Changes in telomerase activity, expression and splicing in response to differentiation of normal and carcinoma colon cells
Background: Telomerase, a ribonucleoprotein complex catalysing synthesis of telomeric DNA, is an essential cellular immortalising factor whose activation is a critical step in the progression to malignancy. An important agent maintaining the balance between proliferation, differentiation and apoptosis of intestinal epithelial cells in crypts is butyrate, which is formed in the gastrointestinal tract by anaerobic bacterial fermentation. It inhibits cell growth., induces differentiation and triggers apoptosis in neoplastic colonocytes. Materials and Methods: In this study, the responses of adenocarcinoma (HT-29) and fetal (FHC) human colon cells to 5 mM sodium butyrate (NaBt) have been compared. Results: Despite the similar general response of both cell lines to NaBt, i.e., G0/G1 arrest, decrease of growth rate and increase of differentiation (as indicated by alkaline phosphatase activity), they differ in the level and dynamics of the measured parameters. Telomerase activity and the level of mRNA for its catalytic subunit (hTERT) decline significantly after 48 hours, reaching a complete inhibition after 144 hours. While both cell lines show similar kinetics of hTERT transcriptional silencing, the down-regulation of telomerase activity is faster in FHC cells. Correspondingly, we show that a candidate posttranscriptional regulation step, differential splicing of hTERT mRNA, may be involved in the faster loss of telomerase activity in FHC cells. Conclusion: Differences in hTERT mRNA splicing may represent a useful marker of telomere metabolism in normal and malignant colon cells and that these changes may be connected with different cytokinetic patterns of these cells.