The epigenetic enzyme DOT1L orchestrates vascular smooth muscle cell-monocyte crosstalk and protects against atherosclerosis via the NF-κB pathway.

AIMS: Histone H3 dimethylation at lysine 79 is a key epigenetic mark uniquely induced by methyltransferase disruptor of telomeric silencing 1-like (DOT1L). We aimed to determine whether DOT1L modulates vascular smooth muscle cell (VSMC) phenotype and how it might affect atherosclerosis in vitro and in vivo, unravelling the related mechanism. METHODS AND RESULTS: Gene expression screening of VSMCs stimulated with the BB isoform of platelet-derived growth factor led us to identify Dot1l as an early up-regulated epigenetic factor. Mouse and human atherosclerotic lesions were assessed for Dot1l expression, which resulted specifically localized in the VSMC compartment. The relevance of Dot1l to atherosclerosis pathogenesis was assessed through deletion of its gene in the VSMCs via an inducible, tissue-specific knock-out mouse model crossed with the ApoE-/- high-fat diet model of atherosclerosis. We found that the inactivation of Dot1l significantly reduced the progression of the disease. By combining RNA- and H3K79me2-chromatin immunoprecipitation-sequencing, we found that DOT1L and its induced H3K79me2 mark directly regulate the transcription of Nf-κB-1 and -2, master modulators of inflammation, which in turn induce the expression of CCL5 and CXCL10, cytokines fundamentally involved in atherosclerosis development. Finally, a correlation between coronary artery disease and genetic variations in the DOT1L gene was found because specific polymorphisms are associated with increased mRNA expression. CONCLUSION: DOT1L plays a key role in the epigenetic control of VSMC gene expression, leading to atherosclerosis development. Results identify DOT1L as a potential therapeutic target for vascular diseases.

miR-128-3p Is a Novel Regulator of Vascular Smooth Muscle Cell Phenotypic Switch and Vascular Diseases.

RATIONALE: MicroRNAs (miRNAs, miRs) are small noncoding RNAs that modulate gene expression by negatively regulating translation of target genes. Although the role of several miRNAs in vascular smooth muscle cells (VSMCs) has been extensively characterized, the function of miRNA-128-3p (miR-128) is still unknown. OBJECTIVE: To determine if miR-128 modulates VSMC phenotype and to define the underlying mechanisms. METHODS AND RESULTS: We screened for miRNAs whose expression is modulated by an altered DNA methylation status in VSMCs, and among the hits, we selected miR-128. We found that miR-128 was expressed in various tissues, primary murine cells, and pathological murine and human vascular specimens. Through gain- and loss-of-function approaches, we determined that miR-128 affects VSMC proliferation, migration, differentiation, and contractility. The alterations of those properties were dependent upon epigenetic regulation of key VSMC differentiation genes; notably, Kruppel-like factor 4 was found to be a direct target of miR-128 and able to modulate the methylation status of the pivotal VSMC gene myosin heavy chain 11 (Myh11). Finally, in vivo lentiviral delivery of miR-128 prevented intimal hyperplasia in a mouse model of carotid restenosis without modifying vital cardiovascular parameters. CONCLUSION: miR-128 is a critical modulator of VSMCs and is regulated by epigenetic modifications upon stress. Its modulation in the context of disease could be exploited for therapeutic purposes.

Circ_Lrp6, a Circular RNA Enriched in Vascular Smooth Muscle Cells, Acts as a Sponge Regulating miRNA-145 Function.

RATIONALE: microRNAs (miRNAs) modulate gene expression by repressing translation of targeted genes. Previous work has established a role for miRNAs in regulating vascular smooth muscle cell (VSMC) activity. Whether circular RNAs are involved in the modulation of miRNA activity in VSMCs is unknown. OBJECTIVE: We aimed to identify circular RNAs interacting with miRNAs enriched in VSMCs and modulating the cells' activity. METHODS AND RESULTS: RNA sequencing and bioinformatics identified several circular RNAs enriched in VSMCs; however, only one, possessing multiple putative binding sites for miR-145, was highly conserved between mouse and man. This circular RNA gemmed from alternative splicing of Lrp6 (lipoprotein receptor 6), a gene highly expressed in vessels and implicated in vascular pathologies and was thus named circ_Lrp6. Its role as a miR-145 sponge was confirmed by determining reciprocal interaction through RNA immunoprecipitation, stimulated emission depletion microscopy, and competitive luciferase assays; functional inhibition of miR-145 was assessed by measuring expression of the target genes ITGß8 (integrin-ß8), FASCIN (fascin actin-bundling protein 1), KLF4 (Kruppel-like factor 4), Yes1 (YES proto-oncogene 1), and Lox (lysyl oxidase). The interaction was preferentially localized to P-bodies, sites of mRNA degradation. Using loss- and gain-of-function approaches, we found that circ_Lrp6 hindered miR-145-mediated regulation of VSMC migration, proliferation, and differentiation. Differential expression of miR-145 and circ_Lrp6 in murine and human vascular diseases suggests that the ratio of circ_Lrp6 bound to miR-145 versus unbound could play a role in vascular pathogenesis. Viral delivery of circ_Lrp6 shRNA prevented intimal hyperplasia in mouse carotids. CONCLUSIONS: circ_Lrp6 is an intracellular modulator and a natural sponge for miR-145, counterbalancing the functions of the miRNA in VSMCs.

Epigenetics and vascular diseases.

Cardiovascular disease remains the number one cause of death and disability worldwide despite significant improvements in diagnosis, prevention, and early intervention efforts. There is an urgent need for improved understanding of cardiovascular processes responsible for disease development in order to develop more effective therapeutic strategies. Recent knowledge gleaned from the study of epigenetic mechanisms in the vasculature has uncovered new potential targets for intervention. Herein, we provide an overview of epigenetic mechanism, and review recent findings related to epigenetics in vascular diseases, highlighting classical epigenetic mechanism such as DNA methylation and histone modification as well as the newly discovered non-coding RNA mechanisms.

Ferritin, cellular iron storage and regulation.

Ferritin is considered the major iron storage protein which maintains a large iron core in its cavity and has ferroxidase activity. There are many types of ferritin particularly in prokaryotes that include the canonical 24-mer FTN molecules, the heme-containing BFR, the smaller 12-mer DPS and the newly recognized EncFtn of encapsulin that forms a very large iron storage compartment. Recent studies show that ferritin function is more dynamic than previous depicted and new mechanisms of ferritin iron recycling are emerging. They participate to the regulation of cellular iron homeostasis as those of ferritin biosynthesis, cooperating also with the iron-dependent mechanism of cellular iron secretion. Some of these basic processes are in common between unicellular and animal cells, and this review aims at discussing the findings on the connections between iron storage, cellular iron regulation and ferritin iron recycling that have been explored in unicellular organisms and in animals. © 2017 IUBMB Life, 69(6):414-422, 2017.

TGFß Triggers miR-143/145 Transfer From Smooth Muscle Cells to Endothelial Cells, Thereby Modulating Vessel Stabilization.

RATIONALE: The miR-143/145 cluster is highly expressed in smooth muscle cells (SMCs), where it regulates phenotypic switch and vascular homeostasis. Whether it plays a role in neighboring endothelial cells (ECs) is still unknown. OBJECTIVE: To determine whether SMCs control EC functions through passage of miR-143 and miR-145. METHODS AND RESULTS: We used cocultures of SMCs and ECs under different conditions, as well as intact vessels to assess the transfer of miR-143 and miR-145 from one cell type to another. Imaging of cocultured cells transduced with fluorescent miRNAs suggested that miRNA transfer involves membrane protrusions known as tunneling nanotubes. Furthermore, we show that miRNA passage is modulated by the transforming growth factor (TGF) ß pathway because both a specific transforming growth factor-ß (TGFß) inhibitor (SB431542) and an shRNA against TGFßRII suppressed the passage of miR-143/145 from SMCs to ECs. Moreover, miR-143 and miR-145 modulated angiogenesis by reducing the proliferation index of ECs and their capacity to form vessel-like structures when cultured on matrigel. We also identified hexokinase II (HKII) and integrin ß 8 (ITGß8)-2 genes essential for the angiogenic potential of ECs-as targets of miR-143 and miR-145, respectively. The inhibition of these genes modulated EC phenotype, similarly to miR-143 and miR-145 overexpression in ECs. These findings were confirmed by ex vivo and in vivo approaches, in which it was shown that TGFß and vessel stress, respectively, triggered miR-143/145 transfer from SMCs to ECs. CONCLUSIONS: Our results demonstrate that miR-143 and miR-145 act as communication molecules between SMCs and ECs to modulate the angiogenic and vessel stabilization properties of ECs.

MicroRNA-133 modulates the ß1-adrenergic receptor transduction cascade.

RATIONALE: The sympathetic nervous system plays a fundamental role in the regulation of myocardial function. During chronic pressure overload, overactivation of the sympathetic nervous system induces the release of catecholamines, which activate ß-adrenergic receptors in cardiomyocytes and lead to increased heart rate and cardiac contractility. However, chronic stimulation of ß-adrenergic receptors leads to impaired cardiac function, and ß-blockers are widely used as therapeutic agents for the treatment of cardiac disease. MicroRNA-133 (miR-133) is highly expressed in the myocardium and is involved in controlling cardiac function through regulation of messenger RNA translation/stability. OBJECTIVE: To determine whether miR-133 affects ß-adrenergic receptor signaling during progression to heart failure. METHODS AND RESULTS: Based on bioinformatic analysis, ß1-adrenergic receptor (ß1AR) and other components of the ß1AR signal transduction cascade, including adenylate cyclase VI and the catalytic subunit of the cAMP-dependent protein kinase A, were predicted as direct targets of miR-133 and subsequently validated by experimental studies. Consistently, cAMP accumulation and activation of downstream targets were repressed by miR-133 overexpression in both neonatal and adult cardiomyocytes following selective ß1AR stimulation. Furthermore, gain-of-function and loss-of-function studies of miR-133 revealed its role in counteracting the deleterious apoptotic effects caused by chronic ß1AR stimulation. This was confirmed in vivo using a novel cardiac-specific TetON-miR-133 inducible transgenic mouse model. When subjected to transaortic constriction, TetON-miR-133 inducible transgenic mice maintained cardiac performance and showed attenuated apoptosis and reduced fibrosis compared with control mice. CONCLUSIONS: miR-133 controls multiple components of the ß1AR transduction cascade and is cardioprotective during heart failure.

RNA (Epi)genetics in cardiovascular diseases.

Next-generation sequencing has greatly improved our knowledge of the mammalian transcriptome, identifying thousands of non-coding RNAs (ncRNAs), which are RNAs that rather than translate for proteins, have regulatory functions. Perhaps unsurprisingly, dysregulation of individual ncRNAs has been associated with the development of pathologies, including of the cardiovascular system. The best-characterized group of ncRNAs is represented by the short, highly conserved RNAs named microRNAs (miRNAs). This ncRNA species, which principally exerts an inhibitory action on gene expression, has been implicated in many cardiovascular diseases. Unfortunately, the complexity of action of other types of ncRNA, such as long ncRNAs, has somewhat hampered the study of their role in cardiovascular pathologies. A detailed characterization of the mechanism of action of these different ncRNA species would be conducive to a better understanding of the cellular processes underlying cardiovascular disease and may lead to the development of innovative therapeutic strategies. Here, we give an overview of the current knowledge on the function of ncRNAs and their roles in cardiovascular disease development, concentrating mainly on microRNAs and long ncRNAs.

MicroRNA-133 controls cardiac hypertrophy.

Growing evidence indicates that microRNAs (miRNAs or miRs) are involved in basic cell functions and oncogenesis. Here we report that miR-133 has a critical role in determining cardiomyocyte hypertrophy. We observed decreased expression of both miR-133 and miR-1, which belong to the same transcriptional unit, in mouse and human models of cardiac hypertrophy. In vitro overexpression of miR-133 or miR-1 inhibited cardiac hypertrophy. In contrast, suppression of miR-133 by 'decoy' sequences induced hypertrophy, which was more pronounced than that after stimulation with conventional inducers of hypertrophy. In vivo inhibition of miR-133 by a single infusion of an antagomir caused marked and sustained cardiac hypertrophy. We identified specific targets of miR-133: RhoA, a GDP-GTP exchange protein regulating cardiac hypertrophy; Cdc42, a signal transduction kinase implicated in hypertrophy; and Nelf-A/WHSC2, a nuclear factor involved in cardiogenesis. Our data show that miR-133, and possibly miR-1, are key regulators of cardiac hypertrophy, suggesting their therapeutic application in heart disease.

Vascular malformation rupture in a patient affected by Costello syndrome.

Costello syndrome (CS) is a rare genetic syndrome affecting multiple organs, generally caused by mutations of the HRAS gene, belonging to the RAS/MAPK genes family.A male patient with CS developed a painful pulsatile mass on the lateral side of the wrist. An initial ultrasonographic investigation confirmed the presence of a radial artery lesion, possibly an arterial aneurysm. On surgical resection, histological evaluation showed a tangle of vascular structures with variable calibre and abnormal wall histology. Immunohistochemical stainings revealed a very poor endothelial contribution to the central vascular wall structure. These histological observations led us to conclude we had managed an acute vascular malformation (VM) rupture, rather than a common arterial aneurysmal condition. Considering the molecular mechanisms regulated by RAS/MAPK genes, CS patients might have a higher risk of developing VMs and, in the presence of a pulsatile mass with acute onset, VM rupture should be considered.

Aggravation of pulmonary fibrosis after knocking down the aryl hydrocarbon receptor in the insulin-like growth factor 1 receptor pathway.

BACKGROUND AND PURPOSE: Idiopathic pulmonary fibrosis is a devastating disease with multiple contributing factors. Insulin-like growth factor 1 receptor (IGF1R), with a reciprocal function to aryl hydrocarbon receptor (AhR), is involved in airway inflammation. The exact relationship between IGF1R and AhR in lung fibrogenesis is unclear. This study aimed to investigate the cascade pathway involving IGF1R and AhR in idiopathic pulmonary fibrosis. EXPERIMENTAL APPROACH: The AhR and IGF1R expressions were determined in the lungs of idiopathic pulmonary fibrosis patients and in a rodent fibrosis model. Pulmonary fibrosis was evaluated in bleomycin (BLM)-induced lung injury in wild type and AhR knockout (Ahr-/- ) mice. The effects of IGF1R inhibition and AhR activation in vitro on TGF-ß1-induced epithelial-mesenchymal transition (EMT) in Beas2B cells and in vivo on BLM-exposed mice were also examined. KEY RESULTS: There were increased IGF1R levels but AhR expression decreased in the lung of idiopathic pulmonary fibrosis patients and BLM-induced mice. Knockout of AhR aggravated lung fibrosis, while the use of IGF1R inhibitor and AhR agonist significantly attenuated such effects and inhibited TGF-ß1-induced epithelial-mesenchymal transition in Beas2B cells. Both TGF-ß1 and BLM markedly suppressed AhR expression through endoplasmic reticulum stress and consequently, IGF1R activation. The IGF1R inhibitor and specific knockdown of IGF1R reversed the activation of the TGF-ß1 signal pathway. CONCLUSION AND IMPLICATIONS: In the development of idiopathic pulmonary fibrosis, AhR and IGF1R play opposite roles via the TGF-ß/Smad/STAT signalling cascade. The AhR/IGF1R axis is a potential target for the treatment of lung injury and fibrosis.

miR-9-5p is involved in the rescue of stress-dependent dendritic shortening of hippocampal pyramidal neurons induced by acute antidepressant treatment with ketamine.

Converging clinical and preclinical evidence demonstrates that depressive phenotypes are associated with synaptic dysfunction and dendritic simplification in cortico-limbic glutamatergic areas. On the other hand, the rapid antidepressant effect of acute ketamine is consistently reported to occur together with the rescue of dendritic atrophy and reduction of spine number induced by chronic stress in the hippocampus and prefrontal cortex of animal models of depression. Nevertheless, the molecular mechanisms underlying these morphological alterations remain largely unknown. Here, we found that miR-9-5p levels were selectively reduced in the hippocampus of rats vulnerable to Chronic Mild Stress (CMS), while acute subanesthetic ketamine restored its levels to basal condition in just 24h; miR-9-5p expression inversely correlated with the anhedonic phenotype. A decrease of miR-9-5p was reproduced in an in vitro model of stress, based on primary hippocampal neurons incubated with the stress hormone corticosterone. In both CMS animals and primary neurons, decreased miR-9-5p levels were associated with dendritic simplification, while treatment with ketamine completely rescued the changes. In vitro modulation of miR-9-5p expression showed a direct role of miR-9-5p in regulating dendritic length and spine density in mature primary hippocampal neurons. Among the putative target genes tested, Rest and Sirt1 were validated as biological targets in primary neuronal cultures. Moreover, in line with miR-9-5p changes, REST protein expression levels were remarkably increased in both CMS vulnerable animals and corticosterone-treated neurons, while ketamine completely abolished this alteration. Finally, the shortening of dendritic length in corticosterone-treated neurons was shown to be partly rescued by miR-9-5p overexpression and dependent on REST protein expression. Overall, our data unveiled the functional role of miR-9-5p in the remodeling of dendritic arbor induced by stress/corticosterone in vulnerable animals and its rescue by acute antidepressant treatment with ketamine.

rs41291957 controls miR-143 and miR-145 expression and impacts coronary artery disease risk.

The role of single nucleotide polymorphisms (SNPs) in the etiopathogenesis of cardiovascular diseases is well known. The effect of SNPs on disease predisposition has been established not only for protein coding genes but also for genes encoding microRNAs (miRNAs). The miR-143/145 cluster is smooth muscle cell-specific and implicated in the pathogenesis of atherosclerosis. Whether SNPs within the genomic sequence of the miR-143/145 cluster are involved in cardiovascular disease development is not known. We thus searched annotated sequence databases for possible SNPs associated with miR-143/145. We identified one SNP, rs41291957 (G > A), located -91 bp from the mature miR-143 sequence, as the nearest genetic variation to this miRNA cluster, with a minor allele frequency > 10%. In silico and in vitro approaches determined that rs41291957 (A) upregulates miR-143 and miR-145, modulating phenotypic switching of vascular smooth cells towards a differentiated/contractile phenotype. Finally, we analysed association between rs41291957 and CAD in two cohorts of patients, finding that the SNP was a protective factor. In conclusion, our study links a genetic variation to a pathological outcome through involvement of miRNAs.

Reciprocal regulation of microRNA-1 and insulin-like growth factor-1 signal transduction cascade in cardiac and skeletal muscle in physiological and pathological conditions.

BACKGROUND: MicroRNAs (miRNAs/miRs) are small conserved RNA molecules of 22 nucleotides that negatively modulate gene expression primarily through base paring to the 3' untranslated region of target messenger RNAs. The muscle-specific miR-1 has been implicated in cardiac hypertrophy, heart development, cardiac stem cell differentiation, and arrhythmias through targeting of regulatory proteins. In this study, we investigated the molecular mechanisms through which miR-1 intervenes in regulation of muscle cell growth and differentiation. METHODS AND RESULTS: On the basis of bioinformatics tools, biochemical assays, and in vivo models, we demonstrate that (1) insulin-like growth factor-1 (IGF-1) and IGF-1 receptor are targets of miR-1; (2) miR-1 and IGF-1 protein levels are correlated inversely in models of cardiac hypertrophy and failure as well as in the C2C12 skeletal muscle cell model of differentiation; (3) the activation state of the IGF-1 signal transduction cascade reciprocally regulates miR-1 expression through the Foxo3a transcription factor; and (4) miR-1 expression correlates inversely with cardiac mass and thickness in myocardial biopsies of acromegalic patients, in which IGF-1 is overproduced after aberrant synthesis of growth hormone. CONCLUSIONS: Our results reveal a critical role of miR-1 in mediating the effects of the IGF-1 pathway and demonstrate a feedback loop between miR-1 expression and the IGF-1 signal transduction cascade.

The involvement of epigenetics in vascular disease development.

Cardiovascular diseases are a major cause of death and disability. Despite enormous progress in diagnosis, prevention, and treatment over the years, the incidence of this group of pathologies continues to increase worldwide. An important step in reversing this situation is filling in the gaps we have in our understanding of cardiovascular homeostasis and of the pathogenic processes leading to disease. On this point, the discovery of epigenetics - heritable chemical modifications of DNA bases and histone proteins, as well as non-coding RNA-based mechanisms regulating gene expression - has opened up new vistas. Here, we will review recent findings regarding the epigenetics of three main vascular diseases (atherosclerosis, restenosis, and aortic aneurysm), with a focus on DNA methylation and histone modification. The emerging fundamental nature of epigenetics for cardiovascular physiopathology and, importantly, the amenability to manipulation with pharmacological techniques are an indication that epigenetics-based prognostic and therapeutics procedures might be developed in the future.

Heart failure: targeting transcriptional and post-transcriptional control mechanisms of hypertrophy for treatment.

Heart failure (HF) is a syndrome caused by diminished heart function that arises from pathologies like hypertension, infarction, and diabetes. Neurohormonal, cardiorenal and cardiocirculatory models have been developed to explain HF but they have not provided sufficient understanding for the elaboration of therapies to conquer the syndrome. In fact, even though progress has been made in improving survival, HF remains a frequent cause of hospitalization and death. Since in most forms of HF, development of the disorder is associated with an alteration of cardiomyocyte structure, perceived as an increase in heart mass due to cell hypertrophy, effort is being directed to address hypertrophy as a therapeutic target. Here, we outline recent understanding of two gene-silencing regulatory mechanisms underlying cardiomyocyte hypertrophy, i.e., transcriptional control by HDACs, and post-transcriptional control by microRNAs.

UHRF1 epigenetically orchestrates smooth muscle cell plasticity in arterial disease.

Adult vascular smooth muscle cells (VSMCs) dedifferentiate in response to extracellular cues such as vascular damage and inflammation. Dedifferentiated VSMCs are proliferative, migratory, less contractile, and can contribute to vascular repair as well as to cardiovascular pathologies such as intimal hyperplasia/restenosis in coronary artery and arterial aneurysm. We here demonstrate the role of ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) as an epigenetic master regulator of VSMC plasticity. UHRF1 expression correlated with the development of vascular pathologies associated with modulation of noncoding RNAs, such as microRNAs. miR-145 - pivotal in regulating VSMC plasticity, which is reduced in vascular diseases - was found to control Uhrf1 mRNA translation. In turn, UHRF1 triggered VSMC proliferation, directly repressing promoters of cell-cycle inhibitor genes (including p21 and p27) and key prodifferentiation genes via the methylation of DNA and histones. Local vascular viral delivery of Uhrf1 shRNAs or Uhrf1 VSMC-specific deletion prevented intimal hyperplasia in mouse carotid artery and decreased vessel damage in a mouse model of aortic aneurysm. Our study demonstrates the fundamental role of Uhrf1 in regulating VSMC phenotype by promoting proliferation and dedifferentiation. UHRF1 targeting may hold therapeutic potential in vascular pathologies.

Epigenetics and Vascular Diseases: Influence of Non-coding RNAs and Their Clinical Implications.

Epigenetics refers to heritable mechanisms able to modulate gene expression that do not involve alteration of the genomic DNA sequence. Classically, mechanisms such as DNA methylation and histone modifications were part of this classification. Today, this field of study has been expanded and includes also the large class of non-coding RNAs (ncRNAs). Indeed, with the extraordinary possibilities introduced by the next-generation sequencing approaches, our knowledge of the mammalian transcriptome has greatly improved. Today, we have identifying thousands of ncRNAs, and unsurprisingly, a direct association between ncRNA dysregulation and development of cardiovascular pathologies has been identified. This class of gene modulators is further divided into short-ncRNAs and long-non-coding RNAs (lncRNAs). Among the short-ncRNA sub-group, the best-characterized players are represented by highly conserved RNAs named microRNAs (miRNAs). miRNAs principally inhibit gene expression, and their involvement in cardiovascular diseases has been largely studied. On the other hand, due to the different roles played by lncRNAs, their involvement in cardiovascular pathology development is still limited, and further studies are needed. For instance, in order to define their roles in the cellular processes associated with the development of diseases, we need to better characterize the details of their mechanisms of action; only then might we be able to develop innovative therapeutic strategies. In this review, we would like to give an overview of the current knowledge on the function of ncRNAs and their involvement in the development of vascular diseases.

MicroRNA-26a/cyclin-dependent kinase 5 axis controls proliferation, apoptosis and in vivo tumor growth of diffuse large B-cell lymphoma cell lines.

Diffuse large B-cell lymphoma (DLBCL) is the most frequent type of non-Hodgkin lymphoma. Despite a favorable therapeutic response to first-line chemo-immunotherapy, still 30-40% of patients is refractory, or relapse after this treatment. Thus, alternative strategies must be sought. Previous studies have indicated that cyclin-dependent kinase 5 (CDK5), a serine/threonine protein kinase, is involved in tumor development and progression, and it may represent a potential therapeutic target. However, its role in modulating DLBCL growth and progression remains largely unexplored. In this study, we show that CDK5 and its activator, cyclin-dependent kinase 5 activator 1 (CDK5R1 or p35), are overexpressed in DLBCL cell lines and that signal transducer and activator of transcription 3 (STAT3) phosphorylation and activity is dependent on CDK5 expression in DLBCL. Using public data sets, we also demonstrate that patients with DLBCL show a higher expression of CDK5 compared with healthy individuals. By using loss-of-function approaches, we demonstrate that CDK5's activity regulates proliferation and survival of DLBCL cells. MicroRNAs (miRNAs or miRs) are small noncoding RNAs that negatively regulating gene expression and are involved in cancer initiation and progression. We identify miR-26a as direct regulator of p35 expression and CDK5 activity. We show that miR-26a expression is lower in DLBCL cell lines compared to B lymphocytes and that its ectopic expression leads to a drastic reduction of DLBCL tumor growth in vivo and decreased proliferation, cell-cycle progression, and survival in vitro. Remarkably, concomitant overexpression of a 3'-UTR-truncated form of p35 promoted tumor growth in vivo and cell proliferation, cell-cycle progression, and cell survival in vitro. In conclusion, these results demonstrate an important role for miR-26a and CDK5 together in the survival and growth of DLBCL cells, suggesting the existence of potential novel therapeutic targets for the treatment of DLBCL.