Hbo1 Links p53-Dependent Stress Signaling to DNA Replication Licensing

Abstract

Hbo1 is a histone acetyltransferase (HAT) that is required for global histone H4 acetylation, steroiddependent transcription, and chromatin loading of MCM2-7 during DNA replication licensing. It is the catalytic subunit of protein complexes that include ING and JADE proteins, growth regulatory factors and candidate tumor suppressors. These complexes are thought to act via tumor suppressor p53, but the molecular mechanisms and links between stress signaling and chromatin, are currently unknown. Here, we show that p53 physically interacts with Hbo1 and negatively regulates its HAT activity in vitro and in cells. Two physiological stresses that stabilize p53, hyperosmotic shock and DNA replication fork arrest, also inhibit Hbo1 HAT activity in a p53-dependent manner. Hyperosmotic stress during G 1 phase specifically inhibits the loading of the MCM2-7 complex, providing an example of the chromatin output of this pathway. These results reveal a direct regulatory connection between p53-responsive stress signaling and Hbo1-dependent chromatin pathways.The dynamic regulation of chromatin structure and function is essential for normal cell proliferation and differentiation. This regulation is mediated by several overlapping pathways, including the posttranslational enzymatic modification of histones, the alteration of nucleosome structure by DNA-dependent ATPase complexes, and changes in the histone variant composition of chromatin (4,34,58). Alterations in histone modification enzymes, particularly histone acetyltransferase (HAT) enzymes, have been linked to human cancer (23, 73). Viral oncoproteins, such as adenovirus E1A or simian virus 40 large T antigen, target a number of these enzymes, including p300, CBP, and PCAF. Furthermore, in addition to modifying histones, these HATs can also directly acetylate and activate tumor suppressors and key growth control transcription factors such as p53, Rb, and E2F (24). The MYST family of histone acetyltransferases, named for the four founding proteins in the family (67), can also contribute to carcinogenesis and tumor progression. The MYST proteins are part of large multisubunit HAT complexes conserved from yeast to humans, and they have diverse roles in gene expression, DNA replication, and DNA repair (72). The human MOZ gene, encoding one of the human MYST enzymes, was first identified as a translocation fusion with CBP in acute myeloid leukemias (9). Subsequently, a number of other translocation fusions involving the MYST HATs MOZ and MORF and partners including CBP, p300, MLL, and TIF2 have been identified. It is thought that the mislocalization or misregulation of the HAT activities of these fusions contributes to tumor formation or progression (72).Hbo1 is a member of the MYST family of HAT enzymes and is conserved from flies to humans. It has essential roles in DNA replication and transcription (1,12,22,32,55,59) and is the catalytic subunit of at least two protein complexes comprised of JADE1/JADE2/JADE3 paralogs, hEaf6, and either ING4 or ING5, two members of the "inh...

Stress-Stimulated Mitogen-Activated Protein Kinases Control the Stability and Activity of the Cdt1 DNA Replication Licensing Factor

“…6A, compare lanes 3 and 4). These results are consistent with prior observations that osmotic stress by NaCl addition to G 1 cells prevents MCM loading (35). To determine whether p38 and JNK have a role in this inhibition, we either treated the cells with MAP kinase inhibitors 15 min prior to sorbitol addition (Fig.…”

“…The newly revealed importance of these particular amino acids in Cdt1 function It had previously been shown that activation of the stress kinase pathway during G 1 is sufficient to block S-phase entry, but MCM loading was not examined in that study (24). Moreover, Iizuka et al found that osmotic stress can block MCM loading, but that study did not explore a role for stress-activated MAP kinases (35). On the basis of the low activity of the phosphomimetic mutant, we suggest that Cdt1 phosphorylation by stress-activated kinases is one event that links MAP kinase activity to inhibition of origin licensing.…”

Exchange of associated factors directs a switch in HBO1 acetyltransferase histone tail specificity

“…We and others have shown that the HBO1 enzyme is purified with JADE scaffold proteins and is responsible for histone H4 tail acetylation (Doyon et al 2006;Iizuka et al 2006Iizuka et al , 2008Foy et al 2008;Miotto and Struhl 2010). We even showed that HBO1 siRNA-mediated knockdown in HeLa cells leads to a global loss of H4 acetylation on Lys5, Lys8, and Lys12, matching in vitro specificity on chromatin and arguing that HBO1 was the main H4-specific HAT in mammals (Doyon et al 2006).…”

Inhibitor of growth-4 promotes IκB promoter activation to suppress NF-κB signaling and innate immunity

“…In addition, biochemical analysis has indicated that ING4 interacts with methylated histone H3 (12)(13)(14) and with the HB01-JADE-hEAF6 histone acetyltransferase complex (11). This latter complex is responsible for most nucleosomal histone H4 acetylation in eukaryotes, and knockdown experiments indicated that Ing4-HB01 association is required for cells to progress properly through the DNA synthesis (S) phase of the cell cycle (15,16).…”