EMT Inducers Catalyze Malignant Transformation of Mammary Epithelial Cells and Drive Tumorigenesis towards Claudin-Low Tumors in Transgenic Mice

The epithelial-mesenchymal transition (EMT) is an embryonic transdifferentiation process consisting of conversion of polarized epithelial cells to motile mesenchymal ones. EMT–inducing transcription factors are aberrantly expressed in multiple tumor types and are known to favor the metastatic dissemination process. Supporting oncogenic activity within primary lesions, the TWIST and ZEB proteins can prevent cells from undergoing oncogene-induced senescence and apoptosis by abolishing both p53- and RB-dependent pathways. Here we show that they also downregulate PP2A phosphatase activity and efficiently cooperate with an oncogenic version of H-RAS in malignant transformation of human mammary epithelial cells. Thus, by down-regulating crucial tumor suppressor functions, EMT inducers make cells particularly prone to malignant conversion. Importantly, by analyzing transformed cells generated in vitro and by characterizing novel transgenic mouse models, we further demonstrate that cooperation between an EMT inducer and an active form of RAS is sufficient to trigger transformation of mammary epithelial cells into malignant cells exhibiting all the characteristic features of claudin-low tumors, including low expression of tight and adherens junction genes, EMT traits, and stem cell–like characteristics. Claudin-low tumors are believed to be the most primitive breast malignancies, having arisen through transformation of an early epithelial precursor with inherent stemness properties and metaplastic features. Challenging this prevailing view, we propose that these aggressive tumors arise from cells committed to luminal differentiation, through a process driven by EMT inducers and combining malignant transformation and transdifferentiation

The cell-of-origin dictates the genomic landscape of breast cancers

Aberrant cell proliferation induced by activated oncogenes triggers oxidative stress and uncontrolled DNA replication, promoting genomic instability. We recently reported that human mammary stem cells exhibit the unique capacity to withstand an oncogenic activation by dint of an anti-oxidant program driven by the ZEB1 transcription factor. This pre-emptive program prevents the onset of chromosomal instability, leading to the development of tumors with unique pathological features

Co-localization in replication foci and interaction of human Y-family members, DNA polymerase polη and REVl protein

The progress of replicative DNA polymerases along the replication fork may be impeded by the presence of lesions in the genome. One way to circumvent such hurdles involves the recruitment of specialized DNA polymerases that perform limited incorporation of nucleotides in the vicinity of the damaged site. This process entails DNA polymerase switch between replicative and specialized DNA polymerases. Five eukaryotic proteins can carry out translesion synthesis (TLS) of damaged DNA in vitro, DNA polymerases ¿, ¿, ¿, and ¿, and REV1. To identify novel proteins that interact with hpol¿, we performed a yeast two-hybrid screen. In this paper, we show that hREV1 interacts with hpol¿ as well as with hpol¿ and poorly with hpol¿. Furthermore, cellular localization analysis demonstrates that hREV1 is present, with hpol¿ in replication factories at stalled replication forks and is tightly associated with nuclear structures. This hREV1 nuclear localization occurs independently of the presence of hpol¿. Taken together, our data suggest a central role for hREV1 as a scaffold that recruits DNA polymerases involved in TLS

Modulation of the Tyrosine Kinase Receptor Ret/Glial Cell-Derived Neurotrophic Factor (GDNF) Signaling: A New Player in Reproduction Induced Anterior Pituitary Plasticity?

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Co-localization in replication foci and interaction of human Y-family members, DNA polymerase pol? and REVl protein

The progress of replicative DNA polymerases along the replication fork may be impeded by the presence of lesions in the genome. One way to circumvent such hurdles involves the recruitment of specialized DNA polymerases that perform limited incorporation of nucleotides in the vicinity of the damaged site. This process entails DNA polymerase switch between replicative and specialized DNA polymerases. Five eukaryotic proteins can carry out translesion synthesis (TLS) of damaged DNA in vitro, DNA polymerases ¿, ¿, ¿, and ¿, and REV1. To identify novel proteins that interact with hpol¿, we performed a yeast two-hybrid screen. In this paper, we show that hREV1 interacts with hpol¿ as well as with hpol¿ and poorly with hpol¿. Furthermore, cellular localization analysis demonstrates that hREV1 is present, with hpol¿ in replication factories at stalled replication forks and is tightly associated with nuclear structures. This hREV1 nuclear localization occurs independently of the presence of hpol¿. Taken together, our data suggest a central role for hREV1 as a scaffold that recruits DNA polymerases involved in TLS

The hamstrings are more impacted than the quadriceps after severe ankle sprain

International audienceAnkle sprains (AS) are common in the military population, with a prevalence 5 to 8 times higher than that for civilians. The aim of this study was to evaluate in patients with severe AS the impact of disuse on thigh muscle induced by unloading and immobilization due to care. This study focused on muscle trophicity and dynamometric strength. In this observational prospective study, assessments were repeated at 3 visits: close to injury, 15 and 30 days following the sprain. The injured limb was compared to the contralateral limb. A dynamometer assessment was used to monitor changes in strength and fatigue of the thigh muscles of both limbs. Isometric and isokinetic concentric evaluation of peak torque (PTiso and PTdyn), total work (Wt), and peak torque time integral (IPT) of thigh muscles. Full follow-up was obtained in 30 subjects. The injured limbs showed significant deficits in the mean (SD). The quadriceps PTiso and IPT deficits were −12.6% ± 1.9% ( P < .0001) and −13.27% ± 1.8% ( P < .0001), respectively. The quadriceps PTdyn showed a significant deficit since V2 (−12.2.5% ± 2.0). The quadriceps Wt presented a significant deficit of −4.2% ± 2.4 ( P < .0007) at 1 month. The hamstring PTdyn deficit presented a mean loss of −16.5% ± 2.4% ( P < .0001). The hamstring Wt deficit was −13.7% ± 2.3% ( P < .001). The analysis of variance showed that the grade of the sprain had a significant effect on the quadriceps PTq deficit ( P < .016) but not the type of discharge. Our study showed that disuse leads to a significant deficit in the strength of knee muscles within 1 month. It is noteworthy that the hamstrings are more affected than the quadriceps. The rehabilitation protocol to prevent the risk of iterative ankle injuries and secondary knee injuries should incorporate early training of both quadriceps and hamstrings

Altered nucleotide misinsertion fidelity associated with polι-dependent replication at the end of a DNA template

A hallmark of human DNA polymerase ι (polι) is the asymmetric fidelity of replication at template A and T when the enzyme extends primers annealed to a single-stranded template. Here, we report on the efficiency and accuracy of polι-dependent replication at a nick, a gap, the very end of a template and from a mispaired primer. Polι cannot initiate synthesis on a nicked DNA substrate, but fills short gaps efficiently. Surprisingly, polι’s ability to blunt-end a 1 bp recessed terminus is dependent upon the template nucleotide encountered and is highly erroneous. At template G, both C and T are inserted with roughly equal efficiency, whilst at template C, C and A are misinserted 8- and 3-fold more often than the correct base, G. Using substrates containing mispaired primer termini, we show that polι can extend all 12 mispairs, but with differing efficiencies. Polι can also extend a tandem mispair, especially when it is located within a short gap. The enzymatic properties of polι appear consistent with that of a somatic hypermutase and suggest that polι may be one of the low-fidelity DNA polymerases hypothesized to participate in the hypermutation of immunoglobulin variable genes in vivo

Role of EMT in the DNA damage response, double-strand break repair pathway choice and its implications in cancer treatment

International audienceNumerous epithelial–mesenchymal transition (EMT) characteristics have now been demonstrated to participate in tumor development. Indeed, EMT is involved in invasion, acquisition of stem cell properties, and therapy-associated resistance of cancer cells. Together, these mechanisms offer advantages in adapting to changes in the tumor microenvironment. However, recent findings have shown that EMT-associated transcription factors (EMT-TFs) may also be involved in DNA repair. A better understanding of the coordination between the DNA repair pathways and the role played by some EMT-TFs in the DNA damage response (DDR) should pave the way for new treatments targeting tumor-specific molecular vulnerabilities, which result in selective destruction of cancer cells. Here we review recent advances, providing novel insights into the role of EMT in the DDR and repair pathways, with a particular focus on the influence of EMT on cellular sensitivity to damage, as well as the implications of these relationships for improving the efficacy of cancer treatments