Global expression profile of telomerase-associated genes in HeLa cells

Telomerase is a specialized nucleoprotein enzyme complex that maintains the telomere length. The telomerase reverse transcriptase (TERT) is the catalytically active component of the telomerase complex. In humans, the protein component (hTERT) and RNA component (hTR) are found to differentially express in cancer cells. In contrast to differentiated cells, most of the cancer cells overexpress hTERT, which is needed to maintain the proliferative potential of cells. The overexpression of telomerase is not proportionate to telomere length in cancer cells, suggesting that the immortalizing phenotype can be mediated through other factors in addition to telomere length. To investigate the role of hTERT in immortalizing process, loss of gene function studies were carried out. Short interfering RNA (siRNA) and short hairpin RNA (shRNA) against hTERT showed the reduction of hTERT transcript, reduction of telomerase activity and alteration of gene expression in HeLa cells. The molecular basis of proliferative capacity of hTERT was investigated by gene expression microarray. Analysis of microarray data for HeLa cells following siRNA and shRNA mediated knockdown of hTERT showed that 80 genes were upregulated and 73 genes downregulated. Out of these, 37 genes are known to be involved in cancer. Further analyses of previously known genes involved in cancer like KLF4, FGF2, IRF-9 and PLAU by Real Time PCR showed their upregulation. We are documenting for the first time the effect of knocking down hTERT on expression of KLF4 and FGF2. Interestingly, it has been earlier reported that KLF4 and FGF2 up-regulate the expression of hTERT in cancer cells. This suggests that hTERT may be subject to its own auto-regulatory effects.