Telomere repeat binding factor 2 (TRF2) has been increasingly recognized to be involved in DNA damage response and telomere maintenance. Our previous report found that salvicine (SAL), a novel topoisomerase II poison, elicited DNA doublestrand breaks and telomere erosion in separate experimental systems. However, it remains to be clarified whether they share a common response to these two events and in particular whether TRF2 is involved in this process. In this study, we found that SAL concurrently induced DNA double-strand breaks, telomeric DNA damage, and telomere erosion in lung carcinoma A549 cells. It was unexpected to find that SAL led to disruption of TRF2, independently of either its transcription or proteasome-mediated degradation. By overexpressing the full-length trf2 gene and transfecting TRF2 small interfering RNAs, we showed that TRF2 protein protected both telomeric and genomic DNA from the SAL-elicited events. It is noteworthy that although both the Ataxia-telangiectasia-mutated (ATM) and the ATM-and Rad3-related (ATR) kinases responded to the SAL-induced DNA damages, only ATR was essential for the telomere erosion. The study also showed that the activated ATR augmented the SAL-triggered TRF2 disruption, whereas TRF2 reduction in turn enhanced ATR function. All of these findings suggest the emerging significance of TRF2 protecting both telomeric DNA and genomic DNA on the one hand and reveal the mutual modulation between ATR and TRF2 in sensing DNA damage signaling during cancer development on the other hand.
Abstract. Alternative splicing of the human telomerase reverse transcriptase subunit (hTERT) suppresses telomerase activity during the development of human fetal kidney cells into mature cells. Tumor cell differentiation is the process of turning abnormal tumor cells into 'normal' cells accompanied by down-regulation of telomerase activity. However, the precise mechanism of the regulation of telomerase activity in differentiated cells is not fully understood. In this study, we observed the role of alternative splicing of hTERT in the regulation of telomerase activity in all-trans-retinoic acid (ATRA)-induced, differentiated HL-60 cells. ATRA-induced downregulation of telomerase activity in differentiated HL-60 cells was associated with a decrease in hTERT and an increase in human telomerase-associated protein-1 (hTP1) transcription. and hTERT b -maintained a relatively stable ratio when telomerase activity decreased largely from treatment with 1 to 5 m M ATRA. Although the splicing pattern of hTERT mRNA was altered in time-effect research, the change was not related to the ATRA-treated decline of telomerase activity. The expression of alternative splicing variants of hTERT also decreased at the protein level. All these results suggested that alternative splicing of hTERT mRNA may not contribute to the suppression of telomerase activity during ATRA-induced HL-60 leukemia cell differentiation.
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