Regulation of the Expression of the Prostate-specific Antigen by Claudin-7

Claudins are a family of proteins involved in forming tight junctions between cells. Here we describe two forms of claudin-7 (CLDN-7), a full-length form of CLDN-7 with 211 amino-acid residues and a C-terminal truncated form with 158 amino-acid residues. These two forms of CLDN-7 are able to regulate the expression of a tissue-specific protein, the prostate-specific antigen (PSA), in the LNCaP prostate cancer cell line. We also found that the expression of CLDN-7 is responsive to androgen stimulation in the LNCaP cell line, suggesting that this protein is involved in the regulatory mechanism of androgen. Both forms of claudin-7 are expressed in human prostate, kidney and lung samples, and in most samples, the full-length form of claudin-7 was predominant. However, in some prostate samples from healthy individuals, the truncated form of claudin-7 is predominantly expressed. Our results demonstrated that unlike other claudins, CLDN-7 has both structural and regulatory functions, and the two forms of CLDN-7 may be related to cell differentiation in organ development.     

Molecular cloning and structural and functional characterization of human cathepsin F, a new cysteine proteinase of the papain family with a long propeptide domain.

A cDNA encoding a new cysteine proteinase belonging to the papain family and called cathepsin F has been cloned from a human prostate cDNA library. This cDNA encodes a polypeptide of 484 amino acids, with the same domain organization as other cysteine proteinases, including a hydrophobic signal sequence, a prodomain, and a catalytic region. However, this propeptide domain is unusually long and distinguishes cathepsin F from other proteinases of the papain family. Cathepsin F also shows all structural motifs characteristic of these proteinases, including the essential cysteine residue of the active site. Consistent with these structural features, cathepsin F produced in Escherichia coli as a fusion protein with glutathione S-transferase degrades the synthetic peptide benzyloxycarbonyl-Phe-Arg-7-amido-4-methylcoumarin, a substrate commonly used for functional characterization of cysteine proteinases. Furthermore, this proteolytic activity is blocked by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane, an inhibitor of cysteine proteinases. The gene encoding cathepsin F maps to chromosome 11q13, close to that encoding cathepsin W. Cathepsin F is widely expressed in human tissues, suggesting a role in normal protein catabolism. Northern blot analysis also revealed a significant level of expression in some cancer cell lines opening the possibility that this enzyme could be involved in degradative processes occurring during tumor progression.     

The affinity and kinetics of inhibition of cysteine proteinases by intact recombinant bovine cystatin C.

Recent studies have shown that the bovine cysteine proteinase inhibitor, cystatin C, is synthesized as a preprotein containing a 118-residue mature protein. However, the forms of the inhibitor isolated previously from bovine tissues had shorter N-terminal regions than expected from these results, and also lower affinity for proteinases than human cystatin C. In this work, we report the properties of recombinant, full-length bovine cystatin C having a complete N-terminal region. The general characteristics of this form of the inhibitor, as reflected by the isoelectric point, the far-ultraviolet circular dichroism spectrum, the thermal stability and the changes of tryptophan fluorescence on interaction with papain, resembled those of human cystatin C. The affinity and kinetics of inhibition of papain and cathepsins B, H and L by the bovine inhibitor were also comparable with those of the human inhibitor, although certain differences were apparent. Notably, the affinity of bovine cystatin C for cathepsin H was somewhat weaker than that of human cystatin C, and bovine cystatin C bound to cathepsin L with about a four-fold higher association rate constant than the human inhibitor. This rate constant is comparable with the highest values reported previously for cystatin-cysteine proteinase reactions. The full-length, recombinant bovine cystatin C bound appreciably more tightly to proteinases than the shorter form characterized previously. Digestion of the recombinant inhibitor with neutrophil elastase resulted in forms with truncated N-terminal regions and appreciably decreased affinity for papain, consistent with the forms of bovine cystatin C isolated previously having arisen by proteolytic cleavage of a mature, full-length inhibitor.     

Synthesis and characterization of a native, oligomeric form of recombinant severe acute respiratory syndrome coronavirus spike glycoprotein

We have expressed and characterized the severe acute respiratory syndrome coronavirus (SARS-CoV) spike protein in cDNA-transfected mammalian cells. The full-length spike protein (S) was newly synthesized as an endoglycosidase H (endo H)-sensitive glycoprotein (gp170) that is further modified into an endo H-resistant glycoprotein (gp180) in the Golgi apparatus. No substantial proteolytic cleavage of S was observed, suggesting that S is not processed into head (S1) and stalk (S2) domains as observed for certain other coronaviruses. While the expressed full-length S glycoprotein was exclusively cell associated, a truncation of S by excluding the C-terminal transmembrane and cytoplasmic tail domains resulted in the expression of an endoplasmic reticulum-localized glycoprotein (gp160) as well as a Golgi-specific form (gp170) which was ultimately secreted into the cell culture medium. Chemical cross-linking, thermal denaturation, and size fractionation analyses suggested that the full-length S glycoprotein of SARS-CoV forms a higher order structure of approximately 500 kDa, which is consistent with it being an S homotrimer. The latter was also observed in purified virions. The intracellular form of the C-terminally truncated S protein (but not the secreted form) also forms trimers, but with much less efficiency than full-length S. Deglycosylation of the full-length homotrimer with peptide N-glycosidase-F under native conditions abolished recognition of the protein by virus-neutralizing antisera raised against purified virions, suggesting the importance of the carbohydrate in the correct folding of the S protein. These data should aid in the design of recombinant vaccine antigens to prevent the spread of this emerging pathogen.     

Identification of unique truncated KC/GRO beta chemokines with potent hematopoietic and anti-infective activities

SK&F 107647, a previously described synthetic immunomodulatory peptide, indirectly stimulates bone marrow progenitor cells and phagocytic cells, and enhances host defense effector mechanisms in bacterial and fungal infection models in vivo. In vitro, SK&F 107647 induces the production of a soluble mediator that augments colony forming cell (CFU-GM) formation in the presence of CSFs. In this paper we purified and sequenced the stromal cell-derived hematopoietic synergistic factors (HSF) secreted from both murine and human cell lines stimulated with SK&F 107647. Murine HSF is an N-terminal 4-aa truncated form of the CXC chemokine, KC, while human HSF was identified as an N-terminal 4-aa truncated form of the CXC chemokine, GRO beta. In comparison to their full-length forms, truncated KC and truncated GRO beta were 10 million times more potent as synergistic growth stimulants for CFU-GM. Enhanced potency of these novel truncated chemokines relative to their full-length forms was also demonstrated in respiratory burst assays, CD11b Ag expression, and intracellular killing of the opportunistic pathogen, Candida albicans. Administration of truncated KC significantly enhanced survival of mice lethally infected with C. albicans. The results reported herein delineate the biological mechanism of action of SK&F 107647, which functions via the induction of unique specific truncated forms of the chemokines KC and GRO beta. To our knowledge, this represents the first example where any form of KC or GRO beta were purified from marrow stromal cells. Additionally, this is the first demonstration of in vivo efficacy of a CXC chemokine in an animal infectious fungal disease model.     

Deletions in the regulatory or kinase domains of protein kinase C-alpha cause association with the cell nucleus.

We have constructed expression plasmids carrying protein kinase C (PKC) cDNAs with deletions in the coding region. Two truncated molecules, consisting only of the kinase domain of PKC-alpha, were generated by removing parts of the cDNA coding for the regulatory region. Another mutant molecule was created by deleting 95 amino acids from the C-terminal part of the molecule. The full-length cDNA coding for PKC-alpha and its deletion constructs was expressed in COS cells. Using cell fractionation experiments and immunofluorescence staining, we demonstrate here that in contrast to the cytosolic localization of full-length PKC-alpha, the truncated forms, coding only for the kinase domain, were found exclusively in the cell nucleus. Further subfractionation of nuclei isolated from these transfected cells indicated partial association with the nuclear envelopes. Expression of the cDNA lacking the C-terminal part of the molecule in COS cells encoded a truncated molecule that was found both in the cytosol and in the nucleus. We also show that translocation of full-length PKC-alpha molecules to the cell nucleus occurred in response to phorbol ester treatment. Thus, it appears that accumulation of PKC-alpha in the nucleus results either by phorbol ester activation or by deletions of specific regions of the molecule. A molecular mechanism for the nuclear translocation of phorbol ester-activated PKC-alpha or its truncated molecules is suggested.     

Domain organization, folding and stability of bacteriophage T4 fibritin, a segmented coiled-coil protein.

Fibritin is a segmented coiled-coil homotrimer of the 486-residue product of phage T4 gene wac. This protein attaches to a phage particle by the N-terminal region and forms fibrous whiskers of 530 A, which perform a chaperone function during virus assembly. The short C-terminal region has a beta-annulus-like structure. We engineered a set of fibritin deletion mutants sequentially truncated from the N-termini, and the mutants were studied by differential scanning calorimetry (DSC) and CD measurements. The analysis of DSC curves indicates that full-length fibritin exhibits three thermal-heat-absorption peaks centred at 321 K (Delta H=1390 kJ x mol trimer(-1)), at 336 K (Delta H=7600 kJ x mol trimer(-1)), and at 345 K (Delta H=515 kJ x mol trimer(-1)). These transitions were assigned to the N-terminal, segmented coiled-coil, and C-terminal functional domains, respectively. The coiled-coil region, containing 13 segments, melts co-operatively as a single domain with a mean enthalpy Delta Hres=21 kJ x mol residue(-1). The ratio of Delta HVH/Delta Hcal for the coiled-coil part of the 120-, 182-, 258- and 281-residue per monomer mutants, truncated from the N-termini, and for full-length fibritin are 0.91, 0.88, 0.42, 0.39, and 0.13, respectively. This gives an indication of the decrease of the 'all-or-none' character of the transition with increasing protein size. The deletion of the 12-residue-long loop in the 120-residue fibritin increases the thermal stability of the coiled-coil region. According to CD data, full-length fibritin and all the mutants truncated from the N-termini refold properly after heat denaturation. In contrast, fibritin XN, which is deleted for the C-terminal domain, forms aggregates inside the cell. The XN protein can be partially refolded by dilution from urea and does not refold after heat denaturation. These results confirm that the C-terminal domain is essential for correct fibritin assembly both in vivo and in vitro and acts as a foldon.     

Isolation and sequencing of a cDNA clone encoding rat liver lysosomal cathepsin D and the structure of three forms of mature enzymes

We isolated and sequenced a cDNA clone corresponding to the entire coding sequence of rat liver lysosomal cathepsin D. The deduced amino acid sequence revealed that cathepsin D consists of 407 amino acid residues (Mr 44,608) and the 20 NH2-terminal residues seem to constitute a cleavable signal peptide after which 44 amino acid residues follow as a propeptide. Two putative N-linked glycosylation sites and aspartic acid in the active site are as well conserved as those of human lysosomal cathepsin D. In the NH2-terminal sequence analysis of two isolated heavy chains of the mature enzyme, the termini were assigned as tryptophan (118th residue) and glycine (165th or 166th residue), respectively, hence demonstrates that the two heavy chains derive from a split of the single chain of cathepsin D at position between 117th and 118th or between 164th and 165th or 165th and 166th amino acids. We conclude that cathepsin D in rat liver lysosomes is a mixture of three forms composed of a single and two two-chain forms. However, the amounts of the two two-chain forms are low compared with that of the single chain form. Densidometric determination after SDS-PAGE revealed that the two two-chain forms account for less than 5% of the single chain form. There is a 82% similarity in amino acid level between rat and human liver lysosomal cathepsin D.     

The exon 6ABC region of amelogenin mRNA contribute to increased levels of amelogenin mRNA through amelogenin protein-enhanced mRNA stabilization

We recently demonstrated that the reuptake of full-length amelogenin protein results in increased levels of amelogenin mRNA through enhanced mRNA stabilization (Xu, L., Harada, H., Tamaki, T. Y., Matsumoto, S., Tanaka, J., and Taniguchi, A. (2006) J. Biol. Chem. 281, 2257-2262). Here, we examined the molecular mechanism of enhanced amelogenin mRNA stabilization. To identify the cis-regulatory region within amelogenin mRNA, we tested various reporter systems using a deletion series of reporter plasmids. A deletion at exon 6ABC of amelogenin mRNA resulted in a 2.5-fold increase in the amelogenin mRNA expression level when compared with that of full-length mRNA, indicating that a cis-element exists in exon 6ABC of amelogenin mRNA. Furthermore, Northwestern analysis demonstrated that amelogenin protein binds directly to its mRNA in vitro, suggesting that amelogenin protein acts as a trans-acting protein that specifically binds to this cis-element. Moreover, recombinant mouse amelogenin protein extended the half-life of full-length amelogenin mRNA but did not significantly alter the half-life of exon 6ABC-deletion mutant mRNA. The splice products produced by deletion of exon 6ABC are known as leucine-rich amelogenin peptides and have signaling effects on cells. Our findings also suggest that the regulation of full-length amelogenin protein expression differs from the regulation of leucine-rich amelogenin peptide expression.     

The transmembrane region of Gurken is not required for biological activity, but is necessary for transport to the oocyte membrane in Drosophila

During Drosophila oogenesis, localization of the transforming growth factor alpha (TGFalpha)-like signaling molecule Gurken to the oocyte membrane is required for polarity establishment of the egg and embryo. To test Gurken domain functions, full-length and truncated forms of Gurken were expressed ectopically using the UAS/Gal4 expression system, or in the germline using the endogenous promoter. GrkDeltaC, a deletion of the cytoplasmic domain, localizes to the oocyte membrane and can signal. GrkDeltaTC, which lacks the transmembrane and cytoplasmic domains, retains signaling ability when ectopically expressed in somatic cells. However, in the germline, the GrkDeltaTC protein accumulates throughout the oocyte cytoplasm and cannot signal. In addition, we found that several strong gurken alleles contain point mutations in the transmembrane region. We conclude that secretion of Gurken requires its transmembrane region, and propose a model in which the gene cornichon mediates this process.     

Inhibition of Cellular Adhesion by Immunological Targeting of Osteopontin Neoepitopes Generated through Matrix Metalloproteinase and Thrombin Cleavage

Osteopontin (OPN), a secreted protein involved in inflammatory processes and cancer, induces cell adhesion, migration, and activation of inflammatory pathways in various cell types. Cells bind OPN via integrins at a canonical RGD region in the full length form as well as to a contiguous cryptic site that some have shown is unmasked upon thrombin or matrix metalloproteinase cleavage. Thus, the adhesive capacity of osteopontin is enhanced by proteolytic cleavage that may occur in inflammatory conditions such as obesity, atherosclerosis, rheumatoid arthritis, tumor growth and metastasis. Our aim was to inhibit cellular adhesion to recombinant truncated proteins that correspond to the N-terminal cleavage products of thrombin- or matrix metalloproteinase-cleaved OPN in vitro. We specifically targeted the cryptic integrin binding site with monoclonal antibodies and antisera induced by peptide immunization of mice. HEK 293 cells adhered markedly stronger to truncated OPN proteins than to full length OPN. Without affecting cell binding to the full length form, the raised monoclonal antibodies specifically impeded cellular adhesion to the OPN fragments. Moreover, we show that the peptides used for immunization were able to induce antisera, which impeded adhesion either to all OPN forms, including the full-length form, or selectively to the corresponding truncated recombinant proteins. In conclusion, we developed immunological tools to selectively target functional properties of protease-cleaved OPN forms, which could find applications in treatment and prevention of various inflammatory diseases and cancers.     

LEF-1的调控及其与肿瘤的关系研究进展

淋巴细胞增强因子（lymphoid enhancer factor,LEF-1）是Wnt信号通路中的一个重要调控因子。其异常表达对肿瘤细胞增殖和凋亡调控起关键作用。LEF-1作为Wnt信号通路核内的转录因子,还与T细胞受体α（TCRα）的增强子相互作用形成特定的构象,从而与其他因子结合共同调节基因的表达。同时,LEF-1为一多启动子基因,编码产生致瘤的全长形式的LEF-1和对Wnt信号通路起负向调控作用的截短形式的LEF-1。诸多研究结果表明肿瘤的发生发展与LEF／TCF各亚型的比例有关。就Wnt／LEF-1信号通路的调控以及与肿瘤的关系做一综述。     

The retinoblastoma gene product regulates progression through the G1 phase of the cell cycle.

The RB gene product is a nuclear phosphoprotein that undergoes cell cycle-dependent changes in its phosphorylation status. To test whether RB regulates cell cycle progression, purified RB proteins, either full-length or a truncated form containing the T antigen-binding region, were injected into cells. Injection of either protein early in G1 inhibits progression into S phase. Co-injection of anti-RB antibodies antagonizes this effect. Injection of RB into cells arrested at G1/S or late in G1 has no effect on BrdU incorporation, suggesting that RB does not inhibit DNA synthesis in S phase. These results indicate that RB regulates cell proliferation by restricting cell cycle progression at a specific point in G1 and establish a biological assay for RB activity. Neither co-injection of RB with a T antigen peptide nor injection into cells expressing T antigen prevents cells from progressing into S phase, which supports the hypothesis that T antigen binding has functional consequences for RB.     

Distinctly different gene structure of KLK4/KLK-L1/prostase/ARM1 compared with other members of the kallikrein family: intracellular localization, alternative cDNA forms, and Regulation by multiple hormones

The tissue kallikreins (KLKs) form a family of serine proteases that are involved in processing of polypeptide precursors and have important roles in a variety of physiologic and pathological processes. Common features of all tissue kallikrein genes identified to date in various species include a similar genomic organization of five exons, a conserved triad of amino acids for serine protease catalytic activity, and a signal peptide sequence encoded in the first exon. Here, we show that KLK4/KLK-L1/prostase/ARM1 (hereafter called KLK4) is the first significantly divergent member of the kallikrein family. The exon predicted to code for a signal peptide is absent in KLK4, which is likely to affect the function of the encoded protein. Green fluorescent protein (GFP)-tagged KLK4 has a distinct perinuclear localization, suggesting that its primary function is inside the cell, in contrast to the other tissue kallikreins characterized so far that have major extracellular functions. There are at least two differentially spliced, truncated variants of KLK4 that are either exclusively or predominantly localized to the nucleus when labeled with GFP. Furthermore, KLK4 expression is regulated by multiple hormones in prostate cancer cells and is deregulated in the androgen-independent phase of prostate cancer. These findings demonstrate that KLK4 is a unique member of the kallikrein family that may have a role in the progression of prostate cancer.