Molecular basis of intracellular regulation of thiol proteinase inhibitors

Functional expression of amyloidogenic human stefins A and B in Pichia pastoris using codon optimization

Complementary DNAs encoding human stefins A (HSA) and B (HSB) were synthesized using Pichia-preferred codons by overlap extension PCR. The full-length genes were ligated downstream of the glyceraldehyde-3-phosphate dehydrogenase promoter in the Pichia expression vector pGAPZαC and successfully expressed in Pichia pastoris strain X-33. Functional recombinant HSA and HSB proteins were purified from culture medium at yields of 121.3 ± 13.5 (n = 3) and 95.4 ± 4.1 (n = 3) mg/L, respectively. Using this expression strategy, we demonstrated that high levels of bioactive recombinant HSA and HSB can be produced by fermentation in P. pastoris.

Posttranslational processing and modification of cathepsins and cystatins

Cathepsins are an essential protease family in all living cells. The cathepsins play an essential roles such as protein catabolism and protein synthesis. To targeting to various organella and to regulate their activity, the post translational-processing and modification play an important role Cathepsins are translated in polysome as the pre-pro-mature forms. The pre-peptide is removed cotranslationally and then translocated to Golgi-apparatus and the pro-part is removed and the mature-part is glycosylated, and the mature-part is targeted into the lysosome mediated by mannose-6-phosphate signal and the mature-part is bound with their coenzymes. The degradation of the mature-part is started by the limited proteolysis of the ordered nicked bonds to make hydrophobic peptides. The peptides are incorporated into phagosome or proteasome after ubiquitinated and are degrade into amino-acids. Cystatins are endogenous inhibitors of cathepsins. Cystatin α which is only located in skin is phosphorylated at the near C-terminus by protein kinase-C, and the phosphorylate-cystatin α is incorporated into cornified envelope and conjugated with filaggrin-fiber by transglutaminase to form the linker-fiber of skin. The cystatin α is modified by glutathione or make their dimmer, and they are inactive. Those modifications are regulated by the redox-potential by the glutathione.

The role of vascular permeability factor and basic fibroblast growth factor in tumor angiogenesis

In the last decade a considerable amount of research has been dedicated to studying the process of angiogenesis. In the field of tumor biology angiogenesis is a relevant subject of investigation as well, since newly formed blood vessels are required for the growth of tumors and provide an exit route for metastasizing tumor cells. In this review we discuss some aspects of tumor angiogenesis with emphasis on the role that growth factors bFGF and VPF play in this process. A number of biochemical characteristics and biological properties of the two factors and their receptors are reviewed, and the expression of bFGF and VPF in both normal tissues and in tumors is discussed. Finally, we speculate on the use of bFGF and VPF expression as a diagnostic parameter and on possible clinical applications.

Immunological significances of invariant chain from the aspect of its structural homology with the cystatin family

The primary structure of p31 of invariant chain (Ii-chain) shows about 50% homology with those of the cystatin family which are endogenous cysteine protease inhibitors. The binding domains between Ii-chain and HLA-DR-7 were estimated from the structural homology between cystatin and Ii-chain and also between cathepsins and DR-7, respectively. The QL64-71 and GS76-88 of Ii-chain were estimated to be the binding domains with GG45-51 and VS57-63 of HLA-DR7, respectively. The purified human Ii-chain from spleen is capable of forming four molecular forms from monomer to tetramer by redox-potential dependent disulfide bond formation. The Ii-chain inhibits cathepsin L and H competitively as a dimer and the K(i) value for cathepsin L was 4.1 x 10(-8) M, but cathepsin B was not inhibited at all. The Ii-chain showed mainly a dimer (60 kDa) under the assay condition of cathepsins with cysteine and was not degraded by these cathepsins. The Ii-chain may play an important role in the regulation of antigenic peptide presentation to MHC class II.

Mechanism and regulation of antigen processing by cathepsin B

Cellular and humoral immune responses to vaccines of hepatitis B and rabies as antigens were suppressed by specific inhibitors of cathepsin B, anti-cathepsin B antibody and the specific substrate of cathepsin B. The antigenic peptides of these vaccines are processed by cathepsin B and the fragments are capable of binding with the desetope of MHC class II, beta-chain, because one of the active sites of cathepsin B (14, 15) VN217-222 shares high homology with a part of the desetope, VN57-62, of MHC class II, beta-chain. Rechallenge of the synthesized antigenic peptides of these vaccine molecules shows a strong proliferative response to the splenocyte primed by these vaccines. However, the response to these antigenic peptides was not inhibited by cathepsin B inhibitors. These findings suggest that cathepsin B inhibitors do not inhibit any other processes of immune responses than the proteolytic processing of antigens. Some investigators reported recently that the Ii-chain is degraded by purified cathepsin B in vitro (23-25). However, we showed that the suppression of these immune responses by cathepsin B inhibitors is not due to the inhibition of invariant chain degradation. We found that the invariant chain shares about 40% homology with the cystatin family which are the endogenous inhibitors of cysteine proteases (23, 24). Therefore, the Ii-chain is one of the members of the cystatin superfamily and may participate in the regulation of presentation of antigenic peptides and also antigen processing by cathepsin B.

Participation of cathepsin B in processing of antigen presentation to MHC class II

Cellular and humoral immune responses to vaccines of hepatitis B type and rabies were inhibited by specific inhibitors of cathepsin B, specific synthetic substrates of cathepsin B and anti-cathepsin B antibody. Therefore the lysosomal cathepsin B of antigen presenting cells plays an essential role in processing of these antigens for presentation to MHC class II. One of the active sites of cathepsin B, VN217-222 shares highly homologous sequences with a part of the desetope, a binding domain of antigenic peptides, VN57-62 of MHC class II, beta-chain. This evidence suggests that the peptides processed by the substrate specificity of cathepsin B exhibit a common affinity to bind with the desetope of MHC class II, beta-chain.

Structural organization of the gene encoding rat cystatin beta

A genomic DNA clone encompassing the gene (cy beta) encoding rat cystatin beta (Cy beta) was isolated by screening with a rat cy beta cDNA as a probe. The gene spans about 2.6 kb and comprises three exons. The first intron is located between Lys22 and Val23 and the second between Lys56 and Val57 in the deduced amino acid sequence of Cy beta. The second exon contains the highly conserved QVVAG sequence which, unlike the sequence of other cystatin family members, is not split by an intron. In the 5'-upstream region, three SP-1-binding sites exist, but no typical TATA-box or CAAT-box sequences are found. The difference in the organization of the rat cy beta gene, encoding a family-1 cystatin, from that encoding members of the other cystatin families, suggests that cy beta diverged from a common ancestral gene earlier than the separation of genes encoding family-2 and family-3 cystatins.

Changes of lysosomal proteinase activities and their expression in rat cultured keratinocytes during differentiation

The cathepsins B, H and L, lysosomal cysteine proteinases, play a major role in intracellular protein degradation. These proteinase activities and expressions were examined in a Ca2+ regulated epidermal culture system which consists of two morphological cell types: undifferentiated cells grown in low Ca2+ (0.1 mM concentration) and differentiated cells grown in high Ca2+ (1.8 mM concentration), respectively. Cathepsin B and L activities of the differentiated cells showed a several-fold increase compared to that of the undifferentiated cells. In addition, by using CM-cellulose column chromatography, cathepsin B and L were separated and the level of cathepsin L activity increased significantly. Cathepsin B, L and H were also detected by using an immunoblotting procedure in which their bands were expressed after differentiation was induced by the increasing calcium concentration. Cathepsin L activity and immunostaining intensity reached a maximum at 1 or 2 days of differentiation. In contrast, cystatin alpha (an endogenous inhibitor of cysteine-dependent cathepsins) appeared in the final stage of differentiation. These results indicate that the expression of epidermal cathepsins and their endogenous inhibitor are involved in part of the program of cell differentiation and the terminal differentiation process in cultured rat keratinocytes.

The cystatins: protein inhibitors of cysteine proteinases

The last decade has witnessed enormous progress of protein inhibitors of cysteine proteinases concerning their structures, functions and evolutionary relationships. Although they differ in their molecular properties and biological distribution, they are structurally related proteins. All three inhibitory families, the stefins, the cystatins and the kininogens, are members of the same superfamily. Recently determined crystal structures of chicken cystatin and human stefin B established a new mechanism of interaction between cysteine proteinases and their inhibitors which is fundamentally different from the standard mechanism for serine proteinases and their inhibitors.

Bacterial expression of human cysteine proteinase inhibitor stefin A

Stefin A, a cysteine proteinase inhibitor of the cystatin superfamily, has been found to be most abundant in epidermal cells. In order to determine its cellular function, we have expressed human stefin A in Escherichia coli using plasmid expression vectors under the control of bacteriophage T7 RNA polymerase. The heat-stable, antibody-positive bacterial product was isolated using a papain-Sepharose affinity column and was shown to inhibit two cysteine proteinases, papain and human cathepsin B. Recombinant stefin A may have commercial and therapeutic potential in situations requiring inhibition of cysteine proteinase activities, and in cosmetics, as an ingredient in skin creams.

Proteinases and their inhibitors in cells and tissues

A large body of evidence has been assembled to indicate the substantial importance of proteolytic processes in various physiological functions. It has recently become clear too that endo-acting peptide bond hydrolases provisionally characterized and classified at present as serine, cysteine, aspartic and metallo together with unknown catalytic mechanism proteinases sometimes act in cascades. They are controlled by natural proteinase inhibitors present in cells and body fluids. In the first part of the present monograph the author was concerned to present an overview on the morphological and physiological approach to localization, surveying reaction principles and methods suitable for visualization of proteolytic enzymes and their natural and synthetic inhibitors. In the second part the roles played by proteinases have been summarized from the point of view of cell biology. The selection of earlier and recent data reviewed on the involvement of proteolysis in the behavior of individual cells reveals that enzymes, whether they be exogeneous or intrinsic, can be effective and sensitive modulators of cellular growth and morphology. There exists a close correlation between malignant growth and degradation of cells. It appears likely that as yet unknown or at least so far inadequately characterized factors that influence the survival or the death of cells may turn out to be proteinases. The causal role of extracellular proteolysis in cancer cell metastases, in stopping cancer cell growth and in cytolysis remains for further investigated. Ovulation, fertilization and implantation are basic biological functions in which proteolytic enzymes play a key role. The emergence of new approaches in reproductive biology and a growing factual basis will inevitably necessitate a reevaluation of present knowledge of proteolytic processes involved. The molecular aspects of intracellular protein catabolism have been discussed in terms of the inhibition of lysosomal and/or non-lysosomal protein breakdown. Peptide and protein hormone biosynthesis and inactivation are still at the centre of interest in cell biology, and a number of proteinases have been implicated in both processes. A number of conjectures partly based on the author's own work have been discussed which suggest the possibility of the involvement of proteolysis in exocytosis and endocytosis. The author's optimistic conclusion is that through the common action of biochemists, cell biologists, cytochemists, and pharmacologists the mystery of cellular proteolysis is beginning to be solved.

Total synthesis of the cystatin alpha gene and its expression in E. coli

A gene encoding cystatin alpha has been chemically synthesized, cloned and expressed in E. coli. The gene of 318 base pairs was assembled by enzymatic ligation of 19 oligonucleotides and cloned into a pBR322-derived expression plasmid down stream of the tac promoter. The expression product of the synthetic gene has been purified by Sephadex G-50 column chromatography and shown to have the same properties as those of the authentic protein isolated from rat epidermis.

Collagenolytic cathepsins of rabbit spleen: a kinetic analysis of collagen degradation and inhibition by chicken cystatin

We have investigated the steady state kinetics of the degradation of native fibrillar collagen at pH 3.4 by four collagenolytic cathepsins of rabbit spleen. For each enzyme, the dependence of initial velocity on collagen concentration was well described by the Michaelis-Menten mechanism. Km, expressed as the concentration of triple-helical chains, and kcat values were determined for cathepsins B, L, N and S. The ratio of Kcat to Km suggest that cathepsins L and N are far more effective at collagen solubilization than either cathepsins S or B. Ki values were determined for the inhibition of collagenolytic activity at pH 3.4 using cystatin, a naturally-occurring cysteine proteinase inhibitor. All four cysteine proteinases were inhibited by cystatin in this assay system, although it was found to be a tighter binding inhibitor of cathepsin L, than for cathepsins N and S (approximately 5-fold less), or cathepsin B (approximately 500-fold less).