Identification of a novel splice variant of X-linked inhibitor of apoptosis-associated factor 1

XAF1 (XIAP-associated factor 1) binds to XIAP and blocks its anti-apoptotic activity. It has been reported that XAF1 is mainly expressed in normal tissues but is missing or present at low levels in most cancer cell lines, which implies a tumor-suppressing function. In the present study we describe the identification of a novel splice variant of human XAF1, designated XAF1C, which contains a cryptic exon. Incorporation of this exon (exon 4b) into the mRNA introduces an in-frame stop codon, resulting in a shortened open-reading frame (ORF) of 495 nucleotides. This ORF is predicted to encode a 164 amino acid (AA) protein lacking the C-terminal domain of the previously described XAF1(A), but containing a unique 24 AA carboxy terminus. Like XAF1(A), XAF1C mRNA expression was detected in a variety of human cancer cell lines and also in normal human tissues. The ratio of XAF1(A) and XAF1C mRNA expression differs amongst the cell lines tested, suggesting differential mRNA stabilities and/or the existence of tissue- or cell type-specific splicing regulation. In transfected cells, xaf1c encodes a truncated protein of 18kDa, which is distributed primarily in the nucleus.     

Role of hunchback in segment patterning of Locusta migratoria manilensis revealed by parental RNAi

In long germ embryos, all body segments are specified simultaneously during the blastoderm stage. In contrast, in short germ embryos, only the anterior segments are specified during the blastoderm stage, leaving the rest of the body plan to be specified later. The striking embryological differences between short and long germ segmentation imply fundamental differences in patterning at the molecular level. To gain insights into the segmentation mechanisms of short germ insects, we have investigated the role of the homologue of the Drosophila gap gene hunchback (hb) in a short germ insect Locusta migratoria manilensi by paternal RNA interference (RNAi). Phenotypes resulting from hb knockdown were categorized into three classes based on severity. In the most extreme case, embryos developed the most anterior structures only, including the labrum, antennae and eyes. The following conclusions were drawn: (i) L. migratoria manilensis hb (Lmm'hb) controls germ band morphogenesis and segmentation in the anterior region; (ii) Lmm'hb may function as a gap gene in a wide domain including the entire gnathum and thorax; and (iii) Lmm'hb is required for proper growth of the posterior germ band. These findings suggest a more extensive role for L. migratoria manilensis hunchback in anterior patterning than those described in Drosophila.     

Tryptase activates PKB in inflammatory reaction in ECV304 cells

Tryptase is involved in proteinase-activated receptor-2 (PAR-2) mediated up-regulation of IL-8 expression. The present report showed the effects of tryptase on gene expression and activation, including up-regulation IL-8 expression. The expression of mRNA for NF-kappaB first increased at 1 h after tryptase-treatment (1 ng/ml) and reached the plateau after 4 h. The NF-kappaB mRNA increased by 3-fold (n = 3, P < 0.05), AP-1 by 2-fold (n = 3, P < 0.05), and PKB by 10-fold (n = 3, P < 0.05). However, tryptase-treatment did not affect the expression of JNK and p38 MAPK when compared with control cells at mRNA level. Furthermore, in addition to increasing phosphorylation of p38 MAPK, tryptase-treatment also increased phosphorylation of PKB by 2-fold at 15 min following the treatment. The up-regulation and phosphorylation of PKB by tryptase could be abolished by either phosphoinositol-3-kinase (PI3K) inhibitor (LY294002) at 10 microM or antisense PKB cDNA transfection. The up-regulation of NF-kappaB expression could be inhibited by LY294002 and antisense PKB cDNA. These results indicate that tryptase can activate PI3K-PKB pathway and enhance IL-8 expression.     

Endonuclease G promotes cell death of non-invasive human breast cancer cells

The invasiveness of breast cancer cells was shown to be associated with the suppressed ability to develop apoptosis. The role of cell death DNases/endonucleases has not been previously examined in relation with the invasiveness of breast cancer cells. We have compared the activity of the endonucleases in seven human breast cancer cell lines different in the level of invasiveness and differentiation. The invasiveness of cell lines was confirmed by an in vitro Matrigel-based assay. The total endonuclease activity in the differentiated non-invasive (WDNI) cell lines was higher than that in the poorly differentiated invasive (PDI) cells. The expression of EndoG strongly correlated with the degree of estrogen receptor expression and showed an inverse correlation with vimentin and matrix metalloproteinase-13. The EndoG-positive WDNI cells were more sensitive to etoposide- or camptothecin-induced cell death than EndoG-negative PDI cells. Silencing of EndoG caused inhibited of SK-BR-3 WDNI cell death induced by etoposide. Human ductal carcinomas in situ expressed high levels of EndoG, while invasive medullar and ductal carcinomas had significantly decreased expression of EndoG. This correlated with decreased apoptosis as measured by TUNEL assay. Our findings suggest that the presence of EndoG in non-invasive breast cancer cells determines their sensitivity to apoptosis, which may be taken into consideration for developing the chemotherapeutic strategy for cancer treatment.     

C-terminal truncation modulates both nucleation and extension phases of tau fibrillization

Proteolytic post-translational modification has been proposed as an early stage event in the aggregation of τ protein and formation of neurofibrillary lesions in Alzheimer’s disease. Caspases and other proteases cleave τ in vivo at discrete locations including Asp⁴²¹ and Glu³⁹¹. Both cleavage products are prone to aggregation relative to wild-type, full-length τ protein. To determine the mechanism underlying this effect, the fibrillization of τ truncated after Asp⁴²¹ and Glu³⁹¹ residues was characterized in a full-length four-repeat τ background using quantitative electron microscopy methods under homogeneous nucleation conditions. Both C-terminal truncations decreased critical concentration relative to full-length τ, resulting in more filament mass at reaction plateau. Moreover, truncation directly augmented the efficiency of the nucleation reaction. The results suggest the mechanism through which C-terminal proteolysis can modulate τ filament accumulation depending on whether it precedes or follows nucleation.     

IGF-1R tyrosine kinase expression and dependency in clones of IGF-1R knockout cells (R-)

Insulin-like growth factor 1 receptor (IGF-1R) plays many crucial roles in cancer, like anti-apoptotic activity and necessity for transformation. IGF-1R knockout cells (R-) represent a useful tool for molecular mapping of biological properties of the receptor. R- cells have been shown to be refractory to transformation by viral and cellular oncogenes, highlighting the necessity of this receptor for transformation. Surprisingly, more recent studies have shown that these cells can undergo spontaneous transformation. This observation raises the question as whether R- cells over the years have acquired some properties mimicking those of IGF-1R. Using an IGF-1R inhibitor (cyclolignan PPP) we have identified clones of R- (R-s) that are sensitive to this compound. Since, PPP is closely related to podophyllotoxin, which is an efficient microtubule inhibitor, we first investigated if such a mechanism could explain the sensitivity to PPP. However, highly purified PPP showed no or very slight tubulin binding. Further analysis of R-s revealed expression of a 90 kDa protein being reactive to IGF-1R beta-subunit antibodies. This protein was weakly but constitutively tyrosine phosphorylated and was downregulated by siRNA targeting IGF-1R. This downregulation was paralleled by decreased R-s survival. Taken together, our study suggests that clones of R- express IGF-1R activity and dependency, which in turn may explain that R- can undergo spontaneous transformation.