Internalization of NK cells into tumor cells requires ezrin and leads to programmed cell-in-cell death

Cytotoxic lymphocytes are key players in the orchestration of immune response and elimination of defective cells. We have previously reported that natural killer （NK） cells enter target tumor ceils, leading to either target cell death or self-destruction within tumor cells. However, it has remained elusive as to the fate of NK cells after internalization and whether the heterotypic cell-in-cell process is different from that of the homotypic cell-in-cell event recently named entosis. Here, we show that NK cells undergo a cell-in-cell process with the ultimate fate of apoptosis within tumor cells and reveal that the internalization process requires the actin cytoskeletal regulator, ezrin. To visualize how NK cells enter into tumor cells, we carried out real-time dual color imaging analyses of NK cell internalization into tumor cells. Surprisingly, most NK cells commit to programmed cell death after their entry into tumor cells, which is distinctively different from entosis observed in the homotypic cell-in-cell process. The apoptotic cell death of the internalized NK cells was evident by activation of caspase 3 and DNA fragmentation. Furthermore, NK cell death after internalization is attenuated by the caspase inhibitor, Z-VAD-FMK, confirming apoptosis as the mode of NK cell death within tumor cells. To determine protein factors essential for the entry of NK cells into tumor cells, we car- ried out siRNA-based knockdown analysis and discovered a critical role of ezrin in NK cell internalization. Impor- tantly, PKA-mediated phosphorylation of ezrin promotes the NK cell internalization process. Our findings suggest a novel regulatory mechanism by which ezrin governs NK cell internalization into tumor cells.

Arrhythmogenic properties of dismantling cadherin-mediated adhesion in murine hearts

Objective： To evaluate the arrhythmogenic effects of dismantling cadherin-mediated adhesion by recombinant mouse aminopeptidase N （rmAPN） in murine hearts. Methods： rmAPN was incubated with cultured neonatal rat cardiomyocytes as well as being infused in adult mice. The cell-cell connections were immunolabelled and observed by laser confocal microscopy. Disruption of the N-terminal of N-cadherin （N-cad） was detected by western blot and quantitative immunofluorescence. The risk of inducible ventricular tachyarrhythmia was evaluated in mice by an electrophysiological study. Results： Disrupted cell-cell contact was observed in cultured neonatal rat cardiomyocytes in response to 30-40 ng/μL rmAPN. Loss of the N-terminal in N-cad and altered distribution of connexin 43 （Cx43） were observed in hearts from rmAPN-infused mice. In addition, a reduction of phosphorylated Cx43 was also detected concomitant with redistribution of Cx43. Electrophysiological studies of rmAPN-infused mice showed prolonged QRS duration and increased inducibility of ventricular tachycardias. Conclusion： Disruption of N-cad by rmAPN contributes to gap junction remodeling and may elicit arrhythmogenic effects. The disorder of adherent junctions by proteolytic enzymes may play an important role in arrhythmogenic mechanisms in correlated diseases.

POSH is involved in Eiger-Basket (TNF-JNK) signaling and embryogenesis in Drosophila

TNFα can trigger different signaling pathways, including the JNK pathway, to regulate various biological functions such as cell death, differentiation and proliferation. The scaffold protein POSH （Plenty of SH3 Domains） has been shown to be an important regulator of the JNK pathway, but whether it is involved in TNF-signaling has not been reported. Although POSH has been implicated to play a role in development in zebrafish, it has not been studied in null mutants and the underlying mechanism of its effects is still not clear. In this study, we provide evidence that the JNK pathway scaffold protein, POSH, is involved in TNF （Eiger） signaling in Drosophila. POSH is likely to act downstream of dTAB2 and upstream of dTAK1 in the TNF-JNK signaling pathway. In addition, we found that POSH is essential during Drosophila embryogenesis, including epidermal dorsal closure, similar to other JNK pathway components such as Silpper, Hemipterous, and Basket. We observed defects in F-actin accumulation and adherens junction formation during dorsal closure in different posh null mutants, suggesting that POSH is required for epidermal cell migration and cell-shape change during epidermal dorsal closure.