Dual-Energy Computed Tomography For Differentiation Between Osteoblastic Metastases and Bone Islands.

Objective: The objective of our study was to evaluate the utility of Rho/Z on dual-energy computed tomography (DECT) for the differentiation of osteoblastic metastases (OBMs) from bone islands (BIs). Methods: DECT images of 110 patients with malignancies were collected. The effective atomic number (Z), electron density (Rho), dual energy index (DEI), and regular CT (rCT) values were measured by two observers. Independent-sample t-test was used to compare these values between OBMs and BIs. The diagnostic performance was assessed by receiver operating characteristic (ROC) analysis and the cutoff values were evaluated according to ROC curves. Results: A total of 205 OBMs and 120 BIs were included. The mean values of Z, Rho, DEI, and rCT of OBMs were significantly lower than those of BIs, whereas the standard deviation values were higher than those of BIs (all p ≤ 0.05). ROC analysis showed that 11.86 was the optimal cutoff value for Z, rendering an area under the ROC curve (AUC) of 0.91, with a sensitivity of 91.2% and a specificity of 82.5%. Conclusion: DECT can provide quantitative values of Z, Rho, and DEI and has good performance in differentiating between OBMs and BIs.

Presenilin1/gamma-secretase promotes the EphB2-induced phosphorylation of ephrinB2 by regulating phosphoprotein associated with glycosphingolipid-enriched microdomains/Csk binding protein.

Reverse signaling through the ephrinB ligands is important for several morphogenetic events, such as axon guidance, neuronal plasticity, spine maturation, and synaptogenesis. Signaling is initiated by binding of EphB receptors to ephrinB ligands, stimulating their tyrosine phosphorylation via an unclear mechanism. Here we show that this mechanism involves presenilin1 (PS1)/γ-secretase regulation of phosphoprotein associated with glycosphingolipid-enriched microdomains/Csk binding protein (PAG/Cbp), an adaptor protein that controls the activity of Src kinases. Using immunoprecipitation and Western blot of mouse primary neuronal and human embryonic kidney (HEK293) cell extracts overexpressing PAG/Cbp, we show that EphB2 induces tyrosine dephosphorylation of PAG/Cbp in a γ-secretase-dependent manner. In these cells, PAG/Cbp dephosphorylation is promoted by the PS1/γ-secretase-produced fragment of ephrinB2 cleavage (ephrinB2/CTF2), which forms complexes with PAG/Cbp when introduced exogenously. EphB2-induced tyrosine phosphorylation of ephrinB2 depends on PAG/Cbp because EphB2 cannot increase ephrinB2 phosphorylation in cells treated with anti-PAG siRNA or in PAG/Cbp-knockout (KO) cells. Furthermore, in contrast to WT PS1, familial Alzheimer disease (FAD) PS1 mutants expressed in PS1-KO mouse embryonic fibroblasts inhibited both the EphB2-induced dephosphorylation of PAG/Cbp and the phosphorylation of ephrinB2. PS1 FAD mutations may thus inhibit the function of ephrinB in the brain, promoting neurodegeneration in Alzheimer disease.

Parcs is a dual regulator of cell proliferation and apaf-1 function.

Here we identify a novel protein, named Parcs for pro-apoptotic protein required for cell survival, that is involved in both cell cycle progression and apoptosis. Parcs interacted with Apaf-1 by binding to the oligomerization domain of Apaf-1. Apaf-1-mediated activation of caspase-9 and caspase-3 was markedly decreased in a cytosolic fraction isolated from HeLa cells with reduced parcs expression. Interestingly, parcs deficiency blocked cell proliferation in non-tumorigenic cells but not in multiple tumor cell lines. In MCF-10A cells, parcs deficiency led to early G1 arrest. Conditional inactivation of parcs in genetically modified primary mouse embryonic fibroblasts using the Cre-LoxP system also resulted in the inhibition of cell proliferation. We conclude that Parcs may define a molecular checkpoint in the control of cell proliferation for normal cells that is lost in tumor cells.

Metalloproteinase/Presenilin1 processing of ephrinB regulates EphB-induced Src phosphorylation and signaling.

Bidirectional signaling triggered by interacting ephrinB receptors (EphB) and ephrinB ligands is crucial for development and function of the vascular and nervous systems. A signaling cascade triggered by this interaction involves activation of Src kinase and phosphorylation of ephrinB. The mechanism, however, by which EphB activates Src in the ephrinB-expressing cells is unknown. Here we show that EphB stimulates a metalloproteinase cleavage of ephrinB2, producing a carboxy-terminal fragment that is further processed by PS1/gamma-secretase to produce intracellular peptide ephrinB2/CTF2. This peptide binds Src and inhibits its association with inhibitory kinase Csk, allowing autophosphorylation of Src at residue tyr418. EphrinB2/CTF2-activated Src phosphorylates ephrinB2 and inhibits its processing by gamma-secretase. These data show that the PS1/gamma-secretase system controls Src activation and ephrinB phosphorylation by regulating production of Src activator ephrinB2/CTF2. Accordingly, gamma-secretase inhibitors prevented the EphB-induced sprouting of endothelial cells and the recruitment of Grb4 to ephrinB. PS1 FAD and gamma-secretase dominant-negative mutants inhibited the EphB-induced cleavage of ephrinB2 and Src autophosphorylation, raising the possibility that FAD mutants interfere with the functions of Src and ephrinB2 in the CNS.

Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 transcriptional activator Rta is an oligomeric DNA-binding protein that interacts with tandem arrays of phased A/T-trinucleotide motifs.

Kaposi's sarcoma associated herpesvirus (KSHV)/human herpesvirus 8 (HHV-8) encodes an immediate early transcriptional activator, Rta, which mediates viral reactivation from latency and lytic viral replication. Here we report the purification and characterizations of HHV-8 Rta and its interaction with Rta-responsive DNA elements. The Rta response element (RtaRE) in the promoter of the KSHV/HHV-8 K8 open reading frame was mapped to a 47-bp sequence (RtaRE1) and a 60-bp sequence (RtaRE2) upstream of the TATA motif. A comparison of the K8 RtaREs with other viral RtaREs revealed a pattern of multiple A/T triplets spaced with a periodicity of 10 or 20 bp. Substitutions of the in-phase A/T trinucleotides of the RtaRE1 with G/C bases greatly diminished Rta responsiveness and Rta binding. By contrast, base substitutions in an out-of-phase A/T-trinucleotide sequence had no effect. Importantly, multimers of (A/T)(3)N(7) and N(5)(A/T)(5)N(6)(A/T)(4) motifs supported a strong Rta response in a copy number-dependent manner. No specific sequence motifs in the spacer regions could be discerned. Potent Rta response, however, was obtained with phased A/T trinucleotides with 7-bp spacers of arbitrary sequences with high G/C content. Lengthening of the phased A/T motifs or lowering of the G/C content of the spacers resulted in a reduction in Rta response. Finally, Escherichia coli-derived Rta is an oligomer of 440 kDa in molecular size and binds RtaRE as an oligomer. These results support a model of Rta transactivation wherein the subunits of the Rta oligomer make multiple contacts with a tandem array of phased A/T triplets in the configuration of (A/T)(3)(G/C)(7) repeats.