The second open reading frame of avian reovirus S1 gene segment encodes a 17 kDa non-structural protein, named p17. The biological role of p17 is fully unknown so far. Using trypan blue dye exclusion and MTT assay, we demonstrated that the ectopic expression of p17 results in the reduction of viable cell number and cell proliferation rate of Vero, BHK, 293, and HeLa cells. Measurement of LDH activity and DNA fragmentation analysis revealed that p17 expression did not cause cell death or apoptosis. These data indicated that the p17 possessed the growth retardation function. Semi-quantitative RT-PCR and Western blotting revealed that p17-expressing cells induced the expression of CDK inhibitor p21cip1/waf1 in a time- and dose-dependent manner, but the transcripts of CDK inhibitor p15INK4b, p16INK4a, or p27kip were not altered. In the presence of p17, the p53 protein level and p53-driven reporter activity were elevated significantly. Dominant negative p53 alleviated the p21 accumulation, p53 activation, and growth inhibition effect induced by p17. Taken together, these studies revealed a possible intrinsic function of p17 in growth regulation through the activation of p53 and p21cip1/waf1.
ARV S1133 infection caused apoptosis in vivo and in vitro; however, the intracellular signaling pathways have not been fully delineated. We have previously demonstrated that ARV S1133 activates proapoptotic signaling from Src to p53, and further investigated how ARV S1133 modulates p53. We found that ARV S1133 forms syncytia and induces apoptosis in CEF, DF1 and Vero cells with different kinetics. Enhancement of p53 phosphorylation and DNA-binding capacity to bax and bad promoters was found in this study to increase bax and bad expression in ARV S1133-infected cells. ARV S1133 activates PKC delta and p38 and JNK/SAPK pathways, and inhibition of Ras, p38, JNK/SAPK and PKC delta works efficiently against apoptosis. Suppression of p38, JNK/SAPK and PKC delta selectively abolished ARV S1133-mediated p53 phosphorylation; moreover, inhibition of Src did not affect ARV S1133-induced p38 and JNK/SAPK activation, whereas blocking of Ras resulted in a reduction in the activities of p38 and JNK/SAPK.
Trichoderma spp. are used as biocontrol agents against phytopathogens such as Rhizoctonia solani, but their biocontrol mechanisms are poorly understood. A novel L-amino oxidase (Th-LAAO) was identified from the extracellular proteins of Trichoderma harzianum ETS 323. Here, we show a FAD-binding glycoprotein with the best substrate specificity constant for L-phenylalanine. Although the amino acid sequence of Th-LAAO revealed limited homology (16-24%) to other LAAO members, a highly conserved FAD-binding motif was identified in the N-terminus. Th-LAAO was shown to be a homodimeric protein, but the monomeric form was predominant when grown in the presence of deactivated Rhizoctonia solani. Furthermore, in vitro assays demonstrated that Th-LAAO had an antagonistic effect against Rhizoctonia solani and a stimulatory one on hyphal density and sporulation in T. harzianum ETS 323. These findings further our understanding of T. harzianum as a biocontrol agent and provide insight into the biological function of l-amino acid oxidase.
Accumulating evidence reveals that aberrant expression of claudins manifests in various tumors; however, their biological functions are poorly understood. Here, we report on the elevated expression of claudin-1 in nasopharyngeal carcinoma (NPC) cell lines under serum deprivation or fluorouracil (5-FU) treatment. Interestingly, an increase in expression of claudin-1 considerably reduced apoptosis rather than enhancing cell proliferation. However, claudin-1 expression and activity were unaffected by external stimuli or Akt and NF-jB activation. Notably, predominant cytoplasmic and nuclear localization of claudin-1 in NPC cells reflected the aforementioned feature. On the other hand, loss of epithelial morphology and E-cadherin expression was associated with serum withdrawal in NPC cells. Interestingly, restoration of E-cadherin inhibited the protein elevation and antiapoptotic activity of claudin-1. In conclusion, our data demonstrate the regulation and novel biological function of claudin-1 and indicate the important role of claudin-1 in NPC tumorigenesis.
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