Tumour necrosis factor-mediated macrophage activation in the target organ is critical for clinical manifestation of uveitis.

Clinically available anti-tumour necrosis factor (TNF) biologics, which inhibit both soluble (sTNF) and transmembrane forms (tmTNF) of TNF, eliminating all TNF signalling, have successfully treated autoimmune diseases including uveitis. These have potentially serious side effects such as reactivation of latent Mycobacterium tuberculosis and, therefore, more specific inhibition of TNF signalling pathways may maintain clinical efficacy while reducing adverse effects. To determine the effects of specific pharmacological inhibition of sTNF on macrophage activation and migration, we used a mouse model of uveitis (experimental autoimmune uveoretinitis; EAU). We show that selective inhibition of sTNF is sufficient to suppress EAU by limiting inflammatory CD11b(+) macrophages and CD4(+) T cell migration into the eye. However, inhibition of both sTNF and tmTNF is required to inhibit interferon-γ-induced chemokine receptor 2, CD40, major histocompatibility complex class II and nitric oxide (NO) up-regulation, and signalling via tmTNF is sufficient to mediate tissue damage. In confirmation, intravitreal inhibition of sTNF alone did not suppress disease, and inflammatory cells that migrated into the eye were activated, generating NO, thus causing structural damage to the retina. In contrast, intravitreal inhibition of both sTNF and tmTNF suppressed macrophage activation and therefore disease. We conclude that sTNF is required for inflammatory cell infiltration into target tissue, but at the tissue site inhibition of both sTNF and tmTNF is required to inhibit macrophage activation and to protect from tissue damage.

An XPG DNA repair defect causing mutagen hypersensitivity in mouse leukemia L1210 cells.

One of the most widely used antitumor drugs is cis-diamminedichloroplatinum(II) (cisplatin), and mechanisms of cisplatin resistance have been investigated in numerous model systems. Many studies have used mouse leukemia L1210/0 as a reference wild-type cell line, and cisplatin-resistant subclones have been derived from it. Increased DNA excision repair capacity is thought to play a key role in the acquired cisplatin resistance, and this has influenced development of drugs for clinical trials. We report here that the L1210/0 line is in fact severely deficient in nucleotide excision repair of damaged DNA in vivo and in vitro. L1210/0 cell extracts could be complemented by extracts from repair-defective human xeroderma pigmentosum (XP) or rodent excision repair cross-complementing (ERCC) mutant cells, except for XPG/ERCC5 mutants. Purified XPG protein could restore repair proficiency to L1210/0 extracts. Expression of mouse XPG mRNA was similar in all L1210 lines studied, suggesting a point mutation or small alteration of XPG in L1210/0 cells. The DNA repair capacity of a cisplatin-resistant subline, L1210/DDP10, is similar to that of type culture collection L1210 cells and to those of other normal mammalian cell lines. Nucleotide excision repair of DNA is thus clearly important in the intrinsic cellular defense against cisplatin. However, in contrast to what is generally believed, enhancement of DNA repair above the normal level in these rodent cells does not appear to be a mechanism of acquired resistance to the drug.

Electron microscopy of DNA excision repair patches produced by human cell extracts.

To characterize the process by which the mammalian nucleotide excision repair complex interacts with DNA to recognize and repair lesions, we have investigated the size and distribution of repair patches induced by human cell extracts in ultraviolet light-irradiated plasmid DNA. Repair synthesis was carried out in a buffer substituting biotinylated dUTP for dTTP, to allow repair patches to be detected by electron microscopy after streptavidin/colloidal gold labelling. Individual repair events on circular plasmids that had undergone repair synthesis in cell extracts were scored as gold particles bound specifically to irradiated molecules. Samples of over 2000 irradiated and unirradiated plasmids were counted. Repair synthesis at ultraviolet light photoproducts typically replaced about 30 nucleotides, since 69% of patches contained only one particle of 10 nm gold and 24% of patches contained two gold particles (each covering approx. 29 nucleotides). In addition, the ordering of repair events among damaged plasmids closely fitted a Poisson distribution, indicating that repair of lesions is achieved via a non-processive, random diffusion mechanism. This suggests that the repair complex is not intrinsically processive.

Non-specific antiviral activity of antisense molecules targeted to the E1 region of human papillomavirus.

Antisense phosphorothioate oligonucleotides (ODN1 0x5 OMe) directed against the E1 start region of human papillomavirus 11 (HPV11) can inhibit papillomavirus induced growth of implanted human foreskin in a mouse xenograft model. Administration of a mismatch control oligonucleotide (ODN9 0x5 OMe), in which guanine was replaced with adenine in the same model, had no effect on papilloma induced growth. However, the apparent antiviral activity of ODN1 0x5 OMe was also shown in a lethal mouse cytomegalovirus (CMV) model, in which the oligonucleotides are not expected to have antisense activity. To understand the mechanisms of action of these oligonucleotides, a mismatch oligonucleotide (ODN61 0x5 OMe) was prepared which retained the CpG motifs of ODN1 0x5 OMe. This was tested in the mouse xenograft model and shown to have moderate inhibitory activity. As a definitive experiment, a comparison was made between the efficacy of the active oligonucleotide ODN1 0x5 OMe against two papilloma viruses HPV11 and HPV40. Both these viruses cause benign genital warts, but differ by four bases in their E1 sequence that was the target for ODN1 0x5 OMe. Papillomavirus induced growth in the mouse xenograft model was inhibited by ODN1 0x5 OMe in both cases, suggesting that oligonucleotide molecules have a non-specific antiviral activity that is not directly related to their antisense sequence.

Identification and characterization of a Dictyostelium discoideum ribosomal protein gene.

We have identified a developmentally repressed large-subunit ribosomal protein gene of Dictyostelium discoideum based on sequence similarity to other ribosomal proteins. Protein rpl7 is homologous to large subunit ribosomal proteins from the rat and possibly to Mycoplasma capricolum and Escherichia coli, but is not similar to three sequenced ribosomal proteins in Dictyostelium. The rpl7 gene is present at one copy per genome, as are six other cloned Dictyostelium ribosomal proteins. Restriction fragment length polymorphisms exist for ribosomal protein genes rpl7, rp1024, and rp110 in strain HU182; most Dictyostelium ribosomal protein genes examined are linked no closer than 30-100 kb to each other in the genome. Dictyostelium ribosomal proteins are known to be developmentally regulated, and levels of rpl7 transcript gradually decrease during the 24-hour development cycle. This drop correlates with that of rp1024, indicating these and other ribosomal protein genes may be coordinately regulated. To determine the cellular location of the protein, we raised antibodies to an rpl7-derived branched synthetic peptide. These antibodies cross-reacted with one protein of the expected size in a ribosomal protein fraction of Dictyostelium, indicating that the product of gene rpl7 is localized in the ribosome.

Co-correction of the ERCC1, ERCC4 and xeroderma pigmentosum group F DNA repair defects in vitro.

The mammalian ERCC1-encoded polypeptide is required for nucleotide excision repair of damaged DNA and is homologous to Saccharomyces cerevisiae RAD10, which functions in repair and mitotic intrachromosomal recombination. Rodent cells representing repair complementation group 1 have nonfunctional ERCC1. We report that repair of UV-irradiated DNA can be reconstituted by combining rodent group 1 cell extracts with correcting protein from HeLa cells. Background repair was minimized by employing fractionated rodent cell extracts supplemented with human replication proteins RPA and PCNA. Group 1-correcting activity has a native molecular mass of 100 kDa and contains the 33 kDa ERCC1 polypeptide, as well as complementing activities for extracts from rodent group 4 and xeroderma pigmentosum group F (XP-F) cells. Extracts of group 1, group 4 or XP-F cells do not complement one another in vitro, although they complement extracts from other groups. The amount of ERCC1 detectable by immunoblotting is reduced in group 1, group 4 and XP-F extracts. Recombinant ERCC1 from Escherichia coli only weakly corrected the group 1 defect. The data suggest that ERCC1 is part of a functional protein complex with group 4 and XP-F correcting activities. The latter two may be equivalent to one another and analogous to S. cerevisiae RAD1.

Repair by human cell extracts of single (6-4) and cyclobutane thymine-thymine photoproducts in DNA.

One cis-syn cyclobutane thymine dimer or one (6-4) thymine-thymine photoproduct was built into an identical sequence of a closed-circular M13 duplex DNA, and nucleotide excision repair synthesis carried out by human cell extracts in the area containing each lesion was determined. Extracts from normal cells repaired the (6-4) photoproduct with a patch size of approximately 20-30 nucleotides, but repair was at least 10-fold lower at the cyclobutane dimer. The (6-4) lesion was repaired with comparable efficiency to a single acetylamino-fluorene-guanine adduct in a similar location. Extract from nucleotide excision repair-deficient xeroderma pigmentosum group A cells could not remove any of these adducts but could complete repair of the lesions after incision with Escherichia coli UvrABC proteins. This direct comparison of repair of two UV photoproducts, in an in vitro system where chromatin assembly and transcription are absent, suggests that the more rapid repair of the (6-4) lesion observed in the mammalian cell genome overall is due in part to a significant difference in the ability of the repair complex to locate and incise these lesions in DNA.

An intrastrand d(GpG) platinum crosslink in duplex M13 DNA is refractory to repair by human cell extracts.

We have examined the ability of human cell extracts to repair the most frequent DNA adduct caused by the cancer chemotherapeutic agent cis-diamminedichloroplatinum(II). A circular DNA duplex with an intrastrand d(GpG) crosslink positioned at a specific site was synthesized. Human cell extracts were unable to induce repair synthesis in a 29-base-pair region encompassing the adduct or in adjacent regions. The same extracts could repair a single defined 2-acetylaminofluorene lesion in a similar location. When molecules containing the platinum adduct were cleaved by Escherichia coli UvrABC enzyme, human cell extracts could perform repair synthesis at the damaged site, suggesting that human enzymes fail to make incisions near the d(GpG) crosslink but can complete repair once incisions are made. This result indicates that most repair synthesis in DNA damaged with multiple cis-diamminedichloroplatinum(II) adducts takes place at lesions other than the predominant d(GpG) crosslink. These data support the idea that the clinical effectiveness of cis-diamminedichloroplatinum(II) may be explained by the inefficient repair of the major DNA adduct caused by this drug.

Differential human nucleotide excision repair of paired and mispaired cisplatin-DNA adducts.

In order to understand the action of the chemotherapeutic drug cisplatin, it is necessary to determine why some types of cisplatin-DNA intrastrand crosslinks are repaired better than others. Using cell extracts and circular duplex DNA, we compared nucleotide excision repair of uniquely placed 1,2-GG, 1,2-AG, and 1,3-GTG cisplatin-crosslinks, and a 2-acetylaminofluorene lesion. The 1,3 crosslink and the acetylaminofluorene lesion were repaired by normal cell extracts approximately 15-20 fold better than the 1,2 crosslinks. No evidence was found for selective shielding of 1,2 cisplatin crosslinks from repair by cellular proteins. Fractionation of cell extracts to remove putative shielding proteins did not improve repair of the 1,2-GG crosslink, and cell extracts did not selectively inhibit access of UvrABC incision nuclease to 1,2-GG crosslinks. The poorer repair of 1,2 crosslinks in comparison to the 1,3 crosslink is more likely a consequence of different structural alterations of the DNA helix. In support of this, a 1,2-GG-cisplatin crosslink was much better repaired when it was opposite one or two non-complementary thymines. Extracts from cells defective in the hMutSalpha mismatch binding activity also showed preferential repair of the 1,3 crosslink over the 1,2 crosslink, and increased repair of the 1,2 adduct when opposite thymines, showing that hMutSalphais not involved in the differential NER of these substrates in vitro. Mismatched cisplatin adducts could arise by translesion DNA synthesis, and improved repair of such adducts could promote cisplatin-induced mutagenesis in some cases.

Cloning of the amino-terminal and 5'-flanking region of the human MUC5AC mucin gene and transcriptional up-regulation by bacterial exoproducts.

To obtain gene regulatory sequence for the mucin gene MUC5AC, we have isolated the MUC5AC amino terminus cDNA and 5'-flanking region. This was possible through the use of rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR) in which the 5' sequence of the human gastric mucin cDNA HGM-1 (1) was used to design the first MUC5AC-specific primer. Primers for subsequent rounds of RACE were designed from the 5'-ends of amplified RACE products. After five rounds of RACE-PCR, we could no longer generate upstream extensions of the cDNA and hypothesized that we had reached the 5'-end. Primer extension and RNase protection analysis confirmed this. Combined nucleotide sequence for the RACE-PCR products was 3.3 kb with an open reading frame encoding 1100 amino acids. A putative translation start site was found at nucleotide +48. This was followed by a 45 nucleotide putative signal sequence. This amino-terminal sequence contains no tandem repeats but is >60% similar to the amino-terminal nucleotide sequence of MUC2. The positions of cysteine residues in this MUC2-similar region are almost 100% conserved between the two genes. Northern analysis showed expression of cognate RNA in the stomach and airway but not muscle and esophagus. This pattern was the same as that obtained using previously reported 3'-MUC5AC sequences. We have cloned approximately 4 kb of genomic DNA upstream of the transcription start site and have sequenced 1366 nucleotides containing a TATA box, a CACCC box, and putative binding sites for NFkappaB and Sp 1. Within 4 kb of the transcription start site are elements mediating transcriptional up-regulation in response to bacterial exoproducts.