Polycomb Group (PcG) members are known transcriptional repressors with an important function in development by means of the control of HOX genes expression. PcG proteins exert its function by forming DNA-binding repressive complexes that are able to change chromatin structure through epigenetic mechanisms. Many studies suggest a role for PcG members in stem cell self-renewal and cell fate decisions. Recent studies have demonstrated the importance of certain PcG proteins in several types of human tumour. For instance BMI1 is involved in lymphomagenesis and other tumours; EZH2 has a role in prostate cancer progression and in neoplastic transformation of breast epithelial cells and SUZ12 mRNA has been found to be up-regulated in a number of different human tumours, including tumours of the colon and breast. We have studied the expression of EZH2 and SUZ12 in non-tumoral (154 samples) and tumoral (550 samples) human tumours by using tissue microarrays. Although these two proteins form part of the same complex, EZH2 was ubiquitously expressed in every normal and tumoral tissue while SUZ12 was selectively expressed in germ cells, proliferating cells (germinal centre cells) in lymph nodes and in epithelial cells of different tissues. SUZ12 protein is also over represented in some tumours in contrast with the normal counterpart. Among these tumours we have found colonic adenomas, lung neuroendocrine small-cell carcinoma, melanoma and mantle cell lymphoma (MCL). MCL patients that overexpress SUZ12 show a shorter survival than patients that do not overexpress this protein. To address the function of SUZ12 in MCL we have performed functional RNAi-based assays against this gene. We have infected Jeko1 and Z138 MCL cell lines with lentivirus carrying either two different shRNAs against SUZ12 or a scramble oligo using GFP as a marker. After successful knock-down, GFP positive cells showed a competitive disadvantage when infected with the SUZ12 silencing oligos compared with GFP negative cells while GFP positive cells in the scramble control had the same behaviour as non-infected cells. After 8 passages the percentage of GFP positive cells was reduced around 50% in the silenced cells and the remaining GFP positive cells did not show repression of SUZ12, suggesting that the effect of the depletion of SUZ12 is stronger than the effect measured by the competition assay. Results of Gene Expression Profile comparing control cells versus SUZ12 deficient cells will be discussed in the poster.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA