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BackgroundCbf11 and Cbf12, the fission yeast CSL transcription factors, have been implicated in the regulation of cell-cycle progression, but no specific roles have been described and their target genes have been only partially mapped.Methodology/Principal FindingsUsing a combination of transcriptome profiling under various conditions and genome-wide analysis of CSL-DNA interactions, we identify genes regulated directly and indirectly by CSL proteins in fission yeast. We show that the expression of stress-response genes and genes that are expressed periodically during the cell cycle is deregulated upon genetic manipulation of cbf11 and/or cbf12. Accordingly, the coordination of mitosis and cytokinesis is perturbed in cells with genetically manipulated CSL protein levels, together with other specific defects in cell-cycle progression. Cbf11 activity is nutrient-dependent and Δcbf11-associated defects are mitigated by inactivation of the protein kinase A (Pka1) and stress-activated MAP kinase (Sty1p38) pathways. Furthermore, Cbf11 directly regulates a set of lipid metabolism genes and Δcbf11 cells feature a stark decrease in the number of storage lipid droplets.Conclusions/SignificanceOur results provide a framework for a more detailed understanding of the role of CSL proteins in the regulation of cell-cycle progression in fission yeast.

Eukaryotic gene expression requires that all the steps of messenger RNA production are regulated in concert to integrate the diverse inputs cells receive. We discuss the functioning of SNW/SKIP, an essential spliceosomal component and transcriptional coregulator, which may provide regulatory coupling of transcription initiation and splicing. SNW/SKIP potentiates the activity of important transcription factors, such as vitamin D receptor, CBF1 (RBP-Jkappa), Smad2/3, and MyoD. It synergizes with Ski in overcoming pRb-mediated cell cycle arrest, and it is targeted by the viral transactivators EBNA2 and E7. SNW/SKIP may aid in conformational transition of the gene expression machine through its avidity to nuclear matrix fractions or by recruiting foldases such as the prolyl isomerase PPIL1. The extensive list of SNW/SKIP partners, its unique primary structure, conserved from yeast to humans, and its essential character suggest a distinct function of general importance.

Tumor cell invasion is the most critical step of metastasis. Determination of the mode of invasion within the particular tumor is critical for effective cancer treatment. Protease-independent amoeboid mode of invasion has been described in carcinoma cells and more recently in sarcoma cells on treatment with protease inhibitors. To analyze invasive behavior, we compared highly metastatic sarcoma cells with parental nonmetastatic cells. The metastatic cells exhibited a functional up-regulation of Rho/ROCK signaling and, similarly to carcinoma cells, an amoeboid mode of invasion. Using confocal and traction force microscopy, we showed that an up-regulation of Rho/ROCK signaling leads to increased cytoskeletal dynamics, myosin light chain localization, and increased tractions at the leading edge of the cells and that all of these contributed to increased cell invasiveness in a three-dimensional collagen matrix. We conclude that cells of mesenchymal origin can use the amoeboid nonmesenchymal mode of invasion as their primary invading mechanism and show the dependence of ROCK-mediated amoeboid mode of invasion on the increased capacity of cells to generate force.

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