The regulation of stem cell self-renewal must balance the regenerative needs of tissues that persist throughout life with the potential for cell overgrowth, transformation and cancer. Here, we attempt to deconstruct the relationship that exists between cell-cycle progression and the self-renewal versus commitment cell-fate decision in embryonic and adult stem cells. Recent genetic studies in mice have provided insights into the regulation of the cell cycle in stem cells, including its potential modulation by the stem cell niche. Although the dynamics of the embryonic and adult stem cell cycles are profoundly dissimilar, we suggest that shared principles underlie the governance of this important decision point in diverse stem cell types.

Several lines of evidence suggest that accumulation of cytoplasmic ␤-catenin transduces an oncogenic signal. We show that ␤-catenin is ubiquitinated and degraded by the proteosome and that ␤-catenin stability is regulated by a diacylglycerol-independent protein kinase Clike kinase activity, which is required for ␤-catenin ubiquitination. We also define a six-amino acid sequence found in both ␤-catenin and the NF-B regulatory protein IB␣, which, upon phosphorylation, targets both proteins for ubiquitination. Mutation of a single serine within the ubiquitination targeting sequence prevents ubiquitination of ␤-catenin. Mutations within the ubiquitination targeting sequence of ␤-catenin may be oncogenic.

The combination of dabrafenib plus trametinib has activity in a subset of patients with BRAF V600-mutant mCRC. Mitogen-activated protein kinase signaling was inhibited in all patients evaluated, but to a lesser degree than observed in BRAF-mutant melanoma with dabrafenib alone. PIK3CA mutations were identified in responding patients and thus do not preclude response to this regimen. Additional studies targeting the mitogen-activated protein kinase pathway in this disease are warranted.

β-Catenin is an important regulator of cell–cell adhesion and embryonic development that associates with and regulates the function of the LEF/TCF family of transcription factors. Mutations of β-catenin and the tumor suppressor gene, adenomatous polyposis coli, occur in human cancers, but it is not known if, and by what mechanism, increased β-catenin causes cellular transformation. This study demonstrates that modest overexpression of β-catenin in a normal epithelial cell results in cellular transformation. These cells form colonies in soft agar, survive in suspension, and continue to proliferate at high cell density and following γ-irradiation. Endogenous cytoplasmic β-catenin levels and signaling activity were also found to oscillate during the cell cycle. Taken together, these data demonstrate that β-catenin functions as an oncogene by promoting the G1 to S phase transition and protecting cells from suspension-induced apoptosis (anoikis).

Throughout development, cell fate decisions are converted into epigenetic information that determines cellular identity. Covalent histone modifications are heritable epigenetic marks and are hypothesized to play a central role in this process. In this report, we assess the concordance of histone H3 lysine 4 dimethylation (H3K4me2) and trimethylation (H3K4me3) on a genome-wide scale in erythroid development by analyzing pluripotent, multipotent, and unipotent cell types. Although H3K4me2 and H3K4me3 are concordant at most genes, multipotential hematopoietic cells have a subset of genes that are differentially methylated (H3K4me2+/me3-). These genes are transcriptionally silent, highly enriched in lineage-specific hematopoietic genes, and uniquely susceptible to differentiation-induced H3K4 demethylation. Self-renewing embryonic stem cells, which restrict H3K4 methylation to genes that contain CpG islands (CGIs), lack H3K4me2+/me3- genes. These data reveal distinct epigenetic regulation of CGI and non-CGI genes during development and indicate an interactive relationship between DNA sequence and differential H3K4 methylation in lineage-specific differentiation.

Continuous daily dosing of trametinib/afuresertib combination was poorly tolerated. Evaluation of intermittent dose schedule showed greater tolerability. Given the interest in combination treatment regimens of MAPK and PI3K/AKT pathway inhibitors, further study of intermittent dose schedule or combination of trametinib with more selective inhibitors may be warranted.

SUMMARY Transcription factor activity and turnover are functionally linked, but the global patterns by which DNA-bound regulators are eliminated remain poorly understood. We established an assay to define the chromosomal location of DNA-associated proteins that are slated for degradation by the ubiquitin-proteasome system. The genome-wide map described here ties proteolysis in mammalian cells to active enhancers and to promoters of specific gene families. Nuclear-encoded mitochondrial genes in particular correlate with protein elimination, which positively affects their transcription. We show that the nuclear receptor corepressor NCoR1 is a key target of proteolysis and physically interacts with the transcription factor CREB. Proteasome inhibition stabilizes NCoR1 in a site-specific manner and restrains mitochondrial activity by repressing CREB-sensitive genes. In conclusion, this functional map of nuclear proteolysis links chromatin architecture with local protein stability and identifies proteolytic derepression as highly dynamic in regulating the transcription of genes involved in energy metabolism.

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