Microarray proteomic analysis discriminates tumorigenic mouse ovarian surface epithelial cells of divergent aggressive potential.

Cancer is an intrinsically heterogeneous disease. Tumors classified under the same etiology and histological type may display divergent growth and invasion properties, resulting in different progression rates and clinical outcomes. Here, we approached this subject in a syngeneic mouse model of ovarian cancer. Antibody microarrays were applied to obtain the proteomic profiles of IF5 and IG10, two spontaneously transformed mouse ovarian surface epithelial (MOSE) cell lines of cognate clonal origin but different tumorigenic behavior in vivo. Repeated dye-swap allowed filter out about 40% of inconsistent signals from a total of 224 arrayed antibodies. Two-class comparison tests resulted in 31 differentially expressed proteins (adjusted p < 0.05). Proteins of the ErbB and focal adhesion signaling pathways showed higher levels in IG10, the most aggressive cell. In contrast, the less aggressive IF5 cell was enriched in proteins related to nuclear chromatin organization and cell-cycle. Additionally, comparison between protein levels and mRNA levels of MOSE cells resulted in a positive rank correlation for 50-60% of protein-mRNA pairs (p < 1.7 × 10(-5)). Importantly, the protein profile of IG10 is linked to invasion and chemotherapy response in human ovarian tumors while the IF5 profile is associated to growth control. The minimal IG10 network contained the proteins Jun, Smad4, Myc, Atf2, and Pak1 as major nodes while Chek2, Mdm2 and Ccna2 were the predominant nodes of the IF5 network. The molecular basis accounting for a high aggressive potential not necessarily related to an increased tumor growth capacity is discussed on a pathway-network basis.

Lsh, an epigenetic guardian of repetitive elements.

The genome is burdened with repetitive sequences that are generally embedded in silenced chromatin. We have previously demonstrated that Lsh (lymphoid-specific helicase) is crucial for the control of heterochromatin at pericentromeric regions consisting of satellite repeats. In this study, we searched for additional genomic targets of Lsh by examining the effects of Lsh deletion on repeat regions and single copy gene sequences. We found that the absence of Lsh resulted in an increased association of acetylated histones with repeat sequences and transcriptional reactivation of their silenced state. In contrast, selected single copy genes displayed no change in histone acetylation levels, and their transcriptional rate was indistinguishable compared to Lsh-deficient cells and wild-type controls. Microarray analysis of total RNA derived from brain and liver tissues revealed that <0.4% of the 15 247 examined loci were abnormally expressed in Lsh-/-embryos and almost two-thirds of these deregulated sequences contained repeats, mainly retroviral LTR (long terminal repeat) elements. Chromatin immunoprecipitation analysis demonstrated a direct interaction of Lsh with repetitive sites in the genome. These data suggest that the repetitive sites are direct targets of Lsh action and that Lsh plays an important role as 'epigenetic guardian' of the genome to protect against deregulation of parasitic retroviral elements.