Acoustic directional source based on Penrose quasi-crystal arrangements of metallic rods embedded in a fluid.

The directional emission properties of a circular device formed of a small number of metallic rods placed at the nodes of Penrose's tiling are investigated. At the center of the device a non-directional primary source emits monochromatic acoustic waves. In a wide frequency range, the beams come out of the device along preferential directions related to the symmetry of order 5 of the tiling and the non-periodicity in the radial direction. There are some frequencies for which the waves are completely trapped by the device. The shape, the distribution and the intensity of the emitted beams outside are closely dependent on the frequency. A comparison between numerical results and experiments is presented.

Reflection and transmission characteristics of a layer obeying the two-pressure field poroelastic phenomenological model of Berryman and Wang.

The characteristics of the reflection and transmission by a fluid-loaded double porosity layer are studied. The medium obeys the two-pressure field poroelastic phenomenological model of Berryman and Wang. The open pore hydraulic conditions applied at the interfaces yield factorized expressions for the coefficients exhibiting on the one hand a separation allowing to distinguish between symmetrical and antisymmetrical motions and on the other hand the way each of the three dilatational waves associate with the shear wave. The numerical study done for a layer of Berea sandstone saturated by water shows clearly the role of each of the dilatational waves. There are peculiarities such as the absence of the fundamental antisymmetrical mode (zero order) and a singular behaviour of the symmetrical fundamental mode. The low frequency approximation for this latter is derived from the proposed formulas and compared with the numerical results.

Multiple scattering by infinitely long cylindrical glass inclusions in a saturated Biot porous medium of glass beads.

The resonance spectrum of sets of two to five infinitely long parallel cylindrical glass inclusions in a fluid saturated porous matrix of unconsolidated glass beads is investigated. The ratio of bead diameters to inclusion diameters is 1/5. The far field form functions and the related phase derivatives are calculated by using an exact multiple scattering formalism and by assuming that the porous medium obeys Biot's model. In order to validate this hypothesis, comparisons between theory and experiments are done in the special case of a fast incident wave on a set of two and three inclusions.

Band gap structures in underwater screens of periodically spaced porous plates.

Acoustic properties of different periodic structures composed of alternating fluid and fluid-saturated porous layers obeying Biot's theory are investigated. At first, the network of modes and the transmission coefficients of finite structures of six plates are studied in the frequency-angle of incidence plane. It is shown that the network of modes concentrates in localized domains of the plane where the transmission coefficients will take the greatest values. With this minimum of six plates, the structures exhibit the main features as for structures containing more plates, especially those with an infinite number of plates. Then, considering infinite structures the band gap calculations are led using the Bloch-Floquet theorem. The evanescent and propagative zones in the frequency-angle of incidence plane are determined. What is proposed here is a class of underwater porous screens that exhibits band gaps extending over great angular domains and enlarging in the frequency domain when the pores at the interfaces of the porous plates are sealed. The effect of porosity on the band gaps is also investigated.

The PIDDosome, DNA-damage-induced apoptosis and beyond.

P53-induced protein with a death domain (PIDD) was cloned as a death domain (DD)-containing protein whose expression is induced by p53. It was later described as the core of a molecular platform-activating caspase-2, named the PIDDosome. These first results pointed towards a role for PIDD in apoptosis, in response to DNA damage. Identification of new PIDDosome complexes involved in DNA repair and nuclear factor-κB signaling challenged this early concept. PIDD functions are growing as new complexes and new interaction partners are being discovered, and as additional functions are being revealed. A fascinating feature of PIDD lies within its complex and tight regulation mechanisms, which allow the molecule to fine-tune its different functions: from transcriptional regulation to the expression of different isoforms, and from the interaction with regulatory proteins to an ingenious post-translational cleavage mechanism generating various active fragments with specific functions. Further studies still need to be carried out to provide answers to many unresolved issues and to reconcile conflicting results. This review aims at providing an overview of the current PIDD knowledge status.

Regulation of PIDD auto-proteolysis and activity by the molecular chaperone Hsp90.

In response to DNA damage, p53-induced protein with a death domain (PIDD) forms a complex called the PIDDosome, which either consists of PIDD, RIP-associated protein with a death domain and caspase-2, forming a platform for the activation of caspase-2, or contains PIDD, RIP1 and NEMO, important for NF-κB activation. PIDDosome activation is dependent on auto-processing of PIDD at two different sites, generating the fragments PIDD-C and PIDD-CC. Despite constitutive cleavage, endogenous PIDD remains inactive. In this study, we screened for novel PIDD regulators and identified heat shock protein 90 (Hsp90) as a major effector in both PIDD protein maturation and activation. Hsp90, together with p23, binds PIDD and inhibition of Hsp90 activity with geldanamycin efficiently disrupts this association and impairs PIDD auto-processing. Consequently, both PIDD-mediated NF-κB and caspase-2 activation are abrogated. Interestingly, PIDDosome formation itself is associated with Hsp90 release. Characterisation of cytoplasmic and nuclear pools of PIDD showed that active PIDD accumulates in the nucleus and that only cytoplasmic PIDD is bound to Hsp90. Finally, heat shock induces Hsp90 release from PIDD and PIDD nuclear translocation. Thus, Hsp90 has a major role in controlling PIDD functional activity.

p53-induced protein with a death domain (PIDD) isoforms differentially activate nuclear factor-kappaB and caspase-2 in response to genotoxic stress.

Cells respond to DNA damage in a complex way and the fate of damaged cells depends on the balance between pro- and antiapoptotic signals. This is of crucial importance in cancer as genotoxic stress is implied both in oncogenesis and in classical tumor therapies. p53-induced protein with a death domain (PIDD), initially described as a p53-inducible gene, is one of the molecular switches able to activate a survival or apoptotic program. Two isoforms of PIDD, PIDD (isoform 1) and LRDD (isoform 2), have already been reported and we describe here a third isoform. These three isoforms are differentially expressed in tissues and cell lines. Genotoxic stress only affects PIDD isoform 3 mRNA levels, whereas isoforms 1 and 2 mRNA levels remain unchanged. All isoforms are capable of activating nuclear factor-kappaB in response to genotoxic stress, but only isoform 1 interacts with RIP-associated ICH-1/CED-3 homologous protein with a death domain and activates caspase-2. Isoform 2 counteracts the pro-apoptotic function of isoform 1, whereas isoform 3 enhances it. Thus, the differential splicing of PIDD mRNA leads to the formation of at least three proteins with antagonizing/agonizing functions, thereby regulating cell fate in response to DNA damage.

Experimental study and signal analysis in the Lamb wave conversion at a bevelled edge.

This paper deals with a quantitative study of the conversion of a Lamb wave at the bevelled edge of a plate. A harmonic wave (successively the A1 and S0 Lamb modes) is generated using a wedge. The normal displacements at the surface of the plate are measured with a laser vibrometer and used to compute an energy evaluation. In order to determine a good mean value of incident and reflected wave amplitudes, the signals are isolated by a Fourier treatment. Then, the energy flow repartition among the converted modes is computed in both cases and for different values of the bevel angle.

Death receptor recruitment of endogenous caspase-10 and apoptosis initiation in the absence of caspase-8.

Caspase-8 is believed to play an obligatory role in apoptosis initiation by death receptors, but the role of its structural relative, caspase-10, remains controversial. Although earlier evidence implicated caspase-10 in apoptosis signaling by CD95L and Apo2L/TRAIL, recent studies indicated that these death receptor ligands recruit caspase-8 but not caspase-10 to their death-inducing signaling complex (DISC) even in presence of abundant caspase-10. We characterized a series of caspase-10-specific antibodies and found that certain commercially available antibodies cross-react with HSP60, shedding new light on previous results. The majority of 55 lung and breast carcinoma cell lines expressed mRNA for both caspase-8 and -10; however, immunoblot analysis revealed that caspase-10 protein expression was more frequently absent than that of caspase-8, suggesting a possible selective pressure against caspase-10 production in cancer cells. In nontransfected cells expressing both caspases, CD95L and Apo2L/TRAIL recruited endogenous caspase-10 as well as caspase-8 to their DISC, where both enzymes were proteolytically processed with similar kinetics. Caspase-10 recruitment required the adaptor FADD/Mort1, and caspase-10 cleavage in vitro required DISC assembly, consistent with the processing of an apoptosis initiator. Cells expressing only one of the caspases underwent ligand-induced apoptosis, indicating that each caspase can initiate apoptosis independently of the other. Thus, apoptosis signaling by death receptors involves not only caspase-8 but also caspase-10, and both caspases may have equally important roles in apoptosis initiation.

An enhancer element 6 kb upstream of the mouse HNF4alpha1 promoter is activated by glucocorticoids and liver-enriched transcription factors.

We have characterized a 700 bp enhancer element around -6 kb relative to the HNF4alpha1 transcription start. This element increases activity and confers glucocorticoid induction to a heterologous as well as the homologous promoters in differentiated hepatoma cells and is transactivated by HNF4alpha1, HNF4alpha7, HNF1alpha and HNF1beta in dedifferentiated hepatoma cells. A 240 bp sub-region conserves basal and hormone-induced enhancer activity. It contains HNF1, HNF4, HNF3 and C/EBP binding sites as shown by DNase I footprinting and electrophoretic mobility shift assays using nuclear extracts and/or recombinant HNF1alpha and HNF4alpha1. Mutation analyses showed that the HNF1 site is essential for HNF1alpha transactivation and is required for full basal enhancer activity, as is the C/EBP site. Glucocorticoid response element consensus sites which overlap the C/EBP, HNF4 and HNF3 sites are crucial for optimal hormonal induction. We present a model that accounts for weak expression of HNF4alpha1 in the embryonic liver and strong expression in the newborn/adult liver via the binding sites identified in the enhancer.

Bcl-rambo, a novel Bcl-2 homologue that induces apoptosis via its unique C-terminal extension.

The Bcl-2 family of proteins plays a central regulatory role in apoptosis. We have identified a novel, widely expressed Bcl-2 member which we have named Bcl-rambo. Bcl-rambo shows overall structural homology to the anti-apoptotic Bcl-2 members containing conserved Bcl-2 homology (BH) motifs 1, 2, 3, and 4. Unlike Bcl-2, however, the C-terminal membrane anchor region is preceded by a unique 250 amino acid insertion containing two tandem repeats. No interaction of Bcl-rambo with either anti-apoptotic (Bcl-2, Bcl-x(L), Bcl-w, A1, MCL-1, E1B-19K, and BHRF1) or pro-apoptotic (Bax, Bak, Bik, Bid, Bim, and Bad) members of the Bcl-2 family was observed. In mammalian cells, Bcl-rambo was localized to mitochondria, and its overexpression induces apoptosis that is specifically blocked by the caspase inhibitors, IAPs, whereas inhibitors controlling upstream events of either the 'death receptor' (FLIP, FADD-DN) or the 'mitochondrial' pro-apoptotic pathway (Bcl-x(L)) had no effect. Surprisingly, the Bcl-rambo cell death activity was induced by its membrane-anchored C-terminal domain and not by the Bcl-2 homology region. Thus, Bcl-rambo constitutes a novel type of pro-apoptotic Bcl-2 member that triggers cell death independently of its BH motifs.