Involvement of 14-3-3 proteins in the second epidermal growth factor-induced wave of Rac1 activation in the process of cell migration

Immense previous efforts have elucidated the core machinery in cell migration, actin remodeling regulated by Rho family small GTPases including RhoA, Cdc42, and Rac1; however, the spatiotemporal regulation of these molecules remains largely unknown. Here, we report that EGF induces biphasic Rac1 activation in the process of cell migration, and UTKO1, a cell migration inhibitor, inhibits the second EGF-induced wave of Rac1 activation but not the first wave. To address the regulation mechanism and role of the second wave of Rac1 activation, we identified 14-3-3ζ as a target protein of UTKO1 and also showed that UTKO1 abrogated the binding of 14-3-3ζ to Tiam1 that was responsible for the second wave of Rac1 activation, suggesting that the interaction of 14-3-3ζ with Tiam1 is involved in this event. To our knowledge, this is the first report to use a chemical genetic approach to demonstrate the mechanism of temporal activation of Rac1.     

Limited expression of reticulocalbin-1 in lymphatic endothelial cells in lung tumor but not in normal lung

Lymphatic endothelial cells in tumors (T-LECs) are considered to have different characteristics from LECs in non-tumor tissues (N-LECs). However, differences between the two types have not been well analyzed at molecular level. In this report, we performed differential proteome analysis of T-LEC and N-LEC models prepared by cultivation of LECs in tumor conditioned medium. By expression profiling of identified proteins using tissue microarrays, reticulocalbin-1 was found to be expressed in clinical specimen-derived T-LECs and lung cancer cells but not N-LECs. It is suggested that reticulocalbin-1 may be an important molecule in understanding T-LEC function and control of lymphatic metastasis.     

Characterization of Cholix toxin-induced apoptosis in HeLa cells

Cholix toxin (Cholix) is a novel ADP-ribosylating cytotoxin produced by Vibrio cholerae, which utilizes eukaryotic elongation factor 2 as a substrate and acts by a mechanism similar to that of diphtheria toxin and Pseudomonas exotoxin A. First it was found that Cholix-treated HeLa cells exhibited caspase-dependent apoptosis, whereas intestinal cells such as Caco-2, HCT116, and RKO did not. Here we investigated Cholix-induced cell death signaling pathways in HeLa cells. Cholix-induced cytochrome c release into cytosol was initiated by specific conformational changes of pro-apoptotic Bak associated with Bax. Silencing of bak/bax genes or bak gene alone using siRNA significantly suppressed cytochrome c release and caspase-7 activation, but not activation of caspases-3 and -9. Although pretreatment with a caspase-8 inhibitor (Z-IETD-FMK) reduced Cholix-induced cytochrome c release and activation of caspases-3, -7, and -9, cytotoxicity was not decreased. Pretreatment with Z-YVAD-FMK, which inhibits caspase-1, -4, and -5, suppressed not only cytochrome c release, activation of caspase-3, -7, -8, or -9, and PARP cleavage, but also cytotoxicity, indicating that caspase-1, -4, and -5 activation is initiated at an early stage of Cholix-induced apoptosis and promotes caspase-8 activation. These results show that the inflammatory caspases (caspase-1, -4, and -5) and caspase-8 are responsible for both mitochondrial signals and other caspase activation. In conclusion, we showed that Cholix-induced caspase activation plays an essential role in generation of apoptotic signals, which are mediated by both mitochondria-dependent and -independent pathways.     

Genome sequence of Photobacterium mandapamensis strain svers.1.1, the bioluminescent symbiont of the cardinal fish Siphamia versicolor

Photobacterium mandapamensis is one of three luminous Photobacterium species able to form species-specific bioluminescent symbioses with marine fishes. Here, we present the draft genome sequence of P. mandapamensis strain svers.1.1, the bioluminescent symbiont of the cardinal fish Siphamia versicolor, the first genome of a symbiotic, luminous Photobacterium species to be sequenced. Analysis of the sequence provides insight into differences between P. mandapamensis and other luminous and symbiotic bacteria in genes involved in quorum-sensing regulation of light production and establishment of symbiosis.     

ADAMTSL6β protein rescues fibrillin-1 microfibril disorder in a Marfan syndrome mouse model through the promotion of fibrillin-1 assembly

Marfan syndrome (MFS) is a systemic disorder of the connective tissues caused by insufficient fibrillin-1 microfibril formation and can cause cardiac complications, emphysema, ocular lens dislocation, and severe periodontal disease. ADAMTSL6β (A disintegrin-like metalloprotease domain with thrombospondin type I motifs-like 6β) is a microfibril-associated extracellular matrix protein expressed in various connective tissues that has been implicated in fibrillin-1 microfibril assembly. We here report that ADAMTSL6β plays an essential role in the development and regeneration of connective tissues. ADAMTSL6β expression rescues microfibril disorder after periodontal ligament injury in an MFS mouse model through the promotion of fibrillin-1 microfibril assembly. In addition, improved fibrillin-1 assembly in MFS mice following the administration of ADAMTSL6β attenuates the overactivation of TGF-β signals associated with the increased release of active TGF-β from disrupted fibrillin-1 microfibrils within periodontal ligaments. Our current data thus demonstrate the essential contribution of ADAMTSL6β to fibrillin-1 microfibril formation. These findings also suggest a new therapeutic strategy for the treatment of MFS through ADAMTSL6β-mediated fibrillin-1 microfibril assembly.     

Cdk5/p35 is required for motor coordination and cerebellar plasticity

Previous studies have implicated the role of Purkinje cells in motor learning and the underlying mechanisms have also been identified in great detail during the last decades. Here we report that cyclin‐dependent kinase 5 (Cdk5)/p35 in Purkinje cell also contributes to synaptic plasticity. We previously showed that p35^?/? (p35 KO) mice exhibited a subtle abnormality in brain structure and impaired spatial learning and memory. Further behavioral analysis showed that p35 KO mice had a motor coordination defect, suggesting that p35, one of the activators of Cdk5, together with Cdk5 may play an important role in cerebellar motor learning. Therefore, we created Purkinje cell‐specific conditional Cdk5/p35 knockout (L7‐p35 cKO) mice, analyzed the cerebellar histology and Purkinje cell morphology of these mice, evaluated their performance with balance beam and rota‐rod test, and performed electrophysiological recordings to assess long‐term synaptic plasticity. Our analyses showed that Purkinje cell‐specific deletion of Cdk5/p35 resulted in no changes in Purkinje cell morphology but severely impaired motor coordination. Furthermore, disrupted cerebellar long‐term synaptic plasticity was observed at the parallel fiber‐Purkinje cell synapse in L7‐p35 cKO mice. These results indicate that Cdk5/p35 is required for motor learning and involved in long‐term synaptic plasticity.

     

Defect of suppression of inflammasome-independent interleukin-8 secretion from SW982 synovial sarcoma cells by familial Mediterranean fever-derived pyrin mutations

Familial Mediterranean fever (FMF) is a recessive inherited autoinflammatory syndrome. Patients with FMF have symptoms such as recurrent fever and abdominal pain, sometimes accompanied by arthralgia. Biopsy specimens have revealed substantial neutrophil infiltration into synovia. FMF patients have a mutation in the Mediterranean fever gene, encoding pyrin, which is known to regulate the inflammasome, a platform for processing interleukin (IL)-1β. FMF patients heterozygous for E148Q mutation, heterozygous for M694I mutation, or combined heterozygous for E148Q and M694I mutations, which were found to be major mutations in an FMF study group in Japan, suffer from arthritis, the severity of which is likely to be lower than in FMF patients with M694V mutations. Expression plasmids of wild-type (WT) pyrin and mutated pyrin, such as E148Q, M694I, M694V, and E148Q+M694I, were constructed, and SW982 synovial sarcoma cells were transfected with these expression plasmids. IL-8 and IL-6 were spontaneously secreted from the culture supernatant of SW982 cells without any stimulation, whereas IL-1β and TNF-α could not be detected even when stimulated with lipopolysaccharide. Notably, two inflammasome components, ASC and caspase-1, could not be detected in SW982 cells by Western blotting. IL-8 but not IL-6 secretion from SW982 cells was largely suppressed by WT pyrin, but less suppressed by mutated pyrin, which appeared to become weaker in the order of E148Q, M694I, E148Q+M694I, and M694V mutations. As for IL-8 and IL-6, similar results were obtained using stable THP-1 cells expressing the WT pyrin or mutated pyrins, such as M694V or E148Q, when stimulated by LPS. In addition, IL-8 secretion from mononuclear cells of FMF patients was significantly higher than that of healthy volunteers when incubated on a culture plate. Thus, our results suggest that IL-8 secretion from SW982 synovial sarcoma cells suppressed by pyrin independently of inflammasome is affected by pyrin mutations, which may reflect the activity in FMF arthritis.     

Understanding the X chromosome inactivation cycle in mice: A comprehensive view provided by nuclear transfer

During mouse development, imprinted X chromosome inactivation (XCI) is observed in preimplantation embryos and is inherited to the placental lineage, whereas random XCI is initiated in the embryonic proper. Xist RNA, which triggers XCI, is expressed ectopically in cloned embryos produced by somatic cell nuclear transfer (SCNT). To understand these mechanisms, we undertook a large-scale nuclear transfer study using different donor cells throughout the life cycle. The Xist expression patterns in the reconstructed embryos suggested that the nature of imprinted XCI is the maternal Xist-repressing imprint established at the last stage of oogenesis. Contrary to the prevailing model, this maternal imprint is erased in both the embryonic and extraembryonic lineages. The lack of the Xist-repressing imprint in the postimplantation somatic cells clearly explains how the SCNT embryos undergo ectopic Xist expression. Our data provide a comprehensive view of the XCI cycle in mice, which is essential information for future investigations of XCI mechanisms.     

NOD-Rag2null IL-2Rγnull Mice: An Alternative to NOG Mice for Generation of Humanized Mice

We have developed NOD-Rag2^null IL-2Rγ^null (NR2G) mice similar to NOD-scidIL-2Rγ^null (NOG) mice that are known as an excellent host to generate humanized mice. To evaluate the usefulness of NR2G mice as a host for humanized mice, the engraftment rates and differentiation of human cells after human hematopoietic stem cell (HSC) transplantation were compared among NR2G, NOG, and NOD-scid mice. For this purpose, the appropriate irradiation doses to expand the niche for human stem cells in the bone marrow were first determined. As a result, 8 and 2.5 Gy in adult, and 4 and 1 Gy in newborn NR2G and NOG mice, respectively, were found to be appropriate. Next, 5 × 10⁴ human umbilical cord blood CD34⁺ cells were intravenously inoculated into irradiated adult or newborn of the immunodeficient mice. These HSC transplantation experiments demonstrated that both NR2G and NOG mice showed high engraftment rates compared with NOD-scid mice, although NOG mice showed a slightly higher engraftment rate than that for NR2G mice. However, no difference was found in the human cell populations differentiated from HSCs between NR2G and NOG mice. The HSC transplantation experiments to adults and newborns of two immunodeficient mice also revealed that the HSC transplantation into newborn mice resulted in higher engraftment rate than those into adults. These results showed that NR2G mice could be used as an alternative host to NOG mice to generate humanized mice.