The archaeal KEOPS complex possesses a functional Gon7 homolog and has an essential function independent of the cellular t^(6)A modification level

Kinase,putative Endopeptidase,and Other Proteins of Small size(KEOPS)is a multisubunit protein complex conserved in eukaryotes and archaea.It is composed of Pcc1,Kae1,Bud32,Cgi121,and Gon7 in eukaryotes and is primarily involved in N^(6)-threonylcarbamoyl adenosine(t^(6)A)modification of transfer RNAs(tRNAs).Recently,it was reported that KEOPS participates in homologous recombination(HR)repair in yeast.To characterize the KEOPS in archaea(aKEOPS),we conducted genetic and biochemical analyses of its encoding genes in the hyperthermophilic archaeon Saccharolobus islandicus.We show that aKEOPS also possesses five subunits,Pcc1,Kae1,Bud32,Cgi121,and Pcc1-like(or Gon7-like),just like eukaryotic KEOPS.Pcc1-like has physical interactions with Kae1 and Pcc1 and can mediate the monomerization of the dimeric subcomplex(Kae1-Pcc1-Pcc1-Kae1),suggesting that Pcc1-like is a functional homolog of the eukaryotic Gon7 subunit.Strikingly,none of the genes encoding aKEOPS subunits,including Pcc1 and Pcc1-like,can be deleted in the wild type and in a t^(6)A modification complementary strain named TsaKI,implying that the aKEOPS complex is essential for an additional cellular process in this archaeon.Knock-down of the Cgi121 subunit leads to severe growth retardance in the wild type that is partially rescued in TsaKI.These results suggest that aKEOPS plays an essential role independent of the cellular t^(6)A modification level.In addition,archaeal Cgi121 possesses dsDNA-binding activity that relies on its tRNA 3ʹCCA tail binding module.Our study clarifies the subunit organization of archaeal KEOPS and suggests an origin of eukaryotic Gon7.The study also reveals a possible link between the function in t^(6)A modification and the additional function,presumably HR.

RNA-binding protein LIN28B inhibits apoptosis through regulation of the AKT2/FOXO3A/BIM axis in ovarian cancer cells

LIN28B is an evolutionarily conserved RNA-binding protein that regulates mRNA translation and miRNA let-7 maturation in embryonic stem cells and developing tissues.Increasing evidence demonstrates that LIN28B is activated in cancer and serves as a critical oncogene.However,the underlying molecular mechanisms of LIN28B function in tumorigenesis are still largely unknown.Here we report that LIN28B was expressed in over half of the patients with epithelial ovarian cancer who were examined(n=584).Functional experiments demonstrated that LIN28B inhibited ovarian cancer cell apoptosis.Furthermore,we showed that the proapoptotic factor BIM played an essential role in the antiapoptotic function of LIN28B.RNA-IP microarray analysis suggested that LIN28B binds to mRNAs that are associated with the DNA damage pathway,such as AKT2,in ovarian cancer cells.By binding to AKT2 mRNA and enhancing its protein expression,LIN28B regulated FOXO3A protein phosphorylation and decreased the transcriptional level of BIM,which antagonized the antiapoptosis activity of LIN28B.Taken together,these results mechanistically linked LIN28B and the AKT2/FOXO3A/BIM axis to the apoptosis pathway.The findings may have important implications in the diagnosis and therapeutics of ovarian cancer.