Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Poly(A) polymerase (EC 2.7.7.19) solubilized from mitochondria of a poorly differentiated rat tumor, Morris hepatoma 3924A, was purified more than 1000-fold by successive column chromatography on phosphocellulose, DEAE-Sephadex, and hydroxylapatite. Purified enzyme catalyzed the incorporation of ATP into poly(A) only upon addition of an exogenous primer. Of several primers tested, synthetic poly(A) was the most effective. The enzyme utilized mitochondrial RNA as a primer at least five times as efficiently as nuclear RNA. The enzyme required Mn2+, and had a pH optimum of 7.8-8.2. The enzyme utilized ATP exclusively as a substrate; the calculated K-m for ATP was 28 muM. The polymerization reaction was not inhibited by RNase, ethidium bromide, distamycin, or alpha-amanitin. The reaction was sensitive to O-n-octyloxime of 3-formylrifamycin SV (AF/013). As estimated from glycerol gradient centrifugation and acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, the molecular weight of the enzyme was 60,000. The product was covalently linked to the polynucleotide primer and the average length of the poly(A) formed was 600 nucleotides.
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PMID:Mitochondrial poly(A) polymerase from a poorly differentiated hepatoma: purification and characteristics. 23 43

To elucidate the mechanism by which poly(A) polymerase functions in the 3'-end processing of pre-mRNAs, polyadenylation-specific RNP complexes were isolated by sedimentation in sucrose density gradients and the fractions were analyzed for the presence of the enzyme. At early stages of the reaction, the RNP complexes were resolved into distinct peaks which sedimented at approximately 18S and 25S. When reactions were carried out under conditions which support cleavage or polyadenylation, the pre-mRNA was specifically assembled into the larger 25S RNP complexes. Polyclonal antibodies raised against the enzyme purified from a rat hepatoma, which have been shown to inhibit cleavage and polyadenylation (Terns, M., and Jacob, S. T., Mol. Cell. Biol. 9:1435-1444, 1989) also prevented assembly of the 25S polyadenylation-specific RNP complexes. Furthermore, formation of these complexes required the presence of a chromatographic fraction containing poly(A) polymerase. UV cross-linking analysis indicated that the purified enzyme could be readily cross-linked to pre-mRNA but in an apparent sequence-independent manner. Reconstitution studies with the fractionated components showed that formation of the 25S RNP complex required the poly(A) polymerase fraction. Although the enzyme has not been directly localized to the specific complexes, the data presented in this report supports the role of poly(A) polymerase as an essential component of polyadenylation-specific complexes which functions both as a structural and enzymatic constituent.
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PMID:Potential role of poly(A) polymerase in the assembly of polyadenylation-specific RNP complexes. 201 73

Sera from rats bearing Morris hepatoma 3924A for 7 weeks contained antibodies against the 48 kd tumor-type poly(A) polymerase, whereas sera from normal rats or rats bearing the tumor for shorter periods did not exhibit immunoreactivity against the enzyme. Purified IgG from the sera of the tumor-bearing rats inhibited both cleavage at the poly(A) site and polyadenylation of adenovirus L3 RNA in nuclear extracts derived from HeLa cells. By contrast, IgG from normal rats did not block the 3'-terminal processing reaction. Control or immune IgG had no effect on the transcription of ribosomal gene in the extracts derived from H-4 hepatoma cells. These data demonstrate the functional specificity of the anti-poly(A) polymerase antibodies found in the sera of the tumor-bearing rats.
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PMID:Anti-poly(A) polymerase antibodies in the sera of tumor-bearing rats can inhibit specific cleavage and polyadenylation reactions. 202 57

Previous studies in this laboratory suggested that in adult liver, either the gene for the tumor-type poly(A) polymerase is poorly transcribed or the mRNA for this enzyme is largely not expressed. To test these possibilities, total RNA from rat liver and Morris hepatoma 3924A RNA were isolated by using a guanidine thiocyanate method; poly(A+) RNA and poly(A-) RNA were separated by oligo(dT)-cellulose chromatography and used for translation in a rabbit reticulocyte lysate system. After in vitro translation, the products were immunoprecipitated with either purified anti-tumor poly(A) polymerase antibodies or control immunoglobulins. When the polypeptides translated from poly(A+) or poly(A-) hepatoma RNA were precipitated with immune sera, a unique [35S]methionine-labeled 35-kilodalton (kDa) protein was observed. This band was not apparent when control serum was used for the immunoprecipitation. The radiolabeled 35-kDa polypeptide was not evident when the products were incubated with highly purified tumor nuclear poly(A) polymerase prior to immunoprecipitation. Prior incubation of the translation products with bovine serum albumin instead of poly(A) polymerase had no effect on the immunoprecipitation. This 35-kDa protein was not apparent when liver poly(A+) RNA was used to direct translation. These data demonstrate that (a) the tumor enzyme is not synthesized as a precursor, (b) tumor mRNA, but not normal liver mRNA, contains detectable sequences coding for tumor-type poly(A) polymerase, and (c) poly(A) polymerase mRNA also exists as a poly(A-) population.
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PMID:Cell-free synthesis of tumor-type poly(A) polymerase. 242 13

Two structurally and immunologically distinct species of nuclear polyadenylate [poly(A)] polymerases have been characterized. One of these enzymes is relatively absent in normal tissues but is predominant in primary and transplanted tumors and transformed cell lines. The presence of the tumor type enzyme in fetal liver, but not in regenerating liver, suggests that it is an oncofetal protein. Antibodies against the tumor-type poly(A) polymerases are present in the sera of rats bearing tumors and in some cancer patients. These antibodies are also found in the sera of rats fed hepatocarcinogen even before preneoplastic nodules were visible, which suggests that elicitation of these antibodies is an early event in neoplastic transformation. Autoantibodies against both liver-type and tumor-type poly(A) polymerase are also present in some rheumatic autoimmune sera. Polyclonal antibodies against purified enzyme from a rat hepatoma, which exhibit a single band upon immunoblot analysis, were used in cell-free extracts to study the role of poly(A) polymerase in the 3'-end processing of pre-mRNA. These studies showed that the antibodies blocked both endonucleolytic cleavage and poly(A) addition at the cleavage site and complex formation between factors in the extract and pre-mRNA. Independent studies in other laboratories have demonstrated that both the cleavage and poly(A) polymerase activities require the same component for their function. These observations suggest that both cleavage and polyadenylation reactions are tightly coupled in a functional complex.
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PMID:Polyadenylate polymerases from normal and cancer cells and their potential role in messenger RNA processing: a review. 254 94

Previous studies (Stetler, D. A., and Jacob, S. T. (1984) J. Biol. Chem. 259, 7239-7244) have shown that poly(A) polymerase from adult rat liver (liver-type) is structurally and immunologically distinct from the corresponding rat hepatoma (tumor-type) enzyme. When hepatoma 7777 (McA-RH 7777) cells were labeled with [32P]inorganic phosphate, followed by immunoprecipitation with anti-hepatoma poly(A) polymerase antibodies and analysis of the RNAs in the immunoprecipitate, only one labeled small nuclear RNA corresponding to U1 RNA was found. Preimmune sera did not form a complex with U1 RNA. Hepatoma poly(A) polymerase antisera did not immunoprecipitate U1 RNA or any other small nuclear RNA from a cell line (H4-11-EC3) which does not contain the tumor-type poly(A) polymerase. Immunoblot analysis of hepatoma 7777 nuclear extract or purified poly(A) polymerase with anti-ribonucleoprotein antisera did not show any cross-reactivity of the latter sera with poly(A) polymerase. The major RNA immunoprecipitated from the hepatoma nuclear extracts using trimethyl cap (m3G) antisera corresponded to the RNA immunoprecipitated with poly(A) polymerase antisera. These data indicate that U1 RNA is closely associated with poly(A) polymerase and suggest the potential involvement of this RNA in the cleavage/polyadenylation of mRNA precursor.
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PMID:Association of poly(A) polymerase with U1 RNA. 284 16

Sera of normal rats contain polynucleotide adenylyltransferase [poly(A) polymerase] activity. The enzymatic activity has been optimized with regard to primer concentration, ion requirements, kinetics, and protein. Results based on inclusion of inhibitors in the assay system show that the enzyme is poly(A) polymerase. High levels of the enzymatic activity were prevalent in sera of (a) BUF/SimfBR rats bearing sc transplanted hepatomas; (b) Sprague-Dawley rats with hepatoma cells grown in ascites; (c) partially hepatectomized Sprague-Dawley rats; and (d) MRL/lpr mice, which are in a massive lymphoproliferative autoimmune state.
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PMID:Poly(A) polymerase activity in murine serum. Elevation in animals with proliferative changes. 284 13

Nuclear poly(A) polymerase was isolated from [35S]methionine-labeled hepatoma McA-RH 7777 cells and subjected to DEAE-Sephadex chromatography. Flow-through and low salt wash fractions containing poly(A) polymerase activity were pooled and subjected to immunoblot analysis using anti-tumor type poly(A) polymerase antibodies and a biotinylated second antibody. The immune complex contained a single 48-kDa polypeptide band corresponding to the tumor-type enzyme. When immunoprecipitations were carried out using the same fraction and antibodies, at least five 35S-methionine-labeled proteins with approximate molecular masses of 74, 48, 35, 30, and 22 kDa were observed. Pulse-chase studies did not indicate a precursor-product relationship between the immunoprecipitated proteins. Preimmune sera did not react with poly(A) polymerase or other components in the protein complex. These data show that poly(A) polymerase exists as part of a complex with at least four other polypeptides and suggest that these polypeptides may be involved in the cleavage and/or polyadenylation reactions.
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PMID:Association of newly synthesized poly(A) polymerase with four distinct polypeptides. 284 20

Poly(A) polymerase was partially purified from isolated nuclei of fetal rat liver. Antibodies produced in rabbits immunized with purified nuclear poly(A) polymerase from a rat hepatoma exhibited nearly identical affinity for the partially purified fetal liver and hepatoma enzymes. The extent of the antibody reaction with adult liver nuclear poly(A) polymerase partially purified in a similar manner was only 1.4% of that obtained with the hepatoma enzyme. Immune complex formation was observed between the antibodies and a major polypeptide in the fetal liver enzyme preparation which corresponded to the hepatoma enzyme (mol. wt. 48 000). No other polypeptide in the fetal liver enzyme preparation reacted with the antibodies. The 48-kDa fetal liver polypeptide produced a CNBr cleavage pattern identical to that of hepatoma poly(A) polymerase which is known to be different from the cleavage pattern of the adult liver major nuclear poly(A) polymerase. A fetal liver polypeptide corresponding to the adult liver enzyme (mol. wt. 38 000) was not evident. These results coupled with other data suggest that the hepatoma nuclear poly(A) polymerase is an oncofetal protein.
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PMID:Structural and immunological identity of rat hepatoma and fetal liver nuclear poly(A) polymerase. 298 14

Poly(A) polymerases were purified from the cytosol fraction of rat liver and Morris hepatoma 3924A and compared to previously purified nuclear poly(A) polymerases. Chromatographic fractionation of the hepatoma cytosol on a DEAE-Sephadex column yielded approximately 5 times as much poly(A) polymerase as was obtained from fractionation of the liver cytosol. Hepatoma cytosol contained a single poly(A) polymerase species [48 kilodaltons (kDa)] which was indistinguishable from the hepatoma nuclear enzyme (48 kDa) on the basis of CNBr cleavage maps. Liver cytosol contained two poly(A) polymerase species (40 and 48 kDa). The CNBr cleavage patterns of these two enzymes were distinct from each other. However, the cleavage pattern of the 40-kDa enzyme was similar to that of the major liver nuclear poly(A) polymerase (36 kDa), and approximately three-fourths of the peptide fragments derived from the 48-kDa species were identical with those from the hepatoma enzymes (48 kDa). NI-type protein kinases from liver or hepatoma stimulated hepatoma nuclear and cytosolic poly(A) polymerases 4-6-fold. In contrast, the liver cytosolic 40- and 48-kDa poly(A) polymerases were stimulated only slightly or inhibited by similar units of the protein kinases. Antibodies produced in rabbits against purified hepatoma nuclear poly(A) polymerase reacted equally well with hepatoma nuclear and cytosolic enzyme but only 80% as well with the liver cytosolic 48-kDa poly(A) polymerase and not at all with liver cytosolic 40-kDa or nuclear 36-kDa enzymes. Anti-poly(A) polymerase antibodies present in the serum of a hepatoma-bearing rat reacted with hepatoma nuclear and cytosolic poly(A) polymerases to the same extent but only 40% as well with the liver cytosolic 48-kDa enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Comparison of cytosolic and nuclear poly(A) polymerases from rat liver and a hepatoma: structural and immunological properties and response to NI-type protein kinases. 300 Apr 24


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