Several members of the Poly(ADP-ribose) polymerase (PARP) family are essential regulators of genome integrity, actively prospected as drug targets for cancer therapy. Among them, PARP3 is well characterized for its functions in double-strand break repair and mitotis. Here we report that PARP3 also plays an integral role in TGFβ and reactive oxygen species (ROS) dependent epithelial-to-mesenchymal transition (EMT) and stem-like cell properties in human mammary epithelial and breast cancer cells. PARP3 expression is higher in breast cancer cells of the mesenchymal phenotype and correlates with the expression of the mesenchymal marker Vimentin while being in inverse correlation with the epithelial marker E-cadherin. Furthermore, PARP3 expression is significantly upregulated during TGFβ-induced EMT in various human epithelial cells. In line with this observation, PARP3 depletion alters TGFβ-dependent EMT of mammary epithelial cells by preventing the induction of the Snail-E-cadherin axis, the dissolution of cell junctions, the acquisition of cell motility and chemoresistance. PARP3 responds to TGFβ-induced ROS to promote a TG2-Snail-E-cadherin axis during EMT. Considering the link between EMT and cancer stem cells, we show that PARP3 promotes stem-like cell properties in mammary epithelial and breast cancer cells by inducing the expression of the stem cell markers SOX2 and OCT4, by increasing the proportion of tumor initiating CD44high/CD24low population and the formation of tumor spheroid bodies, and by promoting stem cell self-renewal. These findings point to a novel role of PARP3 in the control of TGFβ-induced EMT and acquisition of stem-like cell features and further motivate efforts to identify PARP3 specific inhibitors.

Graphene-related materials (GRMs) are widely used in various applications due to their unique properties. A growing number of reports describe the impact of different carbon nanomaterials, including graphene oxide (GO), reduced GO (rGO), and carbon nanotubes (CNT), on immune cells, but there is still a very limited number of studies on graphene. In this work, we investigated the biological responses of few layer graphene (FLG) on mouse macrophages (bone marrow derived macrophages, BMDMs), which are part of the first line of defense in innate immunity. In particular, our paper describes our findings of short-term FLG treatment in BMDMs with a focus on observing material internalization and changes in general cell morphology. Subsequent investigation of cytotoxicity parameters showed that increasing doses of FLG did not hamper the viability of cells and did not trigger inflammatory responses. Basal level induced autophagic activity sufficed to maintain the cellular homeostasis of FLG treated cells. Our results shed light on the impact of FLG on primary macrophages and show that FLG does not elicit immunological responses leading to cell death.

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In breast cancer, Poly(ADP-ribose) polymerase 3 (PARP3) has been identified as a key driver of tumor aggressiveness exemplifying its selective inhibition as a promising surrogate for clinical activity onto difficult-to-treat cancers. Here we explored the role of PARP3 in the oncogenicity of glioblastoma, the most aggressive type of brain cancer. The absence of PARP3 did not alter cell proliferation nor the in vivo tumorigenic potential of glioblastoma cells. We identified a physical and functional interaction of PARP3 with the histone H3 lysine 9 methyltransferase G9a. We show that PARP3 helps to adjust G9a-dependent repression of the adhesion genes Nfasc and Parvb and the hypoxia-responsive genes Hif-2α, Runx3, Mlh1, Ndrg1, Ndrg2 and Ndrg4. Specifically for Nfasc, Parvb and Ndrg4, PARP3/G9a cooperate for an adjusted establishment of the repressive mark H3K9me2. While examining the functional consequence in cell response to hypoxia, we discovered that PARP3 acts to maintain the cytoskeletal microtubule stability. As a result, the absence of PARP3 markedly increases the sensitivity of glioblastoma cells to microtubule-destabilizing agents providing a new therapeutic avenue for PARP3 inhibition in brain cancer therapy.Poly(ADP-ribose) polymerase 3 (PARP3) is a member of the PARP family that catalyzes mono-ADP-ribosylation (or MARylation), the transfer of a single ADP-ribose molecule onto itself, a number of other protein substrates or on terminal phosphate residues at double-and single-strand break termini of DNA molecules 1-5 . PARP3 was originally identified as a key regulator of the classical non-homologous end-joining pathway (C-NHEJ) for the repair of double-strand breaks, and as an important protein securing telomeric segregation during mitosis 3-5 . Subsequently, PARP3 has been proposed to mediate the ADP-ribosylation of chromatin at sites of single strand breaks, to promote chromosomal rearrangements and limit G4 DNA and to stimulate breast tumor aggressiveness exemplifying its selective inhibition as a promising therapeutic strategy to treat highly aggressive cancers [6][7][8][9] . Accumulating studies also suggest emerging roles of PARP3 in the regulation of gene expression mediated by its interaction with chromatin regulators. In humans, PARP3 was reported to associate with several Polycomb group proteins (PcG) of the PRC2 complex namely EZH2, SUZ12, RbAp46/48, YY1 and HDAC1/2, key transcriptional regulators of embryogenesis and development 10 . In line with this, PARP3 was described to have pivotal functions in ectodermal specification and neural crest development in the Zebrafish by regulating the transcriptional expression of key transcription factors 11 . In glioblastoma cells, PARP3 was proposed to enhance the transcriptional activity of FOXM1 to confer glioblastoma cell radioresistance 12 .G9a (also known as EHMT2) and the closely related GLP1 (EHMT1) are SET-domain containing lysine methyltransferases that mono-(for GLP1) and di-methylate (for G9a) respectively histone 3 lysine 9 in euchromatin (H...