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Human RNase H1 is associated with protein P32 and is involved in mitochondrial pre-rRNA processing.

Wu H, Sun H, Liang X, Lima WF, Crooke ST - PLoS ONE (2013)

Bottom Line: P32 enhanced the cleavage activity of RNase H1 by reducing the affinity of the enzyme for the heteroduplex substrate and enhancing turnover, but had no effect on the cleavage pattern.RNase H1 and P32 were partially co-localized in mitochondria and reduction of P32 or RNase H1 levels resulted in accumulation of mitochondrial pre ribosomal RNA [12S/16S] in HeLa cells.Further, the results identify P32 as a member of the 'RNase H1 degradosome' and the key P32 enhances the enzymatic efficiency of human RNase H1.

View Article: PubMed Central - PubMed

Affiliation: Department of Core Antisense Research, Isis Pharmaceuticals, Inc., Carlsbad, California, United States of America.

ABSTRACT
Mammalian RNase H1 has been implicated in mitochondrial DNA replication and RNA processing and is required for embryonic development. We identified the mitochondrial protein P32 that binds specifically to human RNase H1, but not human RNase H2. P32 binds human RNase H1 via the hybrid-binding domain of the enzyme at an approximately 1∶1 ratio. P32 enhanced the cleavage activity of RNase H1 by reducing the affinity of the enzyme for the heteroduplex substrate and enhancing turnover, but had no effect on the cleavage pattern. RNase H1 and P32 were partially co-localized in mitochondria and reduction of P32 or RNase H1 levels resulted in accumulation of mitochondrial pre ribosomal RNA [12S/16S] in HeLa cells. P32 also co-immunoprecipitated with MRPP1, a mitochondrial RNase P protein required for mitochondrial pre-rRNA processing. The P32-RNase H1 complex was shown to physically interact with mitochondrial DNA and pre-rRNA. These results expand the potential roles for RNase H1 to include assuring proper transcription and processing of guanosine-cytosine rich pre-ribosomal RNA in mitochondria. Further, the results identify P32 as a member of the 'RNase H1 degradosome' and the key P32 enhances the enzymatic efficiency of human RNase H1.

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Human RNase H1 is associated with P32.(A) Western blot analysis of cell lysates and immunoprecipitated samples show Flag-tagged RNase H1 and H2 expression from cells stably transformed with RNase H1 (H1) or H2 (H2) or wild type (control) HEK cell lines. (B) Co-selection of RNase H1 binding proteins by immunoprecipitation. Extracts from cells expressing the Flag-H1, Flag-H2, or HA-H1 cell lines were immunoprecipitated with either anti-Flag or anti-HA antibody. Co-precipitated proteins were resolved by SDS-PAGE, and visualized by silver staining. Protein bands that were different from the co-precipitated proteins from control cells were subjected to mass spectrometry. The protein bands corresponding to the tagged RNase H1, H2 and the co-precipitated P32 proteins are indicated. The size marker was SeeBlue Plus2 Pre-Stained Standard (Invitrogen). (C) 2D gel electrophoresis of proteins co-precipitated with Flag-H1 or Flag-H2. About 5 mg cell lysates were prepared for immunoprecipitation with anti-flag beads from cell lines which stably express Flag-H1 or Flag-H2. The immunoprecipitates were washed four times with RIPA buffer and directly sent to Applied Biomics Inc. (San Francisco, CA) for 2D gel electrophoresis coupled with MS analysis. In brief, the co-precipitated proteins from Flag-H1 or Flag-H2 cells were labeled by fluorescent DIGE CyDyers, respectively, followed by 2D gel electrophoresis. The protein image was scanned with a fluorescence detector. The figure illustrates the proteins differentially associated with RNase H1 (green) or H2 (red). The P32 protein was confirmed with mass spectrum from the extracted gel sample. Circled spots were identified as RNase H1, H2 or P32 by mass spectrometric analysis. (D) Both endogenous and expressed RNase H1 are co-precipitated with the expressed P32. Left panel: western blots with P32, RNase H1, or H2 antibodies for proteins co-precipitated using anti-HA antibody from extracts of control HeLa cells or cells transfected with HA-P32 expression plasmid. Right panel: western blots for proteins co-selected using anti-HA antibody from extracts of Flag-H1, Flag-H2 stable cell lines and control cells, all of which were transfected with HA-P32 expression plasmid. (E) Confirmation of the specific interaction between RNase H1 and P32. RNase H cleavage activity indicates that the P32 co-immunoprecipitated material contains only RNase H1 enzyme activity. Upper panel: Cleavage patterns of human RNase H1 and H2 from IP-coupled enzyme activity assays. Immunoprecipitations were performed with either anti-flag, anti-RNase H1 or anti-H2 antibodies from extracts of Flag-H1, Flag-H2 expressing cells or control cells. The co-precipitated samples were incubated for the indicated times with a 32P-labeled RNA/DNA-methoxyethyl (MOE) gapmer duplex and the cleavage products were separated using denaturing gel electrophoresis. The preferred cleavage sites of RNase H1 and H2 are indicated with * or #, respectively. The positions of the preferred cleavage sites in the heteroduplex are shown in the middle panel with the sequences of the RNA substrate (upper strand) and the oligonucleotide (lower strand). The bold nucleotides in the oligonucleotide strand indicate the position of the MOE substitutions. Lower panel: only the RNase H1 enzyme activity was detected in the co-precipitated material from lysates containing tagged P32. Immunoprecipitations were performed with anti-HA antibody from extracts of Flag-H1 or Flag-H2 stable cell lines or control HEK cells, which were all transfected or not transfected with HA-P32 expression plasmid. The precipitated samples were analyzed for cleavage patterns as described above. The position of the cleavage bands relative to the sequence of the cleavage products is shown on the left. A partial alkaline digestion of the same labeled RNA was used as a sequence ladder. The cleavage pattern of purified human RNase H1 is shown at the far right of the lower panel.
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pone-0071006-g001: Human RNase H1 is associated with P32.(A) Western blot analysis of cell lysates and immunoprecipitated samples show Flag-tagged RNase H1 and H2 expression from cells stably transformed with RNase H1 (H1) or H2 (H2) or wild type (control) HEK cell lines. (B) Co-selection of RNase H1 binding proteins by immunoprecipitation. Extracts from cells expressing the Flag-H1, Flag-H2, or HA-H1 cell lines were immunoprecipitated with either anti-Flag or anti-HA antibody. Co-precipitated proteins were resolved by SDS-PAGE, and visualized by silver staining. Protein bands that were different from the co-precipitated proteins from control cells were subjected to mass spectrometry. The protein bands corresponding to the tagged RNase H1, H2 and the co-precipitated P32 proteins are indicated. The size marker was SeeBlue Plus2 Pre-Stained Standard (Invitrogen). (C) 2D gel electrophoresis of proteins co-precipitated with Flag-H1 or Flag-H2. About 5 mg cell lysates were prepared for immunoprecipitation with anti-flag beads from cell lines which stably express Flag-H1 or Flag-H2. The immunoprecipitates were washed four times with RIPA buffer and directly sent to Applied Biomics Inc. (San Francisco, CA) for 2D gel electrophoresis coupled with MS analysis. In brief, the co-precipitated proteins from Flag-H1 or Flag-H2 cells were labeled by fluorescent DIGE CyDyers, respectively, followed by 2D gel electrophoresis. The protein image was scanned with a fluorescence detector. The figure illustrates the proteins differentially associated with RNase H1 (green) or H2 (red). The P32 protein was confirmed with mass spectrum from the extracted gel sample. Circled spots were identified as RNase H1, H2 or P32 by mass spectrometric analysis. (D) Both endogenous and expressed RNase H1 are co-precipitated with the expressed P32. Left panel: western blots with P32, RNase H1, or H2 antibodies for proteins co-precipitated using anti-HA antibody from extracts of control HeLa cells or cells transfected with HA-P32 expression plasmid. Right panel: western blots for proteins co-selected using anti-HA antibody from extracts of Flag-H1, Flag-H2 stable cell lines and control cells, all of which were transfected with HA-P32 expression plasmid. (E) Confirmation of the specific interaction between RNase H1 and P32. RNase H cleavage activity indicates that the P32 co-immunoprecipitated material contains only RNase H1 enzyme activity. Upper panel: Cleavage patterns of human RNase H1 and H2 from IP-coupled enzyme activity assays. Immunoprecipitations were performed with either anti-flag, anti-RNase H1 or anti-H2 antibodies from extracts of Flag-H1, Flag-H2 expressing cells or control cells. The co-precipitated samples were incubated for the indicated times with a 32P-labeled RNA/DNA-methoxyethyl (MOE) gapmer duplex and the cleavage products were separated using denaturing gel electrophoresis. The preferred cleavage sites of RNase H1 and H2 are indicated with * or #, respectively. The positions of the preferred cleavage sites in the heteroduplex are shown in the middle panel with the sequences of the RNA substrate (upper strand) and the oligonucleotide (lower strand). The bold nucleotides in the oligonucleotide strand indicate the position of the MOE substitutions. Lower panel: only the RNase H1 enzyme activity was detected in the co-precipitated material from lysates containing tagged P32. Immunoprecipitations were performed with anti-HA antibody from extracts of Flag-H1 or Flag-H2 stable cell lines or control HEK cells, which were all transfected or not transfected with HA-P32 expression plasmid. The precipitated samples were analyzed for cleavage patterns as described above. The position of the cleavage bands relative to the sequence of the cleavage products is shown on the left. A partial alkaline digestion of the same labeled RNA was used as a sequence ladder. The cleavage pattern of purified human RNase H1 is shown at the far right of the lower panel.

Mentions: To better understand the biological functions of human RNase H1 and its roles in the activity of antisense oligonucleotide-directed substrate RNA degradation, we identified RNase H1-associated proteins by co-immunoprecipitation (co-IP) from cell lines that stably express epitope-tagged human RNase H1 and H2, using antibodies specific to the tags. HEK cell lines were developed to stably express N-terminal Flag-tagged RNase H1 (Flag H1), N-terminal Flag-tagged RNase H2 (Flag H2), or C-terminal HA-tagged RNase H1 (HA H1). Expression of the tagged proteins was confirmed using western analyses with either whole cell lysates or immunoprecipitated materials (Figure 1A). Next, proteins associated with RNase H1 or RNase H2 were co-immunoprecipitated from extracts of cells that stably express the tagged proteins, using either anti-Flag or anti-HA beads (Figure 1B). Co-precipitated proteins were separated by SDS-PAGE and visualized by silver staining. The tagged RNase H1 and H2 proteins were specifically isolated with the corresponding beads, as expected. A protein band (∼28 KDa) was identified that specifically co-precipitated with both Flag H1 and HA H1 RNase H1, but not with Flag H2 (Figure 1B). Mass spectrometric (MS) analysis of the protein band excised from the gel identified the mitochondrial protein, P32 (Gene Bank number NM_001212). The specific co-precipitation of P32 with RNase H1 was also confirmed by 2D gel electrophoresis and MS (Figure 1C). Note that human RNase H1 displays several pIs while RNase H2 displays a single pI of approximately 5. Variable phosphorylation of RNase H1 probably accounts for the multiple PIs.


Human RNase H1 is associated with protein P32 and is involved in mitochondrial pre-rRNA processing.

Wu H, Sun H, Liang X, Lima WF, Crooke ST - PLoS ONE (2013)

Human RNase H1 is associated with P32.(A) Western blot analysis of cell lysates and immunoprecipitated samples show Flag-tagged RNase H1 and H2 expression from cells stably transformed with RNase H1 (H1) or H2 (H2) or wild type (control) HEK cell lines. (B) Co-selection of RNase H1 binding proteins by immunoprecipitation. Extracts from cells expressing the Flag-H1, Flag-H2, or HA-H1 cell lines were immunoprecipitated with either anti-Flag or anti-HA antibody. Co-precipitated proteins were resolved by SDS-PAGE, and visualized by silver staining. Protein bands that were different from the co-precipitated proteins from control cells were subjected to mass spectrometry. The protein bands corresponding to the tagged RNase H1, H2 and the co-precipitated P32 proteins are indicated. The size marker was SeeBlue Plus2 Pre-Stained Standard (Invitrogen). (C) 2D gel electrophoresis of proteins co-precipitated with Flag-H1 or Flag-H2. About 5 mg cell lysates were prepared for immunoprecipitation with anti-flag beads from cell lines which stably express Flag-H1 or Flag-H2. The immunoprecipitates were washed four times with RIPA buffer and directly sent to Applied Biomics Inc. (San Francisco, CA) for 2D gel electrophoresis coupled with MS analysis. In brief, the co-precipitated proteins from Flag-H1 or Flag-H2 cells were labeled by fluorescent DIGE CyDyers, respectively, followed by 2D gel electrophoresis. The protein image was scanned with a fluorescence detector. The figure illustrates the proteins differentially associated with RNase H1 (green) or H2 (red). The P32 protein was confirmed with mass spectrum from the extracted gel sample. Circled spots were identified as RNase H1, H2 or P32 by mass spectrometric analysis. (D) Both endogenous and expressed RNase H1 are co-precipitated with the expressed P32. Left panel: western blots with P32, RNase H1, or H2 antibodies for proteins co-precipitated using anti-HA antibody from extracts of control HeLa cells or cells transfected with HA-P32 expression plasmid. Right panel: western blots for proteins co-selected using anti-HA antibody from extracts of Flag-H1, Flag-H2 stable cell lines and control cells, all of which were transfected with HA-P32 expression plasmid. (E) Confirmation of the specific interaction between RNase H1 and P32. RNase H cleavage activity indicates that the P32 co-immunoprecipitated material contains only RNase H1 enzyme activity. Upper panel: Cleavage patterns of human RNase H1 and H2 from IP-coupled enzyme activity assays. Immunoprecipitations were performed with either anti-flag, anti-RNase H1 or anti-H2 antibodies from extracts of Flag-H1, Flag-H2 expressing cells or control cells. The co-precipitated samples were incubated for the indicated times with a 32P-labeled RNA/DNA-methoxyethyl (MOE) gapmer duplex and the cleavage products were separated using denaturing gel electrophoresis. The preferred cleavage sites of RNase H1 and H2 are indicated with * or #, respectively. The positions of the preferred cleavage sites in the heteroduplex are shown in the middle panel with the sequences of the RNA substrate (upper strand) and the oligonucleotide (lower strand). The bold nucleotides in the oligonucleotide strand indicate the position of the MOE substitutions. Lower panel: only the RNase H1 enzyme activity was detected in the co-precipitated material from lysates containing tagged P32. Immunoprecipitations were performed with anti-HA antibody from extracts of Flag-H1 or Flag-H2 stable cell lines or control HEK cells, which were all transfected or not transfected with HA-P32 expression plasmid. The precipitated samples were analyzed for cleavage patterns as described above. The position of the cleavage bands relative to the sequence of the cleavage products is shown on the left. A partial alkaline digestion of the same labeled RNA was used as a sequence ladder. The cleavage pattern of purified human RNase H1 is shown at the far right of the lower panel.
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pone-0071006-g001: Human RNase H1 is associated with P32.(A) Western blot analysis of cell lysates and immunoprecipitated samples show Flag-tagged RNase H1 and H2 expression from cells stably transformed with RNase H1 (H1) or H2 (H2) or wild type (control) HEK cell lines. (B) Co-selection of RNase H1 binding proteins by immunoprecipitation. Extracts from cells expressing the Flag-H1, Flag-H2, or HA-H1 cell lines were immunoprecipitated with either anti-Flag or anti-HA antibody. Co-precipitated proteins were resolved by SDS-PAGE, and visualized by silver staining. Protein bands that were different from the co-precipitated proteins from control cells were subjected to mass spectrometry. The protein bands corresponding to the tagged RNase H1, H2 and the co-precipitated P32 proteins are indicated. The size marker was SeeBlue Plus2 Pre-Stained Standard (Invitrogen). (C) 2D gel electrophoresis of proteins co-precipitated with Flag-H1 or Flag-H2. About 5 mg cell lysates were prepared for immunoprecipitation with anti-flag beads from cell lines which stably express Flag-H1 or Flag-H2. The immunoprecipitates were washed four times with RIPA buffer and directly sent to Applied Biomics Inc. (San Francisco, CA) for 2D gel electrophoresis coupled with MS analysis. In brief, the co-precipitated proteins from Flag-H1 or Flag-H2 cells were labeled by fluorescent DIGE CyDyers, respectively, followed by 2D gel electrophoresis. The protein image was scanned with a fluorescence detector. The figure illustrates the proteins differentially associated with RNase H1 (green) or H2 (red). The P32 protein was confirmed with mass spectrum from the extracted gel sample. Circled spots were identified as RNase H1, H2 or P32 by mass spectrometric analysis. (D) Both endogenous and expressed RNase H1 are co-precipitated with the expressed P32. Left panel: western blots with P32, RNase H1, or H2 antibodies for proteins co-precipitated using anti-HA antibody from extracts of control HeLa cells or cells transfected with HA-P32 expression plasmid. Right panel: western blots for proteins co-selected using anti-HA antibody from extracts of Flag-H1, Flag-H2 stable cell lines and control cells, all of which were transfected with HA-P32 expression plasmid. (E) Confirmation of the specific interaction between RNase H1 and P32. RNase H cleavage activity indicates that the P32 co-immunoprecipitated material contains only RNase H1 enzyme activity. Upper panel: Cleavage patterns of human RNase H1 and H2 from IP-coupled enzyme activity assays. Immunoprecipitations were performed with either anti-flag, anti-RNase H1 or anti-H2 antibodies from extracts of Flag-H1, Flag-H2 expressing cells or control cells. The co-precipitated samples were incubated for the indicated times with a 32P-labeled RNA/DNA-methoxyethyl (MOE) gapmer duplex and the cleavage products were separated using denaturing gel electrophoresis. The preferred cleavage sites of RNase H1 and H2 are indicated with * or #, respectively. The positions of the preferred cleavage sites in the heteroduplex are shown in the middle panel with the sequences of the RNA substrate (upper strand) and the oligonucleotide (lower strand). The bold nucleotides in the oligonucleotide strand indicate the position of the MOE substitutions. Lower panel: only the RNase H1 enzyme activity was detected in the co-precipitated material from lysates containing tagged P32. Immunoprecipitations were performed with anti-HA antibody from extracts of Flag-H1 or Flag-H2 stable cell lines or control HEK cells, which were all transfected or not transfected with HA-P32 expression plasmid. The precipitated samples were analyzed for cleavage patterns as described above. The position of the cleavage bands relative to the sequence of the cleavage products is shown on the left. A partial alkaline digestion of the same labeled RNA was used as a sequence ladder. The cleavage pattern of purified human RNase H1 is shown at the far right of the lower panel.
Mentions: To better understand the biological functions of human RNase H1 and its roles in the activity of antisense oligonucleotide-directed substrate RNA degradation, we identified RNase H1-associated proteins by co-immunoprecipitation (co-IP) from cell lines that stably express epitope-tagged human RNase H1 and H2, using antibodies specific to the tags. HEK cell lines were developed to stably express N-terminal Flag-tagged RNase H1 (Flag H1), N-terminal Flag-tagged RNase H2 (Flag H2), or C-terminal HA-tagged RNase H1 (HA H1). Expression of the tagged proteins was confirmed using western analyses with either whole cell lysates or immunoprecipitated materials (Figure 1A). Next, proteins associated with RNase H1 or RNase H2 were co-immunoprecipitated from extracts of cells that stably express the tagged proteins, using either anti-Flag or anti-HA beads (Figure 1B). Co-precipitated proteins were separated by SDS-PAGE and visualized by silver staining. The tagged RNase H1 and H2 proteins were specifically isolated with the corresponding beads, as expected. A protein band (∼28 KDa) was identified that specifically co-precipitated with both Flag H1 and HA H1 RNase H1, but not with Flag H2 (Figure 1B). Mass spectrometric (MS) analysis of the protein band excised from the gel identified the mitochondrial protein, P32 (Gene Bank number NM_001212). The specific co-precipitation of P32 with RNase H1 was also confirmed by 2D gel electrophoresis and MS (Figure 1C). Note that human RNase H1 displays several pIs while RNase H2 displays a single pI of approximately 5. Variable phosphorylation of RNase H1 probably accounts for the multiple PIs.

Bottom Line: P32 enhanced the cleavage activity of RNase H1 by reducing the affinity of the enzyme for the heteroduplex substrate and enhancing turnover, but had no effect on the cleavage pattern.RNase H1 and P32 were partially co-localized in mitochondria and reduction of P32 or RNase H1 levels resulted in accumulation of mitochondrial pre ribosomal RNA [12S/16S] in HeLa cells.Further, the results identify P32 as a member of the 'RNase H1 degradosome' and the key P32 enhances the enzymatic efficiency of human RNase H1.

View Article: PubMed Central - PubMed

Affiliation: Department of Core Antisense Research, Isis Pharmaceuticals, Inc., Carlsbad, California, United States of America.

ABSTRACT
Mammalian RNase H1 has been implicated in mitochondrial DNA replication and RNA processing and is required for embryonic development. We identified the mitochondrial protein P32 that binds specifically to human RNase H1, but not human RNase H2. P32 binds human RNase H1 via the hybrid-binding domain of the enzyme at an approximately 1∶1 ratio. P32 enhanced the cleavage activity of RNase H1 by reducing the affinity of the enzyme for the heteroduplex substrate and enhancing turnover, but had no effect on the cleavage pattern. RNase H1 and P32 were partially co-localized in mitochondria and reduction of P32 or RNase H1 levels resulted in accumulation of mitochondrial pre ribosomal RNA [12S/16S] in HeLa cells. P32 also co-immunoprecipitated with MRPP1, a mitochondrial RNase P protein required for mitochondrial pre-rRNA processing. The P32-RNase H1 complex was shown to physically interact with mitochondrial DNA and pre-rRNA. These results expand the potential roles for RNase H1 to include assuring proper transcription and processing of guanosine-cytosine rich pre-ribosomal RNA in mitochondria. Further, the results identify P32 as a member of the 'RNase H1 degradosome' and the key P32 enhances the enzymatic efficiency of human RNase H1.

Show MeSH
Related in: MedlinePlus