The Ku protein complex interacts with YY1, is up-regulated in human heart failure, and represses alpha myosin heavy-chain gene expression

Postprandial cardiac hypertrophy is sustained by mechanics, epigenetic, and metabolic reprogramming in pythons

Constricting pythons, known for their ability to consume infrequent, massive meals, exhibit rapid and reversible cardiac hypertrophy following feeding. Our primary goal was to investigate how python hearts achieve this adaptive response after feeding. Isolated myofibrils increased force after feeding without changes in sarcomere ultrastructure and without increasing energy cost. Ca2+ transients were prolonged after feeding with no changes in myofibril Ca2+ sensitivity. Feeding reduced titin-based tension, resulting in decreased cardiac tissue stiffness. Feeding also reduced the activity of sirtuins, a metabolically linked class of histone deacetylases, and increased chromatin accessibility. Transcription factor enrichment analysis on transposase-accessible chromatin with sequencing revealed the prominent role of transcription factors Yin Yang1 and NRF1 in postfeeding cardiac adaptation. Gene expression also changed with the enrichment of translation and metabolism. Finally, metabolomics analysis and adenosine triphosphate production demonstrated that cardiac adaptation after feeding not only increased energy demand but also energy production. These findings have broad implications for our understanding of cardiac adaptation across species and hold promise for the development of innovative approaches to address cardiovascular diseases.

Modulation of Angiotensin II-Induced Cellular Hypertrophy by Cannflavin-C: Unveiling the Impact on Cytochrome P450 1B1 and Arachidonic Acid Metabolites

This research aimed to clarify the impacts of cannflavin-C on angiotensin II (Ang II)-induced cardiac hypertrophy and their potential role in modulating cytochrome P450 1B1 (CYP1B1) and arachidonic acid (AA) metabolites. Currently there is no evidence to suggest that cannflavin-C, a prenylated flavonoid, has any significant effects on the heart or cardiac hypertrophy. The metabolism of arachidonic acid (AA) into midchain hydroxyeicosatetraenoic acids (HETEs), facilitated by CYP1B1 enzyme, plays a role in the development of cardiac hypertrophy, which is marked by enlarged cardiac cells. Adult human ventricular cardiomyocyte (AC16) cell line was cultured and exposed to cannflavin-C in the presence and absence of Ang II. The assessment of mRNA expression pertaining to cardiac hypertrophic markers and cytochromes P450 (P450s) was conducted via real-time polymerase chain reaction (PCR), whereas the quantification of P450 protein levels was carried out through western blot analysis. Ang II induced hypertrophic markers myosin heavy chain (β/α-MHC), atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) and increased cell surface area, whereas cannflavin-C mitigated these effects. Gene and protein expression analysis revealed that cannflavin-C downregulated CYP1B1 gene expression, protein level, and enzyme activity assessed by 7-methoxyresorufin O-deethylase (MROD). Arachidonic acid metabolites analysis, using liquid chromatography-tandem mass spectrometry (LC-MS/MS), demonstrated that Ang II increased midchain (R/S)-HETE concentrations, which were attenuated by cannflavin-C. This study provides novel insights into the potential of cannflavin-C in modulating arachidonic acid metabolites and attenuating Ang II-induced cardiac hypertrophy, highlighting the importance of this compound as potential therapeutic agents for cardiac hypertrophy. SIGNIFICANCE STATEMENT: This study demonstrates that cannflavin-C offers protection against cellular hypertrophy induced by angiotensin II. The significance of this research lies in its novel discovery, which elucidates a mechanistic pathway involving the inhibition of CYP1B1 by cannflavin-C. This discovery opens up new avenues for leveraging this compound in the treatment of heart failure.

Zinc Ions Modulate YY1 Activity: Relevance in Carcinogenesis

YY1 is widely recognized as an intrinsically disordered transcription factor that plays a role in development of many cancers. In most cases, its overexpression is correlated with tumor progression and unfavorable patient outcomes. Our latest research focusing on the role of zinc ions in modulating YY1's interaction with DNA demonstrated that zinc enhances the protein's multimeric state and affinity to its operator. In light of these findings, changes in protein concentration appear to be just one element relevant to modulating YY1-dependent processes. Thus, alterations in zinc ion concentration can directly and specifically impact the regulation of gene expression by YY1, in line with reports indicating a correlation between zinc ion levels and advancement of certain tumors. This review concentrates on other potential consequences of YY1 interaction with zinc ions that may act by altering charge distribution, conformational state distribution, or oligomerization to influence its interactions with molecular partners that can disrupt gene expression patterns.

DDX5 mRNA-targeting antisense oligonucleotide as a new promising therapeutic in combating castration-resistant prostate cancer

The heat shock protein 27 (Hsp27) has emerged as a principal factor of the castration-resistant prostate cancer (CRPC) progression. Also, an antisense oligonucleotide (ASO) against Hsp27 (OGX-427 or apatorsen) has been assessed in different clinical trials. Here, we illustrate that Hsp27 highly regulates the expression of the human DEAD-box protein 5 (DDX5), and we define DDX5 as a novel therapeutic target for CRPC treatment. DDX5 overexpression is strongly correlated with aggressive tumor features, notably with CRPC. DDX5 downregulation using a specific ASO-based inhibitor that acts on DDX5 mRNAs inhibits cell proliferation in preclinical models, and it particularly restores the treatment sensitivity of CRPC. Interestingly, through the identification and analysis of DDX5 protein interaction networks, we have identified some specific functions of DDX5 in CRPC that could contribute actively to tumor progression and therapeutic resistance. We first present the interactions of DDX5 and the Ku70/80 heterodimer and the transcription factor IIH, thereby uncovering DDX5 roles in different DNA repair pathways. Collectively, our study highlights critical functions of DDX5 contributing to CRPC progression and provides preclinical proof of concept that a combination of ASO-directed DDX5 inhibition with a DNA damage-inducing therapy can serve as a highly potential novel strategy to treat CRPC.

The left ventricle undergoes biomechanical and gene expression changes in response to increased right ventricular pressure overload

Pulmonary hypertension (PH) results in right ventricular (RV) pressure overload and eventual failure. Current research efforts have focused on the RV while overlooking the left ventricle (LV), which is responsible for mechanically assisting the RV during contraction. The objective of this study is to evaluate the biomechanical and gene expression changes occurring in the LV due to RV pressure overload in a mouse model. Nine male mice were divided into two groups: (a) pulmonary arterial banding (PAB, N = 4) and (b) sham surgery (Sham, N = 5). Tagged and steady‐state free precision cardiac MRI was performed on each mouse at 1, 4, and 7 weeks after surgery. At/week7, the mice were euthanized following right/left heart catheterization with RV/LV tissue harvested for histology and gene expression (using RT‐PCR) studies. Compared to Sham mice, the PAB group revealed a significantly decreased LV and RV ejection fraction, and LV maximum torsion and torsion rate, within the first week after banding. In the PAB group, there was also a slight but significant increase in LV perivascular fibrosis, which suggests elevated myocardial stress. LV fibrosis was also accompanied with changes in gene expression in the hypertensive group, which was correlated with LV contractile mechanics. In fact, principal component (PC) analysis of LV gene expression effectively separated Sham and PAB mice along PC2. Changes in LV contractile mechanics were also significantly correlated with unfavorable changes in RV contractile mechanics, but a direct causal relationship was not established. In conclusion, a purely biomechanical insult of RV pressure overload resulted in biomechanical and transcriptional changes in both the RV and LV. Given that the RV relies on the LV for contractile energy assistance, considering the LV could provide prognostic and therapeutic targets for treating RV failure in PH.

Identification of Ku70 Domain-Specific Interactors Using BioID2

Since its inception, proximity-dependent biotin identification (BioID), an in vivo biochemical screening method to identify proximal protein interactors, has seen extensive developments. Improvements and variants of the original BioID technique are being reported regularly, each expanding upon the existing potential of the original technique. While this is advancing our capabilities to study protein interactions under different contexts, we have yet to explore the full potential of the existing BioID variants already at our disposal. Here, we used BioID2 in an innovative manner to identify and map domain-specific protein interactions for the human Ku70 protein. Four HEK293 cell lines were created, each stably expressing various BioID2-tagged Ku70 segments designed to collectively identify factors that interact with different regions of Ku70. Historically, although many interactions have been mapped to the C-terminus of the Ku70 protein, few have been mapped to the N-terminal von Willebrand A-like domain, a canonical protein-binding domain ideally situated as a site for protein interaction. Using this segmented approach, we were able to identify domain-specific interactors as well as evaluate advantages and drawbacks of the BioID2 technique. Our study identifies several potential new Ku70 interactors and validates RNF113A and Spindly as proteins that contact or co-localize with Ku in a Ku70 vWA domain-specific manner.

Biological roles of Yin Yang 2: Its implications in physiological and pathological events

Yin yang 2 (YY2) is a multifunctional zinc finger protein that belongs to the yin yang (YY) family. YY2 has dual function in regulating gene expression, as it could act either as a transcriptional activator or as a repressor of its target genes. YY2 could regulate genes that have been previously identified as targets of yin yang 1 (YY1), another member of the YY family, by binding to their common binding sequences. However, recent studies revealed that YY2 also has its own specific binding sequences, leading to its particular biological functions distinct from those of YY1. Furthermore, they have different levels or even opposite regulatory effects on common target genes, suggesting the importance of balanced YY1 and YY2 regulations in maintaining proper cellular homeostasis and biological functions. Recent studies revealed that YY2 plays crucial roles in maintaining stemness and regulating differentiation potential of embryonic stem cells, as well as in the development of the brain, nervous and cardiovascular systems. YY2 expression is also closely related to diseases, as it could act as a tumour suppressor gene that regulates tumour cell proliferation and metastasis. Moreover, YY2 is also involved in immune regulation and immune surveillance. Herein, we summarize recent perspectives regarding the regulatory functions of YY2, as well as its biological functions and relation with diseases.

Transcriptional regulation of human abraxas brother protein 1 expression by yin yang 1

Abraxas brother protein 1 (ABRO1) is a subunit of the deubiquitinating enzyme BRCC36-containing isopeptidase complex and plays important roles in cellular responses to stress by interacting with its binding partners, such as ubiquitin-specific peptidase 7, p53, activating transcription factor 4, THAP-domain containing 5, and serine hydroxymethyltransferase. However, the transcriptional regulation of ABRO1 remains unexplored. In this study, we identified and characterized the core regulatory elements of the human ABRO1 gene and mapped them to the ABRO1 promoter region. Additionally, 5' rapid amplification of cDNA ends revealed that the transcriptional start site (TSS) was located -13 bp upstream from the start codon. Reporter gene, chromatin immunoprecipitation, and electrophoretic mobility shift assays demonstrated that ABRO1 transcription was regulated through cis-acting elements located in the region -89 to -59 bp upstream of the ABRO1 TSS and that these elements were targeted by yin yang 1 transcription factor (YY1). Moreover, YY1 overexpression increased human ABRO1 mRNA and protein expression, and small-interfering RNA-mediated downregulation of YY1 attenuated ABRO1 expression. These results suggested that YY1 positively regulated human ABRO1 expression by binding to cis-acting elements located in the ABRO1 TSS.

Contribution of Increased Expression of Yin Yang 2 to Development of Cardiomyopathy

Yin Yang 2 (YY2) is a member of the Yin Yang family of transcription factors. Although the bioactivity of YY2 has been previously studied, its role in cardiovascular diseases is not known. We observed the increased expression of YY2 in failing human hearts compared with control hearts, raising the question of whether YY2 is involved in the pathogenesis of cardiomyopathy. To investigate the potential contribution of YY2 to the development of cardiomyopathy, we crossed two independent transgenic (Tg) mouse lines, pCAG-YY2-Tg+and alpha-myosin heavy chain-cre (α-MHC-Cre), to generate two independent double transgenic (dTg) mouse lines in which the conditional cardiomyocyte-specific expression of YY2 driven by the α-MHC promoter was mediated by Cre recombinase, starting at embryonic day 9.0. In dTg mice, we observed partial embryonic lethality and hearts with defective cardiomyocyte proliferation. Surviving dTg mice from both lines developed cardiomyopathy and heart failure that occurred with aging, showing different degrees of severity that were associated with the level of transgene expression. The development of cardiomyopathy was accompanied by increased levels of cardiac disease markers, apoptosis, and cardiac fibrosis. Our studies further revealed that the Cre-mediated cardiomyocyte-specific increase in YY2 expression led to increased levels of Beclin 1 and LC3II, indicating that YY2 is involved in mediating autophagic activity in mouse hearts in vivo. Also, compared with control hearts, dTg mouse hearts showed increased JNK activity. Because autophagy and JNK activity are important for maintaining cardiac homeostasis, the dysregulation of these signaling pathways may contribute to YY2-induced cardiomyopathy and heart failure in vivo.

Pervasive Chromatin-RNA Binding Protein Interactions Enable RNA-Based Regulation of Transcription

Increasing evidence suggests that transcriptional control and chromatin activities at large involve regulatory RNAs, which likely enlist specific RNA-binding proteins (RBPs). Although multiple RBPs have been implicated in transcription control, it has remained unclear how extensively RBPs directly act on chromatin. We embarked on a large-scale RBP ChIP-seq analysis, revealing widespread RBP presence in active chromatin regions in the human genome. Like transcription factors (TFs), RBPs also show strong preference for hotspots in the genome, particularly gene promoters, where their association is frequently linked to transcriptional output. Unsupervised clustering reveals extensive co-association between TFs and RBPs, as exemplified by YY1, a known RNA-dependent TF, and RBM25, an RBP involved in splicing regulation. Remarkably, RBM25 depletion attenuates all YY1-dependent activities, including chromatin binding, DNA looping, and transcription. We propose that various RBPs may enhance network interaction through harnessing regulatory RNAs to control transcription.

Mapping the Ku Interactome Using Proximity-Dependent Biotin Identification in Human Cells

The Ku heterodimer, composed of Ku70 and Ku80, is best characterized for its role in repairing double-stranded DNA breaks but is also known to participate in other regulatory processes. Despite our understanding of Ku protein interplay during DNA repair, the extent of Ku's protein interactions in other processes has never been fully determined. Using proximity-dependent biotin identification (BioID) and affinity purification coupled to mass spectrometry (AP-MS) with wild-type Ku70, we identified candidate proteins that interact with the Ku heterodimer in HEK293 cells, in the absence of exogenously induced DNA damage. BioID analysis identified approximately 250 nuclear proteins, appearing in at least two replicates, including known Ku-interacting factors such as MRE11A, WRN, and NCOA6. Meanwhile, AP-MS analysis identified approximately 50 candidate proteins. Of the novel protein interactors identified, many were involved in functions already suspected to involve Ku such as transcriptional regulation, DNA replication, and DNA repair, while several others suggest that Ku may be involved in additional functions such as RNA metabolism, chromatin-remodeling, and microtubule dynamics. Using a combination of BioID and AP-MS, this is the first report that comprehensively characterizes the Ku protein interaction landscape, revealing new cellular processes and protein complexes involving the Ku complex.

Maternal obesity impairs fetal cardiomyocyte contractile function in sheep

Obesity is a major public health problem worldwide. In the United States, one-third of women of reproductive age are obese. Human studies show that maternal obesity (MO) predisposes offspring to cardiovascular disease. However, the underlying mechanisms remain unclear. Given the similarities between pregnancy in sheep and humans, we studied sheep to examine the impact of MO on fetal cardiomyocyte contractility at term. We observed that MO impaired cardiomyocyte contractility by reducing peak shortening and shortening/relengthening velocity, prolonging time to relengthening. MO disrupted Ca²⁺ homeostasis in fetal cardiomyocytes, increasing intracellular Ca²⁺ and inducing cellular Ca²⁺ insensitivity. The Ca²⁺-release channel was impaired, but Ca²⁺ uptake was unaffected by MO. The upstream kinases that phosphorylate the Ca²⁺-release channel-ryanodine receptor-2, PKA, and calmodulin-dependent protein kinase II-were activated in MO fetuses. Contractile dysfunction was associated with an increased ratio of myosin heavy chain (MHC)-β to MHC-α and upregulated cardiac troponin (cTn)-T and tropomyosin, as well as cTn-I phosphorylation. In summary, this is the first characterization of the effects of MO on fetal cardiomyocyte contractility. Our findings indicate that MO impairs fetal cardiomyocyte contractility through altered intracellular Ca²⁺ handling, overloading fetal cardiomyocyte intracellular Ca²⁺ and aberrant myofilament protein composition. These mechanisms may contribute to developmental programming by MO of offspring cardiac function and predisposition to later life cardiovascular disease in the offspring.-Wang, Q., Zhu, C., Sun, M., Maimaiti, R., Ford, S. P., Nathanielsz, P. W., Ren, J., Guo, W. Maternal obesity impairs fetal cardiomyocyte contractile function in sheep.

YY1 Expression Is Sufficient for the Maintenance of Cardiac Progenitor Cell State

During cardiac development, DNA binding transcription factors and epigenetic modifiers regulate gene expression in cardiac progenitor cells (CPCs). We have previously shown that Yin Yang 1 (YY1) is essential for the commitment of mesodermal precursors into CPCs. However, the role of YY1 in the maintenance of CPC phenotype and their differentiation into cardiomyocytes is unknown. In this study, we found, by genome-wide transcriptional profiling and phenotypic assays, that YY1 overexpression prevents cardiomyogenic differentiation and maintains the proliferative capacity of CPCs. We show further that the ability of YY1 to regulate CPC phenotype is associated with its ability to modulate histone modifications specifically at a developmentally critical enhancer of Nkx2-5 and other key cardiac transcription factor such as Tbx5. Specifically, YY1 overexpression helps to maintain markers of gene activation such as the acetylation of histone H3 at lysine 9 (H3K9Ac) and lysine 27 (H3K27Ac) as well as trimethylation at lysine 4 (H3K4Me3) at the Nkx2-5 cardiac enhancer. Furthermore, transcription factors associated proteins such as PoIII, p300, and Brg1 are also enriched at the Nkx2-5 enhancer with YY1 overexpression. The biological activities of YY1 in CPCs appear to be cell autonomous, based coculture assays in differentiating embryonic stem cells. Altogether, these results demonstrate that YY1 overexpression is sufficient to maintain a CPC phenotype through its ability to sustain the presence of activating epigenetic/chromatin marks at key cardiac enhancers. Stem Cells 2017;35:1913-1923.

Chromatin association of XRCC5/6 in the absence of DNA damage depends on the XPE gene product DDB2

Damaged DNA-binding protein 2 (DDB2), a nuclear protein, participates in both nucleotide excision repair and mRNA transcription. The transcriptional regulatory function of DDB2 is significant in colon cancer, as it regulates metastasis. To characterize the mechanism by which DDB2 participates in transcription, we investigated the protein partners in colon cancer cells. Here we show that DDB2 abundantly associates with XRCC5/6, not involving CUL4 and DNA-PKcs. A DNA-damaging agent that induces DNA double-stranded breaks (DSBs) does not affect the interaction between DDB2 and XRCC5. In addition, DSB-induced nuclear enrichment or chromatin association of XRCC5 does not involve DDB2, suggesting that the DDB2/XRCC5/6 complex represents a distinct pool of XRCC5/6 that is not directly involved in DNA break repair (NHEJ). In the absence of DNA damage, on the other hand, chromatin association of XRCC5 requires DDB2. We show that DDB2 recruits XRCC5 onto the promoter of SEMA3A, a DDB2-stimulated gene. Moreover, depletion of XRCC5 inhibits SEMA3A expression without affecting expression of VEGFA, a repression target of DDB2. Together our results show that DDB2 is critical for chromatin association of XRCC5/6 in the absence of DNA damage and provide evidence that XRCC5/6 are functional partners of DDB2 in its transcriptional stimulatory activity.

Host Proteins Ku and HMGA1 As Participants of HIV-1 Transcription

Human immunodeficiency virus type 1 is known to use the transcriptional machinery of the host cell for viral gene transcription, and the only viral protein that partakes in this process is Tat, the viral trans-activator of transcription. During acute infection, the binding of Tat to the hairpin at the beginning of the transcribed viral RNA recruits the PTEFb complex, which in turn hyperphosphorylates RNA-polymerase II and stimulates transcription elongation. Along with acute infection, HIV-1 can also lead to latent infection that is characterized by a low level of viral transcription. During the maintenance and reversal of latency, there are no detectable amounts of Tat protein in the cell and the mechanism of transcription activation in the absence of Tat protein remains unclear. The latency maintenance is also a problematic question. It seems evident that cellular proteins with a yet unknown nature or role regulate both transcriptional repression in the latent phase and its activation during transition into the lytic phase. The present review discusses the role of cellular proteins Ku and HMGA1 in the initiation of transcription elongation of the HIV-1 provirus. The review presents data regarding Ku-mediated HIV-1 transcription and its dependence on the promoter structure and the shape of viral DNA. We also describe the differential influence of the HMGA1 protein on the induced and basal transcription of HIV-1. Finally, we offer possible mechanisms for Ku and HMGA1 proteins in the proviral transcription regulation.

Transgenic over-expression of YY1 induces pathologic cardiac hypertrophy in a sex-specific manner

YY1 can activate or repress transcription of various genes. In cardiac myocytes in culture YY1 has been shown to regulate expression of several genes involved in myocyte pathology. YY1 can also acutely protect the heart against detrimental changes in gene expression. In this study we show that cardiac over-expression of YY1 induces pathologic cardiac hypertrophy in male mice, measured by changes in gene expression and lower ejection fraction/fractional shortening. In contrast, female animals are protected against pathologic gene expression changes and cardiac dysfunction. Furthermore, we show that YY1 regulates, in a sex-specific manner, the expression of mammalian enable (Mena), a factor that regulates cytoskeletal actin dynamics and whose expression is increased in several models of cardiac pathology, and that Mena expression in humans with heart failure is sex-dependent. Finally, we show that sex differences in YY1 expression are also observed in human heart failure. In summary, this is the first work to show that YY1 has a sex-specific effect in the regulation of cardiac pathology.

Critical role of YY1 in cardiac morphogenesis

BACKGROUND

Yin Yang 1 (YY1), the only DNA binding polycomb group protein, was reported to regulate cardiomyocyte differentiation during early cardiac mesoderm development. However, whether it contributes to cardiac morphogenesis at later developmental stage(s) during embryogenesis is unknown.

RESULTS

We excised YY1 in murine hearts during embryogenesis using two temporal-spatially controlled cre activation approaches, and revealed critical roles of YY1 in cardiac structural formation. Alpha-myosin heavy chain-cre (α-MHC-cre)-mediated cardiomyocyte-specific ablation of YY1 (MHC-YY1) resulted in perinatal death of mutant mice, and Nkx2.5-cre-mediated YY1 null embryos (Nkx2.5-YY1) died embryonically. In the Nkx2.5-YY1 mutants, the endocardial cushions (ECs) of both atrioventricular canal (AVC) and outflow tract (OFT) were hypoplastic due to decreased proliferation and increased apoptosis. Endothelial-to-mesenchymal transition (EMT) progress was also compromised in ECs. Nkx2.5-YY1 mutant hearts had normal formation of extracellular matrix, suggesting that the impaired EMT resulted from the direct loss of YY1. We further uncovered that a number of factors that are involved in normal cardiogenesis were downstream targets of YY1.

CONCLUSIONS

YY1 plays a critical role in cardiac development and occupies a high-level position within the hierarchy of the cardiac transcriptional network that governs normal cardiogenesis.

Function of YY1 in Long-Distance DNA Interactions

During B cell development, long-distance DNA interactions are needed for V(D)J somatic rearrangement of the immunoglobulin (Ig) loci to produce functional Ig genes, and for class switch recombination (CSR) needed for antibody maturation. The tissue-specificity and developmental timing of these mechanisms is a subject of active investigation. A small number of factors are implicated in controlling Ig locus long-distance interactions including Pax5, Yin Yang 1 (YY1), EZH2, IKAROS, CTCF, cohesin, and condensin proteins. Here we will focus on the role of YY1 in controlling these mechanisms. YY1 is a multifunctional transcription factor involved in transcriptional activation and repression, X chromosome inactivation, Polycomb Group (PcG) protein DNA recruitment, and recruitment of proteins required for epigenetic modifications (acetylation, deacetylation, methylation, ubiquitination, sumoylation, etc.). YY1 conditional knock-out indicated that YY1 is required for B cell development, at least in part, by controlling long-distance DNA interactions at the immunoglobulin heavy chain and Igκ loci. Our recent data show that YY1 is also required for CSR. The mechanisms implicated in YY1 control of long-distance DNA interactions include controlling non-coding antisense RNA transcripts, recruitment of PcG proteins to DNA, and interaction with complexes involved in long-distance DNA interactions including the cohesin and condensin complexes. Though common rearrangement mechanisms operate at all Ig loci, their distinct temporal activation along with the ubiquitous nature of YY1 poses challenges for determining the specific mechanisms of YY1 function in these processes, and their regulation at the tissue-specific and B cell stage-specific level. The large numbers of post-translational modifications that control YY1 functions are possible candidates for regulation.

Transcription factors in heart: promising therapeutic targets in cardiac hypertrophy

Regulation of gene expression is central to cell growth, differentiation and diseases. Context specific and signal dependent regulation of gene expression is achieved to a large part by transcription factors. Cardiac transcription factors regulate heart development and are also involved in stress regulation of the adult heart, which may lead to cardiac hypertrophy. Hypertrophy of cardiac myocytes is an outcome of the imbalance between prohypertrophic factors and anti-hypertrophic factors. This is initially a compensatory mechanism but sustained hypertrophy may lead to heart failure. The growing knowledge of transcriptional control mechanisms is helpful in the development of novel therapies. This review summarizes the role of cardiac transcription factors in cardiac hypertrophy, emphasizing their potential as attractive therapeutic targets to prevent the onset of heart failure and sudden death as they can be converging targets for current therapy.

Oxidative DNA damage in neurons: implication of ku in neuronal homeostasis and survival

Oxidative DNA damage is produced by reactive oxygen species (ROS) which are generated by exogenous and endogenous sources and continuously challenge the cell. One of the most severe DNA lesions is the double-strand break (DSB), which is mainly repaired by nonhomologous end joining (NHEJ) pathway in mammals. NHEJ directly joins the broken ends, without using the homologous template. Ku70/86 heterodimer, also known as Ku, is the first component of NHEJ as it directly binds DNA and recruits other NHEJ factors to promote the repair of the broken ends. Neurons are particularly metabolically active, displaying high rates of transcription and translation, which are associated with high metabolic and mitochondrial activity as well as oxygen consumption. In such a way, excessive oxygen radicals can be generated and constantly attack DNA, thereby producing several lesions. This condition, together with defective DNA repair systems, can lead to a high accumulation of DNA damage resulting in neurodegenerative processes and defects in neurodevelopment. In light of recent findings, in this paper, we will discuss the possible implication of Ku in neurodevelopment and in mediating the DNA repair dysfunction observed in certain neurodegenerations.

DNA ends alter the molecular composition and localization of Ku multicomponent complexes

The Ku heterodimer plays an essential role in non-homologous end-joining and other cellular processes including transcription, telomere maintenance and apoptosis. While the function of Ku is regulated through its association with other proteins and nucleic acids, the specific composition of these macromolecular complexes and their dynamic response to endogenous and exogenous cellular stimuli are not well understood. Here we use quantitative proteomics to define the composition of Ku multicomponent complexes and demonstrate that they are dramatically altered in response to UV radiation. Subsequent biochemical assays revealed that the presence of DNA ends leads to the substitution of RNA-binding proteins with DNA and chromatin associated factors to create a macromolecular complex poised for DNA repair. We observed that dynamic remodeling of the Ku complex coincided with exit of Ku and other DNA repair proteins from the nucleolus. Microinjection of sheared DNA into live cells as a mimetic for double strand breaks confirmed these findings in vivo.

YY1 controls immunoglobulin class switch recombination and nuclear activation-induced deaminase levels

Activation-induced deaminase (AID) is an enzyme required for class switch recombination (CSR) and somatic hypermutation (SHM), processes that ensure antibody maturation and expression of different immunoglobulin isotypes. AID function is tightly regulated by tissue- and stage-specific expression, nuclear localization, and protein stability. Transcription factor YY1 is crucial for early B cell development, but its function at late B cell stages is unknown. Here, we show that YY1 conditional knockout in activated splenic B cells interferes with CSR. Knockout of YY1 did not affect B cell proliferation, transcription of the AID and IgM genes, or levels of various switch region germ line transcripts. However, we show that YY1 physically interacts with AID and controls the accumulation of nuclear AID, at least in part, by increasing nuclear AID stability. We show for the first time that YY1 plays a novel role in CSR and controls nuclear AID protein levels.

The DNA repair complex Ku70/86 modulates Apaf1 expression upon DNA damage

Apaf1 is a key regulator of the mitochondrial intrinsic pathway of apoptosis, as it activates executioner caspases by forming the apoptotic machinery apoptosome. Its genetic regulation and its post-translational modification are crucial under the various conditions where apoptosis occurs. Here we describe Ku70/86, a mediator of non-homologous end-joining pathway of DNA repair, as a novel regulator of Apaf1 transcription. Through analysing different Apaf1 promoter mutants, we identified an element repressing the Apaf1 promoter. We demonstrated that Ku70/86 is a nuclear factor able to bind this repressing element and downregulating Apaf1 transcription. We also found that Ku70/86 interaction with Apaf1 promoter is dynamically modulated upon DNA damage. The effect of this binding is a downregulation of Apaf1 expression immediately following the damage to DNA; conversely, we observed Apaf1 upregulation and apoptosis activation when Ku70/86 unleashes the Apaf1-repressing element. Therefore, besides regulating DNA repair, our results suggest that Ku70/86 binds to the Apaf1 promoter and represses its activity. This may help to inhibit the apoptosome pathway of cell death and contribute to regulate cell survival.

Reversible epigenetic modifications of the two cardiac myosin heavy chain genes during changes in expression

The two genes of the cardiac myosin heavy chain (MHC) locus-alpha-MHC (aMHC) and beta-MHC (bMHC)--are reciprocally regulated in the mouse ventricle during development and in adult conditions such as hypothyroidism and pathological cardiac hypertrophy. Their expressions are under the control of thyroid hormone T3 levels. To gain insights into the epigenetic mechanisms that underlie this inducible and reversible switching of the aMHC and bMHC isoforms, we have investigated the histone modification patterns that occur over the two cardiac MHC promoters during T3-mediated reversible switching of gene expression. Mice fed a diet of propylthiouracil (PTU, an inhibitor of T3 synthesis) for 2 weeks dramatically reduce aMHC mRNA expression and increase bMHC mRNA levels to high levels, while a subsequent withdrawal of PTU diet for 2 weeks completely reverses the T3-mediated changes in MHC expression. Using hearts from mice treated in this way, we carried out chromatin immunoprecipitation-qPCR assays with antibodies against acetylated histone H3 (H3ac) and trimethylated histone (H3K4me3)-two well-documented markers of activation. Our results show that the reexpression of bMHC is associated at the bMHC promoter with increased H3ac but not H3K4me3. In contrast, the silencing of aMHC is associated at its promoter with decreased H3K4me3, but not decreased H3ac. The epigenetic changes at the two MHC promoters are completely reversed when the gene expression returns to initial levels. These data indicate that during reciprocal and inducible gene expression H3ac parallels bMHC isoform expression while H3K4me3 parallels expression of the tightly linked aMHC isoform.

Ku proteins interact with activator protein-2 transcription factors and contribute to ERBB2 overexpression in breast cancer cell lines

Introduction

Activator protein-2 (AP-2) α and AP-2γ transcription factors contribute to ERBB2 gene overexpression in breast cancer. In order to understand the mechanism by which the ERBB2 gene is overexpressed we searched for novel AP-2 interacting factors that contribute to its activity.

Methods

Ku proteins were identified as AP-2α interacting proteins by glutathione serine transferase (GST)-pull down followed by mass spectrometry. Transfection of the cells with siRNA, expression vectors and reporter vectors as well as chromatin immunoprecipitation (ChIP) assay were used to ascertain the implication of Ku proteins on ERBB2 expression.

Results

Nuclear proteins from BT-474 cells overexpressing AP-2α and AP-2γ were incubated with GST-AP2 or GST coated beads. Among the proteins retained specifically on GST-AP2 coated beads Ku70 and Ku80 proteins were identified by mass spectrometry. The contribution of Ku proteins to ERBB2 gene expression in BT-474 and SKBR3 cell lines was investigated by downregulating Ku proteins through the use of specific siRNAs. Depletion of Ku proteins led to downregulation of ERBB2 mRNA and protein levels. Furthermore, reduction of Ku80 in HCT116 cell line decreased the AP-2α activity on a reporter vector containing an AP-2 binding site linked to the ERBB2 core promoter, and transfection of Ku80 increased the activity of AP-2α on this promoter. Ku siRNAs also inhibited the activity of this reporter vector in BT-474 and SKBR3 cell lines and the activity of the ERBB2 promoter was further reduced by combining Ku siRNAs with AP-2α and AP-2γ siRNAs. ChIP experiments with chromatin extracted from wild type or AP-2α and AP-2γ or Ku70 siRNA transfected BT-474 cells demonstrated Ku70 recruitment to the ERBB2 proximal promoter in association with AP-2α and AP-2γ. Moreover, Ku70 siRNA like AP-2 siRNAs, greatly reduced PolII recruitment to the ERBB2 proximal promoter.

Conclusions

Ku proteins in interaction with AP-2 (α and γ) contribute to increased ERBB2 mRNA and protein levels in breast cancer cells.

Physical interaction between TBX5 and MEF2C is required for early heart development

TBX5 is a transcription factor which plays important roles in the development of the heart and upper limbs. Mutations in this gene produce the inherited disorder Holt-Oram syndrome. Here, we report a physical interaction between TBX5 and MEF2C leading to a synergistic activation of the alpha-cardiac myosin heavy chain (MYH6). Mutants of TBX5, TBX5G80R, and TBX5R279X that produce severe cardiac phenotypes impair the synergy. Using fluorescence resonance energy transfer, we demonstrate the interaction of TBX5 and MEF2C in living cells. We also show that they physically associate through their DNA-binding domains to form a complex on the MYH6 promoter. Morpholino-mediated knockdowns of Tbx5 and Mef2c in zebrafish suggest that the genetic interaction of these proteins is not only required for MYH6 expression but also essential for the early stages of heart development and survival. This is the first report of a functional interaction between a T-box protein and a MADS box factor that may be crucial in cardiomyocyte differentiation.

Endothelin-stimulated human B-type natriuretic peptide gene expression is mediated by Yin Yang 1 in association with histone deacetylase 2

Increased B-type natriuretic peptide (BNP) gene expression is regarded as one of the hallmarks of cardiac myocyte hypertrophy. Here we demonstrate that both basal- and endothelin-1-dependent stimulation of human (h) BNP gene transcription requires the presence of an intact Yin Yang 1 (YY1) binding site positioned at -62 bp relative to the transcription start site. Mutation of this site reduced both basal and stimulated hBNP promoter activity. This site was shown to bind YY1 both in vitro and within the context of the intact cell. The latter interaction increased after endothelin-1 treatment. Exposure to endothelin-1 also resulted in increased nuclear localization of YY1 and a reduction in acetylation of the YY1 protein. Overexpression of wild-type YY1 increased both basal and endothelin-stimulated hBNP promoter activity, whereas a carboxy-terminal deletion mutant of YY1 was devoid of activity. Treatment with the histone deacetylase inhibitor trichostatin A resulted in decreased hBNP reporter activity. YY1 was shown to associate with histone deacetylase 2, and histone deacetylase 2 was shown to associate directly with the hBNP promoter in the intact cell. Collectively these findings demonstrate that YY1 plays an important role in regulating the transcriptional activity of the hBNP gene promoter. These data suggest a model in which YY1 activates hBNP transcription through interaction with histone deacetylase 2.

Discordant on/off switching of gene expression in myocytes during cardiac hypertrophy in vivo

To determine whether the expression of cardiac genes changes in a graded manner or by on/off switching when cardiac myocytes change genetic programs in living animals, we have studied two indicator genes that change their expression oppositely in mouse binucleate ventricular cardiomyocytes during development and in response to cardiac hypertrophy. One is a single-copy transgene controlled by an alpha-myosin heavy chain (aMHC) promoter and coding for CFP. The other is the endogenous beta-myosin heavy chain (bMHC) gene modified to code for a YFP-bMHC fusion protein. Using high-resolution confocal microscopy, we determined the expression of the two indicator genes in individual cardiomyocytes perinatally and after inducing cardiac hypertrophy by transverse aortic constriction. Our results provide strong evidence that the cardiac genes respond by switching their expression in an on/off rather than graded manner, and that responding genes within a single cell and within the two nuclei of cardiomyocytes do not necessarily switch concordantly.

Activation of SIRT1, a class III histone deacetylase, contributes to fructose feeding-mediated induction of the alpha-myosin heavy chain expression

Fructose feeding has been shown to induce the cardiac alpha-myosin heavy chain (MHC) expression and protect the heart from ischemia- and reperfusion-mediated cell injury. This study was designed to investigate the mechanism involved in the effect of this sugar on MHC gene expression and cardiac protection. Adult mice were fed with a 6-propyl-2-thiouracil (PTU) diet or PTU combined with a fructose-rich diet. PTU treatment made animals hypothyroid and that resulted in total replacement of cardiac alpha-MHC with the beta-MHC isoform. Addition of fructose in the PTU diet led to reexpression of the alpha-MHC isoform to a significant level. Similar induction of alpha-MHC expression was also seen when PTU diet was combined with resveratrol, an agonist of sirtuin (SIRT) 1 deacetylase. Analysis of heart lysate of these animals indicated that fructose feeding augmented the NAD-to-NADH ratio and the cardiac SIRT1 levels, thus suggesting a role of SIRT1 in fructose-mediated activation of alpha-MHC isoform. To analyze a direct effect of SIRT1 on MHC isoform expression, we generated transgenic mice expressing SIRT1 in the heart. Treatment of these transgenic mice with PTU diet did not lead to disappearance of alpha-MHC, as it did in the nontransgenic animals. SIRT1 overexpression also activated the alpha-MHC gene promoter in transient transfection assays, thus confirming a role of SIRT1 in the induction of alpha-MHC expression. Fructose feeding also attenuated the MHC isoform shift and blocked the cardiac hypertrophy response associated with pressure overload, which was again associated with the induction of cardiac SIRT1 levels. These results demonstrate that fructose feeding protects the heart by induction of the SIRT1 deacetylase and highlight its role in the induction of alpha-MHC gene expression.

Separation of large mammalian ventricular myosin differing in ATPase activity

To investigate a possible heterogeneity of human ventricular myosin, papillary muscles of patients with valvular dysfunction were examined using a modified native gel electrophoresis. Myosin was separated into 2 components termed VA and VB, whereby the VA to VB proportion appeared to depend on the ventricular load. The proportion of the faster migrating band VA was correlated (P<0.05) with end-diastolic pressure and the aortic pressure-cardiac index product. The regression based on these variables accounted for 67% of the variation in VA (R2=0.67). The VA proportion was, however, not significantly correlated with cardiac norepinephrine concentration. The ATPase activity of the 2 components of myosin was assessed from the Ca3(PO4)2 precipitation by incubating the gel in the presence of ATP and CaCl2. The ATPase activity of VA was 60% of that of VB. The VA and VB forms were observed also in the cat (31.4% VA), dog (32.1% VA), pig (28.5% VA), wild pig (33.7% VA), and roe deer (30.5% VA). VA and VB were not detected in the rat exhibiting the 3 isoforms V1, V2, and V3, rabbit (100% V3), and hare (86% V1). The data demonstrate a heterogeneity of large mammalian ventricular myosin, whereby an increased cardiac load appeared to be associated with a higher myosin VA proportion that exhibited a reduced ATPase activity.

Factors controlling cardiac myosin-isoform shift during hypertrophy and heart failure

Myosin is a molecular motor, which interacts with actin to convert the energy from ATP hydrolysis into mechanical work. In cardiac myocytes, two myosin isoforms are expressed and their relative distribution changes in different developmental and pathophysiologic conditions of the heart. It has been realized for a long time that a shift in myosin isoforms plays a major role in regulating myocardial contractile activity. With the recent evidence implicating that alteration in myosin isoform ratio may be eventually beneficial for the treatment of a stressed heart, a new interest has developed to find out ways of controlling the myosin isoform shift. This article reviews the published data describing the role of myosin isoforms in the heart and highlighting the importance of various factors shown to influence myosin isofrom shift during physiology and disease states of the heart.

NF-kappaB regulation of YY1 inhibits skeletal myogenesis through transcriptional silencing of myofibrillar genes

NF-kappaB signaling is implicated as an important regulator of skeletal muscle homeostasis, but the mechanisms by which this transcription factor contributes to muscle maturation and turnover remain unclear. To gain insight into these mechanisms, gene expression profiling was examined in C2C12 myoblasts devoid of NF-kappaB activity. Interestingly, even in proliferating myoblasts, the absence of NF-kappaB caused the pronounced induction of several myofibrillar genes, suggesting that NF-kappaB functions as a negative regulator of late-stage muscle differentiation. Although several myofibrillar promoters contain predicted NF-kappaB binding sites, functional analysis using the troponin-I2 gene as a model revealed that NF-kappaB-mediated repression does not occur through direct DNA binding. In the search for an indirect mediator, the transcriptional repressor YinYang1 (YY1) was identified. While inducers of NF-kappaB stimulated YY1 expression in multiple cell types, genetic ablation of the RelA/p65 subunit of NF-kappaB in both cultured cells and adult skeletal muscle correlated with reduced YY1 transcripts and protein. NF-kappaB regulation of YY1 occurred at the transcriptional level, mediated by direct binding of the p50/p65 heterodimer complex to the YY1 promoter. Furthermore, YY1 was found associated with multiple myofibrillar promoters in C2C12 myoblasts containing NF-kappaB activity. Based on these results, we propose that NF-kappaB regulation of YY1 and transcriptional silencing of myofibrillar genes represent a new mechanism by which NF-kappaB functions in myoblasts to modulate skeletal muscle differentiation.

Ku70 and poly(ADP-ribose) polymerase-1 competitively regulate beta-catenin and T-cell factor-4-mediated gene transactivation: possible linkage of DNA damage recognition and Wnt signaling

Formation of the T-cell factor-4 (TCF-4) and beta-catenin nuclear complex is considered crucial to embryonic development and colorectal carcinogenesis. We previously reported that poly(ADP-ribose) polymerase-1 (PARP-1) interacts with the TCF-4 and beta-catenin complex and enhances its transcriptional activity. However, its biological significance remains unexplained. Using immunoprecipitation and mass spectrometry, we found that two Ku proteins, Ku70 and Ku80, were also associated with the complex. Knockdown of Ku70 by RNA interference increased the amount of beta-catenin associated with TCF-4 and enhanced the transcriptional activity. PARP-1 competed with Ku70 for binding to TCF-4. Treatment with bleomycin, a DNA-damaging alkylating agent, induced polyADP-ribosylation of PARP-1 protein and inhibited its interaction with TCF-4. Bleomycin conversely increased the amounts of Ku70 coimmunoprecipitated with TCF-4 and removed beta-catenin from TCF-4. We propose a working model in which the transcriptional activity of TCF-4 is regulated by the relative amount of Ku70, PARP-1, and beta-catenin proteins binding to TCF-4. Identification of the functional interaction of Ku70 as well as PARP-1 with the TCF-4 and beta-catenin transcriptional complex may provide insights into a novel linkage between DNA damage recognition/repair and Wnt signaling.

Astrocyte elevated gene-1: recent insights into a novel gene involved in tumor progression, metastasis and neurodegeneration

Tumor progression and metastasis are complex processes involving intricate interplay among multiple gene products. Astrocyte elevated gene (AEG)-1 was cloned as an human immunodeficiency virus (HIV)-1-inducible and tumor necrosis factor-alpha (TNF-alpha)-inducible transcript in primary human fetal astrocytes (PHFA) by a rapid subtraction hybridization approach. AEG-1 down-regulates the expression of the glutamate transporter EAAT2; thus, it is implicated in glutamate-induced excitotoxic damage to neurons as evident in HIV-associated neurodegeneration. Interestingly, AEG-1 expression is elevated in subsets of breast cancer, glioblastoma multiforme and melanoma cells, and AEG-1 cooperates with Ha-ras to augment the transformed phenotype of normal immortal cells. Moreover, AEG-1 is overexpressed in >95% of human malignant glioma samples when compared with normal human brain. Overexpression of AEG-1 increases and siRNA inhibition of AEG-1 decreases migration and invasion of human glioma cells, respectively. AEG-1 contains a lung-homing domain facilitating breast tumor metastasis to lungs. These findings indicate that AEG-1 might play a pivotal role in the pathogenesis, progression and metastasis of diverse cancers. Our recent observations indicate that AEG-1 exerts its effects by activating the nuclear factor kappa B (NF-kappaB) pathway and AEG-1 is a downstream target of Ha-ras and plays an important role in Ha-ras-mediated tumorigenesis. These provocative findings are intensifying interest in AEG-1 as a crucial regulator of tumor progression and metastasis and as a potential mediator of neurodegeneration. In this review, we discuss the cloning, structure and function(s) of AEG-1 and provide recent insights into the diverse actions and intriguing properties of this molecule.

PARP-3 associates with polycomb group bodies and with components of the DNA damage repair machinery

Poly(ADP-ribose) polymerase 3 (PARP-3) is a novel member of the PARP family of enzymes that synthesize poly(ADP-ribose) on themselves and other acceptor proteins. Very little is known about this PARP, which is closely related to PARP-1 and PARP-2. By sequence analysis, we find that PARP-3 may be expressed in two isoforms which we studied in more detail to gain insight into their possible functions. We find that both PARP-3 isoforms, transiently expressed as GFP or FLAG fusions, are nuclear. Detection of endogenous PARP-3 with a specific antibody also shows a widespread nuclear distribution, appearing in numerous small foci and a small number of larger foci. Through co-localization experiments and immunoprecipitations, the larger nuclear foci were identified as Polycomb group bodies (PcG bodies) and we found that PARP-3 is part of Polycomb group protein complexes. Furthermore, using a proteomics approach, we determined that both PARP-3 isoforms are part of complexes comprising DNA-PKcs, PARP-1, DNA ligase III, DNA ligase IV, Ku70, and Ku80. Our findings suggest that PARP-3 is a nuclear protein involved in transcriptional silencing and in the cellular response to DNA damage.

Early Adaptations to Training

Chronic exercise induces adaptations that increase the functional capacity of the cardiovascular system. Aside from ventricular growth, these adaptations include a shift in the MHC isoenzyme pattern to enhance ventricular contractility. It is unclear whether adaptations by the contractile elements are an early event and specific to exercise, or whether they progress as a function of cardiac growth. Examining early adaptations to training is also important because it is during this period when the greatest imbalance between increased demand and functional capacity exists, and it is likely that the mechanisms responsible for propagating changes in the myocardial phenotype are most active.

PURPOSE

To determine whether changes in left ventricular (LV) contractile elements are an early adaptation to chronic exercise.

METHODS

Rats were randomly assigned to sedentary control or exercise training groups for 1 or 10 wk of training. After training, the LV was analyzed for protein by Western blot or mRNA by Northern and real-time QRT-PCR analysis.

RESULTS

Plantaris cytochrome oxidase activity was significantly (P < 0.05) increased by 1 wk (+28%) or 10 wk (+32%) of training. Training significantly increased LV myofibrillar alpha-MHC protein and alpha-MHC-mRNA after both training periods. No changes in myofibrillar beta-MHC protein or beta-MHC-mRNA were observed. After 1 wk of training, LV skeletal alpha-actin-mRNA was significantly increased, whereas no changes were found for ANF, glyceraldehyde dehydrogenase, or cytochrome oxidase IV. Gel mobility shift analysis determined that YY1 DNA binding was significantly decreased in LV extracts from trained animals, although no change in YY1-mRNA expression was observed.

CONCLUSIONS

Increased myofibrillar alpha-MHC protein and alpha-MHC-mRNA expression are early events in the adaptation to chronic exercise and occur before significant cardiac growth. These adaptations enhance myocardial contractility and permit increases in maximal cardiac output during heavy exercise.

Astrocyte elevated gene-1 (AEG-1) is a target gene of oncogenic Ha-ras requiring phosphatidylinositol 3-kinase and c-Myc

It is well established that Ha-ras and c-myc genes collaborate in promoting transformation, tumor progression, and metastasis. However, the precise mechanism underlying this cooperation remains unclear. In the present study, we document that astrocyte elevated gene-1 (AEG-1) is a downstream target molecule of Ha-ras and c-myc, mediating their tumor-promoting effects. AEG-1 expression is elevated in diverse neoplastic states, it cooperates with Ha-ras to promote transformation, and its overexpression augments invasion of transformed cells, demonstrating its functional involvement in Ha-ras-mediated tumorigenesis. We now document that AEG-1 expression is markedly induced by oncogenic Ha-ras, activating the phosphatidylinositol 3-kinase signaling pathway that augments binding of c-Myc to key E-box elements in the AEG-1 promoter, thereby regulating AEG-1 transcription. In addition, Ha-ras-mediated colony formation is inhibited by AEG-1 siRNA. This is a demonstration that Ha-ras activation of a tumor-promoting gene is regulated directly by c-Myc DNA binding via phosphatidylinositol 3-kinase signaling, thus revealing a previously uncharacterized mechanism of Ha-ras-mediated oncogenesis through AEG-1.

Shuttling of HDAC5 in H9C2 cells regulates YY1 function through CaMKIV/PKD and PP2A

YY1 is a transcription factor that can activate or repress transcription of a variety of genes and is involved in several developmental processes. YY1 is a repressor of transcription in differentiated H9C2 cells and in neonatal cardiac myocytes but an activator of transcription in undifferentiated H9C2 cells. We now present a detailed analysis of the functional domains of YY1 when it is acting as a repressor or an activator and identify the mechanism whereby its function is regulated in the differentiation of H9C2 cells. We show that histone deacetylase 5 (HDAC5) is localized to the cytoplasm in undifferentiated H9C2 cells and that this localization is dependent on Ca(2+)/calmodulin-dependent kinase IV (CaMKIV) and/or protein kinase D (PKD). In differentiated cells, HDAC5 is nuclear and interacts with YY1. Finally, we show that HDAC5 localization in differentiated cells is dependent on phosphatase 2A (PP2A). Our results suggest that a signaling mechanism that involves CaMKIV/PKD and PP2A controls YY1 function through regulation of HDAC5 and is important in the maintenance of muscle differentiation.

Thick Filament Proteins and Performance in Human Heart Failure

Modifications in thick filament protein content and performance are thought to underlie contraction-relaxation dysfunction in human heart failure. It has been found that myofibrillar Mg.ATPase is reduced in failing myocardium, which may be due in part to the reduction in alpha-myosin heavy chain (MHC) isoform content from approximately 5-10% in normal myocardium to <2% in failing myocardium. The physiological importance of this seemingly small amount of alpha-MHC appears substantiated by the development of cardiopathologies in humans with mutated alpha-MHC at normal abundance. Therefore, the replacement of alpha-MHC by beta-MHC (possessing slower actomyosin enzymatic kinetics) may underlie to a significant degree the reduced myocardial shortening velocity and reduced relaxation function in human heart failure. The atrial isoform of myosin essential light chain (ELC) may replace up to 25% of the ventricular isoform in failing ventricles and in so doing promotes myocardial shortening velocity. An elevated accumulation of the higher performing atrial-ELC, unlike the reduced content of the higher performing alpha-MHC, is therefore considered a compensatory response in heart failure. Phosphorylation of the myofilament proteins myosin regulatory light chain and troponin-I are both reduced in heart failure and collectively result in an elevated myofilament sensitivity to calcium activation, which inhibits relaxation function. These and other modifications in thick filament proteins, as discussed in this review, directly affect mechanical power output and relaxation function of the myocardium and thereby may be considered to cause or in some cases to compensate for the otherwise ineffective myocardial performance in heart failure.

Molecular remodeling in the failing human heart

Heart failure is a progressive and fatal disease process. Arrhythmias and progressive cardiac dysfunction account for most of the morbidity and mortality in patients with heart failure. In general, the physiologic mechanisms responsible for progressive myocyte dysfunction, remodeling, and arrhythmias involve signaling mechanisms that alter myocardial gene expression. These changes in gene expression are complex and involve contractile proteins, ion channels, Ca++ handling, apoptosis, cell metabolism, the extracellular matrix, signal transduction pathways, and growth factors.

Yin Yang 1 represses alpha-myosin heavy chain gene expression in pathologic cardiac hypertrophy

In the work presented here, we elucidate a mechanism for the repression of alpha-myosin heavy chain (MyHC) during pathological cardiac hypertrophy. We demonstrate that the transcription factor Yin Yang 1 (YY1) significantly decreases endogenous alpha-MyHC mRNA and protein expression in neonatal rat ventricular myocytes. Furthermore, mutation of the YY1 binding sites in the proximal rat alpha-MyHC promoter increases promoter activity and alleviates YY1-mediated repression of the promoter. Despite the presence of 5 sites that bind YY1, only one site, located at -94bp of the rat alpha-MyHC promoter, is both necessary and sufficient for pathological repression of the promoter by phorbol esters, revealing a unique mechanism for the repression of alpha-MyHC expression during cardiac hypertrophy.