A systematic search for human ribosome biogenesis factors shows conservation of many aspects of eukaryotic ribosome synthesis with the well-studied process in yeast and identifies an export route of 60S subunits that is specific for higher eukaryotes.

hRio1 is an atypical protein kinase of the conserved RIO family. Depletion of hRio1 affects the last step of 18S rRNA maturation and causes defects in recycling of trans-acting factors from pre-40S subunits in the cytoplasm. The kinase activity of hRio1 is essential for recycling of the endonuclease hNob1 and its binding partner hDim2 from pre-40S.

Ribosome biogenesis is a highly complex process requiring many assisting factors. Studies in yeast have yielded comprehensive knowledge of the cellular machinery involved in this process. However, many aspects of ribosome synthesis are different in higher eukaryotes, and the global set of mammalian ribosome biogenesis factors remains unexplored. We used an imaging-based, genome-wide RNAi screen to find human proteins involved in 40S ribosomal subunit biogenesis. Our analysis identified ∼ 300 factors, many part of essential protein modules such as the small subunit (SSU) processome, the eIF3 and chaperonin complexes, and the ubiquitin-proteasome system. We demonstrate a role for the vertebrate-specific factor RBIS in ribosome synthesis, uncover a requirement for the CRL4 E3 ubiquitin ligase in nucleolar ribosome biogenesis, and reveal that intracellular glutamine synthesis supports 40S subunit production.

Dicer is a key player in microRNA (miRNA) and RNA interference (RNAi) pathways, processing miRNA precursors and doublestranded RNA into ∼21-nt-long products ultimately triggering sequence-dependent gene silencing. Although processing of substrates in vertebrate cells occurs in the cytoplasm, there is growing evidence suggesting Dicer is also present and functional in the nucleus. To address this possibility, we searched for a nuclear localization signal (NLS) in human Dicer and identified its C-terminal double-stranded RNA binding domain (dsRBD) as harboring NLS activity. We show that the dsRBD-NLS can mediate nuclear import of a reporter protein via interaction with importins β, 7, and 8. In the context of full-length Dicer, the dsRBD-NLS is masked. However, duplication of the dsRBD localizes the full-length protein to the nucleus. Furthermore, deletion of the N-terminal helicase domain results in partial accumulation of Dicer in the nucleus upon leptomycin B treatment, indicating that CRM1 contributes to nuclear export of Dicer. Finally, we demonstrate that human Dicer has the ability to shuttle between the nucleus and the cytoplasm. We conclude that Dicer is a shuttling protein whose steady-state localization is cytoplasmic.

Edited by Wolfgang Peti Forkhead box protein O1 (FOXO1) is a transcription factor involved in various cellular processes such as glucose metabolism, development, stress resistance, and tumor suppression. FOXO1's transcriptional activity is controlled by different environmental cues through a myriad of posttranslational modifications. In response to growth factors, the serine/threonine kinase AKT phosphorylates Thr 24 and Ser 256 in FOXO1 to stimulate binding of 14-3-3 proteins, causing FOXO1 inactivation. In contrast, low nutrient and energy levels induce FOXO1 activity. AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis, partly mediates this effect through phosphorylation of Ser 383 and Thr 649 in FOXO1. In this study, we identified Ser 22 as an additional AMPK phosphorylation site in FOXO1's N terminus, with Ser 22 phosphorylation preventing binding of 14-3-3 proteins. The crystal structure of a FOXO1 peptide in complex with 14-3-3 at 2.3 Å resolution revealed that this is a consequence of both steric hindrance and electrostatic repulsion. Furthermore, we found that AMPK-mediated Ser 22 phosphorylation impairs Thr 24 phosphorylation by AKT in a hierarchical manner. Thus, numerous mechanisms maintain FOXO1 activity via AMPK signaling. AMPK-mediated Ser 22 phosphorylation directly and indirectly averts binding of 14-3-3 proteins, whereas phosphorylation of Ser 383 and Thr 649 complementarily stimulates FOXO1 activity. Our results shed light on a mechanism that integrates inputs from both AMPK and AKT signaling pathways in a small motif to fine-tune FOXO1 transcriptional activity.

The CRISPR-Cas9 system has increased the speed and precision of genetic editing in cells and animals. However, model generation for drug development is still expensive and time-consuming, demanding more target flexibility and faster turnaround times with high reproducibility. The generation of a tightly controlled ObLiGaRe doxycycline inducible SpCas9 (ODInCas9) transgene and its use in targeted ObLiGaRe results in functional integration into both human and mouse cells culminating in the generation of the ODInCas9 mouse. Genomic editing can be performed in cells of various tissue origins without any detectable gene editing in the absence of doxycycline. Somatic in vivo editing can model non-small cell lung cancer (NSCLC) adenocarcinomas, enabling treatment studies to validate the efficacy of candidate drugs. The ODInCas9 mouse allows robust and tunable genome editing granting flexibility, speed and uniformity at less cost, leading to high throughput and practical preclinical in vivo therapeutic testing.

dThe interleukin enhancer binding factors ILF2 (NF45) and ILF3 (NF90/NF110) have been implicated in various cellular pathways, such as transcription, microRNA (miRNA) processing, DNA repair, and translation, in mammalian cells. Using tandem affinity purification, we identified human NF45 and NF90 as components of precursors to 60S (pre-60S) ribosomal subunits. NF45 and NF90 are enriched in nucleoli and cosediment with pre-60S ribosomal particles in density gradient analysis. We show that association of the NF45/NF90 heterodimer with pre-60S ribosomal particles requires the double-stranded RNA binding domains of NF90, while depletion of NF45 and NF90 by RNA interference leads to a defect in 60S biogenesis. Nucleoli of cells depleted of NF45 and NF90 have altered morphology and display a characteristic spherical shape. These effects are not due to impaired rRNA transcription or processing of the precursors to 28S rRNA. Consistent with a role of the NF45/NF90 heterodimer in nucleolar steps of 60S subunit biogenesis, downregulation of NF45 and NF90 leads to a p53 response, accompanied by induction of the cyclin-dependent kinase inhibitor p21/CIP1, which can be counteracted by depletion of RPL11. Together, these data indicate that NF45 and NF90 are novel higher-eukaryote-specific factors required for the maturation of 60S ribosomal subunits. T he nuclear factors NF45 and NF90 (NFAR-1, DRBP76, MPP4, and TCP80) were originally discovered as a heterodimeric complex binding to the interleukin-2 (IL-2) promoter (1, 2) and are also referred to as interleukin enhancer-binding factors 2 (ILF2) and 3 (ILF3), respectively (3). While NF90 is vertebrate specific, NF45 is found throughout metazoans.In mammals, the NF45/NF90 complex is widely expressed across tissues (4). Over recent years, NF45/NF90 has been implicated in a great variety of biological processes. Apart from regulation of transcription (5-7), the heterodimer has also been linked to numerous other pathways, such as DNA damage response (8, 9), mRNA metabolism (10, 11), microRNA (miRNA) biogenesis (12), and viral infection (13-17). NF90 knockout mice display severe defects in skeletal muscle formation leading to respiratory failure soon after birth (18), indicating an essential role of NF90 function in vertebrate development.Both NF45 and NF90 possess an N-terminal "domain associated with zinc fingers" (DZF) that is found only in metazoan proteins. Recent structural analysis revealed that the DZF domains of NF45 and NF90 resemble template-free nucleotidyltransferases and mediate their heterodimerization through a structurally conserved interface (19). In addition to the DZF domain, NF90 possesses two double-stranded RNA binding domains (dsRBDs) in the C-terminal region (2, 20) that confer binding to highly structured RNAs (21-23).NF90 is expressed from at least five alternatively spliced mRNAs that all encode the DZF and dsRBDs. Some of the splice variants generate C-terminally extended protein isoforms referred to as NF110 (NFAR-2) (24, 25), which also interact with ...

Edited by Felix WielandKeywords: BCCIP Ribosome biogenesis Eukaryotic initiation factor 6 (eIF6) Ribosomal protein RPL23/uL14 a b s t r a c t BRCA2 and CDKN1A(p21,CIP1)-interacting protein (BCCIP) is an evolutionary conserved protein implicated in maintenance of genome stability and cell cycle progression. Two isoforms of BCCIP with distinct C-terminal domains exist in humans. We show that mammalian BCCIPb, but not BCCIPa, forms a ternary complex with the ribosomal protein RPL23/uL14 and the pre-60S transacting factor eIF6. Complex formation is dependent on an intact C-terminal domain of BCCIPb. Depletion of BCCIPb reduces the pool of free RPL23, and decreases eIF6 levels in nucleoli. Overexpression of BCCIPb leads to nucleoplasmic accumulation of extra-ribosomal RPL23 and stabilizes overexpressed RPL23, suggesting that BCCIPb functions as nuclear chaperone for RPL23.