Porphyromonas gingivalis infection sequesters pro-apoptotic Bad through Akt in primary gingival epithelial cells

Porphyromonas gingivalis, a self-limiting oral pathogen, can colonize and replicate in gingival epithelial cells (GECs). P. gingivalis-infected GECs are protected from mitochondrion-dependent apoptosis, partially through activation of phosphatidyl inositol 3-kinase/Akt signaling. Biochemical events associated with P. gingivalis-induced inhibition of apoptosis include the blocking of mitochondrial membrane permeability and cytochrome-c release. We studied functional importance of Akt and the status of associated key mitochondrial molecules, pro-apoptotic Bad and caspase-9, during infection of GECs. We found that P. gingivalis infection caused significant phosphorylation of Bad progressively, while messenger RNA levels for Bad slowly decreased. Fluorescence microscopy showed translocation of the mitochondrial Bad to the cytosol post-infection. Conversely, P. gingivalis lost the ability to promote phosphorylation and translocation of Bad in Akt-deficient GECs. Caspase-9 activation induced by a chemical inducer of apoptosis was significantly inhibited by infection over time. However, Akt depletion by small interfering RNA did not reverse inhibition of caspase-9 activation by infection. Hence, P. gingivalis inactivates pro-apoptotic Bad through Akt. The inhibition of caspase-9 activation appears to be independent of Akt. Overall, our findings suggest that Akt is a key component of anti-apoptotic pathways stimulated by P. gingivalis. The P. gingivalis uses other mitochondrial pathways to protect host cells from cell-death and to ensure its survival in gingival epithelium.

Aberrant distribution of junctional complex components in retinoic acid receptor alpha-deficient mice

Retinoic acid receptor alpha (RARalpha)-deficient mice are sterile, with abnormalities in the progression of spermatogenesis and spermiogenesis. In this study, we investigated whether defective retinoid signaling involved at least in part, disrupted cell-cell interactions. Hypertonic fixation approaches revealed defects in the integrity of the Sertoli-cell barrier in the tubules of RARalpha-deficient testes. Dye transfer experiments further revealed that coupling between cells from the basal to adluminal compartments was aberrant. There were also differences in the expression of several known retinoic acid (RA)-responsive genes encoding structural components of tight junctions and gap junctions. Immunostaining demonstrated a delay in the incorporation of zonula occludens (ZO-1), a peripheral component protein of tight junctions, into the Sertoli cell tight junctions. Markedly reduced expression of connexin-40 in mutant pachytene spermatocytes and round spermatids was found by in situ hybridization. An ectopic distribution of vimentin and disrupted cyclic expression of vimentin, which is usually tightly regulated during spermiogenesis, was found in RARalpha-deficient testes at all ages examined. Thus, the specific defects in spermiogenesis in RARalpha-deficient testes may correlate with a disrupted cyclic expression of RA-responsive structural components, including vimentin, a downregulation of connexin-40 in spermatogenic cells, and delayed assembly of ZO-1 into Sertoli cell tight junctions. Interestingly, bioinformatic analysis revealed that many genes that are components of tight junctions and gap junctions contained potential retinoic acid response element binding sites.

Caspase-dependent generation of reactive oxygen species in human astrocytoma cells contributes to resistance to TRAIL-mediated apoptosis

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF family of cytokines, causes apoptosis by caspase activation in various cell types, particularly in transformed cells. Numerous types of tumors are relatively resistant to TRAIL-induced cytotoxicity; however, the reasons for this are not yet fully understood. We report here a new signal transduction pathway involving protein kinase Cdelta (PKCdelta), NADPH oxidase 4 (NOX4) and reactive oxygen species (ROS), that inhibits caspase-dependent cell death induced by TRAIL ligation in human malignant astrocytoma cells. In our experiments, TRAIL ligation-induced generation of intracellular ROS through caspase-dependent proteolytic activation of PKCdelta and subsequent activation of the NOX4 complex. Suppression of intracellular ROS induction using various pharmacological inhibitors or PKCdelta- or NOX4-specific RNA interference enhanced the enzymatic activity of caspase-3 by blocking the oxidative modification of its catalytic cysteine residue, resulting in marked augmentation of TRAIL-mediated cell death. These results collectively indicate that TRAIL-induced activation of PKCdelta and NOX4 can modulate TRAIL-mediated apoptosis by promoting oxidative modification of active caspase-3 in a negative-feedback manner.

Nanopatterning by multiple-ion-beam sputtering

We conducted a systematic study on nanopatterning by multiple-ion-beam sputtering, focusing on the superposition of the simple patterns formed by individual ion beams. When Au(001) is simultaneously sputtered by two ion beams at grazing incidence, both nanodot and nanohole patterns are obtained. If a rippled surface is subsequently sputtered at normal incidence, a nanobead pattern is obtained. All of the obtained patterns consist of the nanopatterns formed by individual ion beams; however, the superposition of nanopatterns is not realized in its ideal form. We also discuss the microscopic mechanism of pattern formation by multiple-ion-beam sputtering, and consider the questions and possibilities remaining to be explored.