Biological Mechanisms of Sustaining Deep Molecular Response in Chronic Myeloid Leukemia Upon Withdrawal of Tyrosine Kinase Inhibitors

The feasibility of treatment-free follow-up in chronic myeloid leukemia (CML) patients is an important issue in the era of tyrosine kinase inhibitors (TKI). The clinical trials of TKI withdrawal in case of a stable deep molecular response prove the probability of sustaining molecular remission in 40-60 % of patients. Treatment-free remission (TFR), even under persistence of residual leukemia cells, suggests that there are special biologically determined mechanisms of tumor cell proliferation control, which are independent of BCR-ABL kinase activity. The search for factors determining differences in residual leukemia clone kinetics upon TKI withdrawal is an objective which is crucial for understanding TFR as a new biological phenomenon. The review provides worldwide evidence dealing with the study of immunological, genetic, and other biological mechanisms underlying the control of minimal residual disease upon TKI discontinuation in CML patients.

Deficiency of G9a Inhibits Cell Proliferation and Activates Autophagy via Transcriptionally Regulating c-Myc Expression in Glioblastoma

Glioblastoma is an aggressive and difficult to treat cancer. Recent data have emerged implicating that histone modification level may play a crucial role in glioma genesis. The histone lysine methyltransferase G9a is mainly responsible for the mono- and di-methylation of histone H3 lysine 9 (H3K9), whose overexpression is associated with a more aggressive phenotype in cancer. However, the detailed correlations between G9a and glioblastoma genesis remain to be further elucidated. Here, we show that G9a is essential for glioblastoma carcinogenesis and reveal a probable mechanism of it in cell proliferation control. We found that G9a was highly expressed in glioblastoma cells, and knockdown or inhibition of G9a significantly repressed cell proliferation and tumorigenesis ability both in vitro and in vivo. Besides, knockdown or inhibition of G9a led to a cell cycle arrest in G2 phase, as well as decreased the expression of CDK1, CDK2, Cyclin A2, and Cyclin B1, while it induced the activation of autophagy. Further investigation showed that G9a deficiency induced cell proliferation suppression, and activation of autophagy was rescued by overexpression of the full-length c-Myc. Chromatin immunoprecipitation (ChIP) assay showed that G9a was enriched on the −2267 to −1949 region of the c-Myc promoter in LN-229 cells and the −1949 to −1630 region of the c-Myc promoter in U-87 MG cells. Dual-luciferase reporter assay showed that c-Myc promoter activity was significantly reduced after knockdown or inhibition of G9a. Our study shows that G9a controls glioblastoma cell proliferation by transcriptionally modulating oncogene c-Myc and provides insight into the capabilities of G9a working as a potential therapeutic target in glioblastoma.

Proliferation control of kidney interstitial cells

ABSTRACTExpansion of interstitial cells in the adult kidney is a hallmark of chronic disease, whereas their proliferation during fetal development is necessary for organ formation. An intriguing difference between adult and neonatal kidneys is that the neonatal kidney has the capacity to control interstitial cell proliferation when the target number has been reached. In this study, we define the consequences of inactivating the TGFβ/Smad response in the interstitial cell lineage. We find that pathway inactivation through loss of Smad4 leads to over-proliferation of interstitial cells regionally in the kidney medulla. Genetic and molecular interaction studies showed that Smad3/4 participates in the Wnt/β-catenin signaling pathway, which is responsible for promoting proliferation of interstitial cells. Specifically, Smad4 is required for the expression of the Wnt feedback inhibitor Apcdd1, and based on these findings we propose a model for interstitial cell proliferation control in which the Wnt/β-catenin proliferative signal is attenuated by TGFβ/Smad signaling to ensure that proliferation ceases when the target number of interstitial cells has been reached in the neonatal medulla.Summary statementThis study describes a novel function for TGFβ signaling in the developing renal interstitium. Mice with Foxd1-Cre-mediated deletion of Smad4 have interstitial expansion and activated Wnt signaling.

tRNA fragments (tRFs) populations analysis in mutants affecting tRNAs processing and tRNA methylation

AbstracttRNA fragments (tRFs) are a class of small non-coding RNAs (sncRNAs) derived from tRNAs. tRFs are highly abundant in many cell types including stem cells and cancer cells, and are found in all domains of life. Beyond translation control, tRFs have several functions ranging from transposon silencing to cell proliferation control. However, the analysis of tRFs presents specific challenges and their biogenesis is not well understood. They are very heterogeneous and highly modified by numerous post-transcriptional modifications. Here we describe a bioinformatic pipeline to study tRFs populations and shed light onto tRNA fragments biogenesis. Indeed, we used small RNAs Illumina sequencing datasets extracted from wild type and mutant Drosophila ovaries affecting two different highly conserved steps of tRNA biogenesis: 5’pre-tRNA processing (RNase-P subunit Rpp30) and tRNA 2’-O-methylation (CG7009 and CG5220). Using our pipeline, we show how defects in tRNA biogenesis affect nuclear and mitochondrial tRFs populations and other small non-coding RNAs biogenesis, such as small nucleolar RNAs (snoRNAs). This tRF analysis workflow will advance the current understanding of tRFs biogenesis, which is crucial to better comprehend tRFs roles and their implication in human pathology.

DNA damage and S phase-dependent E2F1 stabilization requires the cIAP1 E3-ubiquitin ligase and is associated with K63-poly-ubiquitination on lysine 161/164 residues

The E2F transcription factor 1 is subtly regulated along the cell cycle progression and in response to DNA damage by post-translational modifications. Here, we demonstrated that the E3-ubiquitin ligase cellular inhibitor of apoptosis 1 (cIAP1) increases E2F1 K63-poly-ubiquitination on the lysine residue 161/164 cluster, which is associated with the transcriptional factor stability and activity. Mutation of these lysine residues completely abrogates the binding of E2F1 to CCNE, TP73 and APAF1 promoters, thus inhibiting transcriptional activation of these genes and E2F1-mediated cell proliferation control. Importantly, E2F1 stabilization in response to etoposide-induced DNA damage or during the S phase of cell cycle, as revealed by cyclin A silencing, is associated with K63-poly-ubiquitinylation of E2F1 on lysine 161/164 residues and involves cIAP1. Our results reveal an additional level of regulation of the stability and the activity of E2F1 by a non-degradative K63-poly-ubiquitination and uncover a novel function for the E3-ubiquitin ligase cIAP1.