PICOT is a ubiquitous protein that is critical for mouse embryonic development. It is involved in the regulation of signal transduction in T lymphocytes and cardiac muscle, in cellular iron metabolism and biogenesis of Fe/S proteins. However, very little is known about the physiological role of PICOT, its upstream regulators or downstream target molecules. In a recent work we have adopted the yeast two-hybrid system and screened a Jurkat T cell cDNA library in order to identify PICOT binding partners. We found that PICOT interacts with embryonic ectoderm development (EED), a Polycomb Group (PcG) protein that serves as a core component of the Polycomb repressive complex 2 (PRC2) and contributes to the regulation of chromatin remodeling and cell differentiation. PICOT-EED interaction in human Jurkat T cells was reconfirmed using GST-PICOT and GST-EED fusion proteins in a pull- down assay and reciprocal coimmunoprecipitation studies. In the present work we performed immunofluorescence staining of various cancer cell lines and found a partial colocalization of PICOT and EED, predominantly in cell nuclei. Chromatin immunoprecipitation revealed that PICOT interacts with EED at the chromatin compartment. In addition, PICOT knock- down in Jurkat T cells resulted in a reduced histone H3 lysine 27 trimethylation (H3K27me3), and decreased levels of EZH2 and EED at the PRC2 target gene, cyclin D2 (CCND2) that was accompanied by upregulation of cyclin D2 mRNA and protein expression. Analyses of The Cancer Genome Atlas (TCGA) dataset revealed a negative correlation between PICOT and cyclin D2 mRNA expression in selected types of human cancers, which also directly correlated with poor prognosis of patients’ survival. Our finding suggest that PICOT binding to EED alters PRC2-regulated transcriptional repression at the cyclin D2 genes and potentially contributes to tumor progression.

Key words: PICOT; GRX3; CCND2; Cyclin D2; H3K27me3; human cancer;