Role of diallyl disulfide-mediated cleavage of c-Myc and Sp-1 in the regulation of telomerase activity in human lymphoma cell line U937.
OBJECTIVE
Garlic (Allium sativum) has been considered a wonder herb for years with a reputation of disease prevention. Telomerase, a ribonucleoprotein enzyme responsible for telomere integrity, is strongly up-regulated in different types of cancers. The aim of this study was to reveal the role of diallyl disulfide (DADS), an organosulfur component of garlic, on telomerase activity in human lymphoma with an emphasis on key transcription factors c-Myc and Sp-1.


METHODS
Human lymphoma cell line U937 was used as model cell line. Telomerase activity was measured by telomerase repeat amplification protocol assay, levels of related proteins and mRNAs were measured by Western blot and reverse transcriptase polymerase chain reaction, respectively. Moreover, in vitro binding assay was performed using radiolabeled double-stranded DNA having specific sequences to detect involvement of transcription factors in DADS-dependent modulation of telomerase activity.


RESULTS
The present study demonstrated DADS-mediated decrease in telomerase activity in U937 cells with concomitant transcriptional down-regulation of human telomerase reverse transcriptase (hTERT) that is caused by reduced binding of c-Myc and Sp-1 to their respective binding sites on hTERT promoter. Lowering of DNA-binding activity of c-Myc and Sp-1 due to DADS treatment is caused by the deactivation of these transcription factors due to cleavage. Additionally, Mad1-the repressor protein of hTERT expression-is also overexpressed in DADS-treated U937 cells.


CONCLUSIONS
These findings strongly suggest that DADS down-regulate telomerase activity through c-Myc-, Sp-1-, and Mad1-dependent transcriptional down-regulation of hTERT.
['Dasgupta|Pritha|P|', 'Sengupta|Sumita Bandyopadhyay|SB|']
D000498:Allyl Compounds D016588:Anticarcinogenic Agents D018797:Cell Cycle Proteins D045744:Cell Line, Tumor D004220:Disulfides D015536:Down-Regulation D005737:Garlic D005786:Gene Expression Regulation D006801:Humans D008223:Lymphoma D009687:Nuclear Proteins D010936:Plant Extracts D016271:Proto-Oncogene Proteins c-myc D012333:RNA, Messenger D016329:Sp1 Transcription Factor D019098:Telomerase
c-Myc Sp-1 Telomerase Diallyl disulfide hTERT Apoptosis Myc-nick