Little is known regarding how the Oct1 transcription factor regulates target gene expression. Using murine fibroblasts and two target genes, Polr2a and Ahcy, we show that Oct1 recruits the Jmjd1a/KDM3A lysine demethylase to catalyze the removal of the inhibitory histone H3K9 dimethyl mark and block repression. Using purified murine T cells and the Il2 target locus, and a colon cancer cell line and the Cdx2 target locus, we show that Oct1 recruits the NuRD chromatin-remodeling complex to promote a repressed state, but in a regulated manner can switch to a different capacity and mediate Jmjd1a recruitment to block repression. These findings indicate that Oct1 maintains repression through a mechanism involving NuRD and maintains poised gene expression states through an antirepression mechanism involving Jmjd1a. We propose that, rather than acting as a primary trigger of gene activation or repression, Oct1 is a switchable stabilizer of repressed and inducible states.The POU 2 (Pit-1, Oct1/2, Unc-86) transcription factor family includes ϳ13 mammalian paralogs as well as representatives from other metazoans (1). The best known example, Oct4/POU5F1, regulates embryonic stem (ES) cell identity and is a key factor used to generate induced pluripotent stem cells from somatic cells (2-5). Oct1/POU2F1 is related to Oct4 and possesses similar in vitro DNA binding specificity (for reviewed, see Ref. 6). As with many transcription factors, these proteins are known to regulate gene expression both positively and negatively (e.g. 7, 8); however, their activity has been thought to be determined by gene context and not subject to regulation.Loss of Oct1 inhibits oncogenic transformation in mouse embryonic fibroblasts (MEFs) and tumorigenicity in p53-deficient mice and xenograft assays, while having little effect on cell growth in culture or transformation by serial passage (9). One study indicates that Oct1 levels are increased in some human gastric cancers (10). In contrast, multiple studies have identified coordinate up-regulation of Oct1 target genes in lung and breast adenocarcinomas, leukemias, and myeloid leukemia stem cells, without concurrent up-regulation of Oct1 itself (11)(12)(13)(14), suggesting that Oct1 activity may be deregulated in malignancy. Recent findings showing post-translational regulation of Oct1 support this possibility (15). Although Oct1 has been studied intensively, our current understanding of how it regulates gene transcription is surprisingly limited (see for example, Ref. 16).Here, we show using three different systems (fibroblasts, primary T cells, and a colon cancer cell line) that Oct1 is a bipotential and switchable transcriptional regulator. In fibroblasts, Oct1 mediates recruitment of the Jmjd1a histone demethylase to target genes (Polr2a and Ahcy) following oxidative stress exposure. In the absence of Oct1, Jmjd1a fails to be recruited, H3K9me2 levels are elevated, and inappropriate repression is observed. In contrast, Oct1 recruits the nucleosome remodeling and histone deacetylation (NuRD/Mi...

Vpr and Vpx are a group of highly related accessory proteins from primate lentiviruses. Despite the high degree of amino acid homology within this group, these proteins can be highly divergent in their functions. In this work, we constructed chimeric and mutant proteins between HIV-1 and SIVagm Vpr in order to better understand the structure-function relationships. We tested these constructs for their abilities to induce G2 arrest in human cells and to degrade agmSAMHD1 and Mus81. We found that the C-terminus of HIV-1 Vpr, when transferred onto SIVagm Vpr, provides the latter with the de novo ability to induce G2 arrest in human cells. We confirmed that HIV-1 Vpr induces degradation of Mus81 although, surprisingly, degradation is independent and genetically separable from Vpr’s ability to induce G2 arrest.

Vpr and Vpx are primate lentivirus proteins that manipulate the cellular CRL4 ubiquitin ligase complex. While Vpr is common to all primate lentiviruses, Vpx is only encoded by HIV-2 and a limited range of SIVs. Although Vpr and Vpx share a high degree of homology they are known to induce markedly different effects in host cell biology through the recruitment of different substrates to CRL4. Here we explore the interaction of HIV-1 Vpr and SIVmac Vpx with the CRL4 substrate receptor DCAF1. Through mutational analysis of DCAF1 we demonstrate that although Vpr and Vpx share a highly similar DCAF1-binding motif, they interact with a different set of residues in DCAF1. In addition, we show that Vpx recruits SAMHD1 through a protein-protein interface that includes interactions of SAMHD1 with both Vpx and DCAF1, as was first suggested in crystallography data by Schwefel et al. (Nature 505:234, 2014).

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