Sequence-specific interaction between steroid hormone receptors (R) and DNA hormone-responsive elements (HRE) takes place in vitro irrespective of the presence of hormone and even when R is liganded with an antagonist. In vivo, in contrast, the presence of hormone is mandatory for glucocorticosteroid (G) receptor-HRE interaction to occur and no HRE occupancy is detected in the presence of an antagonist. One possible explanation is that in vivo R is originally complexed with a protein that prevents its binding to target HREs. The hormone would then induce the dissociation of the oligomer, thus unmasking the functional DNA binding domain of the receptor. The unliganded, non DNA-binding 8S-form of the chick GR is a hetero-oligomer including the relative molecular mass (Mr) 94,000 steroid-binding unit (4S-GR), and the non-steroid-binding, non-DNA-binding 90,000 protein common to all classes of 8S-R and identified as heat-shock protein (hsp 90). We report here that triamcinolone acetonide (TA) promotes the transformation of 8S-GR to 4S-GR complexes both in explants and in cell-free conditions and that the high-affinity antiglucocorticosteroid RU 486 stabilizes the 8S-GR, as assessed by gradient sedimentation and HPLC. However, in vitro TA- and RU 486- 4S-GR showed comparable DNA-binding activity. These results suggest that the lack of affinity for DNA of the 8S form of GR may be attributable in vivo to the interaction of the 4S-GR protein with hsp 90, and that hormone binding might trigger a conformational change which results in the release of active 4S-GR.

Two cDNAs coding homologous putative metalloproteases (Metis 1 and Metis 2, expected molecular weights of 55.6 and 56.0 kDa, respectively) were identified from the hard tick Ixodes ricinus. The expression of Metis genes was induced in salivary glands during tick blood meal. RNA interference was used to assess the role of both Metis 1 and Metis 2 in tick feeding. It was found that salivary gland extracts lacking Metis 1-2 had a restricted ability to interfere with fibrinolysis. RNAi against Metis 1-2 also induced a high mortality rate. An immune reaction was raised in repeatedly bitten animals against Metis 1 and 2. Vaccination of hosts with the recombinant Metis 1 protein produced in a eukaryotic system partially interfered with completion of the blood meal. Although vaccination did not alter the survival rate or feeding time of ticks, their weight gain and oviposition rate were reduced. This will affect their reproductive fitness in the field. We believe this is the first report of an anti-tick vaccine trial using a metalloprotease derived from I. ricinus.

Rat hepatocytes have the potential to secrete three similar acidic glycoproteins, serine protease inhibitors 1, 2 and 3 (SPI-1, SPI-2, SPI-3), recognized by the same antibodies. They were synthesized as precursors of comparable sizes (45 kDa), which were post-translationally modified by N-glycosylation at three (SPI-3) or four (SPI-1 and SPI-2) sites. This appeared to account for the size difference of mature proteins. The mRNA sequences, derived from cDNA clones, displayed a high degree of similarity (70-90%), except the sequence of the antiproteasereactive centers which were completely divergent. SPI-1 and SPI-2 mRNAs were of similar sizes (1.8 kb), and were smaller than that of SPI-3 (2.2 kb); the difference corresponded to a longer, 3'-end untranslated sequence. Production of SPI-1 and SPI-2, which was constitutive in the normal animal, could be abolished by hypophysectomy and was strongly decreased during acute inflammation. In contrast, production of SPI-3, which was barely detectable in normal rats, was transiently induced during inflammation.The family of serine proteinase inhibitors, referred to as serpins (for a review, see [l]), appears to display, from a functional point of view, a great deal of diversity. While many members of this continuously growing family (e. g. cc,-antitrypsin, ccl-antichymotrypsin, antithrombin 111, serine proteinase inhibitors, a,-antiplasmin, plasminogen activator inhibitor 1 and horse leukocyte elastase inhibitor) have the wellestablished property of inhibiting serine proteases by forming irreversible complexes in a 1 : 1 molar ratio with proteinases [2], several others are not proteinase inhibitors. This subclass includes precursors of biologically active peptides such as angiotensinogen [3,4], carrier proteins like thyroxine-binding protein [5] and corticosteroid-binding globulin 161, and proteins like ovalbumin [7] and the barley protein Z [S], which do not possess any well-defined function. Another interesting feature of the serpins is the fact that a variety of factors have been shown to control the expression of their genes. Thus, genes encoding ovalbumin and related proteins are regulated by steroid hormones [9], those encoding antiproteases that belong to the group of acute-phase proteins [lo, 111 are under the control of glucocorticoids and inflammatory cytokines (for a review, see [12]) and the gene encoding the plasminogen activator inhibitor type 1 is regulated by various effectors including hormones and growth factors (for a review, see 1131). Serine proteinase inhibitors (SPI), secreted by rat liver, represent a remarkable example of the aforementioned feature. Rat hepatocytes have been shown to secrete proteins Correspondence to A.

No abstract