Protective Effect Against Cancer of Antibodies to the Large Subunits of Both RNA Polymerases I and III in Scleroderma

OBJECTIVE

While compelling data suggest a cancer-induced autoimmunity model in scleroderma patients with anti-RNA polymerase III large subunit (anti-RPC155) antibodies, ~85% of these patients do not manifest cancer. This study was undertaken to determine whether additional autoantigens are targeted in anti-RPC155-positive scleroderma patients without detectable cancer.

METHODS

The study included 168 scleroderma patients with anti-RPC155 antibodies (80 with a history of cancer and 88 with no cancer diagnosis after >5 years of follow-up). Thirty-five sera (17 from patients with cancer and 18 from patients without cancer) were randomly selected for autoantibody discovery using immunoprecipitation (IP). An ~194-kd band was enriched in the subgroup without cancer; this was identified as RNA polymerase I large subunit (RPA194).

RESULTS

RPA194 generated by in vitro transcription/translation was used for IPs performed on the entire cohort to test whether anti-RPA194 was enriched among anti-RPC155-positive patients without cancer. Anti-RPA194 antibodies were significantly more common in the group without cancer (16 [18.2%] of 88) than in the group with cancer (3 [3.8%] of 80) (P = 0.003). Patients with both anti-RPA194 and anti-RPC155 were significantly less likely to have severe gastrointestinal disease than patients with anti-RPC155 only (26.3% versus 51.0%; P = 0.043).

CONCLUSION

Anti-RPA194 antibodies are enriched in anti-RPC155-positive scleroderma patients without cancer. Since somatic mutations in the gene encoding RPC155 in cancer in scleroderma patients appears to play a role in immune response initiation against RPC155 in those patients, these data raise the possibility that the development of immune responses to both RPC155 and RPA194 may influence clinical cancer emergence. Further study is required to define whether different autoantibody combinations have utility as tools for cancer risk stratification in scleroderma.

Immunization of nonautoimmune mice with DNA binding domains of the largest subunit of RNA polymerase I results in production of anti-dsDNA and anti-Sm/RNP antibodies

Antibodies against the N-terminal (NT) but not the basic domain (BD), DNA binding regions of the largest subunit (S1) of RNA polymerase I (RNAPI) were detected in the sera of MRL-lpr/lpr lupus mice. Antibodies against both RNAPI(S1)-NT and -BD, as well as other systemic lupus erythematosus (SLE) autoantigens (La, ribosomal P proteins and Sm/RNP) were produced by rabbits immunized with anti-DNA antibodies that had been affinity purified from SLE patients. Immunization of nonautoimmune mice (Balb/c) with RNAPI(S1)-NT, RNAPI(S1)-BD, or La in the form of GST fusion proteins, induced production of anti-double-stranded (ds) DNA and anti-Sm/RNP. GST-P1 did not induce an anti-dsDNA response in these mice. These results demonstrate that RNAPI(S1)-NT, RNAPI(S1)-BD and La can participate in an anti-autoantigen/anti-DNA antibody loop during an SLE-like autoimmune response.

A case of renal crisis in a Korean scleroderma patient with anti-RNA polymerase I and III antibodies

Scleroderma (SSc) renal crisis has been reported to be associated with anti-RNA polymerase I and III (RNAP I/III) antibodies in Caucasians and the Japanese. However, no report is available for Korean SSc patients. Here, we describe the case of a 65-yr-old female SSc patient who developed renal crisis and whose serum contained anti-RNAP I/III antibodies. She was finally diagnosed as having diffuse cutaneous SSc based on skin thickening proximal to the elbows and knees. Sudden hypertension, oliguria, and pulmonary edema were features of her renal crisis. Despite the use of captopril and adequate blood pressure control, her renal function deteriorated. Subsequent renal biopsy findings showed severe fibrinoid necrosis with luminal obliteration in interlobar arteries and arterioles consistent with SSc renal crisis. Serum anti-RNAP I/III antibodies were detected by radioimmunoprecipitation. This is the first report of a renal crisis in a Korean SSc patient with RNAP I/III antibodies.

Nucleolar staining cannot be used as a screening test for the scleroderma marker anti–RNA polymerase I/III antibodies

OBJECTIVE

Anti-RNA polymerase I/III (anti-RNAP I/III) antibodies are clinically useful markers of scleroderma, and their presence is associated with diffuse skin disease and an increased risk of cardiac and kidney involvement. Although RNAP I antibodies localize to the nucleolus, nucleolar staining by many anti-RNAP antibody-positive sera is not always observed. Nucleolar staining by anti-RNAP antibody-positive sera was examined by double staining with antifibrillarin antibodies to evaluate whether nucleolar staining can be used as a screening test for anti-RNAP I/III antibodies. In addition, the relationships between nucleolar staining and levels of anti-RNAP III antibodies were examined by enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation (IP) assay.

METHODS

Sera were tested using immunofluorescent antinuclear antibodies on HEp-2 cell slides, by anti-RNAP III ELISA, and by IP assay using (35)S-labeled K562 cell extract. Nucleolar staining by anti-RNAP antibody IP-positive sera was confirmed by double staining using antifibrillarin monoclonal antibodies. The levels of anti-RNAP III antibodies were quantitated by ELISA and by IP assay using a serially diluted reference serum as a standard, and their relationship was analyzed.

RESULTS

All 18 anti-RNAP I/III antibody-positive sera showed nuclear speckled patterns, but nucleolar staining was readily noticeable in only 44% of the sera. A positive correlation was found between ELISA and IP units for anti-RNAP III antibodies. The levels of anti-RNAP III antibodies and anti-RNAP I antibodies correlated well, with the exception of a few sera. Levels of anti-RNAP III antibodies were low in sera with nucleolar staining, whereas several sera with high levels of anti-RNAP I antibodies clearly showed nucleolar staining.

CONCLUSION

Although some sera positive for anti-RNAP I/III antibodies clearly stain nucleoli, nucleolar staining is inconsistent and cannot be used to screen for anti-RNAP I/III antibodies.

Autoantibodies and autoantigens in the urine of SLE patients

Autoantibodies against RNA polymerase I (RNAPI), DNA, La and ribosomal P proteins were detected in the urine of systemic lupus erythematosus (SLE) patients, many with normal protein excretion rates. In a number of cases, the antibodies were detectable in the urine but not the serum sample of the same patient. The presence and relative concentrations of the urinary autoantibodies correlated with disease activity. RNAPI antigens were detected in the urine of SLE patients by radioimmunoassay and immunoblotting using rabbit antisera prepared against the purified holoenzyme. Immunoaffinity purification of the rabbit anti-RNAPI with SLE urine proteins resulted in antibodies directed primarily against the largest RNAPI subunit (S1; 194 kDa). Antibodies prepared against recombinant fusion proteins representing the DNA binding regions of human RNAPI(S1) reacted with a 35 kDa SLE urinary protein, a putative fragment of RNAPI(S1). Ribosomal protein P0 was detected in SLE patients' urine by immunoblotting, using rabbit antiserum prepared against recombinant human P1 fusion protein. The relative quantities of urinary P0 correlated with disease status. Analysis of urinary autoantibodies and corresponding antigens in conjunction with analysis of serum autoantibodies may be of value for the purpose of monitoring disease activity.

HLA class II alleles in systemic sclerosis patients with anti-RNA polymerase I/III antibody: associations with subunit reactivities

OBJECTIVE

To examine HLA class II gene associations with anti-RNA polymerase (RNAP) I/III antibody responses in patients with systemic sclerosis (SSc).

METHODS

HLA-DRB1, DRB3, DRB4, and DQB1 alleles were determined using polymerase chain reaction-based methods in 257 SSc patients (129 Japanese and 128 Caucasians) and 271 race-matched regional controls (138 Japanese and 133 Caucasians). Anti-RNAP I/III antibodies were identified by immunoprecipitation assay, and reactivities to individual RNAP subunits were determined by immunoblots using affinity-purified RNAP I, II, and III.

RESULTS

Serum anti-RNAP I/III antibody was detected in 10 (8%) Japanese and 24 (19%) Caucasian patients with SSc. The presence of anti-RNAP I/III antibodies was associated with DRB1*0405, DRB4*01, and DQB1*0401 in Japanese, and with DRB3*02 in Caucasians, but these associations were weak and inconsistent between these 2 ethnic groups. When anti-RNAP I/III-positive SSc patients were divided into 2 groups based on the presence or absence of reactivities to individual RNAP subunit proteins, significant associations of anti-IIa/IIo reactivity with DRB3*02, anti-Ia reactivity with DRB1*04, anti-43-kDa subunit reactivity with DRB4*01, and anti-34-kDa subunit reactivity with DRB1*15 were detected. These HLA associations with subunit reactivities were generally shared by Japanese and Caucasian patients with SSc.

CONCLUSION

Our results suggest that in patients with SSc, anti-RNAP I/III antibodies are composed of subsets defined by combinations of reactivities to individual RNAP subunits having specific HLA class II correlations.

Isolation and characterization of monoclonal antibodies directed against subunits of human RNA polymerases I, II, and III

Human nuclei contain three different RNA polymerases: polymerases I, II, and III. Each polymerase is a multi-subunit enzyme with 12-17 subunits. The localization of these subunits is limited by the paucity of antibodies suitable for immunofluorescence. We now describe eight different monoclonal antibodies that react specifically with RPB6 (also known as RPA20, RPB14.4, or RPC20), RPB8 (RPA18, RPB17, or RPC18), RPC32, or RPC39 and which are suitable for such studies. Each antibody detects one specific band in immunoblots of nuclear extracts; each also immunoprecipitates large complexes containing many other subunits. When used for immunofluorescence, antibodies against the subunits shared by all three polymerases (i.e., RPB6, RPB8) gave a few bright foci in nucleoli and nucleoplasm, as well as many fainter nucleoplasmic foci; all the bright foci were generally distinct from speckles containing Sm antigen. Antibodies against the two subunits found only in polymerase III (i.e., RPC32, RPC39) gave a few bright and many faint nucleoplasmic foci, but no nucleolar foci. Growth in two transcriptional inhibitors-5, 6-dichloro-1-beta-d-ribofuranosylbenzimidazole and actinomycin D-led to the redistribution of each subunit in a characteristic manner.

Analysis of autoantibodies against RNA polymerases using immunoaffinity-purifed RNA polymerase I, II, and III antigen in an enzyme-linked immunosorbent assay

Autoantibodies against RNA polymerases (RNAP) have been reported to occur in patients with a wide variety of connective tissue diseases (CTD), including systemic sclerosis (SSc), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD). The frequency of anti-RNAP antibodies has been reported to vary widely between different CTD diseases in studies examining different patient populations. Furthermore, these studies have been limited by the fact that methods have not previously been available for detecting antibodies against RNAP which are both rapid and quantitative. We have developed an enzyme-linked immunosorbent assay (ELISA) for rapidly quantitating antibodies against RNAP I, II, and III. We have utilized both the ELISA and the immunoprecipitation of 35S-labeled HeLa cells to analyze sera from a large cohort of well-characterized Caucasian CTD patients for the presence of anti-RNAP antibodies. We found excellent concordance for the presence of anti-RNAP antibodies using immunoprecipitation and ELISA. Anti-RNAP antibodies occurred predominantly among female patients with the diffuse form of SSc and were detected in 8/36 (22%) of Caucasian patients with diffuse SSc and 1/53 (2%) with limited SSc. Anti-RNAP antibodies occurred in 1/42 (2%) of patients with SLE. Anti-RNAP antibodies did not occur in MCTD (0/49). Antibodies against RNAP were rare among antinucleolar-reactive sera, occurring in only 3/200 (1.5%). The RNAP ELISA provides a validated method which can be rapidly utilized in a clinical diagnostic laboratory setting to identify SSc patients who are at risk for developing diffuse SSc with multiorgan involvement and hypertensive renal crisis.

Anti-RNA polymerases and other autoantibody specificities in systemic sclerosis

Sera from 735 patients with systemic sclerosis were classified according to antinuclear antibody (ANA) pattern as follows: centromere (25%), homogeneous (26%), fine speckled (21%), fine speckled with nucleolar (14%), coarse speckled (7%), nucleolar only (3%) and cytoplasmic only (3%). Immunoprecipitations using 35S-labelled HeLa cell antigen extract were performed using sera from 374 of these patients to detect the systemic sclerosis-specific antibodies to RNA polymerases I and III. The sera were selected to represent each ANA group, but focused on those giving fine speckled nucleoplasmic staining (with or without nucleolar staining) where all 86 sera positive for these antibodies were concentrated. Immunoprecipitates from a further 93 sera from patients with ANA-positive autoimmune diseases other than systemic sclerosis did not precipitate RNA polymerases. In addition, all sera were tested for antibodies to the extractable nuclear antigens topoisomerase I, nRNP, Ro, La and PM-Scl. Sera positive for antibodies to these antigens gave clear correlations with ANA patterns but, of the examples tested, none contained antibodies precipitating RNA polymerase I or III. Thus, sera containing antibodies to RNA polymerases I and III were exclusive of both anticentromere and anti-topoisomerase I, and formed a major serological subgroup (11.7%). Clinically, 77% were patients with diffuse cutaneous disease reflected by higher skin scores and a significantly higher incidence of renal involvement (33%) than patients with antibodies to topoisomerase I (3%).

Specific intranucleolar distribution of Hsp70 during heat shock in polytene cells

Hsp70, the most abundant and conserved heat shock protein, has been described as strongly concentrating in the nucleolus during heat shock. The important metabolic processes that take place in the nucleolus, rDNA transcription, processing, and assembling with ribosomal proteins, and the nucleolar architecture itself are very sensitive to temperature changes. In this work, we have analyzed in detail the nucleolar changes, in structure and activity, induced by temperature in Chironomus thummi salivary gland cells and the fine subnucleolar localization of Hsp70 during heat shock. The optimum temperature chosen to induce the heat shock response was 35 degrees C. Under these conditions transcription of heat shock genes, inactivation of previously active genes and maximum synthesis of Hsps take place, while survival of larvae and recovery were ensured. After 1 h at 35 degrees C, nucleoli change from a uniform control pattern to a segregated pattern of nucleolar components that can be observed even at the light microscopic level. The dense fibrillar component (DFC) and the granular component appeared perfectly differentiated and spatially separated, the former occupying mainly the central inner region surrounded by a rim of granular component. Hsp70 was specifically localized within the DFC upon heat shock as shown by immunolocalization by both light and electron microscopy. Pulse labeling with [3H]uridine proves that rRNA transcription continues during heat shock. The pattern of Hsp70 distribution within the nucleolus correlates with that of newly produced rRNA transcripts. Hsp70 also colocalizes with RNA polymerase I, both being restricted to the DFC. These data show that the DFC seems to be the intranucleolar target for Hsp70 in heat-shocked cells. We discuss these results in relation to the possible function of Hsp70 in the first steps of preribosome synthesis.

Association of the nucleolar transcription factor UBF with the transcriptionally inactive rRNA genes of pronuclei and early Xenopus embryos

When nuclei (pronuclei) were assembled from sperm chromatin in Xenopus egg extract and examined by immunofluorescence microscopy, UBF was concentrated at a single intranuclear dot-like or more extended necklace-like structure. These UBF-foci contained rDNA as demonstrated by in situ hybridization and hence represent the chromosomal nucleolus organizing regions (NORs). Besides UBF, other components of the transcription machinery such as the TATA-box binding protein (TBP) and RNA polymerase I (pol I) as well as several nucleolar proteins could not be detected at the NORs. Immuno-depletion experiments indicated the UBF is maternally provided and taken up by the pronuclei. Essentially the same results were obtained when we examined the NORs of early Xenopus embryos up to the midblastula stage. After this stage, when transcription of the rRNA genes has begun, nucleoli developed and the NORs acquired TBP and pol I. Our results support the hypothesis that UBF is an architectural element which converts the rDNA chromatin into a transcriptionally competent form.

Molecular cloning and characterization of the cDNA encoding the largest subunit of mouse RNA polymerase I

We describe the cloning and analysis of mRPA1, the cDNA encoding the largest subunit (RPA194) of murine RNA polymerase I. The coding region comprises an open reading frame of 5151 bp that encodes a polypeptide of 1717 amino acids with a calculated molecular mass of 194 kDa. Alignment of the deduced protein sequence reveals homology to the beta' subunit of Escherichia coli RNA polymerase in the conserved regions a-h present in all large subunits of RNA polymerases. However, the overall sequence homology among the conserved regions of RPA1 from different species is significantly lower than that observed in the corresponding beta'-like subunits of class II and III RNA polymerase. We have raised two types of antibodies which are directed against the conserved regions c and f of RPA194. Both antibodies are monospecific for RPA194 and do not cross-react with subunits of RNA polymerase II or III. Moreover, these antibodies immunoprecipitate RNA polymerase I both from murine and human cell extracts and, therefore, represent an invaluable tool for the identification of RNA polymerase I-associated proteins.

Localization of yeast RNA polymerase I core subunits by immunoelectron microscopy

Immunoelectron microscopy was used to determine the spatial organization of the yeast RNA polymerase I core subunits on a three-dimensional model of the enzyme. Images of antibody-labeled enzymes were compared with the native enzyme to determine the localization of the antibody binding site on the surface of the model. Monoclonal antibodies were used as probes to identify the two largest subunits homologous to the bacterial beta and beta' subunits. The epitopes for the two monoclonal antibodies were mapped using subunit-specific phage display libraries, thus allowing a direct correlation of the structural data with functional information on conserved sequence elements. An epitope close to conserved region C of the beta-like subunit is located at the base of the finger-like domain, whereas a sequence between conserved regions C and D of the beta'-like subunit is located in the apical region of the enzyme. Polyclonal antibodies outlined the alpha-like subunit AC40 and subunit AC19 which were found co-localized also in the apical region of the enzyme. The spatial location of the subunits is correlated with their biological activity and the inhibitory effect of the antibodies.

20-Hydroxyecdysone stimulates RNA polymerase I activity in silkmoth wing epidermis by increased synthesis and phosphorylation

The activities of RNA polymerases I and II in the wing epidermis of diapausing silkmoth pupae increased about tenfold during the first day after administration of either 20-hydroxyecdysone (20E) or 20E plus juvenile hormone (Katula et al., 1981a). The aim of these studies was to correlate these increases in RNA polymerase I and II activities to their amounts in hormone stimulated wing epidermis. The enzyme activities were measured by standard procedures while their amounts were determined by the application of a modified ELISA with subunit-specific monoclonal antibodies. Results showed that the increase in the amount of RNA polymerase I during the first 24 h accounted for only about 60% of the increase in activity. Alkaline phosphatase decreased the activity of the newly synthesized enzyme by 40-50%. These results indicate that hormone-stimulation of RNA polymerase I activity is due to a combination of synthesis of the enzyme and phosphorylation of the enzyme and/or tightly associated factors. RNA polymerases II and III determined by differential ELISA using a monoclonal antibody specific to a common subunit followed developmental changes similar to those of RNA polymerase I. The amounts and activity of the enzymes during the first 48 h were similar in wing tissue that followed the second pupal development (20E + juvenile hormone) compared to tissue that developed into adult wings (20E).

The HMG box-containing nucleolar transcription factor UBF interacts with a specific subunit of RNA polymerase I

The mammalian transcription activator protein UBF contains five tandemly repeated HMG homology domains which are required for DNA binding. We have used highly purified RNA polymerase I (Pol I) and upstream binding factor (UBF) and investigated whether these two proteins interact in solution. We show by a variety of different experimental approaches, such as immunoprecipitation, glycerol gradient sedimentation, affinity chromatography and protein blotting, that UBF physically associates with Pol I. Mutational analysis reveals that the HMG boxes play an important role in this specific interaction. UBF binds to mouse and yeast Pol I, demonstrating that the interaction of UBF with Pol I has been conserved during evolution. Interestingly, in both species one Pol I-specific subunit (34.5 kDa in yeast and 62 kDa in mouse) was recognized by UBF. No specific interaction was observed with Pol II. Unexpectedly, UBF was found to associate also with a unique subunit of yeast Pol III. This apparent specific interaction of UBF with the two classes of RNA polymerases may reflect functionally important interactions of HMG box-containing transcription factors with the transcriptional apparatus.

Induction of an anti-Fab, anti-DNA and anti-RNA polymerase I autoantibody response network in rabbits immunized with SLE anti-DNA antibody

Systemic lupus erythematosus (SLE)-like anti-IgG Fab autoantibodies (autoAb) were induced in rabbits by immunization with either human, mouse or rabbit anti-DNA Ab. In direct-binding radioimmunoassay (RIA), affinity-purified anti-normal rabbit (NR) Fab autoAb cross-reacted with normal mouse (NM) Fab, ssDNA (but not dsDNA), poly(dA,dT), and RNA polymerase I (RPI). Affinity-purified anti-NM IgG Ab isolated from the same antisera cross-reacted with NR Fab, ssDNA and RPI. In inhibition RIA, soluble NR Fab inhibited anti-NR Fab binding to NR Fab and ssDNA, but enhanced binding to RPI. In contrast, ssDNA or RPI inhibitors had no effect upon autoAb binding to NR Fab. Anti-DNA, anti-RPI and anti-RPI 190 kD subunit autoAb, induced by immunization with lupus mouse anti-DNA Ab, also reacted with NM Fab, but were idiotypically specific for lupus mouse anti-DNA Fab. Further, rabbit anti-DNA and anti-RPI IgG autoAb, induced by immunization with rabbit anti-DNA IgG, were each idiotypically specific for homologous and autologous rabbit anti-ssDNA Fab. Together, these data provide evidence that anti-DNA, anti-RPI and anti-Fab autoAb are linked in a complex, multiple-specific and perhaps regulatory, immune response idiotype network in SLE.

Immunochemical and molecular characterization of anti-RNA polymerase I autoantibodies produced by tight skin mouse

Autoantibodies against nuclear proteins like RNA polymerase I (RNA pol I) are produced in a number of rheumatic autoimmune diseases. Production of antibodies specific for the 190-kD subunit of RNA pol I appears to be characteristic in the patients with systemic sclerosis. Previous investigations have shown that the tight skin (TSK) mouse is an experimental model for systemic sclerosis. In the present study we show that the TSK mice produce high titers of anti-RNA pol I antibodies, both of IgM and IgG classes. To characterize the immunochemical properties of these antibodies we obtained a large panel of hybridomas from these mice. Analysis of these hybridomas revealed that clonal frequency of autoreactive B cells specific for RNA pol I are higher in the TSK mice that in the controls. mAbs obtained from the TSK mice were specific for the 190-kD subunit and cross-reacted with Escherichia coli and phage T7 RNA polymerases (155-, 150-, and 107-kD polypeptides). We have also demonstrated that these antibodies bind better to the phosphorylated enzymes. The anti-RNA pol I mAbs were divided into three groups in terms of their functional property. The first group of antibodies increased the catalytic activity of the enzyme whereas the antibodies of the second group inhibited the enzymatic activity. Competitive inhibition RIAs showed that these two groups of antibodies bound to distinct epitopes. The third group of antibodies was neutral and had no activity on the enzyme function. These results suggest that TSK mouse anti-RNA pol I antibodies recognize three or more conserved epitopes. To understand the molecular basis of the generation of such autoreactive antibodies we analyzed their V gene repertoire. Northern analysis of RNAs of 14 TSK hybridomas showed that the VH genes encoding these antibodies were mainly from VH J558 family. It is possible that these genes were derived from a single germline gene or from a set of related genes of a single subgroup.

Identification of autoantibodies to RNA polymerase II. Occurrence in systemic sclerosis and association with autoantibodies to RNA polymerases I and III

In this study, autoantibodies to RNA polymerase II from sera of patients with systemic sclerosis have been identified and characterized. These antibodies immunoprecipitated polypeptides of 220 kD (IIA) and 145 kD (IIC), the two largest subunits of RNA polymerase II, and bound both subunits in immunoblots. These polypeptides were immunoprecipitated by the anti-RNA polymerase II monoclonal antibody 8WG16, which recognizes the carboxyl-terminal domain of the 220-kD subunit, and their identity to the proteins bound by human sera was confirmed in immunodepletion studies. Sera with anti-RNA polymerase II antibodies also immunoprecipitated proteins that were consistent with components of RNA polymerases I and III. In vitro transcription experiments showed that the human antibodies were an effective inhibitor of RNA polymerase II activity. In indirect immunofluorescence studies, anti-RNA polymerase II autoantibodies stained the nucleoplasm, as expected from the known location of RNA polymerase II, and colocalized with the anti-RNA polymerase II monoclonal antibody. The human sera also stained the nucleolus, the location of RNA polymerase I. From a clinical perspective, these antibodies were found in 13 of 278 patients with systemic sclerosis, including 10 with diffuse and three with limited cutaneous disease, but were not detected in sera from patients with other connective tissue diseases and from normal controls. We conclude that anti-RNA polymerase II antibodies are specific to patients with systemic sclerosis, and that they are apparently associated with antibodies to RNA polymerases I and III. These autoantibodies may be useful diagnostically and as a probe for further studies of the biological function of RNA polymerases.

A modified PABC immunoassay for the quantitation of DNA dependent RNA polymerase I: a procedure applicable to other proteins present in minute amounts and/or isoforms

An indirect enzyme linked immunoassay (ELISA) has been developed to measure the amount of RNA polymerase I (E.C.2.7.7.6) in silkmoth tissue cell extracts. Subunit specific monoclonal antibodies (MABs) were immobilized on the solid substrate by a variation of the widely used Protein-Avidin-Biotin-Capture (PABC) technique. The use of the commercially available biotinylated anti-mouse antibody as a bridge to bind the monoclonal antibody eliminates the need for the biotinylation of the monoclonal antibody in the laboratory. The RNA polymerase in solution was captured by the monoclonal antibody and was measured by the successive binding of rabbit polyclonal antibody and alkaline phosphatase conjugated anti-rabbit antibody. This procedure is more reliable, reproducible and leads to greater sensitivity compared to the direct binding of the monoclonal antibody to the microtiter plate. RNA polymerase I captured by the antibodies from tissue extracts was measured at levels of 0.5 ng/well. This assay system can be utilized as a general procedure to quantitate the levels of proteins present at very low levels and that are found in different isoforms containing multiple and/or shared subunits.

Cloning and characterization of SRP1, a suppressor of temperature-sensitive RNA polymerase I mutations, in Saccharomyces cerevisiae

The SRP1-1 mutation is an allele-specific dominant suppressor of temperature-sensitive mutations in the zinc-binding domain of the A190 subunit of Saccharomyces cerevisiae RNA polymerase I (Pol I). We found that it also suppresses temperature-sensitive mutations in the zinc-binding domain of the Pol I A135 subunit. This domain had been suggested to be in physical proximity to the A190 zinc-binding domain. We have cloned the SRP1 gene and determined its nucleotide sequence. The gene encodes a protein of 542 amino acids consisting of three domains: the central domain, which is composed of eight (degenerate) 42-amino-acid contiguous tandem repeats, and the surrounding N-terminal and C-terminal domains, both of which contain clusters of acidic and basic amino acids and are very hydrophilic. The mutational alteration (P219Q) responsible for the suppression was found to be in the central domain. Using antibody against the SRP1 protein, we have found that SRP1 is mainly localized at the periphery of the nucleus, apparently more concentrated in certain regions, as suggested by a punctate pattern in immunofluorescence microscopy. We suggest that SRP1 is a component of a larger macromolecular complex associated with the nuclear envelope and interacts with Pol I either directly or indirectly through other components in the structure containing SRP1.

Anti-RNA polymerase I antibodies in the sera of MRL lupus mice at the initial stages of disease are directed primarily against phosphorylation-dependent epitopes

Anti-RNA polymerase I (RPI) antibodies in the sera of MRL/Mp-lpr/lpr and MRL/Mp(-)+/+ mice, which develop an autoimmune disease similar to human systemic lupus erythematosus, were screened for reactivity with purified RPI or RPI which had been dephosphorylated. In every case (n = 10), dephosphorylation of RPI resulted in a significant decrease (33-95%) in antibody binding. The anti-RPI antibodies in the sera of the same mice approximately 6 weeks later also reacted better with untreated as compared to dephosphorylated RPI but, in every case, the decrease in antibody (0-30%) caused by dephosphorylation was substantially diminished. That the proportion of anti-RPI antibodies in the sera of MRL mice decreased with progression of lupus-like disease was confirmed by closely monitoring the antibodies over the course of disease. Anti-RPI antibodies produced at the earliest stages appeared to be directed almost exclusively against phosphorylation-dependent determinants since dephosphorylation of RPI essentially abolished antibody binding. Subsequently, the percentage of the total anti-RPI antibodies in the sera of these mice directed towards phosphorylation-independent epitopes increased linearly with time. The importance of phosphorylation-dependent epitopes on RPI for the development of the anti-RPI autoimmune response was supported by the observation that treatment of mice with alkaline phosphatase partially attenuated anti-RPI antibody production.

Rabbits produce SLE-like anti-RNA polymerase I and anti-DNA autoantibodies in responses to immunization with either human or murine SLE anti-DNA antibodies

Anti-DNA and anti-DNA polymerase I (RPI) autoantibody responses are symptoms of systemic lupus erythematosus (SLE). To investigate the relationship between these antibodies (Ab), rabbits were immunized with one of the following preparations: human SLE anti-DNA Ab; human SLE anti-DNA IgG; normal human anti-DNA Ab; human Grave's disease anti-DNA Ab; murine SLE anti-DNA Ab or anti-DNA IgG Fab; various normal human, murine, or rabbit IgG preparations; or complete Freund's adjuvant (CFA), alone. All of the animals immunized with anti-DNA Ab (n = 14) generated Ab reactive in radioimmunoassay with: ssDNA, dsDNA, RPI, the soluble fraction of rabbit liver crude nuclear extract, and the immunogen. Induced rabbit anti-DNA Ab in turn induced these responses in a different rabbit: a rabbit immunized with rabbit anti-DNA IgG Ab which had been previously induced by immunization with human anti-DNA Ab, produced Ab reactive with ssDNA, dsDNA, RPI, and the soluble fraction of rabbit liver nuclear extract. Although an individual animal's antisera reacted consistently over the course of immunization with the same individual RPI subunit(s), antisera from different animals reacted with different subunits of the 9-subunit RPI complex in Western blot analyses: 190 kD (n = 6); 120 kD (n = 1); 62 kD (n = 4); 45 kD (n = 2); and, no reactivity (n = 2). In contrast, animals immunized with normal IgG or CFA produced responses only against the immunogen. Together, these data suggest that anti-DNA and anti-RPI responses are connected through an autoimmune network in SLE.

A Drosophila anti-RNA polymerase II antibody recognizes a plant nucleolar antigen, RNA polymerase I, which is mostly localized in fibrillar centres

The distribution of nucleolar RNA polymerase in the nucleolus of onion root meristematic cells has been studied by means of an antibody originally raised against Drosophila RNA polymerase II. This antibody recognizes the homologous domains of the large subunit of the enzyme, which are highly conserved throughout evolution in the three classes of eucaryotic RNA polymerases. Given that RNA polymerase I is confined to the nucleolus, and that the onion cell nucleolus lacks digitations of extranucleolar chromatin, we conclude that the nucleolar enzyme localized is RNA polymerase I. A quantitative approach, independent of the existence of borderlines between nucleolar fibrillar centres and the dense fibrillar component, allowed us to show that the enzyme is localized in fibrillar centres and in the transition area between them and the dense fibrillar component, in parallel with the nucleolar DNA. These results, together with previous autoradiographic, cytochemical and immunocytochemical results, in this and other species, lead us to conclude that the activation of rDNA for transcription occurs in the fibrillar centres and pre-rRNA synthesis is expressed at the transition area between fibrillar centres and the dense fibrillar component. Fibrillar centres are connected to each other by extended RNA polymerase-bound DNA fibres, presumably active in transcription. This work provides evidence of the high evolutionary conservation of some domains of the large subunit of RNA polymerases and of the existence of fibrillar centres in the nucleolus of plant cells, totally homologous to those described in mammalian cells.

Anti-RNA polymerase I antibodies in the urine of patients with systemic lupus erythematosus

Urine samples from patients with systemic lupus erythematosus (SLE) (n = 80), patients with rheumatoid arthritis (RA) (n = 21), and healthy controls (n = 36) were analyzed by radio-immunoassay (RIA) for anti-RNA polymerase I (RPI) antibodies. Significant levels of anti-RPI antibodies were detected in the urine of 46% of the patients with SLE but in only 19% of the patients with RA and in no sample from healthy individuals. The presence of anti-RPI antibodies in the urine was confirmed by demonstrating that IgG purified from the urine of patients with SLE was capable of inhibiting the transcriptional activity of RPI in vitro. If the quantity of anti-RPI antibodies excreted is related to disease activity, analysis of urine for these antibodies may be a useful alternative for the purpose of monitoring the progression of disease in individuals with SLE because of the ease by which the sample can be collected.

Class II ribonuclease H comigrates with, but is distinct from, the third largest subunit of calf thymus RNA polymerase I

It has been reported (Iborra et al. (1979) J. Biol. Chem. 254, 10920-10924) that the third and the fifth largest subunit of yeast RNA polymerase I exhibit ribonuclease H activity. The authors suggested that the third largest subunit is identical with the chromatin-associated ribonuclease H49, the putative yeast equivalent of bovine ribonuclease H IIb. Although the third largest subunit of calf thymus RNA polymerase I and ribonuclease H IIb display nearly identical molecular masses under denaturing conditions, serological analysis reveals that, in contrast to their counterparts in yeast, these mammalian proteins are distinct entities. Interestingly, sera from some patients with mixed connective tissue disease which contain antibodies directed against RNA polymerase I, also react with ribonuclease H IIb epitopes. This observation suggests that a protein displaying ribonuclease H IIb antigenicity could be associated with RNA polymerase I. Additional indications supporting this conclusion are discussed.

Nucleolar changes after microinjection of antibodies to RNA polymerase I into the nucleus of mammalian cells

After microinjection of antibodies against RNA polymerase I into the nuclei of cultured rat kangaroo (PtK2) and rat (RVF-SMC) cells alterations in nucleolar structure and composition were observed. These were detected by electron microscopy and double-label immunofluorescence microscopy using antibodies to proteins representative of the three major components of the nucleolus. The microinjected antibodies produced a progressive loss of the material of the dense fibrillar component (DFC) from the nucleoli which, at 4 h after injection, were transformed into bodies with purely granular component (GC) structure with attached fibrillar centers (FCs). Concomitantly, numerous extranucleolar aggregates appeared in the nucleoplasm which morphologically resembled fragments of the DFC and contained a protein (fibrillarin) diagnostic for this nucleolar structure. These observations indicate that the topological distribution of the material constituting the DFC can be experimentally influenced in interphase cells, apparently by modulating the transcriptional activity of the rRNA genes. These effects are different from nucleolar lesions induced by inhibitory drugs such as actinomycin D-dependent "nucleolar segregation". The structural alterations induced by antibodies to RNA polymerase I resemble, however, the initial events of nucleolar disintegration during mitotic prophase.

Correlates between autoantibodies to nucleolar antigens and clinical features in patients with systemic sclerosis (scleroderma)

Immunofluorescence on rat liver sections was used to select high-titer antinucleolar antibodies (ANoA) in the sera of patients with systemic sclerosis (scleroderma). In 646 patients, 53 ANoA sera (8%) were identified, and of these, 46 were available in sufficient quantities for further analysis. The complex of RNA polymerase I was immunoprecipitated by 7 sera (15%), which uniformly produced punctate nucleolar staining. The PM-Scl antigen, a particle consisting of 11 polypeptides, was immunoprecipitated by 8 sera (17%), all of which displayed homogeneous nucleolar staining. A 34-kd nucleolar protein (fibrillarin) of the U3 RNP complex was positive in immunoblotting of 22 sera (48%), which characteristically produced clumpy nucleolar staining. Antibodies against RNA polymerase I were associated with diffuse scleroderma of short duration, which was characterized by a high prevalence of internal organ involvement, including renal crisis. Anti-U3 RNP antibodies had a high prevalence in men with significantly less joint involvement, compared with ANoA-negative patients. Anti-PM-Scl antibodies identified a group of scleroderma patients with a high prevalence of concomitant myositis and renal involvement.

Immunocytogenetics: localization of transcriptionally active rRNA genes in nucleoli and nucleolus organizer regions by use of human autoantibodies to RNA polymerase I

Cytological staining with silver nitrate (AgNO3) has proved useful for the localization of nucleoli in interphase nuclei, as well as of nucleolus organizer regions (NORs) in metaphase chromosomes. The affinity of interphase nucleoli and chromosomal NORs to silver is a direct measure of the ongoing transcriptional activity of the rRNA genes or their activity during the preceding interphase, respectively. Correspondingly, human autoantibodies directed against chromatin-associated RNA polymerase I (RPI) should also be of value in the investigation of transcribed rRNA genes. Indirect immunofluorescence using the anti-RPI antibody as a probe has been employed successfully to visualize the chromosomal distribution of NORs in various mammalian species, as well as in human tumor cells. Immunofluorescence staining even permits the identification of heteromorphisms and small aberrations of the chromosomal NORs. The fluorescent intensity of interphase nucleoli is correlated with the different stages of nucleolar activation. In male gametogenesis, RPI-positive granules are present during meiotic prophase up to pachytene, as well as during the early and middle spermatid stages.

Production of monoclonal antibodies against RNA polymerase I from nonimmunized autoimmune MRL/lpr mice and their use in rDNA transcription analysis

A hybridoma secreting monoclonal antibodies against RNA polymerase I was produced by the fusion of myeloma cells with spleen cells from a nonimmunized MRL/lpr mouse which is known to produce autoantibodies to RNA polymerase I. The antibodies (McAb-2D11) belong to the IgG2b subclass, reacted specifically with the second largest (120 kDa) subunit of RNA polymerase I, and inhibited accurate transcription of cloned rat rDNA in a fractionated cell extract following immunoprecipitation of RNA polymerase I. McAb-2D11 did not inhibit RNA polymerase II-mediated transcription of the mouse metallothionein-I gene. Immunocytochemical procedures with biotinylated second antibody demonstrated specific immunolocalization of RNA polymerase I in the nucleus. These studies have (a) presented direct evidence that autoantibodies to functional RNA polymerase I are produced in a murine model of systemic lupus erythematosus, (b) demonstrated specificity of the monoclonal antibody for RNA polymerase I, and (c) provided a useful tool for the purification of RNA polymerase I and/or transcription factor(s) associated with RNA polymerase I.

Transcription of mouse rDNA is regulated by an activated subform of RNA polymerase I

We have identified the species-nonspecific factor required for mouse rDNA transcription, factor C, as an activated subform of RNA polymerase I. C is an RNA polymerase I since it copurifies with bulk polymerase I activity on the three chromatographic columns used to achieve a virtually homogenous preparation of polymerase I, as well as on four additional matrices; it is quantitatively neutralized as well as immunoprecipitated by two different types of anti-polymerase I antibodies; and it has thermal lability identical to that of bulk polymerase I. However, C is clearly distinct from bulk polymerase I in its ability to participate in the stable rDNA transcription complex and to catalyze accurate initiation of rRNA synthesis. It also has a greater sedimentation coefficient than bulk polymerase I. Furthermore, this activated polymerase subform is specifically lacking in extracts of cells in which rDNA transcription was down-regulated because of cycloheximide treatment or attainment of stationary phase. These data suggest that regulation of rDNA transcription in vivo may involve modulation in availability of the activated polymerase I subform.

Immunological relationships between Artemia RNA polymerases and between RNA polymerases II from different eukaryotic organisms

Rabbit antibodies against Artemia RNA polymerase II have been raised and utilized to study the immunological relationships between the subunits from RNA polymerases I, II and III from this organism and RNA polymerase II from other eukaryotes. We describe here for the first time the subunit structure of Artemia RNA polymerases I and III. These enzymes have 9 and 13 subunits respectively. The anti-RNA polymerase II antibodies recognize two subunits of 19.4 and 18 kDa common to the three enzymes, and another subunit of 25.6 kDa common to RNA polymerases II and III. The antibodies against Artemia RNA polymerase II also react with the subunits of high molecular weight and with subunits of around 25 and 33 kDa of RNA polymerase II from other eukaryotes (Drosophila melanogaster, Chironomus thummi, triticum (wheat) and Rattus (rat]. This interspecies relatedness is a common feature of eukaryotic RNA polymerases.

Autoantibodies against RNA polymerase I in scleroderma and Sjögren's syndrome sera

Anti-RNA polymerase I antibodies were detected by radioimmunoassay in the sera of 8 out of 9 Sjögren's syndrome patients, 11 out of 19 individuals with scleroderma, and 19 out of 19 systemic lupus erythematosus patients. The results of the radioimmunoassay were confirmed by demonstrating the ability of the patients' IgG to inhibit RNA polymerase I activity in vitro. Sera from four patients in each category were also tested for reaction with individual subunits of RNA polymerase I. All 4 SLE sera, 3 out of 4 scleroderma sera and 1 out of 4 Sjögren's syndrome sera contained antibodies against the 65 kDa (S3) subunit of RNA polymerase I in addition to antibodies against one other subunit. Sera from the remaining scleroderma and Sjögren's syndrome patients tested in this assay contained only anti-S3 antibodies. These results demonstrate that anti-RNA polymerase I antibodies are characteristic of a variety of rheumatic autoimmune sera.

Description and partial characterization of a nucleolar RNA-associated autoantigen defined by a human monoclonal antibody

B lymphocytes from a patient with systemic lupus erythematosus (SLE) and several circulating autoantibodies (including antinucleolar antibodies) were immortalized by fusion with a hypoxanthine/guanine phosphoribosyl transferase (HGPRT)-deficient human B cell line. Multiple human monoclonal antibodies (mAb) were obtained which, in solid-phase enzyme immunoassay, were reactive with DNA. One mAb was of special interest because it reacted strongly with both single-stranded DNA and an extractable nuclear antigen found in rabbit thymus extract (RTE). In an immunofluorescent assay using fixed human cells, the latter mAb also bound predominantly to cell nucleoli. A combination of enzyme digestion and metabolic inhibitor studies of the target cells in this immunofluorescent assay suggested that the antigen(s) bound by the mAb was an RNA-associated protein or a ribonucleoprotein that is distinct from intact RNA polymerase I and not associated with the transcriptional units of the nucleolus. In other experiments, using fractions of RTE isolated by ion-exchange chromatography, the antigens bound by the mAb were shown to be highly negatively charged molecules. Immunoprecipitation and SDS-PAGE analyses of labeled cell extracts bound by the mAb revealed a doublet of 17 and 18 kD. Since the original patient's serum autoantibodies also bound to both an RNase-sensitive, acidic, extractable nuclear antigen and to nucleoli, and immunoprecipitated proteins of similar molecular masses in SDS-PAGE, it appears that the described mAb is a product of an immortalized autoantibody-producing B cell clone from the SLE patient's peripheral blood. This mAb probably defines a novel RNA-associated autoantigen residing predominantly in the nucleolus or, less likely, a variant of either RNA polymerase I or the ribosomal autoantigens (P proteins).

Anti-RNA polymerase I antibodies: potential role in the induction and progression of murine lupus nephritis

Antibodies against RNA polymerase I were detected in plasma and kidney eluates of NZB/W mice. Plasma concentrations of the antibodies were the highest in mice with incipient nephritis and the lowest in mice with progressive nephritis. Mice with attenuated nephritis due to immunosuppressive therapy had intermediate plasma concentrations of the antibodies. The specific concentrations (ng/microgram IgG) of anti-RNA polymerase I antibodies in kidney eluates were significantly (10- to 70-fold) greater than the corresponding plasma concentrations. These results indicated that the decreased plasma concentration of the antibodies in mice with more advanced disease was at least partially due to selective concentration of anti-RNA polymerase I antibodies in the kidneys. The degree of this selective concentration was directly proportional (R2 = 0.9962) to the severity of renal disease, as reflected by the concentration (microgram/g tissue) of IgG eluted from the kidneys. The concentration (microgram/g tissue) of anti-RNA polymerase I eluted from the kidneys also was increased in mice with more severe renal disease. Further, the extent of this increase was greater than that of total IgG, again suggesting that anti-RNA polymerase I antibodies had been selectively concentrated in the kidneys. These findings are strongly suggestive of an important role for the RNA polymerase I/anti-RNA polymerase I antibody system in the pathogenesis of murine lupus nephritis.

Autoantibody to RNA polymerase I in scleroderma sera

Autoantibodies to components of the nucleolus are a unique serological feature of patients with scleroderma. There are autoantibodies of several specificities; one type produces a speckled pattern of nucleolar staining in immunofluorescence. In actinomycin D and 5,6-dichloro-beta-D-ribofuranosylbenzimidazole-treated Vero cells, staining was restricted to the fibrillar and not the granular regions. By double immunofluorescence, specific rabbit anti-RNA polymerase I antibodies stained the same fibrillar structures in drug-segregated nucleoli as scleroderma sera. Scleroderma sera immunoprecipitated 13 polypeptides from [35S]methionine-labeled HeLa cell extract with molecular weights ranging from 210,000 to 14,000. Similar polypeptides were precipitated by rabbit anti-RNA polymerase I antibodies, and their common identities were confirmed in immunoabsorption experiments. Microinjection of purified IgG from a patient with speckled nucleolar staining effectively inhibited ribosomal RNA transcription. Autoantibodies to RNA polymerase I were restricted to certain patients with scleroderma and were not found in other autoimmune diseases.

Regulation of the expression of the SV40 T-antigen coding gene under the control of an rDNA promoter

We have constructed a hybrid gene in which the SV40 T-antigen coding gene is driven by a mouse rDNA promoter and we have compared its expression to that of an SV40 T-antigen coding gene under the control of its own promoter. The comparison has been carried out in microinjected cells, in transfected cells, and in stable cell lines carrying the respective T-antigen coding genes in an integrated form. These cell lines were derived from ts AF8 cells, a mutant which is temperature sensitive for RNA polymerase II activity. The hybrid gene clearly expresses T-antigen, albeit less efficiently than when the T antigen coding gene is under the control of the SV40-promoter. We also show that the expression of T-antigen by the hybrid gene is 50% inhibited by an antibody against RNA polymerase I. In tsAF8 cells carrying the hybrid gene, T-antigen is still expressed at the restrictive temperature (where RNA polymerase II is inactive) at a level again about 50% of controls. However, our findings also confirm those of Smale and Tjian (Mol. Cell. Biol. 5:352, 1985) that such hybrid genes are in part transcribed by RNA polymerase II and generate abnormal transcripts.

Effects of glucocorticoid and cycloheximide on the activity and amount of RNA polymerase I in nuclei of rat liver

The activity of the template-engaged form of RNA polymerase I from livers of adrenalectomized rats was about 50-60% of that of normal control rats, and increased about 2-fold at 6 h after the administration of dexamethasone. However, no change was found in the activity of the 'free' form of RNA polymerase I or the template-engaged form of RNA polymerase II. Immunochemical studies using guinea-pig anti-(RNA polymerase I) serum disclosed that the total number of RNA polymerase I molecules did not vary during the treatment with dexamethasone. Cycloheximide caused a rapid decrease in the template-engaged form of RNA polymerase I activity in normal rats and in dexamethasone-treated (6 h) adrenalectomized rats, to the value in adrenalectomized rats, but affected it only slightly in adrenalectomized rats. The elongation rate of rRNA-precursor synthesis in liver nuclei was not affected by a change in the concentration of circulating dexamethasone. From these results, it is concluded that about half the rRNA-precursor synthesis in rat liver is regulated by glucocorticoids, probably through the synthesis of short-lived protein(s) which may play a role in conversion of the 'dormant' form of RNA polymerase I into the 'engaged' form.

Yeast RNA polymerase C and its subunits. Specific antibodies as structural and functional probes

Yeast RNA polymerase C purified by a simple large scale method was resolved into multiple components by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Specific antibodies directed against each polypeptide chain were prepared in rabbits and used as structural and functional probes. With minor exceptions, each antibody recognized specifically the corresponding polypeptide by blot-immunodetection. Cross-reactions with purified RNA polymerases A and B confirmed our previous description of the subunits shared by the three nuclear RNA polymerases. Immunoadsorption of RNA polymerase C at different stages of purification using antibodies to subunits C160 and C128 yielded the same collection of polypeptides as found in the purified enzyme: C160, C128, C82, C53, C40, C37, C34, C31, C27, C25, C23, C19, C14.5, C12.5, and C10. Subunit-specific antibodies were used to probe the activity of RNA polymerase C in a specific, reconstituted transcription system as well as on a nonspecific template. Transcription of the tRNAGlu3 gene in vitro was inhibited when RNA polymerase C was preincubated with antibodies directed to C128, C82, C53, C34, C23, or C19. Antibodies to C82, C53, and C34 were much less inhibitory in the nonspecific assay. Inhibition by anti-C128 or anti-C23 was relieved by preincubation of enzyme C with plasmid DNA prior to antibody addition. These results are discussed in terms of the participation of these polypeptides to the active enzyme molecule, and of their possible role in DNA binding or transcription factor recognition.

Anti-RNA polymerase I antibodies in sera of MRL lpr/lpr and MRL +/+ autoimmune mice. Correlation of antibody production with delayed onset of lupus-like disease in MRL +/+ mice

Sera from individual MRL/lpr and MRL/++ mice, which develop an autoimmune disease similar to human systemic lupus erythematosus (SLE), were screened over a period of approximately 30 wk for the presence of anti-RNA polymerase I and anti-ssDNA antibodies. Even though onset of the disease is delayed in MRL/++ as compared to MRL/lpr mice, anti-ssDNA antibodies were present in comparable concentrations in the sera of all mice by the age of 6 wk. As observed in sera of human SLE patients, anti-RNA polymerase I antibodies were detected in the sera of all MRL mice. However, unlike the anti-ssDNA antibodies, anti-RNA polymerase I antibodies were detected much later in MRL/++ mice (mean age, 22.8 wk) as compared to MRL/lpr mice (mean age, 9.6 wk). The presence of anti-RNA polymerase I antibodies in sera of MRL mice was thus a much better indicator of disease status than the presence of anti-ssDNA antibodies. The appearance and increase in anti-RNA polymerase I antibodies in the sera of MRL/++ mice correlated (R2 = 0.964) with a precipitous decrease in anti-ssDNA antibodies, starting at about 20 wk of age. These results suggest a possible relationship between the RNA polymerase I and DNA autoimmune reactions.

Immunization of rabbits with purified RNA polymerase I induces a distinct population of antibodies against nucleic acids as well as anti-RNA polymerase I antibodies, both characteristic of systemic lupus erythematosus

Rabbits were immunized with either RNA polymerase I or poly(A) polymerase that had been purified to apparent homogeneity and was devoid of nucleic acids. Sera from rabbits thus immunized were screened for antibodies against nucleic acids. All seven rabbits injected with RNA polymerase I but none of the four rabbits immunized with poly(A) polymerase produced anti-nucleic acid antibodies. Anti-RNA polymerase I antibodies were induced after a single injection of the enzyme. Anti-polynucleotide antibodies were not detectable until after the second immunization. Anti-RNA polymerase I antibodies could be detected with as little as 100 pg of purified RNA polymerase I in the radioimmunoassay. At least 50 ng of poly(A) or 200 ng of DNA was required to detect anti-nucleic acid antibodies. The immunoreactivity of anti-RNA polymerase I antisera was greater with synthetic polynucleotides than with DNA, particularly early in the immunization schedule. Alkaline phosphatase treatment of poly(A) to remove 5' phosphates nearly abolished its antigenicity with respect to the early sera and decreased antibody binding of later sera by 60%. These results indicate that the anti-nucleic acid antibodies produced early were primarily directed against determinants including the 5'-terminal phosphates while antibodies produced later were directed against other sites. The antinucleic acid antibodies and anti-RNA polymerase I antibodies formed two distinct populations that were not immunologically crossreactive. We suggest that after injection, RNA polymerase I becomes associated with the nucleic acids present in blood plasma which renders them immunogenic; thus, association of nucleic acids with autoimmunogenic RNA polymerase I may be one of the mechanisms by which anti-DNA antibodies are induced in systemic lupus erythematosus.

Reduction in RNA synthesis following red cell-mediated microinjection of antibodies to RNA polymerase I

Antibody molecules directed against RNA polymerase I, the enzyme responsible for rRNA synthesis, were introduced into rat hepatoma cells by red cell-mediated microinjection. Access of the antibodies to the nucleolus, the site of rRNA synthesis, was facilitated by microinjecting mitotic cells. Using indirect immunofluorescence, anti-RNA polymerase I immunoglobulins, but not control immunoglobulins, were found localized in the nucleoli of microinjected cells. To assess whether intracellular antibodies could alter RNA synthesis, cultures were labeled with [3H] uridine at various times after microinjection. Reduction in RNA synthesis, relative to cells microinjected with non-immune immunoglobulins, was observed within three hours. These results demonstrate that antibodies introduced into the cytoplasm of mitotic cells via red cell-mediated microinjection have free access to nuclear components and that they remain functional within the nuclei of living cells.

Absence of inactivation or phosphorylation of ornithine decarboxylase by nuclear protein kinase NII and of immunological cross-reactivity between RNA polymerase I and ornithine decarboxylase

Incubation with protein kinase NII did not result in phosphorylation or inactivation of mouse kidney ornithine decarboxylase. Partially purified ornithine decarboxylase preparations contained a protein kinase activity and stimulated the activity of RNA polymerase I. However, these properties were due to contaminating protein(s) since further purification reduced the kinase activity and removal of the ornithine decarboxylase with a specific antiserum did not abolish the ability to stimulate RNA polymerase I. Antibodies to RNA polymerase I did not interact with ornithine decarboxylase and antibodies to ornithine decarboxylase did not interact with RNA polymerase I. These results indicate that: a) mammalian ornithine decarboxylase activity is not regulated by phosphorylation by protein kinase NII or the contaminating kinase, and b) the ability of impure preparations of ornithine decarboxylase to stimulate RNA polymerase I is due to a contaminating unrelated protein.

Cellular DNA replication is independent of the synthesis or accumulation of ribosomal RNA

We have used an antibody against RNA polymerase I to investigate the role of rRNA synthesis and/or accumulation in the control of cell proliferation. The antibody was microinjected directly into the nuclei of quiescent Swiss 3T3 cells that were subsequently stimulated with serum. Under the experimental conditions used, the microinjection of the antibody against RNA polymerase I (RNA pol I) caused a 50-70% decrease in nucleolar RNA synthesis that lasted for at least 17 h, a greater than 90% inhibition in the accumulation of nucleolar RNA, and a 70% inhibition in the accumulation of total cellular RNA. A control IgG, similarly microinjected into Swiss 3T3 cells had no inhibitory effect on either the synthesis or accumulation of nucleolar and cellular RNA. Despite the dramatic effect on the synthesis and accumulation of ribosomal RNA (rRNA) the antibody against RNA (rRNA) the antibody against RNA pol I was totally ineffective in inhibiting the entry into S phase of serum-stimulated Swiss 3T3 cells. Cells depleted of cellular RNA by metaphase arrest also entered S phase with subnormal amounts of cellular RNA. The results of these experiments clearly indicate that a normal rate of nucleolar RNA synthesis, and a normal rate of accumulation of total cellular RNA are not a prerequisite for the entry of cells into S phase.

Monoclonal antibody to RNA polymerase I of the silkworm

RNA polymerase I has been purified from the silk glands of the silkworm and antibodies obtained from immunized BALB/C mice. Hybridomas were obtained by fusing spleen cells from the same mice with SP-2/0 cells. One of the cloned hybridomas was injected into mice to produce ascitic fluid. Both polyclonal and monoclonal antibodies were characterized for their reactivity with polymerase I by double immunodiffusion, enzyme-linked immunosorbent assay, and enzyme inhibition. The monoclonal antibody is active even at 1:100,000 dilution, is specific for the second largest subunit of RNA polymerase I, and does show some cross-reactivity with polymerases II and III. The monoclonal antibody when coupled to Sepharose binds polymerase I from crude extracts, and the bound polymerase I can be eluted. This antibody has been employed to localize RNA polymerase to the nuclei of Chironomus salivary glands. This and other monoclonal antibodies will be of considerable help as probes for the study of structure and function of RNA polymerases during active transcription.

Monoclonal antibodies directed against mammalian RNA polymerase I. Identification of the catalytic center

Mouse myeloma cells were fused with splenocytes from a mouse that had been immunized with RNA polymerase I purified from a rat hepatoma. Hybridoma cells were selected and colonies secreting antibodies directed against the enzyme were detected by analysis of cell culture supernatants in a solid phase radioimmunoassay. Two of these cell lines were grown on a larger scale and the interaction between the immunoglobulins obtained from them and RNA polymerase I was studied in detail. Antibodies from both of the hybridoma cell lines were able to inhibit DNA-dependent RNA synthesis catalyzed by RNA polymerases I and III, but not that catalyzed by polymerase II. The antibodies were also capable of reducing the RNA chain elongation reaction catalyzed either by RNA polymerase I associated with isolated nucleoli or by enzyme preinitiated in vitro on calf thymus DNA. Inhibition of RNA polymerase I activity by the monoclonal antibodies was inversely related to the nucleotide concentration. In contrast, the DNA concentration had relatively little effect on inhibition by the antibodies. Analysis of immune complex formation between the antibodies and isolated individual enzyme subunits demonstrated that the monoclonal antibodies were directed against the largest (Mr = 190,000) polypeptide of the polymerase I. These data indicate that the largest subunit of RNA polymerase I contains an immunological determinant in common with RNA polymerase III and suggest that the polymerase I polypeptide of Mr = 190,000 contains a catalytic center involved in RNA chain elongation.