The recent determination of the partial decay widths for the one-proton and the two-nucleon induced Non-Mesonic Weak Decay of Λ-Hypernuclei in the A=5–16 range permitted to reconstruct the full ...pattern of decay widths for 5ΛHe and 11ΛB. A consistency check on 12ΛC decay widths confirms the validity of the adopted method.
The kinase suppressor of Ras 1 (KSR1) has a fundamental role in mitogenic signaling by scaffolding components of the Ras/MAP kinase pathway. In response to Ras activation, KSR1 assembles a tripartite ...kinase complex that optimally transfers signals generated at the cell membrane to activate ERK. We describe a novel mechanism of ERK attenuation based on ubiquitin-dependent proteolysis of KSR1. Stimulation of membrane receptors by hormones or growth factors induced KSR1 polyubiquitination, which paralleled a decline of ERK1/2 signaling. We identified praja2 as the E3 ligase that ubiquitylates KSR1. We showed that praja2-dependent regulation of KSR1 is involved in the growth of cancer cells and in the maintenance of undifferentiated pluripotent state in mouse embryonic stem cells. The dynamic interplay between the ubiquitin system and the kinase scaffold of the Ras pathway shapes the activation profile of the mitogenic cascade. By controlling KSR1 levels, praja2 directly affects compartmentalized ERK activities, impacting on physiological events required for cell proliferation and maintenance of embryonic stem cell pluripotency.
In recent years, several experiments using magnetic spectrometers provided high precision results in the field of Hypernuclear Physics. In particular, the accurate determination of the Λ-binding ...energy, BΛ, contributed to stimulate considerably the discussion about the Charge Symmetry Breaking effect in Λ-hypernuclei isomultiplets.
We have reorganized the results from the FINUDA experiment and we have obtained a series of BΛ values for Λ-hypernuclei with A≤ 16 by taking into account data only from magnetic spectrometers implementing an absolute calibration of the energy scale (FINUDA at DAΦNE and electroproduction experiments at JLab and at MaMi). We have then critically revisited the results obtained at KEK by the SKS Collaboration in order to make possible a direct comparison between data from experiments with and without such an absolute energy scale. A synopsis of recent spectrometric measurements of BΛ is presented, including also emulsion experiment results.
Several interesting conclusions are drawn, among which the equality within the errors of BΛ for the A=7,12,16 isomultiplets, based only on recent spectrometric data. This observation is in nice agreement with a recent theoretical prediction.
Ideas for possible new measurements which should improve the present experimental knowledge are finally put forward.
Cyclic adenosine 3'5' monophosphate (cAMP) and protein kinase A (PKA) cooperate with phosphatidylinositol 3' kinase (PI3K) signals in the control of growth and survival. To determine the molecular ...mechanism(s) involved, we identified and mutagenized a specific serine (residue 83) in p85alpha(PI3K), which is phosphorylated in vivo and in vitro by PKA. Expression of p85alpha(PI3K) mutants (alanine or aspartic substitutions) significantly altered the biological responses of the cells to cAMP. cAMP protection from anoikis was reduced in cells expressing the alanine version p85alpha(PI3K). These cells did not arrest in G1 in the presence of cAMP, whereas cells expressing the aspartic mutant p85D accumulated in G1 even in the absence of cAMP. S phase was still efficiently inhibited by cAMP in cells expressing both mutants. The binding of PI3K to Ras p21 was greatly reduced in cells expressing p85A in the presence or absence of cAMP. Conversely, expression of the aspartic mutant stimulated robustly the binding of PI3K to p21 Ras in the presence of cAMP. Mutation in the Ser 83 inhibited cAMP, but not PDGF stimulation of PI3K. Conversely, the p85D aspartic mutant amplified cAMP stimulation of PI3K activity. Phosphorylation of Ser 83 by cAMP-PKA in p85alpha(PI3K) was also necessary for estrogen signaling as expression of p85A or p85D mutants inhibited or amplified, respectively, the binding of estrogen receptor to p85alpha and AKT phosphorylation induced by estrogens. The data presented indicate that: (1) phosphorylation of Ser 83 in p85alpha(PI3K) is critical for cAMP-PKA induced G1 arrest and survival in mouse 3T3 fibroblasts; (2) this site is necessary for amplification of estrogen signals by cAMP-PKA and related receptors. Finally, these data suggest a general mechanism of PI3K regulation by cAMP, operating in various cell types and under different conditions.
Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Λ-Hypernuclei (A=5–16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced ...decay widths, Γ2N/Γp, are obtained from single proton spectra, Γ2N/Γp=0.50±0.24, and from neutron and proton coincidence spectra, Γ2N/Γp=0.36±0.14stat−0.04sys+0.05sys, in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Λ decay width, Γp/ΓΛ, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.
SuperB is an INFN flagship project for a new high-luminosity heavy-flavor factory. Along with its companion detector, it is dedicated to the search for CP violation effects in the B meson sector with ...the aim of looking for direct and indirect signals of new physics, beyond the Standard Model. However it could offer as well the opportunity for a systematic, high-statistics study of b baryon properties and for a search for bottom super-nuclei, that is bound nuclear systems with an explicit content of beauty.
The decay of Λ-hypernuclei without π emission, known as Non-Mesonic Weak Decay (NMWD), gives an effective tool to investigate ΔS=1 four-baryon interactions. It was theoretically suggested that the ...two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of Γ2N/ΓNMWD=0.21±0.07stat−0.02sys+0.03sys has been deduced, well consistent with the previous determinations.
This Letter is concerned with the study of the Kstop−A→π±Σ∓A′ reaction in p-shell nuclei, i.e., 6,7Li, 9Be, 13C and 16O. The π±Σ∓/Kstop− emission rates are reported as a function of A. These rates ...are discussed in comparison with previous findings. The ratio π−Σ+/π+Σ− in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold Λ(1405). The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the π±Σ∓ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DAΦNEϕ-factory (LNF-INFN, Italy).
PDF
