RIZ1 is an estrogen receptor (ER) coactivator but is also a histone lysine methyltransferase that methylates lysine 9 of histone H3, an activity known to repress transcription. We show here that target organs of mice deficient in RIZ1 exhibit decreased response to female sex hormones. RIZ1 interacted with SRC1 and p300, suggesting that the coactivator function of RIZ1 may be mediated by its interaction with other transcriptional coactivators. In the presence of estrogen, RIZ1 binding to estrogen target genes became less direct and followed the binding of ER to DNA and RIZ1 methyltransferase activity on H3-Lys 9 was inhibited, indicating derepression may play a role in estrogen induction of gene transcription. Reducing RIZ1 level correlated with decreased induction of pS2 gene by estrogen in MCF7 cells. The data suggest that a histone methyltransferase is required for optimal estrogen response in female reproductive tissues and that estrogen-bound ER may turn a transcriptional repressor into a coactivator.Female sex steroid hormones, such as estrogen (E2) and progesterone, play an essential role in various tissues and in numerous physiological processes, including the control of puberty, sexual behavior, bone homeostasis, mammopoiesis, and reproductive functions. Decreased steroid levels and/or responses are associated with aging and its associated syndromes, such as osteoporosis, cardiovascular disease, and Alzheimer's disease. Altered hormone responses are involved in the development and progression of breast cancer, the most common malignancy inflicted upon women, with more than 180,000 new cases each year in the United States alone.The biological actions of E2 and progesterone are mainly mediated by their receptors that are ligand-dependent transcription factors. Upon binding of hormones, the receptors bind to their cognate DNA response elements on target genes and recruit coactivators and general transcription factors to form an active transcriptional complex, resulting in enhancement of target gene expression (13, 34). Three major classes of coactivators or coactivator complexes have been described. One class appears to function as histone/protein acetyltransferases (HATs) or to interact with HATs, which include CBP/ p300 (7), SRC-1 (NCoA-1/p160) (21, 37), SRC-2 (TIF2/ GRIP1) (16, 46), and SRC-3 (AIB1/pCIP/RAC3/ACTR/ TRAM-1) (4, 9, 28, 44). Some HAT complexes also contain an RNA coactivator SRA (26). A physiological role for a HAT coactivator in hormone action is demonstrated by a mouse model deficient in SRC-1 showing partial hormone resistance (50, 52). The second class is the DRIP/TRAP protein complex (11,38). Finally, recent studies indicate that histone/protein methyltransferases (HMTs) are potential coactivators. CARM1 and PRMT1 are arginine HMTs that methylate arginine residues on histones and other proteins such as p300 (8,24,43,48,53). RIZ1 and NSD1 are members of a superfamily of lysine HMTs (1, 17).The RIZ (PRDM2) gene was originally isolated in a functional screening for proteins that bind to th...

Abbreviations: AP-1, activating protein 1; ECM, extracellular matrix; EMSA, electrophoretic mobility shift assay; JNK, c-Jun N-terminal kinase; mAb, monoclonal antibody; MAPK, mitogen-activated protein kinase; MEK, mitogen-activated protein kinase kinase; MMP, matrix metalloproteinase; RT-PCR, reverse transcriptase-polymerase chain reaction; siRNA, small interfering RNA

Interphasic chromatin condenses into the chromosomes in order to facilitate the correct segregation of genetic information. It has been previously reported that the phosphorylation and methylation of the N-terminal tail of histone H3 are responsible for chromosome condensation. In this study, we demonstrate that the deacetylation and methylation of histone H3 lysine 9 (H3K9) are required for proper chromosome condensation. We confirmed that H3K9ac levels were reduced, whereas H3K9me3 levels were increased in mitotic cells, via immunofluorescence and Western blot analysis. Nocodazole treatment induced G2/M arrest but co-treatment with TSA, an HDAC inhibitor, delayed cell cycle progression. However, the HMTase inhibitor, AdoX, had no effect on nocodazole-induced G2/M arrest, thereby indicating that sequential modifications of H3K9 are required for proper chromosome condensation. The expression of SUV39H1 and SETDB1, H3K9me3-responsible HMTases, are specifically increased along with H3K9me3 in nocodazole-arrested buoyant cells, which suggests that the increased expression of those proteins is an important step in chromosome condensation. H3K9me3 was highly concentrated in the vertical chromosomal axis during prophase and prometaphase. Collectively, the results of this study indicate that sequential modifications at H3K9 are associated with correct chromosome condensation, and that H3K9me3 may be relevant to the condensation of chromosome length.

No abstract

It is well established that human cancer can be caused by mutations in the molecular pathways that control cell proliferation, differentiation, and survival. Familial cancer syndromes are associated with mutations in tumor susceptibility genes. However, sporadic common cancers are primarily linked to environmental factors that often lack any obvious mutagens. This raises the question whether mutation is necessary for environmental carcinogens to cause cancer. Histone methyltransferases function to control mitotic inheritance of cell fate and gene expression patterns and can turn environmental effects into heritable changes in cell phenotypes. The discovery of tumor suppressor function for these enzymes has important implications for an epigenetic pathway of cancer.