Histone methyltransferases and demethylases:regulators in balancing osteogenic and adipogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells （MSCs） are characterized by their self-renewing capacity and differentiation potential into multiple tissues. Thus, management of the differentiation capacities of MSCs is important for MSC-based regenerative medicine, such as craniofacial bone regeneration, and in new treatments for metabolic bone diseases, such as osteoporosis. In recent years, histone modification has been a growing topic in the field of MSC lineage specification, in which the Su（var）3-9, enhancer-of-zeste, trithorax （SET） domain-containing family and the Jumonji C （JmjC） domain-containing family represent the major histone lysine methyltransferases （KMTs） and histone lysine demethylases （KDMs）, respectively. In this review, we summarize the current understanding of the epigenetic mechanisms by which SET domain-containine KMTs and JmiC domain-containinlz KDMs balance the osteogenic and adipogenic differentiation of MSCs.

Novel insights into histone lysine methyltransferases in cancer therapy:From epigenetic regulation to selective drugs

The reversible and precise temporal and spatial regulation of histone lysine methyltransferases(KMTs)is essential for epigenome homeostasis.The dysregulation of KMTs is associated with tumor initiation,metastasis,chemoresistance,invasiveness,and the immune microenvironment.Therapeutically,their promising effects are being evaluated in diversified preclinical and clinical trials,demonstrating encouraging outcomes in multiple malignancies.In this review,we have updated recent understandings of KMTs'functions and the development of their targeted inhibitors.First,we provide an updated overview of the regulatory roles of several KMT activities in oncogenesis,tumor suppression,and immune regulation.In addition,we summarize the current targeting strategies in different cancer types and multiple ongoing clinical trials of combination therapies with KMT inhibitors.In summary,we endeavor to depict the regulation of KMT-mediated epigenetic landscape and provide potential epigenetic targets in the treatment of cancers.

Rice SUVH Histone Methyltransferase Genes Display Specific Functions in Chromatin Modification and Retrotransposon Repression

Histone lysine methylation plays an important role in heterochromatin formation and reprogramming of gene expression. SET-domain-containing proteins are shown to have histone lysine methyltransferase activities. A large number of SET-domain genes are identified in plant genomes. The function of most SET-domain genes is not known. In this work, we studied the 12 rice （Oryza sativa） homologs of Su（var）3-9, the histone H3 lysine 9 （H3K9） methyltransferase identified in Drosophila. Several rice SUVHs （i.e. SDG714, SDG727, and SDG710） were found to have an antagonistic func- tion to the histone H3K9 demethylase JMJ706, as down-regulation of these genes could partially complement the jmj706 phenotype and reduced histone H3K9 methylation. Down-regulation of a rice Su（var）3-9 homolog （SUVH）, namely SDG728, decreased H3K9 methylation and altered seed morphology. Overexpression of the gene increased H3K9 methylation. SDG728 and other SUVH genes were found to be involved in the repression of retrotransposons such as Tos17 and a Tyl-copia element. Analysis of histone methylation suggested that SDG728-mediated H3K9 methylation may play an important role in retrotransposon repression.

The engagement of histone lysine methyltransferases with nucleosomes: structural basis, regulatory mechanisms, and therapeutic implications

Histone lysine methyltransferases(HKMTs)deposit methyl groups onto lysine residues on histones and play important roles in regulating chromatin structure and gene expression.The structures and functions of HKMTs have been extensively investigated in recent decades,significantly advancing our understanding of the dynamic regulation of histone methylation.Here,we review the recent progress in structural studies of representative HKMTs in complex with nucleosomes(H3K4,H3K27,H3K36,H3K79,and H4K20 methyltransferases),with emphasis on the molecular mechanisms of nucleosome recognition and trans-histone crosstalk by these HKMTs.These structural studies inform HKMTs'roles in tumorigenesis and provide the foundations for developing new therapeutic approachestargetingHKMTs incancers.

【原创论文】组蛋白甲基转移化酶基因SETDB1促进前列腺癌细胞的增殖、迁徙和侵袭

SETDB1 has been established as an oncogene in a number of human carcinomas. The present study was to evaluate the expression of SETDB1 in prostate cancer （PCa） tissues and cells and to preliminarily investigate the role of SETDB1 in prostate tumorigenesis in vitro. Quantitative reverse transcription polymerase chain reaction （qRT-PCR） and immunohistochemistry （IHC） were used to detect the expression of SETDB1 in PCa tissues, adjacent normal tissues, benign prostatic hyperplasia （BPH） tissues, PCa cell lines and normal prostate epithelial cells. The results suggested that SETDB1 was upregulated in human PCa tissues compared with normal tissues at the mRNA and protein levels. The role of SETDB1 in proliferation was analyzed with cell counting kit-8, colony-forming efficiency and flow cytometry assays. The results indicated that downregulation of SETDB1 by siRNA inhibited PCa cell growth, and induced GO/G1 cell cycle arrest. The PCa cell migration and invasion decreased by silcencing SETDBt which were assessed by using in vitro scratch and transwell invasion assay respectively. Our data suggested that SETDB1 is overexpressed in human PCa. Silencing SETDB1 inhibited PCa cell proliferation, migration and invasion.

DOT1L-long enhances breast cancer metastasis

Objective· To investigate the histone methyltransferase capability of DOT1L-long form and its role in breast cancer metastasis. Methods· The existence of DOT1L-long form was confirmed by PCR, and the mRNA level of DOT1L was tested by real-time PCR. In HEK293T cells in which DOT1L canonical and DOT1L-long were overexpressed respectively, Western blotting was used to test the expression level of DOT1L and the histone methyltransferase capability. In the MCF10A cell line with inducible expression of DOT1L-long, real-time PCR was used to detect the mRNA level of epithelial-mesenchymal transition(EMT) marker, and transwell assay was used to detect the migration of breast cancer cells in which the expression level of DOT1L is low or high. Results· PCR demonstrated the existence of DOT1L-long form, and real-time PCR showed it widely exists in HCT116, T98G, MCF10A cells, etc. Western blotting showed the expression of DOT1L-long form and its H3K79 methyltransferase activity. In MCF10A cells in which overexpressed canonical DOT1L and DOT1L-long, mRNA levels of N-cadherin and fibronectine increased. Transwell showed canonical DOT1L and DOT1L-long both substantially increased the migration of breast cancer cells. Conclusion· The existence of DOT1L-long was confirmed and investigated, which is 202 amino acids longer than the canonical DOT1L, and is coded by a new exon, located between exon 27 and 28. Further, the DOT1L-long has H3K79 methyltransferase activity, and is able to promote breast cancer metastasis.

Cellular functions of MLL/SET-family histone H3 lysine 4 methyltransferase components

The MLL/SET family of histone H3 lysine 4 methyltransferases form enzyme complexes with core subunits ASH2L, WDR5, RbBP5, and DPY-30 （often abbreviated WRAD）, and are responsible for global histone H3 iysine 4 methylation, a hallmark of actively transcribed chromatin in mammalian cells. Accordingly, the function of these proteins is required for a wide variety of processes including stem cell differentiation, cell growth and division, body segmentation, and hematopoiesis. While most work on MLL-WRAD has focused on the function this core complex in histone methylation, recent studies indicate that MLL-WRAD proteins interact with a variety of other proteins and IncRNAs and can localize to cellular organelles beyond the nucleus. In this review, we focus on the recently described activities and interacting partners of MLL-WRAD both inside and outside the nucleus.

Structure of human lysine methyltransferase Smyd2 reveals insights into the substrate divergence in Smyd proteins

The SET-and myeloid-Nervy-DEAF-1(MYND)-domain containing(Smyd)lysine methyltransferases 1–3 share relatively high sequence similarity but exhibit divergence in the substrate specificity.Here we report the crystal structure of the full-length human Smyd2 in complex with S-adenosyl-L-homocysteine(AdoHcy).Although the Smyd1–3 enzymes are similar in the overall structure,detailed comparisons demonstrate that they differ substantially in the potential substrate-binding site.The binding site of Smyd3 consists mainly of a deep and narrow pocket,while those of Smyd1 and Smyd2 consist of a comparable pocket and a long groove.In addition,Smyd2,which has lysine methyltransferase activity on histone H3-lysine 36,exhibits substantial differences in the wall of the substrate-binding pocket compared with those of Smyd1 and Smyd3 which have activity specifically on histone H3-lysine 4.The differences in the substrate-binding site might account for the observed divergence in the specificity and methylation state of the substrates.Further modeling study of Smyd2 in complex with a p53 peptide indicates that mono-methylation of p53-Lys372 might result in steric conflict of the methyl group with the surrounding residues of Smyd2,providing a structural explanation for the inhibitory effect of the SET7/9-mediated mono-methylation of p53-Lys372 on the Smyd2-mediated methylation of p53-Lys370.

EZH2, an epigenetic driver of prostate cancer

The histone methyltransferase EZH2 has been in the limelight of the fi eld of cancer epigenetics for a decade now since it was fi rst discovered to exhibit an elevated expression in metastatic prostate cancer.It persists to attract much scientifi c attention due to its important role in the process of cancer development and its potential of being an effective therapeutic target.Thus here we review the dysregulation of EZH2 in prostate cancer,its function,upstream regulators,downstream effectors,and current status of EZH2-targeting approaches.This review there-fore provides a comprehensive overview of EZH2 in the context of prostate cancer.