Shigella chromosomal IpaH proteins are secreted via the type III secretion system and act as effectors

Shigella possess 220 kb plasmid, and the major virulence determinants, called effectors, and the type III secretion system (TTSS) are exclusively encoded by the plasmid. The genome sequences of S. flexneri strains indicate that several ipaH family genes are located on both the plasmid and the chromosome, but whether their chromosomal IpaH cognates can be secreted from Shigella remains unknown. Here we report that S. flexneri strain, YSH6000 encodes seven ipaH cognate genes on the chromosome and that the IpaH proteins are secreted via the TTSS. The secretion kinetics of IpaH proteins by bacteria, however, showed delay compared with those of IpaB, IpaC and IpaD. Expression of the each mRNA of ipaH in Shigella was increased after bacterial entry into epithelial cells, and the IpaH proteins were secreted by intracellular bacteria. Although individual chromosomal ipaH deletion mutants showed no appreciable changes in the pathogenesis in a mouse pulmonary infection model, the DeltaipaH-null mutant, whose chromosome lacks all ipaH genes, was attenuated to mice lethality. Indeed, the histological examination for mouse lungs infected with the DeltaipaH-null showed a greater inflammatory response than induced by wild-type Shigella, suggesting that the chromosomal IpaH proteins act synergistically as effectors to modulate the host inflammatory responses.     

Nitrogen and phosphorus fertilization negatively affects strigolactone production and exudation in sorghum

Strigolactones (SLs) are essential host recognition signals for both root parasitic plants and arbuscular mycorrhizal fungi, and SLs or their metabolites function as a novel class of plant hormones regulating shoot and root architecture. Our previous study indicated that nitrogen (N) deficiency as well as phosphorus (P) deficiency in sorghum enhanced root content and exudation of 5-deoxystrigol, one of the major SLs produced by sorghum. In the present study, we examined how N and P fertilization affects SL production and exudation in sorghum plants subjected to short- (5 days) or long-term (10 days) N or P deficiency and demonstrated their common and distinct features. The root contents and exudation of SLs in the N- or P-deficient sorghum plants grown for 6, 12 or 24 h with or without N or P fertilization were quantified by LC–MS/MS. In general, without fertilization, root contents and exudation of SLs stayed at similar levels at 6 and 12 h and then significantly increased at 24 h. The production of SLs responded more quickly to P fertilization than the secretion of SLs, while regulation of SL secretion began earlier after N fertilization. It is suggested that sorghum plants regulate SL production and exudation when they are subjected to nutrient deficiencies depending on the type of nutrient and degree of deficiency.     

Rheb (Ras Homologue Enriched in Brain)-dependent Mammalian Target of Rapamycin Complex 1 (mTORC1) Activation Becomes Indispensable for Cardiac Hypertrophic Growth after Early Postnatal Period

Cardiomyocytes proliferate during fetal life but lose their ability to proliferate soon after birth and further increases in cardiac mass are achieved through an increase in cell size or hypertrophy. Mammalian target of rapamycin complex 1 (mTORC1) is critical for cell growth and proliferation. Rheb (Ras homologue enriched in brain) is one of the most important upstream regulators of mTORC1. Here, we attempted to clarify the role of Rheb in the heart using cardiac-specific Rheb-deficient mice (Rheb^−/−). Rheb^−/− mice died from postnatal day 8 to 10. The heart-to-body weight ratio, an index of cardiomyocyte hypertrophy, in Rheb^−/− was lower than that in the control (Rheb^+/+) at postnatal day 8. The cell surface area of cardiomyocytes isolated from the mouse hearts increased from postnatal days 5 to 8 in Rheb^+/+ mice but not in Rheb^−/− mice. Ultrastructural analysis indicated that sarcomere maturation was impaired in Rheb^−/− hearts during the neonatal period. Rheb^−/− hearts exhibited no difference in the phosphorylation level of S6 or 4E-BP1, downstream of mTORC1 at postnatal day 3 but showed attenuation at postnatal day 5 or 8 compared with the control. Polysome analysis revealed that the mRNA translation activity decreased in Rheb^−/− hearts at postnatal day 8. Furthermore, ablation of eukaryotic initiation factor 4E-binding protein 1 in Rheb^−/− mice improved mRNA translation, cardiac hypertrophic growth, sarcomere maturation, and survival. Thus, Rheb-dependent mTORC1 activation becomes essential for cardiomyocyte hypertrophic growth after early postnatal period.     

Osteoactivin fragments produced by ectodomain shedding induce MMP-3 expression via ERK pathway in mouse NIH-3T3 fibroblasts

Intact osteoactivin, a novel type I membrane glycoprotein, were shed at a dibasic motif in the juxtamembrane region in C2C12 myoblasts. Extracellular fragments were secreted into the culture media by a putative metalloprotease. Extracellular fragments of osteoactivin, but not control protein, induced matrix metalloprotease-3 (MMP-3) expression in NIH-3T3 fibroblasts. Epidermal growth factor (ERK) kinase inhibitors inhibited the osteoactivin-mediated MMP-3 expression, whereas the extracellular fragment of osteoactivin activated ERK1/2 and p38 in the mitogen-activated protein kinase pathway. Our results suggest that the extracellular fragments of osteoactivin produced by shedding act as a growth factor to induce MMP-3 expression via the ERK pathway in fibroblasts.     

Contribution of Neuropilin-1 in Radiation-Survived Subclones of NSCLC Cell Line H1299

Non-small cell lung cancer (NSCLC) is an aggressive lung cancer accounting for approximately 85% of all lung cancer patients. For the patients with Stages IIIA, IIIB, and IIIC, the 5-year survival is low though with the combination with radiotherapy and chemotherapy. In addition, the occurrence of tumor cells (repopulated tumors) that survive irradiation remains a challenge. In our previous report, we subcloned the radiation-surviving tumor cells (IR cells) using the human NSCLC cell line, H1299, and found that the expression of neuropilin-1 (NRP-1) was upregulated in IR cells by the microarray analysis. Here, we investigated the contribution of neuropilin-1 to changes in the characteristics of IR cells. Although there were no differences in angiogenic activity in the tube formation assay between parental and IR cells, the cell motility was increased in IR cells compared to parental cells in the cell migration assay. This enhanced cell motility was suppressed by pretreatment with anti-NRP-1 antibody. Although further studies are necessary to identify other molecules associated with NRP-1, the increase in cellular motility in IR cells might be due to the contribution of NRP-1. Inhibition of NRP-1 would help control tumor malignancy in radiation-surviving NSCLC.     

Cloning the tomato curl3 gene highlights the putative dual role of the leucine-rich repeat receptor kinase tBRI1/SR160 in plant steroid hormone and peptide hormone signaling

Brassinosteroids (BRs) are plant steroid hormones that are essential for normal plant development. To gain better understanding of the conservation of BR signaling, the partially BR-insensitive tomato mutant altered brassinolide sensitivity1 (abs1) was identified and found to be a weak allele at the curl3 (cu3) locus. BR content is increased in both of these mutants and is associated with increased expression of DWARF: The tomato homolog of the Arabidopsis Brassinosteroid Insensitive1 Leu-rich repeat (LRR) receptor-like kinase, named tBri1, was isolated using degenerate primers. Sequence analysis of tBRI1 in the mutants cu3 and abs1 revealed that cu3 is a nonsense mutant and that abs1 is a missense mutant. A comparison of BRI1 homolog sequences highlights conserved features of BRI1 sequences, with the LRRs in close proximity to the island domain showing more conservation than N-terminal LRRs. The most homologous sequences were found in the kinase and transmembrane regions. tBRI1 (SR160) also has been isolated as the putative receptor for systemin, a plant peptide hormone. This finding suggests a possible dual role for tBRI1 in steroid hormone and peptide hormone signaling.