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Results for “RNA, Heterogeneous Nuclear”

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PubMed1984

Interactions of U1 RNP with heterogeneous nuclear RNA in rat Novikoff hepatoma nuclei.

The nature of the association of U1 RNA with rapidly sedimenting RNP structures in rat hepatoma nuclei was investigated. The effects of salt and proteinase K treatment on the stability of this 'bound' form of U1 RNA were studied using sucrose density gradient analyses. Quantitation of the amount of U1 RNA remaining associated with large structures after treatment was used to assess the relative contribution of protein-protein (and protein-RNA) versus RNA-RNA interactions. Forty-eight percent of the total nuclear U1 RNA released by sonication was found in a 'bound' form when the sonicate was centrifuged through gradients containing 50 mM NaCl. Fifty percent of this 'bound' U1 RNA remained associated with rapidly sedimenting RNPs when the NaCl concentration was raised to 500 mM. To assess the contribution of protein independent interactions, large RNPs were completely deproteinized and their RNA moieties were then recentrifuged on gradients. By this analysis, 27% of the U1 RNA originally 'bound' to hnRNPs was associated with rapidly sedimenting (greater than 30 S) RNA (at 50 mM NaCl) suggesting their association by RNA-RNA hydrogen bonds. When the concentration of NaCl was 500 mM, 31% of the U1 RNA was associated with large RNA. Hence, approximately 30% of the U1 RNA molecules originally 'bound' (or about 15% of the total nuclear U1 RNA) were found to be associated by RNA-RNA hydrogen bonds while the remainder of the binding of U1 RNP to hnRNP was by protein-protein and/or protein-RNA interactions.

Animals↗
PubMed1984

Decrease in the phosphorylation of the proteins associated with heterogeneous nuclear RNA after the application of 3'-methyl-4-dimethylaminoazobenzene.

The effect of 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB) on the phosphorylation of the proteins of the nuclear ribonucleoprotein (RNP) particles was studied in liver of rats. Forty eight hours after the application of 4 mg of the hepatocarcinogen per 100 g of body wt. by stomach intubation the particle proteins contained only 7% as much phosphate per mg of protein as the proteins of the same particles isolated from liver of control animals. Determination of the protein kinase and protein phosphatase activities in the total fraction of the non-histone nuclear proteins 48 h after the application of the carcinogen have shown an increase (200% and 159%, respectively) in both enzymatic activities. These results suggest that the hepatocarcinogen could induce the observed high turnover of the phosphates on the proteins of the liver nuclear ribonucleoprotein particles and the resulting dephosphorylation of these particles by stimulation of nuclear protein kinases and phosphatases. Qualitatively the same, but quantitatively much smaller changes were also observed 48 h after the application of the non-carcinogenic p-aminoazobenzene (AB) by stomach intubation and in regenerating liver. After the application of AB phosphorylation of the proteins of rat liver nuclear ribonucleoprotein particles decreased to 70% and in regenerating liver to 61% of the phosphorylation of particle proteins in control liver. Since it is assumed that nuclear RNP particles are involved in the processing and transport of newly synthesized premessenger RNA it is possible that the drastic dephosphorylation of the particle proteins induced by the carcinogen could be connected with the distortion of RNA processing which is observed in liver of animals treated with hepatocarcinogens.

Animals↗
PubMed1998

Organization of highly acetylated chromatin around sites of heterogeneous nuclear RNA accumulation.

Histones found within transcriptionally competent and active regions of the genome are highly acetylated. Moreover, these highly acetylated histones have very short half-lives. Thus, both histone acetyltransferases and histone deacetylases must enrich within or near these euchromatic regions of the interphase chromatids. Using an antibody specific for highly acetylated histone H3, we have investigated the organization of transcriptionally active and competent chromatin as well as nuclear histone acetyltransferase and deacetylase activities. We observe an exclusion of highly acetylated chromatin around the periphery of the nucleus and an enrichment near interchromatin granule clusters (IGCs). The highly acetylated chromatin is found in foci that may reflect the organization of highly acetylated chromatin into "chromonema" fibers. Transmission electron microscopy of Indian muntjac fibroblast cell nuclei indicates that the chromatin associated with the periphery of IGCs remains relatively condensed, most commonly found in domains containing chromatin folded beyond 30 nm. Using electron spectroscopic imaging, we demonstrate that IGCs are clusters of ribonucleoprotein particles. The individual granules comprise RNA-rich fibrils or globular regions that fold into individual granules. Quantitative analysis of individual granules indicates that they contain variable amounts of RNA estimated between 1.5 and >10 kb. We propose that interchromatin granules are heterogeneous nuclear RNA-containing particles, some of which may be pre-mRNA generated by nearby transcribed chromatin. An intermediary zone between the IGC and surrounding chromatin is described that contains factors with the potential to provide specificity to the localization of sequences near IGCs.

Acetylation↗
PubMed2003

Surface expression of heterogeneous nuclear RNA binding protein M4 on Kupffer cell relates to its function as a carcinoembryonic antigen receptor.

Elevated concentrations of carcinoembryonic antigen (CEA) in the blood are associated with the development of hepatic metastases from colorectal cancers. Clearance of circulating CEA occurs through endocytosis by liver macrophages, Kupffer cells. Previously we identified heterogeneous nuclear ribonucleoproteins M4 (hnRNP M4) as a receptor (CEAR) for CEA. HnRNP M4 has two isoform proteins (p80, p76), the full-length hnRNP M4 (CEARL) and a truncated form (CEARS) with a deletion of 39 amino acids between RNA binding domains 1 and 2, generated by alternative splicing. The present study was undertaken to clarify any isoform-specific differences in terms of their function as CEA receptor and localization. We develop anti-CEAR isoform-specific antibodies and show that both CEAR splicing isoforms are expressed on the surface of Kupffer cells and can function as CEA receptor. Alternatively, in P388D1 macrophages CEARS protein has nuclear and CEARL has cytoplasmic localization. In MIP101 colon cancer and HeLa cells the CEARS protein is localized to the nucleus and CEARL to the cytoplasm. These findings imply that different functions are assigned to CEAR isoforms depending on the cell type. The search of 39 amino acids deleted region against the Prosite data base revealed the presence of N-myristylation signal PGGPGMITIP that may be involved in protein targeting to the plasma membrane. Overall, this report demonstrates that the cellular distribution, level of expression, and relative amount of CEARL and CEARS isoforms determine specificity for CEA binding and the expression of alternative spliced forms of CEAR is regulated in a tissue-specific manner.

Alternative Splicing↗
PubMed2004

Translational upregulation of folate receptors is mediated by homocysteine via RNA-heterogeneous nuclear ribonucleoprotein E1 interactions.

Cellular acquisition of folate is mediated by folate receptors (FRs) in many malignant and normal human cells. Although FRs are upregulated in folate deficiency and downregulated following folate repletion, the mechanistic basis for this relationship is unclear. Previously we demonstrated that interaction of an 18-base cis-element in the 5'-untranslated region of FR mRNA and a cystolic trans-factor (heterogeneous nuclear ribonucleoprotein E1 [hnRNP E1]) is critical for FR synthesis. However, the molecular mechanisms controlling this interaction, especially within the context of FR regulation and folate status, have remained obscure. Human cervical carcinoma cells exhibited progressively increasing upregulation of FRs after shifting of folate-replete cells to low-folate media, without a proportionate rise in FR mRNA or rise in hnRNP E1. Translational FR upregulation was accompanied by a progressive accumulation of the metabolite homocysteine within cultured cells, which stimulated interaction of the FR mRNA cis-element and hnRNP E1 as well as FR biosynthesis in a dose-dependent manner. Abrupt reversal of folate deficiency also led to a rapid parallel reduction in homocysteine and FR biosynthesis to levels observed in folate-replete cells. Collectively, these results suggest that homocysteine is the key modulator of translational upregulation of FRs and establishes the linkage between perturbed folate metabolism and coordinated upregulation of FRs.

5' Untranslated Regions↗
PubMed1990

Developmental changes in levels of proopiomelanocortin intron A-containing heterogeneous nuclear RNA and mature messenger RNA in the anterior and neurointermediate lobes of the rat pituitary.

The POMC cells of the rat pituitary undergo dynamic phenotypic changes during differentiation. Here we have determined that alterations in the relative levels of a POMC precursor RNA species and POMC mRNA occur during development and may represent another level at which the POMC phenotype is developmentally regulated. We performed solution hybridization/nuclease protection assays using a POMC exon 1/intron A splice junction probe to quantitate levels of both intron A-containing POMC heterogeneous nuclear (hnRNA) and fully processed POMC mRNA in separated anterior and neurointermediate lobes of the fetal, neonatal, and adult pituitary. The levels of POMC hnRNA per anterior lobe increased 7-fold from embryonic day 15 to adulthood (0.022 to 0.159 fmol/lobe), while POMC mRNA levels increased 121-fold (0.15 to 18.2 fmol/lobe). POMC hnRNA levels per neurointermediate lobe increased 23-fold from embryonic day 18 to adulthood (0.024 to 0.54 fmol/lobe), while POMC mRNA levels increased 69-fold (0.65 to 44.6 fmol/lobe). Thus, both anterior and neurointermediate lobes contain higher relative abundances of POMC hnRNA compared to mRNA during early development. These subsequently decrease (from 1:7 to 1: approximately 110 in the anterior lobe and from 1:27 to 1:83 in the intermediate lobe over the ages examined) as the levels of POMC mRNA in both anterior and neurointermediate lobe increase at a greater rate than POMC hnRNA as development progresses. These results provide the first measurements of POMC mRNA and hnRNA levels during ontogeny and suggest that there may be a developmental change in the regulation of POMC primary transcript processing.

Animals↗
PubMed1985

Mammalian single-stranded DNA binding proteins and heterogeneous nuclear RNA proteins have common antigenic determinants.

Antibodies were raised in rabbit against a pure subset of calf thymus single-stranded DNA binding proteins (ssDBPs) and purified by affinity chromatography on antigen-Sepharose. In Western blot experiments these antibodies were shown to react to the same extent with the whole family of bovine ssDBPs, as well as with ssDBPs from HeLa cells. When used to stain total cell extracts from both calf thymus and HeLa cells the antibodies reacted only with bands corresponding to the ssDBPs and with a set of bands of higher molecular weight, whose electrophoretic pattern matched that of the 40S hnRNP core proteins. In effect we observed that purified 40S hnRNP core proteins from HeLa cells were strongly reactive with the antibodies. Moreover after partial tryptic digestion HeLa cells ssDBPs and hnRNPs produced immunoreactive fragments of the same molecular weight and isoelectric point. Extensive structural homologies can thus be evidenced between these two classes of proteins, which share the property of selective binding to single-stranded nucleic acids.

Animals↗
PubMed1979

Low molecular weight RNAs as components of nuclear ribonucleoprotein particles containing heterogeneous nuclear RNA.

70-130 S polyparticles as well as 38 S monoparticles were isolated from rat liver nuclei and analyzed in respect to their RNA components by microgel polyacrylamide electrophoresis in formamide. In addition to the high molecular weight polydisperse hnRNA of polyparticles several low molecular weight RNAs (snRNA) were detected. There are at least six distinct snRNA species in polyparticles. Except for one species, which is missing, 38 S monoparticles showed a similar snRNA pattern. From densitometer tracings of microgels the snRNAs were estimated to represent about 11% of the total polyparticle RNA. The number of nucleotides for the various snRNAs were determined from a plot of relative electrophoretic mobility versus log number of nucleotides. The possibility that the snRNAs are degradation products of the hnRNA was excluded on the basis of the following findings. (1) The snRNA pattern was similar in mono- and polyparticles. (2) Whereas the hnRNA of polyparticles incubated at 37 degrees C was extensively degraded, the snRNA did not show a corresponding increase. (3) After a 30 min pulse with [3H]orotate the hn RNA was readily labeled; none of the snRNAs, however, incorporated radioactivity. The snRNAs were still found after treatment of polyparticles with 2 M NaCl excluding contamination by nucleoplasm.

Animals↗
PubMed1979

Proteinases as probes of the structure of rat liver ribonucleoprotein particles carrying heterogeneous nuclear RNA.

Three proteolytic enzymes with different specificities produced essentially the same degradation pattern of the proteins of ribonucleoprotein particles. Proteins with apparent molecular weights of 144 000, 133 000 and 115 000 were hydrolyzed most readily which may indicate an exterior location in the ribonucleoprotein complex. The major particle proteins in the range of 30 000-42 000 daltons were much less susceptible to proteinases than the high molecular weight species. Proteins of 31 000, 33 000 and 42 000 daltons were resistant to proteolysis. The degradation rates of the proteins in intact ribonucleoprotein particles were considerably lower than rates obtained with the same proteins separated from the RNA. Incubation with trypsin and recentrifugation of polyparticles led to a shift in the sedimentation constant from 90 S to 0-20 S, corresponding to a decrease in the protein to RNA ratio from 4 to 1.3. No significant change in the small molecular weight RNA pattern was detected after trypsin digestion.

Animals↗