Silencing of RNA Helicase II/Guα Inhibits Mammalian Ribosomal RNA Production

Abstract

The intricate production of ribosomal RNA is well defined in yeast, but its complexity in higher organisms is barely understood. We recently showed that down-regulation of nucleolar protein RNA helicase II/Guα (RH-II/Guα or DDX21) in Xenopus oocytes inhibited processing of 20 S rRNA to 18 S and contributed to degradation of 28 S rRNA (Yang, H., Zhou, J., Ochs, R. L., Henning, D., Jin, R., and Valdez, B. C. (2003) J. Biol. Chem. 278, 38847–38859). Since no nucleolar RNA helicase has been functionally characterized in mammalian cells, we used short interfering RNA to search for functions for RH-II/Guα and its paralogue RH-II/Guβ in rRNA production. Silencing of RH-II/Guα by more than 80% in HeLa cells resulted in an almost 80% inhibition of 18 and 28 S rRNA production. This inhibition could be reversed by exogenous expression of wild type RH-II/Guα. A helicase-deficient mutant form having ATPase activity was able to rescue the production of 28 S but not 18 S rRNA. A phenotype exhibiting inhibition of 18 S and 28 S rRNA production was also observed when the paralogue RH-II/Guβ was overexpressed. Both down-regulation of RH-II/Guα and overexpression of RH-II/Guβ slowed cell proliferation. The opposite effects of the two paralogues suggest antagonistic functions. The intricate production of ribosomal RNA is well defined in yeast, but its complexity in higher organisms is barely understood. We recently showed that down-regulation of nucleolar protein RNA helicase II/Guα (RH-II/Guα or DDX21) in Xenopus oocytes inhibited processing of 20 S rRNA to 18 S and contributed to degradation of 28 S rRNA (Yang, H., Zhou, J., Ochs, R. L., Henning, D., Jin, R., and Valdez, B. C. (2003) J. Biol. Chem. 278, 38847–38859). Since no nucleolar RNA helicase has been functionally characterized in mammalian cells, we used short interfering RNA to search for functions for RH-II/Guα and its paralogue RH-II/Guβ in rRNA production. Silencing of RH-II/Guα by more than 80% in HeLa cells resulted in an almost 80% inhibition of 18 and 28 S rRNA production. This inhibition could be reversed by exogenous expression of wild type RH-II/Guα. A helicase-deficient mutant form having ATPase activity was able to rescue the production of 28 S but not 18 S rRNA. A phenotype exhibiting inhibition of 18 S and 28 S rRNA production was also observed when the paralogue RH-II/Guβ was overexpressed. Both down-regulation of RH-II/Guα and overexpression of RH-II/Guβ slowed cell proliferation. The opposite effects of the two paralogues suggest antagonistic functions. The use of short interfering RNA (siRNA) 1The abbreviations used are: siRNAshort interfering RNAIPTGisopropyl-β-d-thiogalactopyranosideRH-II/GuRNA helicase II/Gu proteinrRNAribosomal RNARTreverse transcriptionntnucleotides.1The abbreviations used are: siRNAshort interfering RNAIPTGisopropyl-β-d-thiogalactopyranosideRH-II/GuRNA helicase II/Gu proteinrRNAribosomal RNARTreverse transcriptionntnucleotides. has revolutionized the way in which the functions and interactions of multiple genes and their encoded proteins are deciphered. Short double-stranded RNA mediates the recognition and degradation of its homologous RNA, leading to the down-regulation of expression of the target gene; the mechanism involves a multiprotein complex (1Elbashir S.M. Harborth J. Lendeckel W. Yalcin A. Weber K. Tuschl T. Nature. 2001; 411: 494-498Crossref PubMed Scopus (8018) Google Scholar, 2McManus M.T. Sharp P.A. Nat. Rev. Genet. 2002; 3: 737-747Crossref PubMed Scopus (1201) Google Scholar, 3Paddison P.J. Hannon G.J. Cancer Cells. 2002; 2: 17-23Abstract Full Text Full Text PDF PubMed Scopus (190) Google Scholar). The application of siRNA facilitates the study of complex cellular processes including the biogenesis of ribosomal RNA (rRNA). short interfering RNA isopropyl-β-d-thiogalactopyranoside RNA helicase II/Gu protein ribosomal RNA reverse transcription nucleotides. short interfering RNA isopropyl-β-d-thiogalactopyranoside RNA helicase II/Gu protein ribosomal RNA reverse transcription nucleotides. Synthesis and processing of pre-rRNA, maturation of the final products, and formation of ribosomes occur in the nucleolus. The identification of ∼350 nucleolar proteins (4Andersen J.S. Lyon C.E. Fox A.H. Leung A.K.L. Lam Y.W. Steen H. Mann M. Lamond A.I. Curr. Biol. 2002; 12: 1-11Abstract Full Text Full Text PDF PubMed Scopus (805) Google Scholar, 5Scherl A. Coute Y. Deon C. Calle A. Kindbeiter K. Sanchez J-C. Greco A. Hochstrasser D. Diaz J.-J. Mol. Biol. Cell. 2002; 13: 4100-4109Crossref PubMed Scopus (394) Google Scholar) and the use of siRNA to silence each encoding gene provide the genetic and biochemical screenings that are necessary to elucidate the mechanism of rRNA production in mammalian cells, a process that is more defined in yeast (6Harnpicharnchai P. Jakovljevic J. Horsey E. Miles T. Roman J. Rout M. Meagher D. Imai B. Guo Y. Brame C.J. Shabanowitz J. Hunt D.F. Woolford Jr., J.L. Mol. Cell. 2001; 8: 505-515Abstract Full Text Full Text PDF PubMed Scopus (252) Google Scholar, 7Venema J. Tollervey D. Annu. Rev. Genet. 1999; 33: 261-311Crossref PubMed Scopus (649) Google Scholar, 8Warner J.R. Cell. 2001; 107: 133-136Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar). A number of nucleolar proteins have been functionally associated with mammalian rRNA production mostly based on in vitro experiments and indirect in vivo observations (9Leary D.J. Huang S. FEBS Lett. 2001; 509: 145-150Crossref PubMed Scopus (103) Google Scholar, 10Olson M.O. Hingorani K. Szebeni A. Int. Rev. Cytol. 2002; 219: 199-266Crossref PubMed Scopus (174) Google Scholar, 11Pederson T. Nucleic Acids Res. 1998; 26: 3871-3876Crossref PubMed Scopus (430) Google Scholar, 12Visintin R. Amon A. Curr. Opin. Cell Biol. 2000; 12: 372-377Crossref PubMed Scopus (150) Google Scholar, 13Wang C. Query C.C. Meier U.T. Mol. Cell. Biol. 2002; 22: 8457-8466Crossref PubMed Scopus (56) Google Scholar). More direct lines of evidence are limited to Bop1 (14Strezoska Z. Pestov D.G. Lau L.F. J. Biol. Chem. 2002; 277: 29617-29625Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar), p19arf (15Sugimoto M. Kuo M-L. Roussel M.F. Sherr C.J. Mol. Cell. 2003; 11: 415-424Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar), and the DKC1 gene product dyskerin (16Meier U.T. Nat. Genet. 2003; 33: 116-117Crossref PubMed Scopus (17) Google Scholar, 17Ruggero D. Grisendi S. Piazza F. Rego E. Mari F. Rao P.H. Cordon-Cardo C. Pandolfi P.P. Science. 2003; 299: 259-262Crossref PubMed Scopus (329) Google Scholar). Although our laboratory recently showed that antisense-mediated down-regulation of RNA helicase II/Guα in Xenopus laevis oocytes resulted in inhibition of production of 18 S rRNA and degradation of 28 S rRNA (18Yang H. Zhou J. Ochs R.L. Henning D. Jin R. Valdez B.C. J. Biol. Chem. 2003; 278: 38847-38859Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), we have not reported that this enzyme has a similar function in mammalian cells. RNA helicase II/Guα (RH-II/Guα or DDX21) is a DEAD box nucleolar protein that we previously cloned and characterized (19Flores-Rozas H. Hurwitz J. J. Biol. Chem. 1993; 268: 21372-21383Abstract Full Text PDF PubMed Google Scholar, 20Valdez B.C. Henning D. Busch R.K. Woods K. Flores-Rozas H Hurwitz J. Perlaky L. Busch H. Nucleic Acids Res. 1996; 24: 1220-1224Crossref PubMed Scopus (70) Google Scholar). The cDNA-derived amino acid sequence shows RNA helicase motifs at the middle region, which is responsible for its 5′ to 3′ RNA unwinding activity, and a functionally distinct domain at its C terminus that is able to introduce secondary structure to single-stranded RNA (21Valdez B.C. Henning D. Perumal K. Busch H. Eur. J. Biochem. 1997; 250: 800-807Crossref PubMed Scopus (47) Google Scholar). Its paralogue, RNA helicase II/Guβ, has a marginal RNA helicase activity in vitro, and it does not possess an RNA folding activity (22Valdez B.C. Perlaky L. Henning D. Exp. Cell Res. 2002; 276: 249-263Crossref PubMed Scopus (16) Google Scholar). The high homology in the structures of the two paralogues and close proximity of their genes on human chromosome 10 suggest evolution by gene duplication (23Valdez B.C. Yang H. Hong F. Sequitin A.M. Gene (Amst.). 2002; 284: 53-61Crossref PubMed Scopus (10) Google Scholar). Their nucleolar localization suggests a functional relationship with the production of rRNA. To gain more information about the roles of RH-II/Guα and RH-II/Guβ in rRNA biosynthesis, we employed the use of siRNA and overexpression of their wild type or negative mutant forms. Down-regulation of RH-II/Guα slowed the production of 18 and 28 S rRNA. These effects were reversed when wild type RH-II/Guα was overexpressed, whereas inducible expression of a helicase-deficient mutant reversed the inhibitory effects on 28 S rRNA but not on 18 S rRNA production. siRNA-mediated silencing of RH-II/Guβ did not inhibit rRNA biosynthesis, but overexpression of its wild type form inhibited rRNA production. In addition to affecting rRNA production, silencing of RH-II/Guα or overexpression of RH-II/Guβ resulted in inhibition of cell proliferation. The results suggest antagonistic roles of the two paralogues in rRNA production and cell proliferation. Cell Culture and Transfection—HeLa cells were grown in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum, 100 IU/ml penicillin G, and 100 μg/ml streptomycin sulfate. LAP3 cells are genetically modified NIH3T3 cells that are capable of expressing exogenous genes upon IPTG induction as previously described (24Pestov D.G. Lau L.F. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 12549-12553Crossref PubMed Scopus (32) Google Scholar). These cells were grown in similar medium containing 10% newborn calf serum. Cells were transfected with synthetic siRNA oligoribonucleotides (Dharmacon Research, Inc.) using LipofectAMINE 2000 (Invitrogen). The siRNAs used are listed in Table I.Table IsiRNAs used in cell transfectionIDSequenceTargetsi-934GGGAAAUCACCCUGAAAGGdTdTdTdTCCCUUUAGUGGGACUUUCCHuman and mouse Guαsi-934ScrGUAACAAUGAGAGCACGGCdTdTdTdTCAUUGUUACUCUCGUGCCGScrambled si-934 sequencesi-935GAAUGGACUCUCCCAACCUdTdTdTdTCUUACCUGAGAGGGUUGGAMouse Guαsi-936CACCAGGUCGUAUCAAAGAdTdTdTdTGUGGUCCAGCAUAGUUUCUHuman Guα Open table in a new tab Reverse Transcription-Polymerase were cells using (Invitrogen). was using the A of RNA, of enzyme and for were also in the were used as but multiple were results were using for C protein number Research, Inc.) was used to reverse transcription at for by for to reverse and The 20 of at for at for and at for A final was at for 10 The product was with of and of the was using at 100 the was and to a were using the The used for are in Table used for Guα Guα Guα Guα Open table in a new tab were in and for were 10% and by was using the The of and were previously described B.C. Henning D. Busch R.K. Woods K. Flores-Rozas H Hurwitz J. Perlaky L. Busch H. Nucleic Acids Res. 1996; 24: 1220-1224Crossref PubMed Scopus (70) Google Scholar, B.C. Henning D. Busch R.K. M. Busch H. Mol. PubMed Scopus Google Scholar). was P. K. of and were and of each with it was and with or of were transfected with 10 or siRNA for as described Cells were in medium for was with medium containing at with was for Cells were with a The was by the cells in a medium containing at and RNA was using and the RNA was at of RNA was on a and a The was and in a for or the RNA was with to of LAP3 human and mouse B.C. Henning D. Busch R.K. Woods K. Flores-Rozas H Hurwitz J. Perlaky L. Busch H. Nucleic Acids Res. 1996; 24: 1220-1224Crossref PubMed Scopus (70) Google Scholar, B.C. Yang H. Hong F. Sequitin A.M. Gene (Amst.). 2002; 284: 53-61Crossref PubMed Scopus (10) Google Scholar, B.C. W. 2000; PubMed Scopus Google Scholar) were the and of Both wild type and mutant (21Valdez B.C. Henning D. Perumal K. Busch H. Eur. J. Biochem. 1997; 250: 800-807Crossref PubMed Scopus (47) Google Scholar) were by using the listed in Table used for of wild type and mutant 3′ Open table in a new tab and were used to human and and were used for its mouse The mouse RH-II/Guβ was using and and a and IPTG induction of LAP3 cells were as previously described Z. Pestov D.G. Lau L.F. Mol. Cell. Biol. 2000; PubMed Scopus Google Scholar). cells, which were transfected two with 10 siRNA for a of were and cell were new for well or cells Cells were and were with of medium for that have a of 100 and or cells A was by of HeLa cells, the was cells well and the was cells were to and for at and The cell was used to for cells. an of to at the were on an at siRNA-mediated Down-regulation of study the use of human and mouse cell We siRNA to target human and mouse RH-II/Guα as well as siRNAs that were Down-regulation was at the and protein experiments that 20 of with the of and the use of as a was than of HeLa and LAP3 cells with si-934 resulted in a in the of RH-II/Guα in cell lines in a 10 si-934 was the human by whereas the mouse by A and siRNA that mouse RH-II/Guα by affecting the human which was to human RH-II/Guα in HeLa cells by with a on the of of the mouse siRNAs did not the of RH-II/Guβ in HeLa and LAP3 cells A and A in the protein of mouse RH-II/Guα was observed using 100 si-934 and 100 which resulted in and This in the protein with the in the of the of si-934 and we to use siRNAs in the To the of down-regulation of the human RH-II/Guα at the and protein at were by and shows a in the on the protein The to to 10% and a in the protein was not observed The of si-934 on the protein of RH-II/Guα is to a of the of the when the protein was in the study of its function as Down-regulation of RH-II/Guα of that down-regulation of RH-II/Guα in an processing of rRNA. of siRNA cells were with and with a negative an siRNA with si-934 sequence was of the showed a in RH-II/Guα in HeLa cells with and did not the of RH-II/Guα Both and cells showed in the processing of of The activity at of that by the cells been rRNA. of RNA and the of S and 28 and 18 S rRNA were of cells with which a in RH-II/Guα resulted in an inhibition of rRNA production The in the was not as as the in the final products, 28 and 18 S rRNA. We observed an of the S rRNA. This could be to to the with the use of si-934 resulted in an and in the of 28 and 18 S a The of S rRNA to a a the of S by a the by whereas 28 and 18 S rRNA by and The results suggest that the production of 28 and 18 S rRNA was by the down-regulation of RH-II/Guα with the production of S rRNA. The observed inhibition of rRNA production by down-regulation of RH-II/Guα is similar to the effects by of the DKC1 gene that a that is in rRNA D. Grisendi S. Piazza F. Rego E. Mari F. Rao P.H. Cordon-Cardo C. Pandolfi P.P. Science. 2003; 299: 259-262Crossref PubMed Scopus (329) Google Scholar). To of RNA, the was with the final products, 28 and 18 S which were in were RH-II/Guα but Its of rRNA is of a RNA that has RNA unwinding activity in This but is not limited and A. H. Nucleic Acids Res. 2001; PubMed Scopus Google Scholar), RNA helicase Hurwitz J. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar, S. F. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar), A. J. 11: PubMed Scopus Google Scholar), B. J. 1998; PubMed Scopus Google Scholar), S.M. J. 1993; Scopus Google Scholar), S. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar), L. Biochem. PubMed Scopus Google Scholar), and M. R. H. Cell. Full Text PDF PubMed Scopus Google Scholar). To or not the helicase activity of was for the production of we LAP3 that wild type and mutant of human RH-II/Guα upon IPTG We previously showed that the RH-II/Guα the was to did not RNA unwinding activity in vitro the of ATPase activity (21Valdez B.C. Henning D. Perumal K. Busch H. Eur. J. Biochem. 1997; 250: 800-807Crossref PubMed Scopus (47) Google Scholar). Cells were with IPTG for to with a mouse shows expression and nucleolar localization of the human RH-II/Guα wild type and mutant upon IPTG was to the mouse expressing the human and for of inhibition of rRNA production. We showed in that expression of mouse RH-II/Guα by a on human RH-II/Guα. shows that of a with resulted in in 28 and 18 S rRNA a This was reversed by exogenous expression of human wild type that the human functionally the mouse enzyme and To our expression of the human mutant the inhibitory effects on 28 S rRNA but not on 18 S rRNA and in This suggests that the unwinding activity of RH-II/Guα is for of 18 S rRNA. a in the of RH-II/Guα in the production of 28 S rRNA. that the we observed be to RNA on the shows To this we the of 28 to 18 S rRNA. are to and in the and wild type human RH-II/Guα the mutant were and in the or of a in 18 S rRNA in the mutant to 28 S rRNA. The RNA were for the of mouse and human RH-II/Guα by of the with resulted in in mouse RH-II/Guα the of when human RH-II/Guα type or was mouse Guα in and in is that human and mouse RH-II/Guα for in a mouse cell but shows that does not have an on human RH-II/Guα in HeLa cells. is more that the human RH-II/Guα the expression of the mouse RH-II/Guα as in and the helicase activity of human RH-II/Guα is not for this wild type and mutant RH-II/Guα have similar Down-regulation of RH-II/Guα Cell of HeLa cells with we observed a slowed We to the of the cells. shows a in of cells with whereas cells with showed 10% to the cells. using showed a si-934 and or of the and protein of RH-II/Guα shows almost silencing and The in in and the of RH-II/Guα suggests a by of cells with si-934 did not cell not The results suggest a of cellular of RH-II/Guβ rRNA is that down-regulation of RH-II/Guα could in of expression of the activity of for the activity of RH-II/Guα. of HeLa cells with which the of RH-II/Guβ We that this was to for the in and our was to expression of mouse RH-II/Guα with and for rescue by expression of exogenous mouse To our overexpression of mouse RH-II/Guβ inhibited the production of rRNA down-regulation of the form The rRNA production in a RH-II/Guα is similar to the with IPTG and This is with the of effects on rRNA production when RH-II/Guβ is to with siRNA not phenotype overexpression of RH-II/Guβ is a cell not which be when rRNA production is of the or down-regulation of the rRNA production and cell an antagonistic relationship the two The of processing in and are Both of the and leading to the production of and S rRNA R. J. PubMed Scopus Google Scholar, B. R. A. and in Scholar). This mechanism is in evolution as as the functions of the are We recently showed that antisense-mediated down-regulation of RH-II/Guα in Xenopus resulted in inhibition of production of 28 and 18 S (18Yang H. Zhou J. Ochs R.L. Henning D. Jin R. Valdez B.C. J. Biol. Chem. 2003; 278: 38847-38859Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). In that of 20 S rRNA and the of 28 S degradation were that RH-II/Guα is in the processing of 20 S rRNA to 18 S rRNA and 28 S rRNA. The study was to or not mammalian RH-II/Guα has functions similar to the siRNA-mediated down-regulation of the human and mouse RH-II/Guα resulted in a 28 and 18 S rRNA production. we did not of 20 S product or 28 S degradation in the not the of of human and RH-II/Guα are mammalian is to be in processing and of ribosomal proteins and H. F. P. J. 1998; PubMed Scopus Google Scholar, P. E. Annu. Rev. Cell Biol. 11: PubMed Scopus Google Scholar). Its yeast is also for processing in yeast M. P.A. 1996; PubMed Scopus Google Scholar). has been to be a of in processing T. M. Y. T. T. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar, M. A. K. Y. T. 2001; PubMed Scopus Google Scholar), has been in yeast mammalian the yeast mutant D. T. Mol. Cell. Biol. 12: PubMed Scopus Google Scholar), in their of could be a mechanism for the observed down-regulation of RH-II/Guα and inhibition of mammalian rRNA RH-II/Guα has RNA unwinding activity, and it also introduce secondary structure to single-stranded RNA, two by RNA including and A. H. Nucleic Acids Res. 2001; PubMed Scopus Google Scholar). The RNA unwinding activity of but not its is by its to which its RNA folding activity (21Valdez B.C. Henning D. Perumal K. Busch H. Eur. J. Biochem. 1997; 250: 800-807Crossref PubMed Scopus (47) Google Scholar). The mutant did not rescue the siRNA-mediated inhibition of 18 S rRNA production the of its RNA helicase the this mutant did reverse the siRNA-mediated inhibition of 28 that its RNA helicase activity not be as as its RNA folding activity, with nucleolar for the production of 28 S rRNA. The ATPase activity of RH-II/Guα be in the formation and of for 28 S rRNA production similar to the of ATPase activity in the of by RNA helicase E. S. A.M. Science. 2001; PubMed Scopus (251) Google Scholar). The RNA folding activity of mutant to this we in the RH-II/Guα 28 S rRNA by secondary structure of 28 S rRNA by its direct with ribosomal protein Henning and B. C. Valdez, and This is by the of RH-II/Guα and in which were and were by T. M. Y. T. T. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google Scholar, M. A. K. Y. T. 2001; PubMed Scopus Google Scholar). In addition to 28 and 18 S rRNA production, the of RH-II/Guα to a in rRNA gene transcription or rRNA be a that when the of nucleolar protein to mammalian rRNA production or a the of processing to RNA or is that the rRNA production on cellular (9Leary D.J. Huang S. FEBS Lett. 2001; 509: 145-150Crossref PubMed Scopus (103) Google Scholar, Y. J.R. Mol. Cell. Biol. 2003; PubMed Scopus Google Scholar). This down-regulation of RH-II/Guα or dyskerin D. Grisendi S. Piazza F. Rego E. Mari F. Rao P.H. Cordon-Cardo C. Pandolfi P.P. Science. 2003; 299: 259-262Crossref PubMed Scopus (329) Google Scholar) or of p19arf (15Sugimoto M. Kuo M-L. Roussel M.F. Sherr C.J. Mol. Cell. 2003; 11: 415-424Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar) results in similar inhibitory effects on rRNA production. Although this mechanism not a direct of RH-II/Guα as by a more inhibition of 28 and 18 S rRNA production than the S rRNA and the of RH-II/Guα mutant to reverse 28 S but not 18 S rRNA production the that indirect the of RH-II/Guα with J. C. R. J. M. W. B. M. Valdez B.C. D. J. 2002; PubMed Scopus Google Scholar). Down-regulation of RH-II/Guα could expression of proteins to the processing and of a more direct of RH-II/Guα in rRNA production as by its nucleolar the of the mutant to reverse the inhibition of 28 S rRNA production but not 18 the RH-II/Guα with and its in We RH-II/Guβ in the processing of rRNA as We a relationship in the cellular functions of the and our suggest overexpression of RH-II/Guα did not rRNA production, overexpression of RH-II/Guβ inhibited this cellular process of the inhibition by RH-II/Guα down-regulation This antagonistic relationship is with the marginal in vitro RNA unwinding activity of RH-II/Guβ and its of RNA folding activity (22Valdez B.C. Perlaky L. Henning D. Exp. Cell Res. 2002; 276: 249-263Crossref PubMed Scopus (16) Google Scholar). the expression of the form is than the expression of the form in cells in and human (22Valdez B.C. Perlaky L. Henning D. Exp. Cell Res. 2002; 276: 249-263Crossref PubMed Scopus (16) Google Scholar). to be the of the two paralogues are cell or We to higher of expression of RH-II/Guα in cells. A was that overexpression of RH-II/Guβ slowed cell proliferation. This is with our higher expression of RH-II/Guβ in when with (22Valdez B.C. Perlaky L. Henning D. Exp. Cell Res. 2002; 276: 249-263Crossref PubMed Scopus (16) Google Scholar). The effects of the two paralogues on rRNA production and cell suggest that the form as a negative of RH-II/Guα in addition to having functions. The observed of cell when RH-II/Guα was or when RH-II/Guβ was be a of in rRNA production. is that production of rRNA is with cell and and the are to be understood. p19arf was recently to formation by rRNA production in addition to a mechanism (15Sugimoto M. Kuo M-L. Roussel M.F. Sherr C.J. Mol. Cell. 2003; 11: 415-424Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar). of a mutant of Bop1 inhibited rRNA maturation and a cell D.G. Z. Lau L.F. Mol. Cell. Biol. 2001; PubMed Scopus Google Scholar). the the in cell observed silencing of RH-II/Guα could also be to inhibition of that on the and RH-II/Guα J. C. R. J. M. W. B. M. Valdez B.C. D. J. 2002; PubMed Scopus Google Scholar). The indirect effects of si-934 on of genes in cell and E. M. Nat. Cell Biol. 2002; PubMed Scopus Google Scholar) to be The effects of RH-II/Guβ on the expression of genes are also In silencing RH-II/Guα have or A negative on rRNA production in protein inhibition of cell and proliferation. the effects of si-934 were inhibition of the activity of of cell and to rRNA and of ribosomes R. A. and in Scholar). Both are with our A of the of provide with of the intricate relationship biogenesis and We L. for the