Phosphorylation by Cdk2 is required for Myc to repress Ras-induced senescence in cotransformation.

The MYC and RAS oncogenes are frequently activated in cancer and, together, are sufficient to transform rodent cells. The basis for this cooperativity remains unclear. We found that although Ras interfered with Myc-induced apoptosis, Myc repressed Ras-induced senescence, together abrogating two main barriers of tumorigenesis. Inhibition of cellular senescence required phosphorylation of Myc at Ser-62 by cyclin E/cyclin-dependent kinase (Cdk) 2. Cdk2 interacted with Myc at promoters, where it affected Myc-dependent regulation of genes, including Bmi-1, p16, p21, and hTERT, which encode proteins known to control senescence. Repression of senescence by Myc was abrogated by the Cdk inhibitor p27Kip1, which is induced by antiproliferative signals like IFN-gamma or by pharmacological inhibitors of Cdk2 but not by inhibitors of other Cdks. In contrast, a phospho-mimicking Myc-S62D mutant was resistant to these manipulations. Inhibition of cyclin E/Cdk2 reversed the senescence-associated gene expression pattern imposed by Myc/cyclin E/Cdk2. This indicates a role of Cdk2 as a transcriptional cofactor and activator of the antisenescence function of Myc and provides mechanistic insight into the Myc-p27Kip1 antagonism. Finally, our findings highlight that pharmacological inhibition of Cdk2 activity is a potential therapeutical principle for cancer therapy, in particular for tumors with activated Myc or Ras.

Texture and Magnetic Property of Fe-6.5 wt % Si Steel Strip with Cu-Rich Particles Modification.

Based on the ordered phase effectively suppressed by rapid solidification technology, the grain refinement concept using Cu is incorporated into the soft magnetic materials. Cu dosage not only could refine the grain size with an average grain size of 8.7 µm but also improve the continuity and consistency of Fe-6.5 wt % Si steel strip. It mainly attributes to the Cu-rich particles precipitating at the grain boundary, nailing the grain boundaries movement and inhibiting the grain growth, and then improving the magnetic properties and mechanical properties. The 1.5 wt % Cu sample exhibits an excellent magnetic property with the saturation magnetization of 236.54 emu/g, which mainly attributes to the strong η, λ, Goss texture formation and the band structure optimization of Si-Cu comodification. Furthermore, the mechanical properties of the steel strip are effectively improved, and the failure plastic deformation of 1.5 wt % Cu steel strip is about 11%. The rapid solidification with Cu-dosage refinement technology also has a remarkable reference on the mechanical properties and magnetic properties modification of other metal materials.

Characterization of the Fe-6.5wt%Si Strip with Rapid Cooling Coupling Deep Supercooled Solidification.

The phase transition law between ordered and disordered phases, second phase reinforcement, microstructure, and mechanical properties were systematically studied in the rapid cooling coupling deep supercooled solidification process through an arc melting furnace, electromagnetic induction heating, and high-speed cooling single-roll technology. The results show that uniform nucleation and grain refinement are promoted under rapid cooling coupling deep supercooled solidification, and the phase transition from the disordered phase (A2) to the ordered phase (B2 and DO3) is also effectively suppressed. The decreased crystalline grain size and optimized microstructure morphology improved the plasticity and magnetic property. The Fe-6.5wt%Si steel strip at 42 m/s has a good phase composition of Fe (predominant), Fe2Si, and SiC. The sample showed an equiaxed ferrite crystal structure, and the saturation magnetizations were 302.5 and 356.6 emu/g in the parallel magnetic direction and the vertical magnetic direction, respectively. This phase transition behavior contributed to the exceptional magnetic property of the Fe-6.5wt%Si steel.

Combined IFN-gamma and retinoic acid treatment targets the N-Myc/Max/Mad1 network resulting in repression of N-Myc target genes in MYCN-amplified neuroblastoma cells.

The MYCN protooncogene is involved in the control of cell proliferation, differentiation, and survival of neuroblasts. Deregulation of MYCN by gene amplification contributes to neuroblastoma development and is strongly correlated to advanced disease and poor outcome, emphasizing the urge for new therapeutic strategies targeting MYCN function. The transcription factor N-Myc, encoded by MYCN, regulates numerous genes together with its partner Max, which also functions as a cofactor for the Mad/Mnt family of Myc antagonists/transcriptional repressors. We and others have previously reported that IFN-gamma synergistically potentiates retinoic acid (RA)-induced sympathetic differentiation and growth inhibition in neuroblastoma cells. This study shows that combined treatment of MYCN-amplified neuroblastoma cells with RA+IFN-gamma down-regulates N-Myc protein expression through increased protein turnover, up-regulates Mad1 mRNA and protein, and reduces N-Myc/Max heterodimerization. This results in a shift of occupancy at the ornithine decarboxylase N-Myc/Mad1 target promoter in vivo from N-Myc/Max to Mad1/Max predominance, correlating with histone H4 deacetylation, indicative of a chromatin structure typical of a transcriptionally repressed state. This is further supported by data showing that RA+IFN-gamma treatment strongly represses expression of N-Myc/Mad1 target genes ornithine decarboxylase and hTERT. Our results suggest that combined IFN-gamma and RA signaling can form a basis for new therapeutic strategies targeting N-Myc function for patients with high-risk, MYCN-amplified neuroblastoma.

Interferon-γ-induced p27KIP1 binds to and targets MYC for proteasome-mediated degradation.

The Myc oncoprotein is tightly regulated at multiple levels including ubiquitin-mediated protein turnover. We recently demonstrated that inhibition of Cdk2-mediated phosphorylation of Myc at Ser-62 pharmacologically or through interferon (IFN)-γ-induced expression of p27(Kip1) (p27) repressed Myc's activity to suppress cellular senescence and differentiation. In this study we identified an additional activity of p27 to interfere with Myc independent of Ser-62 phosphorylation. p27 is required and sufficient for IFN-γ-induced turnover of Myc. p27 interacted with Myc in the nucleus involving the C-termini of the two proteins, including Myc box 4 of Myc. The C-terminus but not the Cdk2 binding fragment of p27 was sufficient for inducing Myc degradation. Protein expression data of The Cancer Genome Atlas breast invasive carcinoma set revealed significantly lower Myc protein levels in tumors with highly expressed p27 lacking phosphorylation at Thr-157--a marker for active p27 localized in the nucleus. Further, these conditions correlated with favorable tumor stage and patient outcome. This novel regulation of Myc by IFN-γ/p27(KIP1) potentially offers new possibilities for therapeutic intervention in tumors with deregulated Myc.

Bayesian inference of evolutionary history from chloroplast microsatellites in the cosmopolitan weed Capsella bursa-pastoris (Brassicaceae).

Besides showing an extraordinary degree of phenotypic variability, Capsella bursa-pastoris (Brassicaceae) is also one of the world's most common plant species and a serious weed in many countries. We have employed a coalescent-based Bayesian analysis of chloroplast microsatellite data to infer demographic and evolutionary parameters of this species. Two different demographic models applied to data from seven chloroplast microsatellite loci among 59 accessions show that the effective population size of C. bursa-pastoris is very small indicating a rapid expansion of the species, a result that is in accordance with fossil and historical data. Against this background, analysis of flowering time variation among accessions suggests that ecotypic differentiation in flowering time has occurred recently in the species' history. Finally, our results also indicate that mononucleotide repeat loci in the chloroplast genome can deteriorate in relatively short periods of evolutionary time.