ABSTRACT: Tet3 converts 5-methylcyotsine to 5-hydroxymethylcytosine (5hmC), although it remains unclear how its functions can be regulated. We showed that Tet3 is phosphorylated by cyclin-dependent kinase 5 at a highly conserved serine residue within its catalytic domain, which leads to an increase in its dioxygenase activity in vitro. Interestingly, when stably expressed in Tet triple-knockout mouse embryonic stem cells (mESCs), wild-type Tet3 elicited higher 5hmC enrichment and expression of genes involved in neurogenesis whereas phosphor-mutant Tet3 caused elevated 5hmC and expression of metabolic pathways genes. Expression of wild-type, but not phosphor-mutant Tet3 in Tet3-knockout mESCs, causes optimal expression of BRN2, Hes1 and Hey2 transcription factors which lead to robust terminal differentiation measured by MAP2 expression. Taken together, our results suggest that cdk5-mediated phosphorylation of Tet3 ensures robust activation of neuronal transcriptional programs during differentiation.
Project description:Ten-eleven translocation (Tet) hydroxylases (Tet1-3) oxidize 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). In neurons increased 5hmC levels within gene bodies correlate positively with gene expression. The mechanisms controlling Tet activity and 5hmC levels are poorly understood. In particular, it is not known how the neuronal Tet3 isoform lacking a DNA binding domain is targeted to the DNA. To identify factors binding to Tet3 we screened for proteins that co-precipitate with Tet3 from mouse retina and identified the transcriptional repressor Rest as a highly enriched Tet3-specific interactor. Rest was able to enhance Tet3 hydroxylase activity after co-expression and overexpression of Tet3 activated transcription of Rest-target genes. Moreover, we found that Tet3 also interacts with Nsd3 and two other H3K36 methyltransferases and is able to induce H3K36 trimethylation. We propose a mechanism for transcriptional activation in neurons that involves Rest-guided targeting of Tet3 to the DNA for directed 5hmC-generation and Nsd3-mediated H3K36 trimethylation.
Project description:Tet-family dioxygenases catalyze conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. Here, we show that Tet3 deficiency impairs neural differentiation of mouse ESCs, resulting in skewing towards cardiac mesoderm; conversely, ectopic expression of Tet3 enhances neural differentiation and limits cardiac mesoderm specification. To determine the effects of Tet3 gain and loss on global gene expression profiles during mESC differentiation, we performed whole transcriptome RNA-sequencing (RNA-seq) analysis of (i) WT and Tet3 KO mESCs differentiating into neuroectoderm under SFEB culture (days 6 and 10); and (ii) Control and Tet3-overexpressing mESCs in non-permissive neural differentiation conditions containing FBS (days 4 and 7). Genome-wide analyses showed that Tet3 mediates cell-fate decision by inhibiting Wnt signaling.
Project description:Pancreatic neuroendocrine tumors (PanNETs) are a heterogeneous population of neoplasms that arise from hormone-secreting islet cells of the pancreas and have increased markedly in incidence over the past four decades. Non-functional PanNETs, which occur more frequently than hormone-secreting tumors, are often not diagnosed until later stages of tumor development and have poorer prognoses. Development of successful therapeutics for PanNETs has been slow, partially due to a lack of diverse animal models for pre-clinical testing. Here, we report development of an inducible, conditional mouse model of PanNETs by using a bitransgenic system for regulated expression of the aberrant activator of Cdk5, p25, specifically in b-islet cells. This model produces a heterogeneous population of PanNETs that includes a subgroup of well-differentiated, non-functional tumors. The utility of this model is enhanced by ability to form tumor-derived allografts. Production of these tumors demonstrates the causative potential of aberrantly active Cdk5 for generation of PanNETs. Further, we show that human PanNETs express Cdk5 pathway components, are dependent on Cdk5 for growth, and share genetic and transcriptional overlap with the INS-p25OE model. This new model of PanNETs will facilitate molecular delineation of Cdk5-dependent PanNETs and the development of new targeted therapeutics.
Project description:The degradation tag (dTAG) system for target protein degradation can remove proteins from biological systems without the drawbacks of some genetic methods, such as slow kinetics, lack of reversibility, low specificity, and the inability to titrate dosage. These drawbacks can make it difficult to compare toxicity resulting from genetic and pharmacological interventions, especially in vivo. Because the dTAG system has not been studied extensively in vivo, we explored the use of this system to study the physiological sequalae resulting from CDK2 or CDK5 degradation in adult mice. Mice with knock-in of the dTAG sequence onto the C-terminus of CDK2 and CDK5 were born at Mendelian ratios despite decreased CDK2 or CDK5 protein levels in comparison to wild-type mice. In bone marrow cells and duodenum organoids derived from these mice, treatment with the dTAG degrader dTAG-13 resulted in rapid and robust protein degradation but caused no appreciable change in viability or the transcriptome. Repeated delivery of dTAG-13 in vivo for toxicity studies proved challenging; we explored multiple formulations in an effort to maximize degradation while minimizing formulation-related toxicity. Degradation of CDK2 or CDK5 in all organs except the brain, where dTAG-13 likely did not cross the blood brain barrier, only caused microscopic changes in the testis of CDK2dTAG mice. These findings were corroborated with conditional CDK2 knockout in adult mice. Our results suggest that the dTAG system can provide robust protein degradation in vivo and that loss of CDK2 or CDK5 in adult mice causes no previously unknown phenotypes.
Project description:Despite the development of adjuvant therapies, glioblastoma (GBM) patients remain incurable and justify the urgent need of new therapies. CDK5 functions a critical role in GBM and is a potential target for GBM. However, the mechanism by which CDK5 promotes GBM tumorigenicity remains largely unknown. Here we identify TRIM59 as a substrate of CDK5. EGFR-activated CDK5 directly binds to and phosphorylates TRIM59, a ubiquitin ligase at serine 308, which recruits PIN1 for cis-trans isomerization of TRIM59, leading to TRIM59 binding to importin a5 and nuclear translocation. Nuclear TRIM59 induces ubiquitination and degradation of the tumor suppressive histone variant macroH2A1, leading to enhanced STAT3 signaling activation and tumorigenicity. These findings are confirmed by inhibition of CDK5-activated TRIM59 activity that results in suppression of intracranial tumor growth. Correlative expressions of the components of this pathway are clinically prognostic. Our findings suggest targeting CDK5/TRIM59 signaling axis as a putative strategy for treating GBM.
Project description:The degradation tag (dTAG) system for target protein degradation can remove proteins from biological systems without the drawbacks of some genetic methods, such as slow kinetics, lack of reversibility, low specificity, and the inability to titrate dosage. These drawbacks can make it difficult to compare toxicity resulting from genetic and pharmacological interventions, especially in vivo. Because the dTAG system has not been studied extensively in vivo, we explored the use of this system to study the physiological sequalae resulting from CDK2 or CDK5 degradation in adult mice. Mice with knock-in of the dTAG sequence onto the C-terminus of CDK2 and CDK5 were born at Mendelian ratios despite decreased CDK2 or CDK5 protein levels in comparison to wild-type mice. In bone marrow cells and duodenum organoids derived from these mice, treatment with the dTAG degrader dTAG-13 resulted in rapid and robust protein degradation but caused no appreciable change in viability or the transcriptome. Repeated delivery of dTAG-13 in vivo for toxicity studies proved challenging; we explored multiple formulations in an effort to maximize degradation while minimizing formulation-related toxicity. Degradation of CDK2 or CDK5 in all organs except the brain, where dTAG-13 likely did not cross the blood brain barrier, only caused microscopic changes in the testis of CDK2dTAG mice. These findings were corroborated with conditional CDK2 knockout in adult mice. Our results suggest that the dTAG system can provide robust protein degradation in vivo and that loss of CDK2 or CDK5 in adult mice causes no previously unknown phenotypes.
Project description:To investigate the molecular mechanism underlying activity-dependent dendrite development regulated by Cdk5, an unbiased microarray analysis was performed to identify activity-dependent genes differentially regulated in cortical neurons from E18 Cdk5-knockout embryos.
Project description:Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer that shows high infiltration of cancer stem cells (CSCs), which correlates with poor clinical outcome. Here, we have demonstrated that an aberrant activation of CDK5/pho-PPARg axis associated with TNBC progression closely. CDK5 blockade sufficiently abrogates stemness transformation of TNBC cells, resulting in a significant inhibition of tumor metastatic progression. Moreover, CDK5 inhibitor Rosc attenuates CD44v+ BCSCs, hereby reversing immunosuppressive microenvironment and enhancing anti-PD-1 effects on TNBC. Mechanistically, CDK5/pho-PPARgaxis modulates the ESRP1 degradation via E3 ligase-like activity, leading to CD44 variant (CD44v) expression. Our finding indicates that CDK5 blockade could be a potent strategy to target CSCs in TNBC, and to increase the response to PD-1 blockade in TNBC therapy.
Project description:Tumor resistance to radiotherapy is a therapeutic challenge in the treatment of patients with lung cancer. Cyclin-dependent kinase 5 (CDK5) has been proposed to participate in cell proliferation, migration and invasion; drug resistance; and immune evasion. However, the functions and regulatory mechanisms of CDK5 in lung cancer radioresistance have not been investigated.SiRNAs and ShRNAs were used to knock down CDK5 in A549 and H1299 cells. The effects of CDK5 depletion on the tumorigenic behaviors of non-small cell lung cancer (NSCLC) cells were evaluated in vitro and in vivo. Gene expression was examined by RNA-seq and quantitative real-time PCR.