The human epigenetic cell-cycle regulator HCF-1 undergoes an unusual proteolytic maturation process resulting in stably associated HCF-1(N) and HCF-1(C) subunits that regulate different aspects of the cell cycle. Proteolysis occurs at six centrally located HCF-1(PRO)-repeat sequences and is important for activation of HCF-1(C)-subunit functions in M phase progression. We show here that the HCF-1(PRO) repeat is recognized by O-linked β-N-acetylglucosamine transferase (OGT), which both O-GlcNAcylates the HCF-1(N) subunit and directly cleaves the HCF-1(PRO) repeat. Replacement of the HCF-1(PRO) repeats by a heterologous proteolytic cleavage signal promotes HCF-1 proteolysis but fails to activate HCF-1(C)-subunit M phase functions. These results reveal an unexpected role of OGT in HCF-1 proteolytic maturation and an unforeseen nexus between OGT-directed O-GlcNAcylation and proteolytic maturation in HCF-1 cell-cycle regulation.

Chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) experiments are widely used to determine, within entire genomes, the occupancy sites of any protein of interest, including, for example, transcription factors, RNA polymerases, or histones with or without various modifications. In addition to allowing the determination of occupancy sites within one cell type and under one condition, this method allows, in principle, the establishment and comparison of occupancy maps in various cell types, tissues, and conditions. Such comparisons require, however, that samples be normalized. Widely used normalization methods that include a quantile normalization step perform well when factor occupancy varies at a subset of sites, but may miss uniform genome-wide increases or decreases in site occupancy. We describe a spike adjustment procedure (SAP) that, unlike commonly used normalization methods intervening at the analysis stage, entails an experimental step prior to immunoprecipitation. A constant, low amount from a single batch of chromatin of a foreign genome is added to the experimental chromatin. This “spike” chromatin then serves as an internal control to which the experimental signals can be adjusted. We show that the method improves similarity between replicates and reveals biological differences including global and largely uniform changes.

The genomic loci occupied by RNA polymerase (RNAP) III have been characterized in human culture cells by genomewide chromatin immunoprecipitations, followed by deep sequencing (ChIP-seq). These studies have shown that onlỹ 40% of the annotated 622 human tRNA genes and pseudogenes are occupied by RNAP-III, and that these genes are often in open chromatin regions rich in active RNAP-II transcription units. We have used ChIP-seq to characterize RNAP-III-occupied loci in a differentiated tissue, the mouse liver. Our studies define the mouse liver RNAP-III-occupied loci including a conserved mammalian interspersed repeat (MIR) as a potential regulator of an RNAP-III subunit-encoding gene. They reveal that synteny relationships can be established between a number of human and mouse RNAP-III genes, and that the expression levels of these genes are significantly linked. They establish that variations within the A and B promoter boxes, as well as the strength of the terminator sequence, can strongly affect RNAP-III occupancy of tRNA genes. They reveal correlations with various genomic features that explain the observed variation of 81% of tRNA scores. In mouse liver, loci represented in the NCBI37/mm9 genome assembly that are clearly occupied by RNAP-III comprise 50 Rn5s (5S RNA) genes, 14 known non-tRNA RNAP-III genes, nine Rn4.5s (4.5S RNA) genes, and 29 SINEs. Moreover, out of the 433 annotated tRNA genes, half are occupied by RNAP-III. Transfer RNA gene expression levels reflect both an underlying genomic organization conserved in dividing human culture cells and resting mouse liver cells, and the particular promoter and terminator strengths of individual genes.[Supplemental material is available for this article.]RNA polymerase III (RNAP-III) synthesizes short RNAs involved in essential cellular processes, including protein synthesis, RNA maturation, and transcriptional control, but until recently, the full extent of the genomic loci occupied, and therefore probably transcribed, by RNAP-III in vivo, was unknown. Several groups have now used the ChIP-seq technique, i.e., chromatin immunoprecipitation followed by deep sequencing, to localize genome-wide RNAP-III and some of its transcription factors in several human cultured cell lines. These experiments have revealed a relatively modest number of new RNAP-III transcription units, from a few 10s to about 200, depending on the criteria applied (Barski et al. 2010;Canella et al. 2010;Moqtaderi et al. 2010;Oler et al. 2010). In addition, most previously known RNAP-III genes were occupied by RNAP-III. Thus, in such cells RNAP-III and some of its transcription factors occupied 17 RN5S loci annotated on chromosome 1 in the NCBI/hg18 genome assembly, the VTRNA1-1, VTRNA1-2, VTRNA1-3, and VTRNA2-1 (hsa-mir-886) genes coding for vault RNAs, three SRP genes, 14 SNAR genes, five RNU6 genes, the RNU6ATAC gene, the RN7SK, RMRP, and RPPH1 genes, and the RNY1, RNY3, RNY4, and RNY5 (hsa-mir-1975) genes. Noticeably, however, a large fraction of the annotated tRNA genes was devoid of...

Early in female mammalian embryonic development, cells randomly inactivate one of the two X chromosomes to achieve overall equal inactivation of parental X-linked alleles. Hcfc1 is a highly conserved X-linked mouse gene that encodes HCF-1 - a transcriptional co-regulator implicated in cell proliferation in tissue culture cells. By generating a Cre-recombinase inducible Hcfc1 knock-out (Hcfc1(lox)) allele in mice, we have probed the role of HCF-1 in actively proliferating embryonic cells and in cell-cycle re-entry of resting differentiated adult cells using a liver regeneration model. HCF-1 function is required for both extraembryonic and embryonic development. In heterozygous Hcfc1(lox/+) female embryos, however, embryonic epiblast-specific Cre-induced Hcfc1 deletion (creating an Hcfc1(epiKO) allele) around E5.5 is well tolerated; it leads to a mixture of HCF-1-positive and -negative epiblast cells owing to random X-chromosome inactivation of the wild-type or Hcfc1(epiKO) mutant allele. At E6.5 and E7.5, both HCF-1-positive and -negative epiblast cells proliferate, but gradually by E8.5, HCF-1-negative cells disappear owing to cell-cycle exit and apoptosis. Although generating a temporary developmental retardation, the loss of HCF-1-negative cells is tolerated, leading to viable heterozygous offspring with 100% skewed inactivation of the X-linked Hcfc1(epiKO) allele. In resting adult liver cells, the requirement for HCF-1 in cell proliferation was more evident as hepatocytes lacking HCF-1 fail to re-enter the cell cycle and thus to proliferate during liver regeneration. The survival of the heterozygous Hcfc1(epiKO/+) female embryos, even with half the cells genetically compromised, illustrates the developmental plasticity of the post-implantation mouse embryo - in this instance, permitting survival of females heterozygous for an X-linked embryonic lethal allele.

Host-cell factor 1 (HCF-1) is an unusual transcriptional regulator that undergoes a process of proteolytic maturation to generate N-(HCF-1 N ) and C-(HCF-1 C ) terminal subunits noncovalently associated via self-association sequence elements. Here, we present the crystal structure of the self-association sequence 1 (SAS1) including the adjacent C-terminal HCF-1 nuclear localization signal (NLS). SAS1 elements from each of the HCF-1 N and HCF-1 C subunits form an interdigitated fibronectin type 3 (Fn3) tandem repeat structure. We show that the C-terminal NLS recruited by the interdigitated SAS1 structure is required for effective formation of a transcriptional regulatory complex: the herpes simplex virus VP16-induced complex. Thus, HCF-1 N -HCF-1 C association via an integrated Fn3 structure permits an NLS to facilitate formation of a transcriptional regulatory complex.crystallography | chromatin | nuclear localization sequence H ost cell factor-1 (HCF-1; also known as HCFC1) is a metazoan transcriptional regulator. HCF-1 was initially identified as a human coactivator for immediate-early gene expression of herpes simplex virus (HSV) by forming a complex (VP16-induced complex, VIC) with the HSV protein VP16 and the cellular transcriptional regulator Oct-1 (1). HCF-1 regulates cell-cycle progression by mediating associations between DNA-binding transcription factors and chromatin modifying complexes (2-12).Many HCF-1 proteins, including all known vertebrate HCF-1s, undergo a process of proteolytic maturation. Thus, human HCF-1 is synthesized as a 2035-aa precursor, which is cleaved and modified by O-GlcNAC transferase (13) to generate HCF-1 N and HCF-1 C subunits possessing different roles in, for example, cell-cycle regulation (14). After cleavage, the two resulting HCF-1 N and HCF-1 C subunits remain noncovalently associated via two "selfassociation sequences" called SAS1 and SAS2: SAS1 is the primary association element and its sequence is conserved in HCF-1, whereas SAS2 is secondary, less well conserved, and not considered in this study (15).SAS1 is composed of a short 43-aa HCF-1 N segment called SAS1N and a 197-aa HCF-1 C segment called SAS1C (Fig. 1A). Wilson et al. (15) suggested that SAS1C has two tandem fibronectin type 3 (Fn3) repeat structures forming a binding site for the 43-aa SAS1N to promote HCF-1 N -HCF-1 C association.To understand the mechanism of HCF-1 self-association, we have determined the crystal structure of SAS1 with the neighboring nuclear localization signal (called here SAS1-NLS). Contrary to expectation, SAS1N and SAS1C together-not SAS1C aloneform an integrated tandem Fn3 structure. Furthermore, we show that the self-association tethers the basic NLS to the HCF-1 N Kelch domain to facilitate VP16-induced complex formation. ResultsCrystal Structure of the HCF-1 SAS1 Self-Association Domain. The SAS1-NLS crystal structure (Fig. 1B) was determined to 2.7 Å resolution using the Se single-wavelength anomalous dispersion (SAD) method (Table S1 and Fig. S1). Fig. S2 details schematically...