The Polycomb group (PcG) proteins are essential for embryogenesis, and their expression is often found deregulated in human cancer. The PcGs form two major protein complexes, called polycomb repressive complexes 1 and 2 (PRC1 and PRC2) whose function is to maintain transcriptional repression. Here, we demonstrate that the chromodomain-containing protein, CBX8, which is part of one of the PRC1 complexes, regulates proliferation of diploid human and mouse fibroblasts through direct binding to the INK4A-ARF locus. Furthermore, we demonstrate that CBX8 is limiting for the regulation of INK4A-ARF, and that ectopic expression of CBX8 leads to repression of the Ink4a-Arf locus and bypass of senescence, leading to cellular immortalization. Gene expression and location analysis demonstrate that besides the INK4A-ARF locus, CBX8 also regulates a number of other genes important for cell growth and survival. On the basis of these results, we conclude that CBX8 is an essential component of one of the PRC1 complexes, which directly regulate the expression of numerous target genes, including the INK4A-ARF locus, involved in cell-fate decisions.

The ACB1 gene encoding the acyl-CoA-binding protein (ACBP) was disrupted in Saccharomyces cerevisiae. The disruption did not affect the growth rate on glucose but reduced the growth rate on ethanol slightly. Although the growth rate of the acb1-disrupted cells was unaffected or only slightly affected, the acb1-disrupted strain was unable to compete with wild type cells when grown in mixed culture. The acyl-CoA level in the disrupted cells was increased from 1.5- to 2.5-fold during exponential growth. The increase in the acyl-CoA level was caused solely by an increase in de novo synthesized stearoyl-CoA. Experiments with purified yeast fatty acid synthetase show that it will synthesize long chain acyl-CoAs in the absence of acyl-CoA-binding protein. The addition of ACBP to the incubation medium resulted in a dramatic decrease in the chain length of the synthesized acyl-CoA esters. Despite the fact that the stearoyl-CoA concentration was increased 7-fold and the Delta9-desaturase mRNA level was increased 3-fold, the synthesis of oleic acid was unchanged in the acb1-disrupted strain. The results strongly indicate that ACBP in yeast is involved in the transport of newly synthesized acyl-CoA esters from the fatty acid synthetase to acyl-CoA-consuming processes.

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Phenotypic and genotypic diversifications of Pseudomonas aeruginosa in the airways of patients with cystic fibrosis (CF) promote long-term survival of bacteria during chronic lung infection. Twelve clonally related, sequential mucoid and non-mucoid paired P. aeruginosa isolates obtained from three Danish CF patients were investigated. The in vitro biofilm formation capacity was studied under static and flow through conditions and the global gene expression profiles were investigated by Affymetrix GeneChip. Regulatory genes of alginate production and quorum sensing (QS) system were sequenced and measurements of the alginate production and the detection of the QS signal molecules were performed. Comparisons of mucoid and non-mucoid isolates from early and late stages of the infection showed that the mucoid phenotype maintained over a decade the capacity to form in vitro biofilm and showed an unaltered transcriptional profile, whereas substantial alterations in the transcriptional profiles and loss of the capacity to form in vitro biofilms were observed in corresponding isolates of the non-mucoid phenotype. The conserved gene expression pattern in the mucoid isolates vs the diversity of changes in non-mucoid isolates observed in this particular P. aeruginosa clone reflects different adaptation strategies used by these two phenotypes in the different niches of the CF lung environment.