SMYD1 is a heart and muscle specific SET-MYND domain containing protein, which functions as a histone methyltransferase and regulates downstream gene transcription. We demonstrated that the expression of SMYD1 is restricted in the heart and skeletal muscle tissues in human. To reveal the regulatory mechanisms of SMYD1 expression during myogenesis and cardiogenesis, we cloned and characterized the human SMYD1 promoter, which contains highly conserved serum response factor (SRF) and myogenin binding sites. Overexpression of SRF and myogenin significantly increased the endogenous expression level of Smyd1 in C2C12 cells, respectively. Deletion of Srf in the heart of mouse embryos dramatically decreased the expression level of Smyd1 mRNA and the expression of Smyd1 can be rescued by exogenous SRF introduction in SRF null ES cells during differentiation. Furthermore, we demonstrated that SRF binds to the CArG site and myogenin binds to the E-box element on Smyd1 promoter region using EMSA and ChIP assays. Moreover, forced expression of SMYD1 accelerates myoblast differentiation and myotube formation in C2C12 cells. Taken together, these studies demonstrated that SMYD1 is a key regulator of myogenic differentiation and acts as a downstream target of muscle regulatory factors, SRF and myogenin.
Smyd1, the founding member of the Smyd family including Smyd-1, 2, 3, 4 and 5, is a SET and MYND domain containing protein that plays a key role in myofibril assembly in skeletal and cardiac muscles. Bioinformatic analysis revealed that zebrafish genome contains two highly related smyd1 genes, smyd1a and smyd1b. Although Smyd1b function is well characterized in skeletal and cardiac muscles, the function of Smyd1a is, however, unknown.
To investigate the function of Smyd1a in muscle development, we isolated smyd1a from zebrafish, and characterized its expression and function during muscle development via gene knockdown and transgenic expression approaches. The results showed that smyd1a was strongly expressed in skeletal muscles of zebrafish embryos. Functional analysis revealed that knockdown of smyd1a alone had no significant effect on myofibril assembly in zebrafish skeletal muscles. However, knockdown of smyd1a and smyd1b together resulted in a complete disruption of myofibril organization in skeletal muscles, a phenotype stronger than knockdown of smyd1a or smyd1b alone. Moreover, ectopic expression of zebrafish smyd1a or mouse Smyd1 transgene could rescue the myofibril defects from the smyd1b knockdown in zebrafish embryos.
Collectively, these data indicate that Smyd1a and Smyd1b share similar biological activity in myofibril assembly in zebrafish embryos. However, Smyd1b appears to play a major role in this process.
Smyd1b is a member of the Smyd family that plays a key role in sarcomere assembly during myofibrillogenesis. Smyd1b encodes two alternatively spliced isoforms, smyd1b_tv1 and smyd1b_tv2, that are expressed in skeletal and cardiac muscles and play a vital role in myofibrillogenesis in skeletal muscles of zebrafish embryos.
To better understand Smyd1b function in myofibrillogenesis, we analyzed the subcellular localization of Smyd1b_tv1 and Smyd1b_tv2 in transgenic zebrafish expressing a myc-tagged Smyd1b_tv1 or Smyd1b_tv2. The results showed a dynamic change of their subcellular localization during muscle cell differentiation. Smyd1b_tv1 and Smyd1b_tv2 were primarily localized in the cytosol of myoblasts and myotubes at early stage zebrafish embryos. However, in mature myofibers, Smyd1b_tv1, and to a small degree of Smyd1b_tv2, exhibited a sarcomeric localization. Double staining with sarcomeric markers revealed that Smyd1b_tv1was localized on the M-lines. The sarcomeric localization was confirmed in zebrafish embryos expressing the Smyd1b_tv1-GFP or Smyd1b_tv2-GFP fusion proteins. Compared with Smyd1b_tv1, Smyd1b_tv2, however, showed a weak sarcomeric localization. Smyd1b_tv1 differs from Smyd1b_tv2 by a 13 amino acid insertion encoded by exon 5, suggesting that some residues within the 13 aa insertion may be critical for the strong sarcomeric localization of Smyd1b_tv1. Sequence comparison with Smyd1b_tv1 orthologs from other vertebrates revealed several highly conserved residues (Phe223, His224 and Gln226) and two potential phosphorylation sites (Thr221 and Ser225) within the 13 aa insertion. To determine whether these residues are involved in the increased sarcomeric localization of Smyd1b_tv1, we mutated these residues into alanine. Substitution of Phe223 or Ser225 with alanine significantly reduced the sarcomeric localization of Smyd1b_tv1. In contrast, other substitutions had no effect. Moreover, replacing Ser225 with threonine (S225T) retained the strong sarcomeric localization of Smyd1b_tv1.
Together, these data indicate that Phe223 and Ser225 are required for the M-line localization of Smyd1b_tv1.
SET and MYND domain (Smyd) proteins are involved in the transcriptional regulation of cellular proliferation and development in vertebrates. However, the in vivo functions and mechanisms by which these proteins act are poorly understood.
We have used biochemical and genetic approaches to study the role of a Smyd protein in Drosophila. We identified eleven Drosophila genes that encode Smyd proteins. CG14122 encodes a Smyd4 homologue that we have named dSmyd4. dSmyd4 repressed transcription and recruited class I histone deacetylases (HDACs). A region of dSmyd4 including the MYND domain interacted directly with ∼150 amino acids at the N-termini of dHDAC1 and dHDAC3. dSmyd4 interacts selectively with Ebi, a component of the dHDAC3/SMRTER co-repressor complex. During embryogenesis dSmyd4 was expressed throughout the mesoderm, with highest levels in the somatic musculature. Muscle-specific RNAi against dSmyd4 resulted in depletion of the protein and lead to severe lethality. Eclosion is the final moulting stage of Drosophila development when adult flies escape from the pupal case. 80% of dSmyd4 knockdown flies were not able to eclose, resulting in late pupal lethality. However, many aspects of eclosion were still able to occur normally, indicating that dSmyd4 is likely to be involved in the development or function of adult muscle.
Repression of transcription by dSmyd4 and the involvement of this protein in development suggests that aspects of Smyd protein function are conserved between vertebrates and invertebrates.
Epigenetic modifications of histone play important roles for regulation of cell activity, such as cell division, cell death, and cell differentiation. A SET domain consisting of about 130 amino acids has lysine methyltransferase activity in the presence of the cosubstrate S-adenosyl-methionine. More than 60 SET domain-containing proteins have been predicted in various organisms. One of them, the SMYD family genes which contain a SET domain and a zinc-finger MYND domain are reported to regulate cell cycle and muscle formation. Here we examined the expression and function of smyd1 and 2 in Xenopus. smyd1 and 2 were expressed in various muscle tissues. While smyd1 expression was observed mainly in cardiac muscle and skeletal muscle, smyd2 expression was done abundantly in skeletal muscle and face region. Moreover, by loss-of-function experiments using antisense morpholino oligonucleotides, it was suggested that smyd1 and 2 related to muscle cells differentiation.
Heart; Muscle; MYND; Myogenesis; SET; smyd; Xenopus laevis
Modifications of histone tails are involved in the regulation of a wide range of biological processes including cell cycle, cell survival, cell division, and cell differentiation. Among the modifications, histone methylation plays a critical role in cardiac and skeletal muscle differentiation. In our earlier studies, we found that SMYD3 has methyltransferase activity to histone H3 lysine 4, and that its up-regulation is involved in the tumorigenesis of human colon, liver, and breast. To clarify the role of Smyd3 in development, we have studied its expression patterns in zebrafish embryos and the effect of its suppression on development using Smyd3-specific antisense morpholino-oligonucleotides. We here show that transcripts of smyd3 were expressed in zebrafish embryos at all developmental stages examined and that knockdown of smyd3 in embryos resulted in pericardial edema and defects in the trunk structure. In addition, these phenotypes were associated with abnormal expression of three heart-chamber markers including cmlc2, amhc and vmhc, and abnormal expression of myogenic regulatory factors including myod and myog. These data suggest that Smyd3 plays an important role in the development of heart and skeletal muscle.
SmyD2 belongs to a new class of chromatin regulators that control gene expression in heart development and tumorigenesis. Besides methylation of histone H3 K4, SmyD2 can methylate non-histone targets including p53 and the retinoblastoma tumor suppressor. The methyltransferase activity of SmyD proteins has been proposed to be regulated by autoinhibition via the intra- and interdomain bending of the conserved C-terminal domain (CTD). However, there has been no direct evidence of a conformational change in the CTD. Here, we report two crystal structures of SmyD2 bound either to the cofactor product S-adenosylhomocysteine or to the inhibitor sinefungin. SmyD2 has a two-lobed structure with the active site located at the bottom of a deep crevice formed between the CTD and the catalytic domain. By extensive engagement with the methyltransferase domain, the CTD stabilizes the autoinhibited conformation of SmyD2 and restricts access to the catalytic site. Unexpectedly, despite that the two SmyD2 structures are highly superimposable, significant differences are observed in the first two helices of the CTDs: the two helices bend outwards and move away from the catalytic domain to generate a less closed conformation in the sinefungin-bound structure. Although the overall fold of the individual domains is structurally conserved among SmyD proteins, SmyD2 appear to be a conformational “intermediate” between a close form of SmyD3 and an open form of SmyD1. In addition, the structures reveal that the CTD is structurally similar to tetratricopeptide repeats (TPR), a motif through which many cochaperones bind to the heat shock protein Hsp90. Our results thus provide the first evidence for the intradomain flexibility of the TPR-like CTD, which may be important for the activation of SmyD proteins by Hsp90.
Myofibrillogenesis is critical for muscle cell differentiation and contraction. This study shows that Smyd1b plays a key role in myofibrillogenesis in muscle cells. Knockdown of smyd1b results in up-regulation of hsp90α1 and unc45b gene expression, increased myosin degradation, and disruption of sarcomere organization in zebrafish embryos.
Smyd1b is a member of the Smyd family that is specifically expressed in skeletal and cardiac muscles. Smyd1b plays a key role in thick filament assembly during myofibrillogenesis in skeletal muscles of zebrafish embryos. To better characterize Smyd1b function and its mechanism of action in myofibrillogenesis, we analyzed the effects of smyd1b knockdown on myofibrillogenesis in skeletal and cardiac muscles of zebrafish embryos. The results show that knockdown of smyd1b causes significant disruption of myofibril organization in both skeletal and cardiac muscles of zebrafish embryos. Microarray and quantitative reverse transcription-PCR analyses show that knockdown of smyd1b up-regulates heat shock protein 90 (hsp90) and unc45b gene expression. Biochemical analysis reveals that Smyd1b can be coimmunoprecipitated with heat shock protein 90 α-1 and Unc45b, two myosin chaperones expressed in muscle cells. Consistent with its potential function in myosin folding and assembly, knockdown of smyd1b significantly reduces myosin protein accumulation without affecting mRNA expression. This likely results from increased myosin degradation involving unc45b overexpression. Together these data support the idea that Smyd1b may work together with myosin chaperones to control myosin folding, degradation, and assembly into sarcomeres during myofibrillogenesis.
Disrupting the balance of histone lysine methylation alters the expression of genes involved in tumorigenesis including proto-oncogenes and cell cycle regulators. Methylation of lysine residues is commonly catalyzed by a family of proteins that contain the SET domain. Here, we report the identification and characterization of the SET domain-containing protein, Smyd2.
Smyd2 mRNA is most highly expressed in heart and brain tissue, as demonstrated by northern analysis and in situ hybridization. Over-expressed Smyd2 localizes to the cytoplasm and the nucleus in 293T cells. Although accumulating evidence suggests that methylation of histone 3, lysine 36 (H3K36) is associated with actively transcribed genes, we show that the SET domain of Smyd2 mediates H3K36 dimethylation and that Smyd2 represses transcription from an SV40-luciferase reporter. Smyd2 associates specifically with the Sin3A histone deacetylase complex, which was recently linked to H3K36 methylation within the coding regions of active genes in yeast. Finally, we report that exogenous expression of Smyd2 suppresses cell proliferation.
We propose that Sin3A-mediated deacetylation within the coding regions of active genes is directly linked to the histone methyltransferase activity of Smyd2. Moreover, Smyd2 appears to restrain cell proliferation, likely through direct modulation of chromatin structure.
Hepatoma Derived Growth Factor (HDGF) is a nuclear protein with both mitogenic and angiogenic activity, it is highly expressed in the developing heart and vasculature. To date the mechanisms of HDGF’s function are unknown. Oligonucleotide microarray analysis was used to gain insights into HDGF function. Adenoviral expression of HDGF significantly (≥ 2 fold) downregulated a large group (66) of genes, and increased expression of a relatively small number of genes (9). Two groups of target genes which are involved in cardiovascular development and transcriptional regulation were validated by real time PCR, including the skeletal/cardiac muscle specific SET and MYND domain containing 1 (SMYD1) gene. This suggested that HDGF could function as a transcriptional repressor. In a one-hybrid system, GBD-HDGF significantly repressed reporter gene activity in a dose dependent manner. This demonstrated that HDGF has transcriptional repressive activity. Moreover, in G-7 myoblast cells, overexpression of a GFP-HDGF fusion specifically downregulated SMYD1 mRNA expression and the activity of the human SMYD1 promoter. HDGF repressed SMYD1 gene transcription through interaction with a transcriptional corepressor C-terminal binding protein (CtBP). Overexpressing of CtBP potentiated the trans-repressive activity of HDGF; on the other hand, knocking down CtBP attenuated the trans-repressive effect of HDGF. HDGF binds CtBP through a non-canonical binding motif (PKDLF) within the PWWP domain, as substitutional mutation of DL to AS abolished HDGF and CtBP interaction and diminished the trans-repressive effect of HDGF without affecting DNA binding. Finally, fluorescent microscopy studies showed that HDGF induced the nuclear accumulation of CtBP suggesting that HDGF forms a transcriptional complex with CtBP. Taken together, our data demonstrate that HDGF functions as a transcriptional repressor of the SMYD1 gene, through interaction with the transcriptional corepressor CtBP. Because of moderate conservation of the CtBP binding motif in HDGF family members, trans-repressive activity mediated by CtBP may be a common function among HDGF proteins.
HDGF; SMYD1; CtBP; transcription; repressor
It is well known that RB functions are regulated by posttranslational modifications such as phosphorylation and acetylation, but the significance of lysine methylation on RB has not been fully elucidated. Our expression analysis of SMYD2 by quantitative real-time polymerase chain reaction showed that expression levels of SMYD2 are significantly elevated in human bladder carcinomas compared with nonneoplastic bladder tissues (P < .0001), and its expression levels in tumor tissues were much higher than those of any other normal tissues. SMYD2 knockdown resulted in the suppression of cancer cell growth, and cell cycle analysis indicated that SMYD2 might play a crucial role in the G1/S transition. According to an in vitro methyltransferase assay, we found that SMYD2 methylates RB1 protein, and liquid chromatography-tandem mass spectrometry analysis revealed lysine 810 of RB1 to be methylated by SMYD2. Importantly, this methylation enhanced Ser 807/811 phosphorylation of RB1 both in vitro and in vivo. Furthermore, we demonstrated that methylated RB1 accelerates E2F transcriptional activity and promotes cell cycle progression. SMYD2 is an important oncoprotein in various types of cancer, and SMYD2-dependent RB1 methylation at lysine 810 promotes cell cycle progression of cancer cells. Further study may explore SMYD2-dependent RB1 methylation as a potential therapeutic target in human cancer.
The SET- and MYND-domain containing (Smyd) proteins constitute a special subfamily of the SET-containing lysine methyltransferases. Here we present the structure of full-length human Smyd3 in complex with S-adenosyl-l-homocysteine at 2.8 Å resolution. Smyd3 affords the first example that other region(s) besides the SET domain and its flanking regions participate in the formation of the active site. Structural analysis shows that the previously uncharacterized C-terminal domain of Smyd3 contains a tetratrico-peptide repeat (TPR) domain which together with the SET and post-SET domains forms a deep, narrow substrate binding pocket. Our data demonstrate the important roles of both TPR and post-SET domains in the histone lysine methyltransferase (HKMT) activity of Smyd3, and show that the hydroxyl group of Tyr239 is critical for the enzymatic activity. The characteristic MYND domain is located nearby to the substrate binding pocket and exhibits a largely positively charged surface. Further biochemical assays show that DNA binding of Smyd3 can stimulate its HKMT activity and the process may be mediated via the MYND domain through direct DNA binding.
Upregulation of the matrix metalloproteinase MMP-9 plays a central role in tumor progression and metastasis by stimulating cell migration, tumor invasion and angiogenesis. To gain insights into MMP-9 expression, we investigated its epigenetic control in a reversible model of cancer that is initiated by infection with intracellular Theileria parasites. Gene induction by parasite infection was associated with tri-methylation of histone H3K4 (H3K4me3) at the MMP-9 promoter. Notably, we found that the H3K4 methyltransferase SMYD3 was the only histone methyltransferase upregulated upon infection. SMYD3 is overexpressed in many types of cancer cells, but its contributions to malignant pathophysiology are unclear. We found that overexpression of SMYD3 was sufficient to induce MMP-9 expression in transformed leukocytes and fibrosarcoma cells, and that pro-inflammatory phorbol esters further enhanced this effect. Further, SMYD3 was sufficient to increase cell migration associated with MMP-9 expression. In contrast, RNAi-mediated knockdown of SMYD3 decreased H3K4me3 modification of the MMP-9 promoter, reduced MMP-9 expression and reduced tumor cell proliferation. Furthermore, SMYD3 knockdown also reduced cellular invasion in a zebrafish xenograft model of cancer. Together, our results define SMYD3 as an important new regulator of MMP-9 transcription, and they provide a molecular link between SMYD3 overexpression and metastatic cancer progression.
epigenetic; metastasis; chromatin; SMYD3; MMP-9
Mef2 transcription factors have been strongly linked with early heart development. D-mef2 is required for heart formation in Drosophila, but whether Mef2 is essential for vertebrate cardiomyocyte (CM) differentiation is unclear. In mice, although Mef2c is expressed in all CMs, targeted deletion of Mef2c causes lethal loss of second heart field (SHF) derivatives and failure of cardiac looping, but first heart field CMs can differentiate. Here we examine Mef2 function in early heart development in zebrafish. Two Mef2c genes exist in zebrafish, mef2ca and mef2cb. Both are expressed similarly in the bilateral heart fields but mef2cb is strongly expressed in the heart poles at the primitive heart tube stage. By using fish mutants for mef2ca and mef2cb and antisense morpholinos to knock down either or both Mef2cs, we show that Mef2ca and Mef2cb have essential but redundant roles in myocardial differentiation. Loss of both Mef2ca and Mef2cb function does not interfere with early cardiogenic markers such as nkx2.5, gata4 and hand2 but results in a dramatic loss of expression of sarcomeric genes and myocardial markers such as bmp4, nppa, smyd1b and late nkx2.5 mRNA. Rare residual CMs observed in mef2ca;mef2cb double mutants are ablated by a morpholino capable of knocking down other Mef2s. Mef2cb over-expression activates bmp4 within the cardiogenic region, but no ectopic CMs are formed. Surprisingly, anterior mesoderm and other tissues become skeletal muscle. Mef2ca single mutants have delayed heart development, but form an apparently normal heart. Mef2cb single mutants have a functional heart and are viable adults. Our results show that the key role of Mef2c in myocardial differentiation is conserved throughout the vertebrate heart.
Second heart field; mef2c; mef2ca; mef2cb; mef2a; Heart; Hand2; Myl7; bulbus arteriosus; outflow tract; cardiomyocyte; differentiation
The SET and MYND (SMYD) family of lysine methyltransferases is defined by a SET domain that is split into two segments by a MYND domain, followed by a cysteine-rich post-SET domain. While members of the SMYD family are important in the SET-mediated regulation of gene transcription, pathological consequences have also been associated with aberrant expression of SMYD proteins. The last decade has witnessed a rapid increase in the studies and corresponding understanding of these highly impactful enzymes. Herein, we review the current body of knowledge related to the SMYD family of lysine methyltransferases and their role in transcriptional regulation, epigenetics, and tumorigenesis.
SET; MYND; Smyd1; Smyd2; Smyd3; transcriptional regulation; chromatin modifications; epigenetics; tumorigenesis
15-Lipoxygenase-1 (15-LOX-1) oxidizes polyunsaturated fatty acids to a rich spectrum of biologically active metabolites and is implicated in physiological membrane remodelling, inflammation and apoptosis. Its deregulation is involved in the pathogenesis of diverse cancer and immune diseases. Recent experimental evidence reveals that dynamic histone methylation/demethylation mediated by histone methyltransferases and demethylases plays a critical role in regulation of chromatin remodelling and gene expression. In the present study, we compared the histone 3 lysine 4 (H3-K4) methylation status of the 15-LOX-1 promoter region of the two Hodgkin lymphoma (HL) cell lines L1236 and L428 with abundant and undetectable 15-LOX-1 expression, respectively. We identified a potential role of H3-K4 methylation in positive regulation of 15-LOX-1 transcription. Furthermore, we found that histone methyltransferase SMYD3 inhibition reduced 15-LOX-1 expression by decreasing promoter activity in L1236 cells. SMYD3 knock down in these cells abolished di−/trimethylation of H3-K4, attenuated the occupancy by the transactivator STAT6, and led to diminished histone H3 acetylation at the 15-LOX-1 promoter. In contrast, inhibition of SMCX, a JmjC-domain-containing H3-K4 tri-demethylase, upregulated 15-LOX-1 expression through induction of H3-K4 trimethylation, histone acetylation and STAT6 recruitment at the 15-LOX-1 promoter in L428 cells. In addition, we observed strong SMYD3 expression in the prostate cancer cell line LNCaP and its inhibition led to decreased 15-LOX-1 expression. Taken together, our data suggest that regulation of histone methylation/demethylation at the 15-LOX-1 promoter is important in 15-LOX-1 expression.
Regulation of genes that initiate and amplify inflammatory programs of gene expression is achieved by signal-dependent exchange of co-regulator complexes that function to read, write and erase specific histone modifications linked to transcriptional activation or repression. Here, we provide evidence for the role of trimethylated histone H4 lysine 20 (H4K20me3) as a repression checkpoint that restricts expression of toll like receptor 4 (TLR4) target genes in macrophages. H4K20me3 is deposited at the promoters of a subset of these genes by the SMYD5 histone methyltransferase through its association with NCoR corepressor complexes. Signal-dependent erasure of H4K20me3 is required for effective gene activation and is achieved by NF-κB-dependent delivery of the histone demethylase PHF2. Liver X receptors antagonize TLR4-dependent gene activation by maintaining NCoR/SMYD5-mediated repression. These findings reveal a histone H4K20 tri-methylation/de-methylation strategy that integrates positive and negative signaling inputs that control immunity and homeostasis.
The SET and MYND Domain (SMYD) proteins comprise a unique family of multi-domain SET histone methyltransferases that are implicated in human cancer progression. Here we report an analysis of the crystal structure of the full length human SMYD3 in a complex with an analog of the S-adenosyl methionine (SAM) methyl donor cofactor. The structure revealed an overall compact architecture in which the “split-SET” domain adopts a canonical SET domain fold and closely assembles with a Zn-binding MYND domain and a C-terminal superhelical 9 α-helical bundle similar to that observed for the mouse SMYD1 structure. Together, these structurally interlocked domains impose a highly confined binding pocket for histone substrates, suggesting a regulated mechanism for its enzymatic activity. Our mutational and biochemical analyses confirm regulatory roles of the unique structural elements both inside and outside the core SET domain and establish a previously undetected preference for trimethylation of H4K20.
Smyd3 is a lysine methyltransferase implicated in chromatin and cancer regulation. Here we show that Smyd3 catalyzes histone H4 methylation at lysine 5 (H4K5me). This novel histone methylation mark is detected in diverse cell types and its formation is attenuated by depletion of Smyd3 protein. Further, Smyd3-driven cancer cell phenotypes require its enzymatic activity. Thus, Smyd3, via H4K5 methylation, provides a potential new link between chromatin dynamics and neoplastic disease.
cancer; epigenetics; lysine; methylation; oncogene; oncology; Smyd3
The human genome displays extensive copy-number variation (CNV). Recent discoveries have shown that large segments of DNA, ranging in size from hundreds to thousands of nucleotides, are either deleted or duplicated. This CNV may encompass genes, leading to a change in phenotype, including drug response phenotypes. Gemcitabine and 1-β-D-arabinofuranosylcytosine (AraC) are cytidine analogues used to treat a variety of cancers. Previous studies have shown that genetic variation may influence response to these drugs. In the present study, we set out to test the hypothesis that variation in copy number might contribute to variation in cytidine analogue response phenotypes.
We used a cell-based model system consisting of 197 ethnically-defined lymphoblastoid cell lines for which genome-wide SNP data were obtained using Illumina 550 and 650 K SNP arrays to study cytidine analogue cytotoxicity. 775 CNVs with allele frequencies > 1% were identified in 102 regions across the genome. 87/102 of these loci overlapped with previously identified regions of CNV. Association of CNVs with gemcitabine and AraC IC50 values identified 11 regions with permutation p-values < 0.05. Multiplex ligation-dependent probe amplification assays were performed to verify the 11 CNV regions that were associated with this phenotype; with false positive and false negative rates for the in-silico findings of 1.3% and 0.04%, respectively. We also had basal mRNA expression array data for these same 197 cell lines, which allowed us to quantify mRNA expression for 41 probesets in or near the CNV regions identified. We found that 7 of those 41 genes were highly expressed in our lymphoblastoid cell lines, and one of the seven genes (SMYD3) that was significant in the CNV association study was selected for further functional experiments. Those studies showed that knockdown of SMYD3, in pancreatic cancer cell lines increased gemcitabine and AraC resistance during cytotoxicity assay, consistent with the results of the association analysis.
These results suggest that CNVs may play a role in variation in cytidine analogue effect. Therefore, association studies of CNVs with drug response phenotypes in cell-based model systems, when paired with functional characterization, might help to identify CNV that contributes to variation in drug response.
The regulation of multipotent cardiac progenitor cell (CPC) expansion and subsequent differentiation into cardiomyocytes, smooth muscle, or endothelial cells is a fundamental aspect of basic cardiovascular biology and cardiac regenerative medicine. However, the mechanisms governing these decisions remain unclear. Here, we show that Wnt/β-Catenin signaling, which promotes expansion of CPCs1–3, is negatively regulated by Notch1-mediated control of phosphorylated β-Catenin accumulation within CPCs, and that Notch1 activity in CPCs is required for their differentiation. Notch1 positively, and β-Catenin negatively, regulated expression of the cardiac transcription factors, Isl1, Myocd and Smyd1. Surprisingly, disruption of Isl1, normally expressed transiently in CPCs prior to their differentiation4, resulted in expansion of CPCs in vivo and in an embryonic stem (ES) cell system. Furthermore, Isl1 was required for CPC differentiation into cardiomyocyte and smooth muscle cells, but not endothelial cells. These findings reveal a regulatory network controlling CPC expansion and cell fate that involve unanticipated functions of β-Catenin, Notch1 and Isl1 that may be leveraged for regenerative approaches involving CPCs.
β-Catenin; Notch1; Isl1; cardiac progenitors; Myocd
The organized societies of ants include short-lived worker castes displaying specialized behavior and morphology, and long-lived queens dedicated to reproduction. We sequenced and compared the genomes of two socially divergent ant species: Camponotus floridanus and Harpegnathos saltator. Both genomes contained high amounts of CpG, despite the presence of DNA methylation, which in non-Hymenoptera correlates with CpG depletion. Comparison of gene expression in different castes identified upregulation of telomerase and sirtuin deacetylases in longer-lived H. saltator reproductives, caste-specific expression of miRNAs and SMYD histone methyl-transferases, and differential regulation of genes implicated in neuronal function and chemical communication. Our findings provide clues on the molecular differences between castes in these two ants, and establish a new experimental model to study epigenetics in aging and behavior.
Transgenerational epigenetic inheritance, while poorly understood, is of great interest because it might help explain the increase in the incidence of diseases with an environmental contribution in humans, such as cancer, diabetes, and heart disease. Here, we review five Drosophila examples of transgenerational epigenetic inheritance and propose a unified mechanism that involves Polycomb Response Element/Trithorax Response Element (PRE/TRE) occupancy by either Polycomb Group (PcG) protein complexes or Trithorax group (TrxG) complexes. Among their other activities, PcG complexes cause histone 3 lysine 27 tri-methylation associated with repressed chromatin, whereas Trithorax group (TrxG) complexes induce histone 3 lysine 4 tri-methylation associated with actively transcribed chromatin. In this model, Hsp90 is an environmentally sensitive chromatin remodeling regulator that causes a switch in the chromatin from a permissive state to a non-permissive state for transcription. Consistent with this model, Hsp90 has recently been shown to be a chaperone for Tah1p (TPR-containing protein associated with Hsp90) and Pih1p (protein interacting with Hsp90), which connect to the chromatin remodelling factor Rvb1p (RuvB-like protein 1)/Rvb2p in yeast . Also, Hsp90 is required for optimal activity of the histone H3 lysine-4 methyltransferase SMYD3 in mammals [2, 3]. Since PcG and TrxG complexes are involved in the post-translational modifications of histones, and since such modifications have been shown to be required to maintain imprinted marks, this unified mechanism might also help to explain transgenerational epigenetic inheritance in humans.
The tumor suppressor p53 is the most frequently inactivated gene in human cancers. The p53 protein functions as a sequence-specific transcription factor to regulate key cellular processes, including cell-cycle arrest, DNA repair, apoptosis, and senescence in response to stress signals. P53 is maintained at a low level in the cell, but becomes rapidly stabilized and activated in response to DNA damage, hypoxia, hyperproliferation, and other types of cellular stresses. The stability and transcriptional activity of p53 are tightly regulated through multiple post-translational modifications, such as phosphorylation, acetylation, and ubiquitination. Within the past few years, several studies have established that protein methylation is a novel mechanism by which p53 is regulated. Indeed, histone lysine methyltransferases KMT5 (Set9), KMT3C (Smyd2), and KMT5A (Set8) methylate p53 at specific C-terminal lysines. Lysine methylation enhances or suppresses p53 transcriptional activity depending on the methylation site. Furthermore, the lysine-specific demethylase KDM1 (LSD1) mediates p53 demethylation, which prevents p53 interaction with its co-activator 53BP1 to induce apoptosis. Finally, protein arginine methyltransferases CARM1 and PRMT1 are co-activators of p53 involved in the methylation of histones H3 and H4 to facilitate p53-mediated transcription. In response to cellular stresses, the interplay between p53 methylation, demethylation, and other post-translational modifications fine-tunes the activity of p53 to ultimately prevent tumor formation.
p53; methylation; methyltransferases; transcription; cancer
Mutations of the KRAS oncogene are predictive for resistance to treatment with antibodies against the epithelial growth factor receptor in patients with colorectal cancer. Overcoming this therapeutic dilemma could potentially be achieved by the introduction of drugs that inhibit signaling pathways that are activated by KRAS mutations. To identify comprehensively such signaling pathways we profiled pretreatment biopsies and normal mucosa from 65 patients with locally advanced rectal cancer - 30 of which carried mutated KRAS - using global gene expression microarrays. By comparing all tumor tissues exclusively to matched normal mucosa, we could improve assay sensitivity, and identified a total of 22,297 features that were differentially expressed (adjusted P-value <0.05) between normal mucosa and cancer, including several novel potential rectal cancer genes. We then used this comprehensive description of the rectal cancer transcriptome as the baseline for identifying KRAS-dependent alterations. The presence of activating KRAS mutations is significantly correlated to an upregulation of 13 genes (adjusted P-value <0.05), among them DUSP4, a MAP-kinase phosphatase, and SMYD3, a histone methyltransferase. Inhibition of the expression of both genes has previously been shown using the MEK1-inhibitor PD98059 and the antibacterial compound Novobiocin, respectively. These findings suggest a potential approach to overcome resistance to treatment with antibodies against the epithelial growth factor receptor in patients with KRAS-mutant rectal carcinomas.