Tissue-of-origin-specific gene repositioning in breast and prostate cancer.

Genes have preferential non-random spatial positions within the cell nucleus. The nuclear position of a subset of genes differ between cell types and some genes undergo repositioning events in disease, including cancer. It is currently unclear whether the propensity of a gene to reposition reflects an intrinsic property of the locus or the tissue. Using quantitative FISH analysis of a set of genes which reposition in cancer, we test here the tissue specificity of gene repositioning in normal and malignant breast or prostate tissues. We find tissue-specific organization of the genome in normal breast and prostate with 40 % of genes occupying differential positions between the two tissue types. While we demonstrate limited overlap between gene sets that repositioned in breast and prostate cancer, we identify two genes that undergo disease-related gene repositioning in both cancer types. Our findings indicate that gene repositioning in cancer is tissue-of-origin specific.

Locus-specific gene repositioning in prostate cancer.

Genes occupy preferred spatial positions within interphase cell nuclei. However, positioning patterns are not an innate feature of a locus, and genes can alter their localization in response to physiological and pathological changes. Here we screen the radial positioning patterns of 40 genes in normal, hyperplasic, and malignant human prostate tissues. We find that the overall spatial organization of the genome in prostate tissue is largely conserved among individuals. We identify three genes whose nuclear positions are robustly altered in neoplastic prostate tissues. FLI1 and MMP9 position differently in prostate cancer than in normal tissue and prostate hyperplasia, whereas MMP2 is repositioned in both prostate cancer and hyperplasia. Our data point to locus-specific reorganization of the genome during prostate disease.

PAD4 mediated histone hypercitrullination induces heterochromatin decondensation and chromatin unfolding to form neutrophil extracellular trap-like structures.

NETosis, the process wherein neutrophils release highly decondensed chromatin called neutrophil extracellular traps (NETs), has gained much attention as an alternative means of killing bacteria. In vivo, NETs are induced by bacteria and pro-inflammatory cytokines. We have reported that peptidylarginine deiminase 4 (PAD4), an enzyme that converts Arg or monomethyl-Arg to citrulline in histones, is essential for NET formation. The areas of extensive chromatin decondensation along the NETs were rich in histone citrullination. Here, upon investigating the effect of global citrullination in cultured cells, we discovered that PAD4 overexpression in osteosarcoma U2OS cells induces extensive chromatin decondensation independent of apoptosis. The highly decondensed chromatin is released to the extracellular space and stained strongly by a histone citrulline-specific antibody. The structure of the decondensed chromatin is reminiscent of NETs but is unique in that it occurs without stimulation of cells with pro-inflammatory cytokines and bacteria. Furthermore, histone citrullination during chromatin decondensation can dissociate heterochromatin protein 1 beta (HP1ß) thereby offering a new molecular mechanism for understanding how citrullination regulates chromatin function. Taken together, our study suggests that PAD4 mediated citrullination induces chromatin decondensation, implicating its essential role in NET formation under physiological conditions in neutrophils.