No abstract

Proteinase 3 (Pr3), the main target of anti-neutrophil cytoplasmic antibodies, is a neutrophil serine protease that may be constitutively expressed at the surface of quiescent circulating neutrophils. This raises the question of the simultaneous presence in the circulation of constitutive membrane-bound Pr3 (mPr3) and its plasma inhibitor ␣1-protease inhibitor (␣1-Pi). We have looked at the fate of constitutive mPr3 at the surface of circulating blood neutrophils and of induced mPr3 on triggered neutrophils. We found significant Pr3 activity at the surface of activated neutrophils but not at the surface of quiescent neutrophils whatever the constitutive expression. This suggests that constitutive mPr3 is enzymatically inactive or its active site is not accessible to the substrate. Supporting this conclusion, we have not been able to demonstrate any interaction between constitutive mPr3 and ␣1-Pi, whereas induced mPr3 is cleared from the cell surface when activated cells are incubated with this inhibitor. But, unlike membrane-bound elastase that is also cleared from the surface of activated cells, mPr3 remained bound to the membrane when inhibited by elafin or by a low molecular weight chloromethyl ketone inhibitor, which shows that it binds more tightly to the neutrophil membrane. mPr3 may thus be present at the surface of circulating neutrophils in an environment replete with ␣1-Pi. The permanent presence of inactive Pr3 at the surface of quiescent neutrophils may explain why Pr3 is a major target of anti-neutrophil cytoplasmic antibodies, whose binding activates neutrophils and triggers inflammation, as in Wegener granulomatosis.

Glioblastomas (GBMs) are the most frequent and the most aggressive brain tumors, known for their chemo- and radio-resistance, making them often incurable. We also know that SETMAR is a protein involved in chromatin dynamics and genome plasticity, of which overexpression confers chemo- and radio-resistance to some tumors. The relationships between SETMAR and GBM have never been explored. To fill this gap, we define the SETMAR status of 44 resected tumors and of GBM derived cells, at both the mRNA and the protein levels. We identify a new, small SETMAR protein (so called SETMAR-1200), enriched in GBMs and GBM stem cells as compared to the regular enzyme (SETMAR-2100). We show that SETMAR-1200 is able to increase DNA repair by non-homologous end-joining, albeit with a lower efficiency than the regular SETMAR protein. Interestingly, the regular/small ratio of SETMAR in GBM cells changes depending on cell type, providing evidence that SETMAR expression is regulated by alternative splicing. We also demonstrate that SETMAR expression can be regulated by the use of an alternative ATG. In conclusion, various SETMAR proteins can be synthesized in human GBM that may each have specific biophysical and/or biochemical properties and characteristics. Among them, the small SETMAR may play a role in GBMs biogenesis. On this basis, we would like to consider SETMAR-1200 as a new potential therapeutic target to investigate, in addition to the regular SETMAR protein already considered by others.

Background Mariner elements represent the most successful family of autonomous DNA transposons, being present in various plant and animal genomes, including humans. The introduction and co-evolution of mariners within host genomes imply a strict regulation of the transposon activity. Biochemical data accumulated during the past decade have led to a convergent picture of the transposition cycle of mariner elements, suggesting that mariner transposition does not rely on host-specific factors. This model does not account for differences of transposition efficiency in human cells between mariners. We thus wondered whether apparent similarities in transposition cycle could hide differences in the intrinsic parameters that control mariner transposition.Principal FindingsWe find that Mos1 transposase concentrations in excess to the Mos1 ends prevent the paired-end complex assembly. However, we observe that Mos1 transposition is not impaired by transposase high concentration, dismissing the idea that transposase over production plays an obligatory role in the down-regulation of mariner transposition. Our main finding is that the paired-end complex is formed in a cooperative way, regardless of the transposase concentration. We also show that an element framed by two identical ITRs (Inverted Terminal Repeats) is more efficient in driving transposition than an element framed by two different ITRs (i.e. the natural Mos1 copy), the latter being more sensitive to transposase concentration variations. Finally, we show that the current Mos1 ITRs correspond to the ancestral ones.ConclusionsWe provide new insights on intrinsic properties supporting the self-regulation of the Mos1 element. These properties (transposase specific activity, aggregation, ITR sequences, transposase concentration/transposon copy number ratio…) could have played a role in the dynamics of host-genomes invasion by Mos1, accounting (at least in part) for the current low copy number of Mos1 within host genomes.