Regulation of the hTERT promoter activity by MSH2, the hnRNPs K and D, and GRHL2 in human oral squamous cell carcinoma cells

Higher expression of human telomerase reverse transcriptase (hTERT) and subsequent activation of telomerase occur during cellular immortalization and are maintained in cancer cells. To understand the mode of hTERT expression in cancer cells, we identified cancer-specific trans-regulatory proteins that interact with the hTERT promoter, using the promoter magnetic precipitation assay coupled to mass spectrometry (PMS-MS). The identified proteins include MutS homologue 2 (MSH2), heterogeneous nuclear ribonucleoprotein (hnRNP) D, hnRNP K, and Grainyhead-like 2 (GRHL2). We noticed higher expression of these proteins in human oral squamous cell carcinoma (OSCC) cells than in normal cells, which do not exhibit telomerase activity. Knockdown of MSH2, hnRNP D and GRHL2 resulted in notable reduction of the hTERT promoter activity in tested cancer cells. Silencing of the above genes resulted in the significant reduction of telomerase activity in OSCC cells. Interestingly, among the four identified genes, silencing of GRHL2 was essential in reducing telomerase activity and viability of tested cancer cells. These results suggest a possible role of GRHL2 in telomerase activation during cellular immortalization.