Thyroid hormone-dependent and independent processes of red blood cell transition from larval to adult type during metamorphosis in Xenopus laevis.

Amphibian metamorphosis results in drastic whole-body remodeling. Thyroid hormone (TH) drives most of these metamorphic changes. A prominent event during this remodeling is the red blood cell (RBC) transition from larval to adult forms, which exclusively contain larval and adult hemoglobin, respectively. However, the role of TH in RBC transition remains unclear. Here we reconfirmed that RBC transition of Xenopus laevis is completed much later than morphological metamorphosis. Further, larval and adult RBCs/erythroblasts proliferated both in the erythropoietic liver and in circulation during metamorphic climax. RBC transition was also confirmed in Rana ornativentris, but in contrast to X. laevis, adult RBC-specific proliferation was observed from the early climax stages. We also revealed in either species that RBC transition occurs in the liver prior to circulating RBCs. Moreover, anemia induction using phenylhydrazine during the prometamorphosis of X. laevis caused precocious RBC transition even when TH synthesis was blocked, resulting in metamorphosis-arrested larvae in which most of RBCs were of adult type. These results indicate that a decline in larval RBCs facilitates RBC transition during metamorphosis in a TH-independent manner. Further, combined administration of phenylhydrazine and TH induced precocious appearance of adult RBCs in early prometamorphic X. laevis tadpoles, whereas individual treatment with phenylhydrazine or TH did not cause precocious RBC transition; this suggests that TH is required to initiate RBC transition by promoting the differentiation of adult erythroblasts during early prometamorphosis in X. laevis. These results show that TH-dependent and independent processes are present in RBC transition in X. laevis.

Quinacrine Inhibits ICAM-1 Transcription by Blocking DNA Binding of the NF-κB Subunit p65 and Sensitizes Human Lung Adenocarcinoma A549 Cells to TNF-α and the Fas Ligand.

Quinacrine has been used for therapeutic drugs in some clinical settings. In the present study, we demonstrated that quinacrine decreased the expression of intercellular adhesion molecule-1 (ICAM-1) induced by tumor necrosis factor (TNF)-α and interleukin-1 (IL-1) α in human lung adenocarcinoma A549 cells. Quinacrine inhibited ICAM-1 mRNA expression and nuclear factor κB (NF-κB)-responsive luciferase reporter activity following a treatment with TNF-α and IL-1α. In the NF-κB signaling pathway, quinacrine did not markedly affect the TNF-α-induced degradation of the inhibitor of NF-κB or the TNF-α-induced phosphorylation of the NF-κB subunit, p65, at Ser-536 and its subsequent translocation to the nucleus. In contrast, a chromatin immunoprecipitation assay showed that quinacrine prevented the binding of p65 to the ICAM-1 promoter following TNF-α stimulation. Moreover, TNF-α and the Fas ligand effectively reduced the viability of A549 cells in the presence of quinacrine only. Quinacrine down-regulated the constitutive and TNF-α-induced expression of c-FLIP and Mcl-1 in A549 cells. These results revealed that quinacrine inhibits ICAM-1 transcription by blocking the DNA binding of p65 and sensitizes A549 cells to TNF-α and the Fas ligand.

The C-terminal domain of the long form of cellular FLICE-inhibitory protein (c-FLIPL) inhibits the interaction of the caspase 8 prodomain with the receptor-interacting protein 1 (RIP1) death domain and regulates caspase 8-dependent nuclear factor κB (NF-κB) activation.

Caspase 8 plays an essential role in the regulation of apoptotic and non-apoptotic signaling pathways. The long form of cellular FLICE-inhibitory protein (c-FLIPL) has been shown previously to regulate caspase 8-dependent nuclear factor κB (NF-κB) activation by receptor-interacting protein 1 (RIP1) and TNF receptor-associated factor 2 (TRAF2). In this study, the molecular mechanism by which c-FLIPL regulates caspase 8-dependent NF-κB activation was further explored in the human embryonic kidney cell line HEK 293 and variant cells barely expressing caspase 8. The caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone greatly diminished caspase 8-dependent NF-κB activation induced by Fas ligand (FasL) when c-FLIPL, but not its N-terminal fragment c-FLIP(p43), was expressed. The prodomain of caspase 8 was found to interact with the RIP1 death domain and to be sufficient to mediate NF-κB activation induced by FasL or c-FLIP(p43). The interaction of the RIP1 death domain with caspase 8 was inhibited by c-FLIPL but not c-FLIP(p43). Thus, these results reveal that the C-terminal domain of c-FLIPL specifically inhibits the interaction of the caspase 8 prodomain with the RIP1 death domain and, thereby, regulates caspase 8-dependent NF-κB activation.