Cdk9/Cyclin T1 complex: A key player during the activation/differentiation process of normal lymphoid B cells

Cyclin-Dependent kinase 9 (CDK9) inhibitor Atuveciclib ameliorates Imiquimod-Induced Psoriasis-Like dermatitis in mice by inhibiting various inflammation factors via STAT3 signaling pathway

Psoriasis is a chronic, autoimmune skin disease characterized by the deregulated secretion of inflammatory factors in multiple organs. The aberrant activation of signal transducer and activator of transcription 3 (STAT3) signaling pathway mediated by cyclin-dependent kinase 9 (CDK9) is vital for the pathology of psoriasis, leading to the accumulation of inflammatory factors and the progression of skin damage. In this study, we explored the effect of CDK9 inhibition on attenuating the secretion of inflammatory factors and alleviating skin damage in psoriasis models both in vitro and in vivo. Results showed that Atuveciclib, a highly selective CDK9 inhibitor, significantly relieved skin lesions in Imiquimod (IMQ)-induced mice models by lowering the expression of CDK9 and p-RNA Pol II Ser2. Meanwhile, Atuveciclib significantly inhibited STAT3 phosphorylation in mice skin and reduced the levels of key inflammatory cytokines in mice skin, plasma and spleen. In addition to suppressing the secretion of inflammatory cytokines, Atuveciclib ablated the activation of STAT3 induced by tumor necrosis factor-α (TNF-α)/interferon-γ (IFN-γ). Overall, our findings indicated that the overexpression and hyperfunction of CDK9 promote the progression of psoriasis. Moreover, Atuveciclib interfered with the abnormal STAT3 signaling pathway through the inhibition of CDK9, which ultimately ameliorated psoriatic-like skin inflammation. These suggested that CDK9 inhibition is a potential strategy for batting psoriasis.

Lymphoma in Border Collies: Genome-Wide Association and Pedigree Analysis

There has been considerable interest in studying cancer in dogs and its potential as a model system for humans. One area of research has been the search for genetic risk variants in canine lymphoma, which is amongst the most common canine cancers. Previous studies have focused on a limited number of breeds, but none have included Border Collies. The aims of this study were to identify relationships between Border Collie lymphoma cases through an extensive pedigree investigation and to utilise relationship information to conduct genome-wide association study (GWAS) analyses to identify risk regions associated with lymphoma. The expanded pedigree analysis included 83,000 Border Collies, with 71 identified lymphoma cases. The analysis identified affected close relatives, and a common ancestor was identified for 54 cases. For the genomic study, a GWAS was designed to incorporate lymphoma cases, putative "carriers", and controls. A case-control GWAS was also conducted as a comparison. Both analyses showed significant SNPs in regions on chromosomes 18 and 27. Putative top candidate genes from these regions included DLA-79, WNT10B, LMBR1L, KMT2D, and CCNT1.

Oncogenic dysregulation of pre-mRNA processing by protein kinases: challenges and therapeutic opportunities

Alternative splicing and polyadenylation represent two major steps in pre-mRNA-processing, which ensure proper gene expression and diversification of human transcriptomes. Deregulation of these processes contributes to oncogenic programmes involved in the onset, progression and evolution of human cancers, which often result in the acquisition of resistance to existing therapies. On the other hand, cancer cells frequently increase their transcriptional rate and develop a transcriptional addiction, which imposes a high stress on the pre-mRNA-processing machinery and establishes a therapeutically exploitable vulnerability. A prominent role in fine-tuning pre-mRNA-processing mechanisms is played by three main families of protein kinases: serine arginine protein kinase (SRPK), CDC-like kinase (CLK) and cyclin-dependent kinase (CDK). These kinases phosphorylate the RNA polymerase, splicing factors and regulatory proteins involved in cleavage and polyadenylation of the nascent transcripts. The activity of SRPKs, CLKs and CDKs can be altered in cancer cells, and their inhibition was shown to exert anticancer effects. In this review, we describe key findings that have been reported on these topics and discuss challenges and opportunities of developing therapeutic approaches targeting splicing factor kinases.

Cellular and Molecular Mechanisms of R/S-Roscovitine and CDKs Related Inhibition under Both Focal and Global Cerebral Ischemia: A Focus on Neurovascular Unit and Immune Cells

Ischemic stroke is the second leading cause of death worldwide. Following ischemic stroke, Neurovascular Unit (NVU) inflammation and peripheral leucocytes infiltration are major contributors to the extension of brain lesions. For a long time restricted to neurons, the 10 past years have shown the emergence of an increasing number of studies focusing on the role of Cyclin-Dependent Kinases (CDKs) on the other cells of NVU, as well as on the leucocytes. The most widely used CDKs inhibitor, (R)-roscovitine, and its (S) isomer both decreased brain lesions in models of global and focal cerebral ischemia. We previously showed that (S)-roscovitine acted, at least, by modulating NVU response to ischemia. Interestingly, roscovitine was shown to decrease leucocytes-mediated inflammation in several inflammatory models. Specific inhibition of roscovitine majors target CDK 1, 2, 5, 7, and 9 showed that these CDKs played key roles in inflammatory processes of NVU cells and leucocytes after brain lesions, including ischemic stroke. The data summarized here support the investigation of roscovitine as a potential therapeutic agent for the treatment of ischemic stroke, and provide an overview of CDK 1, 2, 5, 7, and 9 functions in brain cells and leucocytes during cerebral ischemia.

CDK9 as an Appealing Target for Therapeutic Interventions

Cyclin Dependent Kinase 9 (CDK9) as a serine/threonine kinase belongs to a great number of CDKs. CDK9 is the main core of PTEF-b complex and phosphorylates RNA polymerase (RNAP) II besides other transcription factors which regulate gene transcription elongation in numerous physiological processes. Multi-functional nature of CDK9 in diverse cellular pathways proposes that it is as an appealing target. In this review, we summarized the recent findings on the molecular interaction of CDK9 with critical participant molecules to modulate their activity in various diseases. Furthermore, the presented review provides a rationale supporting the use of CDK9 as a therapeutic target in clinical developments for crucial diseases; particularly cancers will be reviewed.

Cyclin-dependent kinase 9 expression and its association with CD8+ T cell infiltration in microsatellite-stable colorectal cancer

Programmed death 1 (PD-1)-targeted therapy has benefited patients with microsatellite instability-high metastatic colorectal cancer (mCRC). However, the efficacy of PD-1-targeted therapy is poor in patients with microsatellite-stable (MSS) mCRC. Therefore, it is imperative to explore additional co-inhibitory molecular signalling pathways to improve the efficacy of immunotherapy in MSS mCRC treatment. In the present study, the association between cyclin-dependent kinase 9 (CDK9) expression and the survival of patients with CRC was analysed using RNA sequencing data from 605 patients, including 121 cases of mortality, from human cancer datasets. Furthermore, 35 clinical MSS stage III–IV CRC specimens were collected to assess CDK9 protein expression by immunohistochemistry, and the frequency of tumor-infiltrating CD8⁺ T cells was assessed by flow cytometry. The human cancer datasets demonstrated that upregulation CDK9 significantly shortened the survival of patients with stage II–IV colon cancer. Additionally, CDK9 mRNA expression was positively correlated with the expression levels of genes associated with immune evasion in the tumor. Notably, CDK9 was expression was upregulated in stage IV CRC compared with para-cancerous tissues and early-stage tumors. Interestingly, CDK9 expression was negatively associated with the infiltration of CD8⁺ T cells at the tumor site. In addition, the expression levels of T-cell immunoglobulin mucin family member 3 and CD39, proteins associated with exhaustion, on tumor-infiltrating CD8⁺ T cells were significantly elevated in patients with abnormal CDK9 expression levels. The present study demonstrated that CDK9 expression was negatively associated with CD8⁺ T cell infiltration and positively associated with CD8⁺ T cell exhaustion in MSS mCRC. In conclusion, CDK9 may be utilized to evaluate the prognosis and the immune-type of the tumor microenvironment in patients with MSS mCRC.

The CDK9-cyclin T1 complex mediates saturated fatty acid-induced vascular calcification by inducing expression of the transcription factor CHOP

Vascular calcification (or mineralization) is a common complication of chronic kidney disease (CKD) and is closely associated with increased mortality and morbidity rates. We recently reported that activation of the activating transcription factor 4 (ATF4) pathway through the saturated fatty acid (SFA)-induced endoplasmic reticulum (ER) stress response plays a causative role in CKD-associated vascular calcification. Here, using mouse models of CKD, we 1) studied the contribution of the proapoptotic transcription factor CCAAT enhancer-binding protein homologous protein (CHOP) to CKD-dependent medial calcification, and 2) we identified an additional regulator of ER stress-mediated CHOP expression. Transgenic mice having smooth muscle cell (SMC)-specific CHOP expression developed severe vascular apoptosis and medial calcification under CKD. Screening of a protein kinase inhibitor library identified 16 compounds, including seven cyclin-dependent kinase (CDK) inhibitors, that significantly suppressed CHOP induction during ER stress. Moreover, selective CDK9 inhibitors and CRISPR/Cas9-mediated CDK9 reduction blocked SFA-mediated induction of CHOP expression, whereas inhibitors of other CDK isoforms did not. Cyclin T1 knockout inhibited SFA-mediated induction of CHOP and mineralization, whereas deletion of cyclin T2 and cyclin K promoted CHOP expression levels and mineralization. Of note, the CDK9-cyclin T1 complex directly phosphorylated and activated ATF4. These results demonstrate that the CDK9-cyclin T1 and CDK9-cyclin T2/K complexes have opposing roles in CHOP expression and CKD-induced vascular calcification. They further reveal that the CDK9-cyclin T1 complex mediates vascular calcification through CHOP induction and phosphorylation-mediated ATF4 activation.

CDK9: A key player in cancer and other diseases

Cyclin-Dependent Kinase 9 (CDK9) is part of a functional diverse group of enzymes responsible for cell cycle control and progression. It associates mainly with Cyclin T1 and forms the Positive Transcription Elongation Factor b (p-TEFb) complex responsible for regulation of transcription elongation and mRNA maturation. Recent studies have highlighted the importance of CDK9 in many relevant pathologic processes, like cancer, cardiovascular diseases, and viral replication. Herein we provide an overview of the different pathways in which CDK9 is directly and indirectly involved.

Serum cyclin-dependent kinase 9 is a potential biomarker of atherosclerotic inflammation

Atherosclerotic coronary artery disease (CAD) is one of the most prevalent diseases worldwide. Atherosclerosis was considered to be the single most important contributor to CAD. In this study, a distinct serum protein expression pattern in CAD patients was demonstrated by proteomic analysis with two-dimensional gel electrophoresis coupled with mass spectrometry. In particular, CDK9 was found to be highly elevated in serum, monocytes and artery plaque samples of CAD patients. Furthermore, there was high infiltration of CD14+ monocytes/macrophages within artery plaques correlated with the expression of CDK9. Moreover, Flavopiridol (CDK9 inhibitor) could inhibit THP-1 cell (monocytic acute leukemia cell line) proliferation by targeting CDK9. Altogether, These findings indicate that CDK9 represent an important role for inflammation in the pathogenesis of atherosclerosis. It may be a potential biomarker of atherosclerotic inflammation and offer insights into the pathophysiology and targeted therapy for atherosclerotic CAD.

Inhibition of CDK9 as a therapeutic strategy for inflammatory arthritis

Rheumatoid arthritis is characterised by synovial inflammation and proliferation of fibroblast-like synoviocytes. The induction of apoptosis has long been proposed as a target for proliferative autoimmune diseases, and has further been shown to act as a successful treatment of experimental models of arthritis, such as collagen-induced arthritis. Here we examined the effects of specific oral small-molecule inhibitors of the transcription regulating cyclin-dependent kinase 9 on the development and progression of collagen-induced arthritis. DBA/1 mice were immunised with bovine collagen type II and treated orally with specific CDK9 inhibitors. The effects of CDK9 inhibition on RNA levels and protein expression, apoptosis induction, caspase activation and lymphocyte phenotype were further analysed. Mice showed a significant delay in disease onset and a reduction in disease severity following treatment with CDK9 inhibitors. Inhibiting CDK9 activity in peripheral blood mononuclear cells resulted in the loss of Mcl-1 expression at both the protein and RNA levels, along with a subsequent increase in apoptosis. CDK9 specific inhibitors may be a potential alternative treatment not only of cancer, but also for autoimmune- and inflammatory diseases. Taken together, these results show that transient inhibition of CDK9 induces apoptosis in leukocyte subsets and modulates the immune response.

Deregulations in the cyclin-dependent kinase-9-related pathway in cancer: implications for drug discovery and development

The CDK9-related pathway is an important regulator of mammalian cell biology and is also involved in the replication cycle of several viruses, including the human immunodeficiency virus type 1. CDK9 is present in two isoforms termed CDK9-42 and CDK9-55 that bind noncovalently type T cyclins and cyclin K. This association forms a heterodimer, where CDK9 carries the enzymatic site and the cyclin partner functions as a regulatory subunit. This heterodimer is the main component of the positive transcription elongation factor b, which stabilizes RNA elongation via phosphorylation of the RNA pol II carboxyl terminal domain. Abnormal activities in the CDK9-related pathway were observed in human malignancies and cardiac hypertrophies. Thus, the elucidation of the CDK9 pathway deregulations may provide useful insights into the pathogenesis and progression of human malignancies, cardiac hypertrophy, AIDS and other viral-related maladies. These studies may lead to the improvement of kinase inhibitors for the treatment of the previously mentioned pathological conditions. This review describes the CDK9-related pathway deregulations in malignancies and the development of kinase inhibitors in cancer therapy, which can be classified into three categories: antagonists that block the ATP binding site of the catalytic domain, allosteric inhibitors, and small molecules that disrupt protein-protein interactions.

Cyclin-dependent kinase modulators and cancer therapy

The cell cycle of eukaryotic cells varies greatly from species to species and tissue to tissue. Since an erroneous control of the cell cycle can have disastrous consequences for cellular life, there are genetically programmed signals, so-called cell cycle checkpoints, which ensure that all events of each stage are completed before beginning the next phase. Among the numerous molecules involved in this process, the most important are the cyclin-dependent kinases (CDKs), proteins that are activated only when bound to cyclins (regulatory proteins with fluctuating concentrations). In general, more CDKs are overexpressed in cancer cells than in normal cells, which explains why cancer cells divide uncontrollably. Succeeding in modulating CDK activity with pharmacological agents could result in decreasing the abnormal proliferation rate of cancer cells. This review offers an overview of CDK-cyclin complexes in relation to different cell cycle phases, an analysis of CDK activation and inhibition of molecular mechanisms, and an extensive report, including clinical trials, regarding four new drugs acting as CDK modulators: alvocidib, P276-00, SNS-032 and seliciclib.

Cyclin-dependent kinase modulators and cancer therapy

The cell cycle of eukaryotic cells varies greatly from species to species and tissue to tissue. Since an erroneous control of the cell cycle can have disastrous consequences for cellular life, there are genetically programmed signals, so-called cell cycle checkpoints, which ensure that all events of each stage are completed before beginning the next phase. Among the numerous molecules involved in this process, the most important are the cyclin-dependent kinases (CDKs), proteins that are activated only when bound to cyclins (regulatory proteins with fluctuating concentrations). In general, more CDKs are overexpressed in cancer cells than in normal cells, which explains why cancer cells divide uncontrollably. Succeeding in modulating CDK activity with pharmacological agents could result in decreasing the abnormal proliferation rate of cancer cells. This review offers an overview of CDK-cyclin complexes in relation to different cell cycle phases, an analysis of CDK activation and inhibition of molecular mechanisms, and an extensive report, including clinical trials, regarding four new drugs acting as CDK modulators: alvocidib, P276-00, SNS-032 and seliciclib.

Regulation of cyclin T1 expression and function by an alternative splice variant that skips exon 7 and contains a premature termination codon

Cyclin T1 (CCNT1), a gene containing nine exons, forms the positive transcription elongation factor b (P-TEFb) complex and regulates a wide variety of biological processes including transcription. We discovered a novel splice variant of CCNT1 that lacks exon 7 (dE7). RT-PCR analysis revealed that the dE7 transcript was detected in almost all tissues examined. The dE7/FL transcript ratio was high in quiescent peripheral blood mononuclear cells (PBMC) and in tissues poor in cell division; however, it was low in activated PBMC and in tissues with high cell proliferative potential. These results suggest that exon 7 skipping is linked to cell cycle progression. Increasing the dE7/FL transcript ratio resulted in the reduction of CCNT1 protein levels, indicating that the expression of CCNT1 protein is controlled by exon skipping. Exon 7 skipping yields a +1 frameshift at exon 8, which generates a premature termination codon (PTC). The dE7 transcript levels increased when cells were treated with the protein synthesis inhibitor cycloheximide (CHX) or a kinase inhibitor wortmannin (WORT), whilst the FL transcript levels were unchanged, suggesting that the dE7 transcript is a target of nonsense-mediated decay (NMD). Importantly, reduction of dE7 transcript by WORT correlated well with the decrement of CCNT1 protein expression. The dE7 transcript would produce an approximately 23kDa protein that covers approximately 70% of the cyclin box. The ectopically expressed dE7 protein physically interacted with CDK9 and competed with FL CCNT1 for CDK9, thus should act dominant-negatively on FL CCNT1. The replication of human immunodeficiency virus type 1 (HIV-1), heavily dependent on the CCNT1 function, was inhibited by dE7 protein through the attenuation of Tat/long terminal repeat (LTR)-driven transcription. Taken together, these results suggest that dE7 is a novel splice variant that regulates the expression and function of CCNT1.

A Network of Regulations by Small Non-Coding RNAs: The P-TEFb Kinase in Development and Pathology

Part of the heterodimeric P-TEF-b element of the Pol II transcription machinery, the cyclin-dependent kinase 9 plays a critical role in gene expression. Phosphorylation of several residues in the polymerase is required for elongation of transcript. It determines the rates of transcription and thus, plays a critical role in several differentiation pathways, best documented in heart development. The synthesis and activity of the protein are tightly regulated in a coordinated manner by at least three non-coding RNAs. First, its kinase activity is reversibly inhibited by formation of a complex with the 334 nt 7SK RNA, from which it is released under conditions of stress. Then, heart development requires a maximal rate of synthesis during cardiomyocyte differentiation, followed by a decrease in the differentiated state. The latter is insured by microRNA-mediated translational inhibition. In a third mode of RNA control, increased levels of transcription are induced by small non-coding RNA molecules with sequences homologous to the transcript. Designated paramutation, this epigenetic variation, stable during development, and hereditarily transmitted in a non-Mendelian manner over several generations, is thought to be a response to the inactivation of one of the two alleles by an abnormal recombination event such as insertion of a transposon.

B-cell differentiation in EBV-positive Burkitt lymphoma is impaired at posttranscriptional level by miRNA-altered expression

Endemic, sporadic and HIV-associated Burkitt lymphoma (BL) all have a B-cell phenotype and a MYC translocation, but a variable association with the Epstein-Barr virus (EBV). However, there is still no satisfactory explanation of how EBV participates in the pathogenesis of BL. A recent investigation suggested that EBV-positive and EBV-negative BL have different cells of origin. In particular, according to immunoglobulin gene mutation analysis, EBV-negative BLs may originate from early centroblasts, whereas EBV-positive BLs seem to arise from postgerminal center B cells or memory B cells. The appearance of a germinal center phenotype in EBV-positive cells might thus derive from a block in B-cell differentiation. The exit from the germinal center involves a complex series of events, which require the activation of BLIMP-1, and the consequent downregulation of several target genes. Here, we investigated the expression of specific miRNAs predicted to be involved in B-cell differentiation and found that hsa-miR-127 is differentially expressed between EBV-positive and EBV-negative BLs. In particular, it was strongly upregulated only in EBV-positive BL samples, whereas EBV-negative cases showed levels of expression similar to normal controls, including microdissected germinal centers (GC) cells. In addition, we found evidence that hsa-miR-127 is involved in B-cell differentiation process through posttranscriptional regulation of BLIMP1 and XBP1. The overexpression of this miRNA may thus represent a key event in the lymphomagenesis of EBV positive BL, by blocking the B-cell differentiation process.