engleski

The role of poly(ADP-ribosyl)ation in regulation of BORIS transcription

The expression BORIS, a paralogue of multifunctional transcription factor CTCF, is confined to a subpopulation of spermatocytes. It is absent in normal somatic cells and aberrantly expressed in a variety of cancers. Its transcription is modulated by CpG methylation, CTCF and p53, all influenced by ADP-ribosylation. The sequence of events which precede BORIS expression during male gametogenesis, includes a peak in PARP activity, erasure of methylation marks, and complete lack of PARP activity in BORIS- expressing cells. We aimed to determine if inhibiting PARP activity would lead to its expression in BORIS-non-expressing normal human fibroblasts and several tumor cell lines. Human tumor cell lines HT-29, HCT116, Cal27, HeLa, Detroit562, Hep-2, SW620 and normal human fibroblasts Wi38 were treated with 3- aminobenzamide or 5-azacytidine. Both agents inhibit ADP-ribosylation but have opposing effect on DNA methylation. The expression of BORIS and CTCF was analyzed by real-time PCR. All untreated cell lines, except Wi38, express BORIS. The highest level of BORIS was observed in Hep-2 and HeLa cells with wt p53 but with increased p53 degradation due to the presence of E6. Unexpectedly, cell lines HT-29, Cal27, Detroit562 and SW620 with mutant p53 had less pronounced BORIS expression. The p53 mutations present in analyzed cell lines fall into p53 DNA binding domain but do not preclude the association of p53 with Sp1 to negatively influence its transactivation of BORIS promoter. We show that expression of BORIS is upregulated by inhibition of ADP-ribosylation by both agents in all tested cell lines, to different extent, dependent on their p53 status and ADP-ribosylating capacity. The upregulation of BORIS expression in most cell lines, upon 5- azacytidine treatment, was accompanied by upregulation of CTCF rather than its downregulation, suggesting that mechanisms other than presence of CTCF and its association with BORIS promoter are superimposed in regulation of BORIS transcription.

poly(ADP-ribosyl)ation; BORIS; CTCF; transcription

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