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The effect of RAA on mRNA degradation in THP-1 human leukemic monocytes Mak, Isabella Wing Yan


Dysregulation of mRNA levels is a genetic hallmark of cancer. The Shaw-Kamen (SK) box, an AU-rich element (ARE ) found in the 3'UTR, is an mRNA stability determinant in many cytokines, growth factors, transcription factors, and proto-oncogene mRNAs. A fungal metabolite, Radicicol Analog A (RAA) , was found to destabilize only S K box-containing mRNAs in THP-1 human leukemic monocytes (Cytokine, 1996, 8, 751-761). Given the small number of genes analyzed in this study, SAGE was used to examine the transcriptome-wide effect of RAA on mRNA expression in THP-1 cells. To determine whether RAA only down-regulated SK box-containing mRNAs, two ~45,000-short-tag SAGE libraries were prepared from total mRNA isolated from THP-1 cells stimulated with IFNγ/LPS ± RAA (lp:M). Surprisingly, only 0.27% of the total unique SAGE tags ( p<0.001) were downregulated by RAA treatment. Tag-to-gene identities for these 48 down-regulated SAGE tags were validated and quantified using real-time RT-PCR. Although 73% of these RAA-down-regulated tags encoded SK box-containing mRNAs, no linear correlation was observed between the fold decrease in mRNA expression and the number of the SK boxes. mRNA half-lives for ten genes, were determined in unstimulated, and 2 and 16 hour post-IFNγ/LPS stimulated THP-1 cells. The mRNA half-lives of two SK box-containing mRNAs, TNF-a and NFKBIA , were unaffected by RAA, suggesting that RAA may affect transcription. Interestingly, all mRNAs stabilized upon IFNγ/LPS treatment were destabilized by RAA at the post-transcriptional level. Hopefully, by studying the effect of RAA on mRNA regulation, a new approach to cancer treatment and other diseases, may be gained.

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