DNA lesions block cellular processes such as transcription, inducing apoptosis, tissue failures, and premature aging. To counteract the deleterious effects of DNA damage, cells are equipped with various DNA repair pathways. Transcription-coupled repair specifically removes helix-distorting DNA adducts in a coordinated multistep process. This process has been extensively studied; however, once the repair reaction is accomplished, little is known about how transcription restarts. In this study, we show that, after UV irradiation, the cyclin-dependent kinase 9 (CDK9)/cyclin T1 kinase unit is specifically released from the HEXIM1 complex and that this released fraction is degraded in the absence of the Cockayne syndrome group B protein (CSB). We determine that UV irradiation induces a specific Ser2 phosphorylation of the RNA polymerase II and that this phosphorylation is CSB dependent. Surprisingly, CDK9 is not responsible for this phosphorylation but instead might play a nonenzymatic role in transcription restart after DNA repair.

We recently identified the CDC25A phosphatase as a key actor in proliferation and differentiation in acute myeloid leukemia which expresses the FLT3-ITD mutation. In this paper we demonstrate that CDC25A level is controlled by a complex STAT5/miR-16 transcription and translation pathway working downstream of this receptor. First, we established by CHIP analysis that STAT5 is directly involved in FLT3-ITD-dependent CDC25A gene transcription. In addition, we determined that miR-16 expression is repressed by FLT3-ITD activity, and that STAT5 participates in this repression. In accordance with these results, miR-16 expression was significantly reduced in a panel of AML primary samples carrying the FLT3-ITD mutation when compared with FLT3wt cells. The expression of a miR-16 mimic reduced CDC25A protein and mRNA levels, and RNA interference-mediated down modulation of miR-16 restored CDC25A expression in response to FLT3-ITD inhibition. Finally, decreasing miR-16 expression partially restored the proliferation of cells treated with the FLT3 inhibitor AC220, while the expression of miR-16 mimic stopped this proliferation and induced monocytic differentiation of AML cells. In summary, we identified a FLT3-ITD/STAT5/miR-16/CDC25A axis essential for AML cell proliferation and differentiation.

NUCLEOTIDE EXCISION REPAIR; RNAP2: RNA POLYMERASE II 24 25 26 2 AUTHOR SUMMARY 27 DNA lesions block cellular processes such as transcription, inducing apoptosis, tissue failures and 28 premature ageing. To counteract the deleterious effects of DNA damage, cells are equipped with 29 various DNA repair pathways. Transcription Coupled Repair specifically removes helix--distorting DNA 30adducts in a coordinated multi--step process. This process has been extensively studied, however 31 once the repair reaction is accomplished, little is known about how transcription restarts. In this 32 study, we show that, after UV irradiation, the CDK9/CyclinT1 kinase unit is specifically released from 33 the HEXIM1 complex and that this released fraction is degraded in the absence of CSB. We determine 34 that UV--irradiation induces a specific Ser2 phosphorylation of the RNA polymerase II and that this 35 phosphorylation is CSB dependent. Surprisingly CDK9 is not responsible for this phosphorylation but 36 instead plays a non--enzymatic role in transcription restart after DNA repair. 37 38 3 Introduction 39 Cells are the units of organic life and store in their nuclei, under the form of the DNA 40 molecule, what constitutes the instruction manual for proper cellular functioning. Despite the 41 protection offered by the cellular environment, the integrity of DNA is continuously challenged by a 42 variety of endogenous and exogenous agents (e.g. ultraviolet light, cigarette smoke, environmental 43 pollution, oxidative damage, etc …) that cause DNA lesions, interfering with proper cellular functions, 44 in fine causing the aging or premature aging of the tissue and later on of the whole organism.45 To prevent the deleterious consequences of persisting DNA lesions, all organisms are 46 equipped with a network of efficient DNA damage responses and DNA repair systems. One of these 47 systems is the Nucleotide Excision Repair (NER). NER removes helix--distorting DNA adducts such as 48 UV--induced lesions (Cyclo--Pyrimidine Dimers and 6--4 Photoproducts, CPD and 6--4PP) in a 49 coordinated multi--step process (1). 50The NER system has been linked to rare human diseases classically grouped into three 51 distinct NER--related syndromes. These include the highly cancer prone disorder xeroderma 52 pigmentosum (XP) and the two progeroid diseases: Cockayne syndrome (CS) and trichothiodystrophy 53 (TTD) (2). Importantly, CS and TTD patients are not cancer--prone but present severe neurological and 54 developmental features. 55NER exists in two distinct sub--pathways depending where DNA lesions are located within the 56 genome. Global Genome Repair (GG--NER or GGR) will repair DNA lesion located on non--transcribed 57 DNA. While, the second sub--pathway is directly coupled to transcription elongation and repairs DNA 58 lesions located on the transcribed strand of active genes and it is designated as Transcription-- 59Coupled Repair (TC--NER or TCR). 60RNAP2 frequently deals with obstacles that need to be removed through the TCR process for 61 resu...

We recently identified the CDC25A phosphatase as a key actor in proliferation and differentiation in acute myeloid leukemia expressing the FLT3-ITD mutation. In this paper we demonstrate that CDC25A level is controlled by a complex STAT5/miR-16 transcription and translation pathway working downstream of this receptor. First, we established by CHIP analysis that STAT5 is directly involved in FLT3-ITD-dependent CDC25A gene transcription. In addition, we determined that miR-16 expression is repressed by FLT3-ITD activity, and that STAT5 participates in this repression. In accordance with these results, miR-16 expression was significantly reduced in a panel of AML primary samples carrying the FLT3-ITD mutation when compared with FLT3wt cells. The expression of a miR-16 mimic reduced CDC25A protein and mRNA levels, and RNA interference-mediated down modulation of miR-16 restored CDC25A expression in response to FLT3-ITD inhibition. Finally, decreasing miR-16 expression partially restored the proliferation of cells treated with the FLT3 inhibitor AC220, while the expression of miR-16 mimic stopped this proliferation and induced monocytic differentiation of AML cells. In summary, we identified a FLT3-ITD/STAT5/miR-16/CDC25A axis essential for AML cell proliferation and differentiation.