains tryptophan-tryptophylquinone (TTQ) as a cofactor, and its redox partner, the blue copper protein amicyanin; (2) the ternary complex between the same two proteins and cytochrome c-551i. Continuous wave electron paramagnetic resonance has been used to compare the state of copper in polycrystalline powders of the two systems. While catalysis and intermolecular electron transfer from reduced TTQ to copper are too fast to be accessible to our measurements, heme reduction occurs over a period of several minutes. The observed rate constant is about four orders of magnitude lower than in solution. The analysis of the temperature dependence of this apparent constant provides values for the parameters H(AB), related to electronic coupling between the two centers, and lambda, the reorganizational energy, that are compatible with electron transfer being the rate-determining step. From these parameters and the known distance between copper and heme, it is possible to calculate the parameter beta, which depends on the nature of the intervening medium, obtaining a value typical of electron transfer across a protein matrix. These findings suggest that the ternary complex in solution might achieve a higher efficiency than the rigid crystal structure thanks to an as yet unidentified role of protein dynamics.