HIRA, the Human Homologue of Yeast Hir1p and Hir2p, Is a Novel Cyclin-cdk2 Substrate Whose Expression Blocks S-Phase Progression

Fox Chase Cancer Center, Filadelfia, Pennsylvania, United States
Molecular and Cellular Biology (Impact Factor: 4.78). 04/2001; 21(5):1854-65. DOI: 10.1128/MCB.21.5.1854-1865.2001
Source: PubMed


Substrates of cyclin-cdk2 kinases contain two distinct primary sequence motifs: a cyclin-binding RXL motif and one or more
phosphoacceptor sites (consensus S/TPXK/R or S/TP). To identify novel cyclin-cdk2 substrates, we searched the database for
proteins containing both of these motifs. One such protein is human HIRA, the homologue of two cell cycle-regulated repressors
of histone gene expression in Saccharomyces cerevisiae, Hir1p and Hir2p. Here we demonstrate that human HIRA is an in vivo substrate of a cyclin-cdk2 kinase. First, HIRA bound
to and was phosphorylated by cyclin A- and E-cdk2 in vitro in an RXL-dependent manner. Second, HIRA was phosphorylated in
vivo on two consensus cyclin-cdk2 phosphoacceptor sites and at least one of these, threonine 555, was phosphorylated by cyclin
A-cdk2 in vitro. Third, phosphorylation of HIRA in vivo was blocked by cyclin-cdk2 inhibitor p21cip1. Fourth, HIRA became phosphorylated on threonine 555 in S phase when cyclin-cdk2 kinases are active. Fifth, HIRA was localized
preferentially to the nucleus, where active cyclin A- and E-cdk2 are located. Finally, ectopic expression of HIRA in cells
caused arrest in S phase and this is consistent with the notion that it is a cyclin-cdk2 substrate that has a role in control
of the cell cycle.

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    • "The HIR complex functions in several chromatin-related processes including chromatin assembly (Sharp et al. 2001; Green et al. 2005; Prochasson et al. 2005), kinetochore function (Sharp et al. 2002), and transcription elongation (Formosa et al. 2002; Nourani et al. 2006). HIRA, the human homolog of yeast Hir1 and Hir2 (Hall et al. 2001), is also a histone chaperone (Ray-Gallet et al. 2002), and Hira of S. pombe is required for both heterochromatin formation and repression of antisense transcription (Blackwell et al. 2004; Anderson et al. 2009; Yamane et al. 2011). The CAF-1 complex was originally identified from Hela cells as an activity that assembles nucleosomes onto replicating DNA (Stillman 1986; Smith and Stillman 1989). "
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    ABSTRACT: Understanding the mechanisms by which chromatin structure controls eukaryotic transcription has been an intense area of investigation for the past 25 years. Many of the key discoveries that created the foundation for this field came from studies of Saccharomyces cerevisiae, including the discovery of the role of chromatin in transcriptional silencing, as well as the discovery of chromatin-remodeling factors and histone modification activities. Since that time, studies in yeast have continued to contribute in leading ways. This review article summarizes the large body of yeast studies in this field.
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    • "No. 610001), Anti-beta actin (Abcam clone AC-15) were from the indicated suppliers. Anti-macroH2A and anti-HIRA antibodies were described previously [20,31]. SAHF (DAPI foci) were detected by staining with 0.13 μg/ml DAPI for 2 min at room temperature (as opposed to standard conditions of 1 μg/ml for 5 min). "
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    • "The ingenuity pathway also showed that HIRA can bind with Histine H2 [62]. HIRA is a homologue of two cell cycle-regulated repressors of histone gene expression in Saccharomyces cerevisiae, whose expression blocks S-phase progression [63]. Although there is not much known on the role of PTTG in histone regulation, from the available literature it is evident that the overexpression of PTTG can induce apoptosis by up-regulating histone proteins. "
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