328 Role of the Fragile X Mental Retardation Protein in Tumor Progression and Metastasis Formation

Abstract

pression in isogenic normal (MRC5), immortal (pre-malignant) (MRC5hTERT) and tumorigenic (MRC5hTERT TZ) human myofibroblasts, which are p53defective, as well as tumour-derived fibrosarcoma cells (HT1080). Results and Discussion: SiRNA-mediated repression of DKC1 or TERT expression induced acute proliferative arrest of immortal and tumorigenic cells, while having no adverse effect on the proliferation of isogenic normal cells. Furthermore, suppression of DKC1 or TERT gene expression also impaired anchorage-independent growth of tumorigenic cells. In comparison, treatment with a control siRNA, siRNA targeting TERC or the small molecule telomerase enzyme inhibitor BIBR1532, had no acute effect on proliferation in these short term assays. While the growth arrest mediated by DKC1 or TERT repression was not dependent on p53 function, loss of p53 function altered the cell cycle phase in which the cells arrested. The growth arrest induced by DKC1 repression remained unaffected by TERC overexpression suggesting a telomere independent role for DKC1. Microarray analysis of gene expression and Gene Set Enrichment analysis (GSEA) of siRNA-transfected normal, immortal and tumorigenic MRC5 cells was employed to gain insight to the mechanisms that underpinned the acute anti-proliferative effects of TERT and DKC1 repression. Investigations are currently underway to determine the effect of stable repression of TERT and DKC1 on subcutaneous tumour formation in immunocompromised mice. Conclusions: Together, these results demonstrate that telomeraseimmortalised pre-malignant and tumorigenic cells required continued expression of TERT and DKC1 for replication. This provides further evidence of telomere length-independent functions of TERT and DKC1 in these cells since there was insufficient time for telomere shortening to occur. The potent and specific anti-proliferative effects resulting from repression of DKC1 and TERT in immortal and tumorigenic cells demonstrate that directly targeting these telomerase components has potential as a potent and specific approach to treatment of the broad spectrum of cancers that express telomerase.