SummaryRNA polymerase I (Pol I) transcription is essential for the cell cycle, growth and protein synthesis in eukaryotes. In the present study, we found that phosphatidylinositol 4,5-bisphosphate (PIP2) is a part of the protein complex on the active ribosomal promoter during transcription. PIP2 makes a complex with Pol I and the Pol I transcription factor UBF in the nucleolus. PIP2 depletion reduces Pol I transcription, which can be rescued by the addition of exogenous PIP2. In addition, PIP2 also binds directly to the pre-rRNA processing factor fibrillarin (Fib), and co-localizes with nascent transcripts in the nucleolus. PIP2 binding to UBF and Fib modulates their binding to DNA and RNA, respectively. In conclusion, PIP2 interacts with a subset of Pol I transcription machinery, and promotes Pol I transcription.

The development of fluorogenic reactions which lead to the formation of fluorescent products from two nonfluorescent starting materials is highly desirable, but challenging. Reported herein is a new concept of fluorescent product formation upon the inverse electron‐demand Diels–Alder reaction of 1,2,4,5‐tetrazines with particular trans‐cyclooctene (TCO) isomers. In sharp contrast to known fluorogenic reagents the presented chemistry leads to the rapid formation of unprecedented fluorescent 1,4‐dihydropyridazines so that the fluorophore is built directly upon the chemical reaction. Attachment of an extra fluorophore moiety is therefore not needed. The photochemical properties of the resulting dyes can be easily tuned by changing the substitution pattern of the starting 1,2,4,5‐tetrazine. We support the claim with NMR measurements and rationalize the data by computational study. Cell‐labeling experiments were performed to demonstrate the potential of the fluorogenic reaction for bioimaging.

Fractionated ionizing radiation combined with surgery or hormone therapy represents the first-choice treatment for medium to high-risk localized prostate carcinoma. One of the main reasons for the failure of radiotherapy in prostate cancer is radioresistance and further dissemination of surviving cells. In this study, exposure of four metastasis-derived human prostate cancer cell lines (DU145, PC-3, LNCaP and 22RV1) to clinically relevant daily fractions of ionizing radiation (35 doses of 2 Gy) resulted in generation of two radiation-surviving populations: adherent senescent-like cells expressing common senescenceassociated markers and non-adherent anoikis-resistant stem cell-like cells with active Notch signaling and expression of stem cell markers CD133, Oct-4, Sox2 and Nanog. While a subset of the radiation-surviving adherent cells resumed proliferation shortly after completion of the irradiation regimen, the non-adherent cells started to proliferate only on their reattachment several weeks after the radiation-induced loss of adhesion. Like the parental non-irradiated cells, radiation-surviving re-adherent DU145 cells were tumorigenic in immunocompromised mice. The radiation-induced loss of adhesion was dependent on expression of Snail, as siRNA/shRNA-mediated knockdown of Snail prevented cell detachment. On the other hand, survival of the non-adherent cells required active Erk signaling, as chemical inhibition of Erk1/2 by a MEK-selective inhibitor or Erk1/2 knockdown resulted in anoikis-mediated death in the non-adherent cell fraction. Notably, whereas combined inhibition of Erk and PI3K-Akt signaling triggered cell death in the non-adherent cell fraction and blocked proliferation of the adherent population of the prostate cancer cells, such combined treatment had only marginal if any impact on growth of control normal human diploid cells. These results contribute to better understanding of radiation-induced stress response and heterogeneity of human metastatic prostate cancer cells, document treatment-induced plasticity and phenotypically distinct cell subsets, and suggest the way to exploit their differential sensitivity to radiosensitizing drugs in overcoming radioresistance. Cell Death and Differentiation (2015) 22, 898-911; doi:10.1038/cdd.2014.97; published online 11 July 2014Prostate carcinoma (CaP) is the most frequent type of cancer in men, and the sixth cause of cancer-associated death in men worldwide. 1 Despite the advances in diagnosis and therapy of CaP, the mortality has remained almost unchanged for the last decades. Currently, the most successful treatment for localized CaP is prostatectomy with postoperative fractionated radiotherapy, significantly improving metastasis-free and overall survival, where the median of a 15-year survival is around 47% of patients. 2,3 The rest of the patients develop a metastatic disease that is incurable due to the resistance of CaP to androgen ablation, radiotherapy and chemotherapy. Therefore, understanding the mechanisms of radioresistance and chemoresista...

BackgroundNuclear myosin I (NM1) was the first molecular motor identified in the cell nucleus. Together with nuclear actin, they participate in crucial nuclear events such as transcription, chromatin movements, and chromatin remodeling. NM1 is an isoform of myosin 1c (Myo1c) that was identified earlier and is known to act in the cytoplasm. NM1 differs from the “cytoplasmic” myosin 1c only by additional 16 amino acids at the N-terminus of the molecule. This amino acid stretch was therefore suggested to direct NM1 into the nucleus.Methodology/Principal FindingsWe investigated the mechanism of nuclear import of NM1 in detail. Using over-expressed GFP chimeras encoding for truncated NM1 mutants, we identified a specific sequence that is necessary for its import to the nucleus. This novel nuclear localization sequence is placed within calmodulin-binding motif of NM1, thus it is present also in the Myo1c. We confirmed the presence of both isoforms in the nucleus by transfection of tagged NM1 and Myo1c constructs into cultured cells, and also by showing the presence of the endogenous Myo1c in purified nuclei of cells derived from knock-out mice lacking NM1. Using pull-down and co-immunoprecipitation assays we identified importin beta, importin 5 and importin 7 as nuclear transport receptors that bind NM1. Since the NLS sequence of NM1 lies within the region that also binds calmodulin we tested the influence of calmodulin on the localization of NM1. The presence of elevated levels of calmodulin interfered with nuclear localization of tagged NM1.Conclusions/SignificanceWe have shown that the novel specific NLS brings to the cell nucleus not only the “nuclear” isoform of myosin I (NM1 protein) but also its “cytoplasmic” isoform (Myo1c protein). This opens a new field for exploring functions of this molecular motor in nuclear processes, and for exploring the signals between cytoplasm and the nucleus.

Fluorescent probest hat light-up upon reaction with complementary bioorthogonal reagents are superior tools for no-wash fluorogenic bioimaging applications.I n this work, at horough study is presented on as et of seventeen structurally diverse coumarin-tetrazine probes that produce fluorescent dyes with exceptional turn-onr atios when reacted with trans-cyclooctene (TCO) and bicyclononyne (BCN) dienophiles. In general,f ormation of the fully aromatic pyridazine-containing dyes resulting fromt he reaction with BCN was found superiori nt erms of fluorogenicity.H owever, evaluation of the probesi nc ellular imaging experiments revealed that other factors, such as reaction kinetics and good cell permeability,p revail over the fluorescence turn-on properties. The best compound identified in this study showed excellent performance in live cell-labeling experimentsa nd enabledn o-wash fluorogenic imaging on at imescale of seconds.

Actin is a well-known protein that has shown a myriad of activities in the cytoplasm. However, recent findings of actin involvement in nuclear processes are overwhelming. Actin complexes in the nucleus range from very dynamic chromatin-remodeling complexes to structural elements of the matrix with single partners known as actin-binding proteins (ABPs). This review summarizes the recent findings of actin-containing complexes in the nucleus. Particular attention is given to key processes like chromatin remodeling, transcription, DNA replication, nucleocytoplasmic transport and to actin roles in nuclear architecture. Understanding the mechanisms involving ABPs will definitely lead us to the principles of the regulation of gene expression performed via concerting nuclear and cytoplasmic processes.

Cationic colloidal gold nanorods (GNRs) have a great potential as a theranostic tool for diverse medical applications. GNRs' properties such as cellular internalization and stability are determined by physicochemical characteristics of their surface coating. GNRs modified by (16-mercaptohexadecyl)trimethylammonium bromide (MTAB), GNRs, show excellent cellular uptake. Despite their promise for biomedicine, however, relatively little is known about the cellular pathways that facilitate the uptake of GNRs, their subcellular fate and intracellular persistence. Here we studied the mechanism of cellular internalization and long-term fate of GNRs coated with MTAB, for which the synthesis was optimized to give higher yield, in various human cell types including normal diploid versus cancerous, and dividing versus nondividing (senescent) cells. The process ofGNRs internalization into their final destination in lysosomes proceeds in two steps: (1) fast passive adhesion to cell membrane mediated by sulfated proteoglycans occurring within minutes and (2) slower active transmembrane and intracellular transport of individual nanorods via clathrin-mediated endocytosis and of aggregated nanorods via macropinocytosis. The expression of sulfated proteoglycans was the major factor determining the extent of uptake by the respective cell types. Upon uptake into proliferating cells, GNRs were diluted equally and relatively rapidly into daughter cells; however, in nondividing/senescent cells the loss ofGNRs was gradual and very modest, attributable mainly to exocytosis. Exocytosed GNRs can again be internalized. These findings broaden our knowledge about cellular uptake of gold nanorods, a crucial prerequisite for future successful engineering of nanoparticles for biomedical applications such as photothermal cancer therapy or elimination of senescent cells as part of the emerging rejuvenation approach.

BackgroundNuclear myosin I (NM1) is a nuclear isoform of the well-known “cytoplasmic” Myosin 1c protein (Myo1c). Located on the 11th chromosome in mice, NM1 results from an alternative start of transcription of the Myo1c gene adding an extra 16 amino acids at the N-terminus. Previous studies revealed its roles in RNA Polymerase I and RNA Polymerase II transcription, chromatin remodeling, and chromosomal movements. Its nuclear localization signal is localized in the middle of the molecule and therefore directs both Myosin 1c isoforms to the nucleus.Methodology/Principal FindingsIn order to trace specific functions of the NM1 isoform, we generated mice lacking the NM1 start codon without affecting the cytoplasmic Myo1c protein. Mutant mice were analyzed in a comprehensive phenotypic screen in cooperation with the German Mouse Clinic. Strikingly, no obvious phenotype related to previously described functions has been observed. However, we found minor changes in bone mineral density and the number and size of red blood cells in knock-out mice, which are most probably not related to previously described functions of NM1 in the nucleus. In Myo1c/NM1 depleted U2OS cells, the level of Pol I transcription was restored by overexpression of shRNA-resistant mouse Myo1c. Moreover, we found Myo1c interacting with Pol II. The ratio between Myo1c and NM1 proteins were similar in the nucleus and deletion of NM1 did not cause any compensatory overexpression of Myo1c protein.Conclusion/SignificanceWe observed that Myo1c can replace NM1 in its nuclear functions. Amount of both proteins is nearly equal and NM1 knock-out does not cause any compensatory overexpression of Myo1c. We therefore suggest that both isoforms can substitute each other in nuclear processes.