Differential Activation of P-TEFb Complexes in the Development of Cardiomyocyte Hypertrophy following Activation of Distinct G Protein-Coupled Receptors

KCTD Proteins Have Redundant Functions in Controlling Cellular Growth

We explored the functional redundancy of three structurally related KCTD (Potassium Channel Tetramerization Domain) proteins, KCTD2, KCTD5, and KCTD17, by progressively knocking them out in HEK 293 cells using CRISPR/Cas9 genome editing. After validating the knockout, we assessed the effects of progressive knockout on cell growth and gene expression. We noted that the progressive effects of knockout of KCTD isoforms on cell growth were most pervasive when all three isoforms were deleted, suggesting some functions were conserved between them. This was also reflected in progressive changes in gene expression. Our previous work indicated that Gβ1 was involved in the transcriptional control of gene expression, so we compared the gene expression patterns between GNB1 and KCTD KO. Knockout of GNB1 led to numerous changes in the expression levels of other G protein subunit genes, while knockout of KCTD isoforms had the opposite effect, presumably because of their role in regulating levels of Gβ1. Our work demonstrates a unique relationship between KCTD proteins and Gβ1 and a global role for this subfamily of KCTD proteins in maintaining the ability of cells to survive and proliferate.

Comparing the signaling and transcriptome profiling landscapes of human iPSC-derived and primary rat neonatal cardiomyocytes

The inaccessibility of human cardiomyocytes significantly hindered years of cardiovascular research efforts. To overcome these limitations, non-human cell sources were used as proxies to study heart function and associated diseases. Rodent models became increasingly acceptable surrogates to model the human heart either in vivo or through in vitro cultures. More recently, due to concerns regarding animal to human translation, including cross-species differences, the use of human iPSC-derived cardiomyocytes presented a renewed opportunity. Here, we conducted a comparative study, assessing cellular signaling through cardiac G protein-coupled receptors (GPCRs) in rat neonatal cardiomyocytes (RNCMs) and human induced pluripotent stem cell-derived cardiomyocytes. Genetically encoded biosensors were used to explore GPCR-mediated nuclear protein kinase A (PKA) and extracellular signal-regulated kinase 1/ 2 (ERK1/2) activities in both cardiomyocyte populations. To increase data granularity, a single-cell analytical approach was conducted. Using automated high content microscopy, our analyses of nuclear PKA and ERK_1/2 signaling revealed distinct response clusters in rat and human cardiomyocytes. In line with this, bulk RNA-seq revealed key differences in the expression patterns of GPCRs, G proteins and downstream effector expression levels. Our study demonstrates that human stem cell-derived models of the cardiomyocyte offer distinct advantages for understanding cellular signaling in the heart.

Phosphorylation Signals Downstream of Dopamine Receptors in Emotional Behaviors: Association with Preference and Avoidance

Dopamine regulates emotional behaviors, including rewarding and aversive behaviors, through the mesolimbic dopaminergic pathway, which projects dopamine neurons from the ventral tegmental area to the nucleus accumbens (NAc). Protein phosphorylation is critical for intracellular signaling pathways and physiological functions, which are regulated by neurotransmitters in the brain. Previous studies have demonstrated that dopamine stimulated the phosphorylation of intracellular substrates, such as receptors, ion channels, and transcription factors, to regulate neuronal excitability and synaptic plasticity through dopamine receptors. We also established a novel database called KANPHOS that provides information on phosphorylation signals downstream of monoamines identified by our kinase substrate screening methods, including dopamine, in addition to those reported in the literature. Recent advances in proteomics techniques have enabled us to clarify the mechanisms through which dopamine controls rewarding and aversive behaviors through signal pathways in the NAc. In this review, we discuss the intracellular phosphorylation signals regulated by dopamine in these two emotional behaviors.

Emerging therapies for autosomal dominant polycystic kidney disease with a focus on cAMP signaling

Autosomal dominant polycystic kidney disease (ADPKD), with an estimated genetic prevalence between 1:400 and 1:1,000 individuals, is the third most common cause of end stage kidney disease after diabetes mellitus and hypertension. Over the last 3 decades there has been great progress in understanding its pathogenesis. This allows the stratification of therapeutic targets into four levels, gene mutation and polycystin disruption, proximal mechanisms directly caused by disruption of polycystin function, downstream regulatory and signaling pathways, and non-specific pathophysiologic processes shared by many other diseases. Dysfunction of the polycystins, encoded by the PKD genes, is closely associated with disruption of calcium and upregulation of cyclic AMP and protein kinase A (PKA) signaling, affecting most downstream regulatory, signaling, and pathophysiologic pathways altered in this disease. Interventions acting on G protein coupled receptors to inhibit of 3',5'-cyclic adenosine monophosphate (cAMP) production have been effective in preclinical trials and have led to the first approved treatment for ADPKD. However, completely blocking cAMP mediated PKA activation is not feasible and PKA activation independently from cAMP can also occur in ADPKD. Therefore, targeting the cAMP/PKA/CREB pathway beyond cAMP production makes sense. Redundancy of mechanisms, numerous positive and negative feedback loops, and possibly counteracting effects may limit the effectiveness of targeting downstream pathways. Nevertheless, interventions targeting important regulatory, signaling and pathophysiologic pathways downstream from cAMP/PKA activation may provide additive or synergistic value and build on a strategy that has already had success. The purpose of this manuscript is to review the role of cAMP and PKA signaling and their multiple downstream pathways as potential targets for emergent therapies for ADPKD.

Epigenetic Reader Bromodomain Containing Protein 2 Facilitates Pathological Cardiac Hypertrophy via Regulating the Expression of Citrate Cycle Genes

The bromodomain and extra-terminal domain proteins (BETs) family serve as epigenetic “readers”, which recognize the acetylated histones and recruit transcriptional regulator complexes to chromatin, eventually regulating gene transcription. Accumulating evidences demonstrate that pan BET inhibitors (BETi) confer protection against pathological cardiac hypertrophy, a precursor progress for developing heart failure. However, the roles of BET family members, except BRD4, remain unknown in pathological cardiac hypertrophy. The present study identified BRD2 as a novel regulator in cardiac hypertrophy, with a distinct mechanism from BRD4. BRD2 expression was elevated in cardiac hypertrophy induced by β-adrenergic agonist isoprenaline (ISO) in vivo and in vitro. Overexpression of BRD2 upregulated the expression of hypertrophic biomarkers and increased cell surface area, whereas BRD2 knockdown restrained ISO-induced cardiomyocyte hypertrophy. In vivo, rats received intramyocardial injection of adeno-associated virus (AAV) encoding siBRD2 significantly reversed ISO-induced pathological cardiac hypertrophy, cardiac fibrosis, and cardiac function dysregulation. The bioinformatic analysis of whole-genome sequence data demonstrated that a majority of metabolic genes, in particular those involved in TCA cycle, were under regulation by BRD2. Real-time PCR results confirmed that the expressions of TCA cycle genes were upregulated by BRD2, but were downregulated by BRD2 silencing in ISO-treated cardiomyocytes. Results of mitochondrial oxygen consumption rate (OCR) and ATP production measurement demonstrated that BRD2 augmented cardiac metabolism during cardiac hypertrophy. In conclusion, the present study revealed that BRD2 could facilitate cardiac hypertrophy through upregulating TCA cycle genes. Strategies targeting inhibition of BRD2 might suggest therapeutic potential for pathological cardiac hypertrophy and heart failure.

Biosensor-based profiling to track cellular signalling in patient-derived models of dilated cardiomyopathy

Dilated cardiomyopathies (DCM) represent a diverse group of cardiovascular diseases impacting the structure and function of the myocardium. To better treat these diseases, we need to understand the impact of such cardiomyopathies on critical signalling pathways that drive disease progression downstream of receptors we often target therapeutically. Our understanding of cellular signalling events has progressed substantially in the last few years, in large part due to the design, validation and use of biosensor-based approaches to studying such events in cells, tissues and in some cases, living animals. Another transformative development has been the use of human induced pluripotent stem cells (hiPSCs) to generate disease-relevant models from individual patients. We highlight the importance of going beyond monocellular cultures to incorporate the influence of paracrine signalling mediators. Finally, we discuss the recent coalition of these approaches in the context of DCM. We discuss recent work in generating patient-derived models of cardiomyopathies and the utility of using signalling biosensors to track disease progression and test potential therapeutic strategies that can be later used to inform treatment options in patients.

A role for BET proteins in regulating basal, dopamine-induced and cAMP/PKA-dependent transcription in rat striatal neurons

The activity of striatal medium-spiny projection neurons is regulated by D1 and D2 dopamine receptors. The D1 receptor (D1R) is a Gα_s/olf-coupled GPCR which activates a cAMP/PKA/DARPP-32 signalling cascade that increases excitability and facilitates plasticity, partly through the regulation of transcription. Upon activation via D1R, PKA can translocate to the nucleus to regulate transcription through the phosphorylation of various targets. One candidate effector of PKA-dependent transcriptional regulation is the BET protein Brd4. It is known that when Brd4 is activated by phosphorylation, it binds more readily to acetylated histones at promoters and enhancers; moreover, in non-neuronal cells, PKA signalling has been shown to increase recruitment of Brd4 to chromatin. However, it is unknown whether BET proteins, or Brd4 specifically, are involved in transcriptional activation by cAMP/PKA in neurons. Here, we demonstrate that in adult rats, inhibition of BET proteins with the bromodomain inhibitor JQ1 suppressed the expression of ~25% of D1R-upregulated genes, while also increasing the expression of a subset of immediate-early genes. We further found that cAMP/PKA signalling promotes Brd4 recruitment to dopamine-induced genes in striatal neurons, and that knockdown of Brd4 attenuates D1R-induced gene expression. Finally, we report that JQ1 treatment downregulated expression of many GPCRs and also impaired ERK1/2 signalling in striatal neurons. Our findings identify the BET protein family, and Brd4 in particular, as novel regulators of basal and D1R-dependent transcription in rat striatal neurons, and delineate complex bi-directional effects of bromodomain inhibitors on neuronal transcription.

Measuring hypertrophy in neonatal rat primary cardiomyocytes and human iPSC-derived cardiomyocytes

In the heart, left ventricular hypertrophy is initially an adaptive mechanism that increases wall thickness to preserve normal cardiac output and function in the face of coronary artery disease or hypertension. Cardiac hypertrophy develops in response to pressure and volume overload but can also be seen in inherited cardiomyopathies. As the wall thickens, it becomes stiffer impairing the distribution of oxygenated blood to the rest of the body. With complex cellular signalling and transcriptional networks involved in the establishment of the hypertrophic state, several model systems have been developed to better understand the molecular drivers of disease. Immortalized cardiomyocyte cell lines, primary rodent and larger animal models have all helped understand the pathological mechanisms underlying cardiac hypertrophy. Induced pluripotent stem cell-derived cardiomyocytes are also used and have the additional benefit of providing access to human samples with direct disease relevance as when generated from patients suffering from hypertrophic cardiomyopathies. Here, we briefly review in vitro and in vivo model systems that have been used to model hypertrophy and provide detailed methods to isolate primary neonatal rat cardiomyocytes as well as to generate cardiomyocytes from human iPSCs. We also describe how to model hypertrophy in a "dish" using gene expression analysis and immunofluorescence combined with automated high-content imaging.

The Functions of BET Proteins in Gene Transcription of Biology and Diseases

The BET (bromodomain and extra-terminal domain) family proteins, consisting of BRD2, BRD3, BRD4, and testis-specific BRDT, are widely acknowledged as major transcriptional regulators in biology. They are characterized by two tandem bromodomains (BDs) that bind to lysine-acetylated histones and transcription factors, recruit transcription factors and coactivators to target gene sites, and activate RNA polymerase II machinery for transcriptional elongation. Pharmacological inhibition of BET proteins with BD inhibitors has been shown as a promising therapeutic strategy for the treatment of many human diseases including cancer and inflammatory disorders. The recent advances in bromodomain protein biology have further uncovered the complex and versatile functions of BET proteins in the regulation of gene expression in chromatin. In this review article, we highlight our current understanding of BET proteins' functions in mediating protein-protein interactions required for chromatin-templated gene transcription and splicing, chromatin remodeling, DNA replication, and DNA damage repair. We further discuss context-dependent activator vs. repressor functions of individual BET proteins, isoforms, and bromodomains that may be harnessed for future development of BET bromodomain inhibitors as emerging epigenetic therapies for cancer and inflammatory disorders.

CDK9 keeps RNA polymerase II on track

Cyclin-dependent kinase 9 (CDK9), the kinase component of positive transcription elongation factor b (P-TEFb), is essential for transcription of most protein-coding genes by RNA polymerase II (RNAPII). By releasing promoter-proximally paused RNAPII into gene bodies, CDK9 controls the entry of RNAPII into productive elongation and is, therefore, critical for efficient synthesis of full-length messenger (m)RNAs. In recent years, new players involved in P-TEFb-dependent processes have been identified and an important function of CDK9 in coordinating elongation with transcription initiation and termination has been unveiled. As the regulatory functions of CDK9 in gene expression continue to expand, a number of human pathologies, including cancers, have been associated with aberrant CDK9 activity, underscoring the need to properly regulate CDK9. Here, I provide an overview of CDK9 function and regulation, with an emphasis on CDK9 dysregulation in human diseases.

Ubiquitin-protein ligase Ubr5 cooperates with hedgehog signalling to promote skeletal tissue homeostasis

Mammalian Hedgehog (HH) signalling pathway plays an essential role in tissue homeostasis and its deregulation is linked to rheumatological disorders. UBR5 is the mammalian homologue of the E3 ubiquitin-protein ligase Hyd, a negative regulator of the Hh-pathway in Drosophila. To investigate a possible role of UBR5 in regulation of the musculoskeletal system through modulation of mammalian HH signaling, we created a mouse model for specific loss of Ubr5 function in limb bud mesenchyme. Our findings revealed a role for UBR5 in maintaining cartilage homeostasis and suppressing metaplasia. Ubr5 loss of function resulted in progressive and dramatic articular cartilage degradation, enlarged, abnormally shaped sesamoid bones and extensive heterotopic tissue metaplasia linked to calcification of tendons and ossification of synovium. Genetic suppression of smoothened (Smo), a key mediator of HH signalling, dramatically enhanced the Ubr5 mutant phenotype. Analysis of HH signalling in both mouse and cell model systems revealed that loss of Ubr5 stimulated canonical HH-signalling while also increasing PKA activity. In addition, human osteoarthritic samples revealed similar correlations between UBR5 expression, canonical HH signalling and PKA activity markers. Our studies identified a crucial function for the Ubr5 gene in the maintenance of skeletal tissue homeostasis and an unexpected mode of regulation of the HH signalling pathway.

LINC01094 Down-Regulates miR-330-3p and Enhances the Expression of MSI1 to Promote the Progression of Glioma

Background

This study aims at probing into the expression, function, and mechanism of LINC01094 and miR-330-3p in glioma.

Materials and Methods

qRT-PCR was employed to examine LINC01094 and miR-330-3p expressions in gliomas. After gain-of-function and loss-of-function models were constructed, CCK-8 and Transwell assays were used to detect the proliferation, migration and invasion of LN229 and U251 cells, respectively. Additionally, dual luciferase reporter gene assay was utilized to verify the binding site between m4iR-330-3p and LINC01094, miR-330-3p, and the 3ʹUTR of musashi RNA binding protein 1 (MSI1). Then, RNA pull-down, RIP, qRT-PCR and Western blot were employed to detect the regulatory relationships among LINC01094, miR-330-3p, and MSI1.

Results

The expression of LINC01094 was elevated in glioma tissues and cell lines, and the high expression of LINC01094 was associated with high grade of glioma. In contrast, miR-330-3p was lowly expressed in glioma tissue. Overexpression of LINC01094 or down-regulation of miR-330-3p promoted the proliferation, migration, and invasion of glioma cells, while LINC01094 knockdown or miR-330-3p up-regulation impeded these processes. miR-330-3p was identified as a target miRNA of LINC01094, and it could be negatively regulated by LINC01094. In addition, miR-330-3p antagonized the function of LINC01094 by negatively regulating MSI1.

Conclusion

LINC01094 promotes the proliferation, migration, and invasion of glioma cells by adsorbing miR-330-3p and up-regulating the expression of MSI1.